Merge branch 'jh/trace2'

A more structured way to obtain execution trace has been added.

* jh/trace2:
  trace2: add for_each macros to clang-format
  trace2: t/helper/test-trace2, t0210.sh, t0211.sh, t0212.sh
  trace2:data: add subverb for rebase
  trace2:data: add subverb to reset command
  trace2:data: add subverb to checkout command
  trace2:data: pack-objects: add trace2 regions
  trace2:data: add trace2 instrumentation to index read/write
  trace2:data: add trace2 hook classification
  trace2:data: add trace2 transport child classification
  trace2:data: add trace2 sub-process classification
  trace2:data: add editor/pager child classification
  trace2:data: add trace2 regions to wt-status
  trace2: collect Windows-specific process information
  trace2: create new combined trace facility
  trace2: Documentation/technical/api-trace2.txt

.clang-format

@@ -149,7 +149,7 @@ Cpp11BracedListStyle: false
 
 # A list of macros that should be interpreted as foreach loops instead of as
 # function calls.
-ForEachMacros: ['for_each_string_list_item']
+ForEachMacros: ['for_each_string_list_item', 'for_each_wanted_builtin', 'for_each_builtin', 'for_each_ut']
 
 # The maximum number of consecutive empty lines to keep.
 MaxEmptyLinesToKeep: 1

Makefile

@@ -773,6 +773,7 @@ TEST_BUILTINS_OBJS += test-string-list.o
 TEST_BUILTINS_OBJS += test-submodule-config.o
 TEST_BUILTINS_OBJS += test-submodule-nested-repo-config.o
 TEST_BUILTINS_OBJS += test-subprocess.o
+TEST_BUILTINS_OBJS += test-trace2.o
 TEST_BUILTINS_OBJS += test-urlmatch-normalization.o
 TEST_BUILTINS_OBJS += test-xml-encode.o
 TEST_BUILTINS_OBJS += test-wildmatch.o
@@ -1017,6 +1018,16 @@ LIB_OBJS += tempfile.o
 LIB_OBJS += thread-utils.o
 LIB_OBJS += tmp-objdir.o
 LIB_OBJS += trace.o
+LIB_OBJS += trace2.o
+LIB_OBJS += trace2/tr2_cfg.o
+LIB_OBJS += trace2/tr2_cmd_name.o
+LIB_OBJS += trace2/tr2_dst.o
+LIB_OBJS += trace2/tr2_sid.o
+LIB_OBJS += trace2/tr2_tbuf.o
+LIB_OBJS += trace2/tr2_tgt_event.o
+LIB_OBJS += trace2/tr2_tgt_normal.o
+LIB_OBJS += trace2/tr2_tgt_perf.o
+LIB_OBJS += trace2/tr2_tls.o
 LIB_OBJS += trailer.o
 LIB_OBJS += transport.o
 LIB_OBJS += transport-helper.o
@@ -1596,7 +1607,9 @@ ifdef NO_INET_PTON
 	LIB_OBJS += compat/inet_pton.o
 	BASIC_CFLAGS += -DNO_INET_PTON
 endif
-ifndef NO_UNIX_SOCKETS
+ifdef NO_UNIX_SOCKETS
+	BASIC_CFLAGS += -DNO_UNIX_SOCKETS
+else
 	LIB_OBJS += unix-socket.o
 	PROGRAM_OBJS += credential-cache.o
 	PROGRAM_OBJS += credential-cache--daemon.o

builtin/am.c

@@ -453,6 +453,7 @@ static int run_post_rewrite_hook(const struct am_state *state)
 
 	cp.in = xopen(am_path(state, "rewritten"), O_RDONLY);
 	cp.stdout_to_stderr = 1;
+	cp.trace2_hook_name = "post-rewrite";
 
 	ret = run_command(&cp);
 

builtin/checkout.c

@@ -325,6 +325,8 @@ static int checkout_paths(const struct checkout_opts *opts,
 	struct lock_file lock_file = LOCK_INIT;
 	int nr_checkouts = 0, nr_unmerged = 0;
 
+	trace2_cmd_mode(opts->patch_mode ? "patch" : "path");
+
 	if (opts->track != BRANCH_TRACK_UNSPECIFIED)
 		die(_("'%s' cannot be used with updating paths"), "--track");
 
@@ -1014,6 +1016,9 @@ static int switch_branches(const struct checkout_opts *opts,
 	void *path_to_free;
 	struct object_id rev;
 	int flag, writeout_error = 0;
+
+	trace2_cmd_mode("branch");
+
 	memset(&old_branch_info, 0, sizeof(old_branch_info));
 	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
 	if (old_branch_info.path)
@@ -1251,6 +1256,8 @@ static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
 	int status;
 	struct strbuf branch_ref = STRBUF_INIT;
 
+	trace2_cmd_mode("unborn");
+
 	if (!opts->new_branch)
 		die(_("You are on a branch yet to be born"));
 	strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);

builtin/pack-objects.c

@@ -33,6 +33,7 @@
 #include "object-store.h"
 #include "dir.h"
 #include "midx.h"
+#include "trace2.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -3473,6 +3474,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	trace2_region_enter("pack-objects", "enumerate-objects",
+			    the_repository);
 	prepare_packing_data(the_repository, &to_pack);
 
 	if (progress)
@@ -3487,12 +3490,23 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (include_tag && nr_result)
 		for_each_ref(add_ref_tag, NULL);
 	stop_progress(&progress_state);
+	trace2_region_leave("pack-objects", "enumerate-objects",
+			    the_repository);
 
 	if (non_empty && !nr_result)
 		return 0;
-	if (nr_result)
+	if (nr_result) {
+		trace2_region_enter("pack-objects", "prepare-pack",
+				    the_repository);
 		prepare_pack(window, depth);
+		trace2_region_leave("pack-objects", "prepare-pack",
+				    the_repository);
+	}
+
+	trace2_region_enter("pack-objects", "write-pack-file", the_repository);
 	write_pack_file();
+	trace2_region_leave("pack-objects", "write-pack-file", the_repository);
+
 	if (progress)
 		fprintf_ln(stderr,
 			   _("Total %"PRIu32" (delta %"PRIu32"),"

builtin/rebase.c

@@ -1027,6 +1027,14 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		ACTION_EDIT_TODO,
 		ACTION_SHOW_CURRENT_PATCH,
 	} action = NO_ACTION;
+	static const char *action_names[] = { N_("undefined"),
+					      N_("continue"),
+					      N_("skip"),
+					      N_("abort"),
+					      N_("quit"),
+					      N_("edit_todo"),
+					      N_("show_current_patch"),
+					      NULL };
 	const char *gpg_sign = NULL;
 	struct string_list exec = STRING_LIST_INIT_NODUP;
 	const char *rebase_merges = NULL;
@@ -1212,6 +1220,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		die(_("The --edit-todo action can only be used during "
 		      "interactive rebase."));
 
+	if (trace2_is_enabled()) {
+		if (is_interactive(&options))
+			trace2_cmd_mode("interactive");
+		else if (exec.nr)
+			trace2_cmd_mode("interactive-exec");
+		else
+			trace2_cmd_mode(action_names[action]);
+	}
+
 	switch (action) {
 	case ACTION_CONTINUE: {
 		struct object_id head;

builtin/receive-pack.c

@@ -694,6 +694,8 @@ static int run_and_feed_hook(const char *hook_name, feed_fn feed,
 	proc.argv = argv;
 	proc.in = -1;
 	proc.stdout_to_stderr = 1;
+	proc.trace2_hook_name = hook_name;
+
 	if (feed_state->push_options) {
 		int i;
 		for (i = 0; i < feed_state->push_options->nr; i++)
@@ -807,6 +809,7 @@ static int run_update_hook(struct command *cmd)
 	proc.stdout_to_stderr = 1;
 	proc.err = use_sideband ? -1 : 0;
 	proc.argv = argv;
+	proc.trace2_hook_name = "update";
 
 	code = start_command(&proc);
 	if (code)
@@ -1190,6 +1193,7 @@ static void run_update_post_hook(struct command *commands)
 	proc.no_stdin = 1;
 	proc.stdout_to_stderr = 1;
 	proc.err = use_sideband ? -1 : 0;
+	proc.trace2_hook_name = "post-update";
 
 	if (!start_command(&proc)) {
 		if (use_sideband)

builtin/reset.c

@@ -341,6 +341,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	if (patch_mode) {
 		if (reset_type != NONE)
 			die(_("--patch is incompatible with --{hard,mixed,soft}"));
+		trace2_cmd_mode("patch-interactive");
 		return run_add_interactive(rev, "--patch=reset", &pathspec);
 	}
 
@@ -357,6 +358,11 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	if (reset_type == NONE)
 		reset_type = MIXED; /* by default */
 
+	if (pathspec.nr)
+		trace2_cmd_mode("path");
+	else
+		trace2_cmd_mode(reset_type_names[reset_type]);
+
 	if (reset_type != SOFT && (reset_type != MIXED || get_git_work_tree()))
 		setup_work_tree();
 

builtin/submodule--helper.c

@@ -1816,11 +1816,10 @@ static int update_submodules(struct submodule_update_clone *suc)
 {
 	int i;
 
-	run_processes_parallel(suc->max_jobs,
-			       update_clone_get_next_task,
-			       update_clone_start_failure,
-			       update_clone_task_finished,
-			       suc);
+	run_processes_parallel_tr2(suc->max_jobs, update_clone_get_next_task,
+				   update_clone_start_failure,
+				   update_clone_task_finished, suc, "submodule",
+				   "parallel/update");
 
 	/*
 	 * We saved the output and put it out all at once now.

builtin/worktree.c

@@ -402,6 +402,7 @@ done:
 			cp.dir = path;
 			cp.env = env;
 			cp.argv = NULL;
+			cp.trace2_hook_name = "post-checkout";
 			argv_array_pushl(&cp.args, absolute_path(hook),
 					 oid_to_hex(&null_oid),
 					 oid_to_hex(&commit->object.oid),

cache.h

@@ -9,6 +9,7 @@
 #include "gettext.h"
 #include "convert.h"
 #include "trace.h"
+#include "trace2.h"
 #include "string-list.h"
 #include "pack-revindex.h"
 #include "hash.h"

common-main.c

@@ -25,12 +25,19 @@ static void restore_sigpipe_to_default(void)
 
 int main(int argc, const char **argv)
 {
+	int result;
+
 	/*
 	 * Always open file descriptors 0/1/2 to avoid clobbering files
 	 * in die().  It also avoids messing up when the pipes are dup'ed
 	 * onto stdin/stdout/stderr in the child processes we spawn.
 	 */
 	sanitize_stdfds();
+	restore_sigpipe_to_default();
+
+	trace2_initialize();
+	trace2_cmd_start(argv);
+	trace2_collect_process_info();
 
 	git_resolve_executable_dir(argv[0]);
 
@@ -40,7 +47,9 @@ int main(int argc, const char **argv)
 
 	attr_start();
 
-	restore_sigpipe_to_default();
+	result = cmd_main(argc, argv);
 
-	return cmd_main(argc, argv);
+	trace2_cmd_exit(result);
+
+	return result;
 }

compat/mingw.c

@@ -1551,19 +1551,23 @@ static int try_shell_exec(const char *cmd, char *const *argv)
 		return 0;
 	prog = path_lookup(interpr, 1);
 	if (prog) {
+		int exec_id;
 		int argc = 0;
 		const char **argv2;
 		while (argv[argc]) argc++;
 		ALLOC_ARRAY(argv2, argc + 1);
 		argv2[0] = (char *)cmd;	/* full path to the script file */
 		memcpy(&argv2[1], &argv[1], sizeof(*argv) * argc);
+		exec_id = trace2_exec(prog, argv2);
 		pid = mingw_spawnv(prog, argv2, 1);
 		if (pid >= 0) {
 			int status;
 			if (waitpid(pid, &status, 0) < 0)
 				status = 255;
+			trace2_exec_result(exec_id, status);
 			exit(status);
 		}
+		trace2_exec_result(exec_id, -1);
 		pid = 1;	/* indicate that we tried but failed */
 		free(prog);
 		free(argv2);
@@ -1576,12 +1580,17 @@ int mingw_execv(const char *cmd, char *const *argv)
 	/* check if git_command is a shell script */
 	if (!try_shell_exec(cmd, argv)) {
 		int pid, status;
+		int exec_id;
 
+		exec_id = trace2_exec(cmd, (const char **)argv);
 		pid = mingw_spawnv(cmd, (const char **)argv, 0);
-		if (pid < 0)
+		if (pid < 0) {
+			trace2_exec_result(exec_id, -1);
 			return -1;
+		}
 		if (waitpid(pid, &status, 0) < 0)
 			status = 255;
+		trace2_exec_result(exec_id, status);
 		exit(status);
 	}
 	return -1;

compat/mingw.h

@@ -147,8 +147,7 @@ static inline int fcntl(int fd, int cmd, ...)
 	errno = EINVAL;
 	return -1;
 }
-/* bash cannot reliably detect negative return codes as failure */
-#define exit(code) exit((code) & 0xff)
+
 #define sigemptyset(x) (void)0
 static inline int sigaddset(sigset_t *set, int signum)
 { return 0; }

compat/win32/trace2_win32_process_info.c

@@ -0,0 +1,147 @@
+#include "../../cache.h"
+#include "../../json-writer.h"
+#include <Psapi.h>
+#include <tlHelp32.h>
+
+/*
+ * An arbitrarily chosen value to limit the size of the ancestor
+ * array built in git_processes().
+ */
+#define NR_PIDS_LIMIT 10
+
+/*
+ * Find the process data for the given PID in the given snapshot
+ * and update the PROCESSENTRY32 data.
+ */
+static int find_pid(DWORD pid, HANDLE hSnapshot, PROCESSENTRY32 *pe32)
+{
+	pe32->dwSize = sizeof(PROCESSENTRY32);
+
+	if (Process32First(hSnapshot, pe32)) {
+		do {
+			if (pe32->th32ProcessID == pid)
+				return 1;
+		} while (Process32Next(hSnapshot, pe32));
+	}
+	return 0;
+}
+
+/*
+ * Accumulate JSON array of our parent processes:
+ *     [
+ *         exe-name-parent,
+ *         exe-name-grand-parent,
+ *         ...
+ *     ]
+ *
+ * Note: we only report the filename of the process executable; the
+ *       only way to get its full pathname is to use OpenProcess()
+ *       and GetModuleFileNameEx() or QueryfullProcessImageName()
+ *       and that seems rather expensive (on top of the cost of
+ *       getting the snapshot).
+ *
+ * Note: we compute the set of parent processes by walking the PPID
+ *       link in each visited PROCESSENTRY32 record.  This search
+ *       stops when an ancestor process is not found in the snapshot
+ *       (because it exited before the current or intermediate parent
+ *       process exited).
+ *
+ *       This search may compute an incorrect result if the PPID link
+ *       refers to the PID of an exited parent and that PID has been
+ *       recycled and given to a new unrelated process.
+ *
+ *       Worse, it is possible for a child or descendant of the
+ *       current process to be given the recycled PID and cause a
+ *       PPID-cycle.  This would cause an infinite loop building our
+ *       parent process array.
+ *
+ * Note: for completeness, the "System Idle" process has PID=0 and
+ *       PPID=0 and could cause another PPID-cycle.  We don't expect
+ *       Git to be a descendant of the idle process, but because of
+ *       PID recycling, it might be possible to get a PPID link value
+ *       of 0.  This too would cause an infinite loop.
+ *
+ * Therefore, we keep an array of the visited PPIDs to guard against
+ * cycles.
+ *
+ * We use a fixed-size array rather than ALLOC_GROW to keep things
+ * simple and avoid the alloc/realloc overhead.  It is OK if we
+ * truncate the search and return a partial answer.
+ */
+static void get_processes(struct json_writer *jw, HANDLE hSnapshot)
+{
+	PROCESSENTRY32 pe32;
+	DWORD pid;
+	DWORD pid_list[NR_PIDS_LIMIT];
+	int k, nr_pids = 0;
+
+	pid = GetCurrentProcessId();
+	while (find_pid(pid, hSnapshot, &pe32)) {
+		/* Only report parents. Omit self from the JSON output. */
+		if (nr_pids)
+			jw_array_string(jw, pe32.szExeFile);
+
+		/* Check for cycle in snapshot. (Yes, it happened.) */
+		for (k = 0; k < nr_pids; k++)
+			if (pid == pid_list[k]) {
+				jw_array_string(jw, "(cycle)");
+				return;
+			}
+
+		if (nr_pids == NR_PIDS_LIMIT) {
+			jw_array_string(jw, "(truncated)");
+			return;
+		}
+
+		pid_list[nr_pids++] = pid;
+
+		pid = pe32.th32ParentProcessID;
+	}
+}
+
+/*
+ * Emit JSON data for the current and parent processes.  Individual
+ * trace2 targets can decide how to actually print it.
+ */
+static void get_ancestry(void)
+{
+	HANDLE hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+
+	if (hSnapshot != INVALID_HANDLE_VALUE) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_array_begin(&jw, 0);
+		get_processes(&jw, hSnapshot);
+		jw_end(&jw);
+
+		trace2_data_json("process", the_repository, "windows/ancestry",
+				 &jw);
+
+		jw_release(&jw);
+		CloseHandle(hSnapshot);
+	}
+}
+
+/*
+ * Is a debugger attached to the current process?
+ *
+ * This will catch debug runs (where the debugger started the process).
+ * This is the normal case.  Since this code is called during our startup,
+ * it will not report instances where a debugger is attached dynamically
+ * to a running git process, but that is relatively rare.
+ */
+static void get_is_being_debugged(void)
+{
+	if (IsDebuggerPresent())
+		trace2_data_intmax("process", the_repository,
+				   "windows/debugger_present", 1);
+}
+
+void trace2_collect_process_info(void)
+{
+	if (!trace2_is_enabled())
+		return;
+
+	get_is_being_debugged();
+	get_ancestry();
+}

config.c

@@ -2657,6 +2657,8 @@ int git_config_set_gently(const char *key, const char *value)
 void git_config_set(const char *key, const char *value)
 {
 	git_config_set_multivar(key, value, NULL, 0);
+
+	trace2_cmd_set_config(key, value);
 }
 
 /*

config.mak.uname

@@ -393,6 +393,7 @@ ifeq ($(uname_S),Windows)
 	BASIC_CFLAGS = -nologo -I. -I../zlib -Icompat/vcbuild -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
 	COMPAT_OBJS = compat/msvc.o compat/winansi.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
+		compat/win32/trace2_win32_process_info.o \
 		compat/win32/dirent.o
 	COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DNOGDI -DHAVE_STRING_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
 	BASIC_LDFLAGS = -IGNORE:4217 -IGNORE:4049 -NOLOGO -SUBSYSTEM:CONSOLE
@@ -546,6 +547,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	COMPAT_CFLAGS += -DNOGDI -Icompat -Icompat/win32
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
 	COMPAT_OBJS += compat/mingw.o compat/winansi.o \
+		compat/win32/trace2_win32_process_info.o \
 		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
 		compat/win32/dirent.o

connect.c

@@ -1248,6 +1248,7 @@ struct child_process *git_connect(int fd[2], const char *url,
 		conn = NULL;
 	} else if (protocol == PROTO_GIT) {
 		conn = git_connect_git(fd, hostandport, path, prog, version, flags);
+		conn->trace2_child_class = "transport/git";
 	} else {
 		struct strbuf cmd = STRBUF_INIT;
 		const char *const *var;
@@ -1290,9 +1291,11 @@ struct child_process *git_connect(int fd[2], const char *url,
 				strbuf_release(&cmd);
 				return NULL;
 			}
+			conn->trace2_child_class = "transport/ssh";
 			fill_ssh_args(conn, ssh_host, port, version, flags);
 		} else {
 			transport_check_allowed("file");
+			conn->trace2_child_class = "transport/file";
 			if (version > 0) {
 				argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
 						 version);

editor.c

@@ -78,6 +78,7 @@ static int launch_specified_editor(const char *editor, const char *path,
 		p.argv = args;
 		p.env = env;
 		p.use_shell = 1;
+		p.trace2_child_class = "editor";
 		if (start_command(&p) < 0)
 			return error("unable to start editor '%s'", editor);
 

exec-cmd.c

@@ -209,6 +209,8 @@ static int git_get_exec_path(struct strbuf *buf, const char *argv0)
 		return -1;
 	}
 
+	trace2_cmd_path(buf->buf);
+
 	return 0;
 }
 

git-compat-util.h

@@ -1259,6 +1259,13 @@ static inline int is_missing_file_error(int errno_)
 
 extern int cmd_main(int, const char **);
 
+/*
+ * Intercept all calls to exit() and route them to trace2 to
+ * optionally emit a message before calling the real exit().
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+#define exit(code) exit(trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
 /*
  * You can mark a stack variable with UNLEAK(var) to avoid it being
  * reported as a leak by tools like LSAN or valgrind. The argument

git.c

@@ -147,16 +147,20 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 				git_set_exec_path(cmd + 1);
 			else {
 				puts(git_exec_path());
+				trace2_cmd_name("_query_");
 				exit(0);
 			}
 		} else if (!strcmp(cmd, "--html-path")) {
 			puts(system_path(GIT_HTML_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--man-path")) {
 			puts(system_path(GIT_MAN_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "--info-path")) {
 			puts(system_path(GIT_INFO_PATH));
+			trace2_cmd_name("_query_");
 			exit(0);
 		} else if (!strcmp(cmd, "-p") || !strcmp(cmd, "--paginate")) {
 			use_pager = 1;
@@ -285,6 +289,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			(*argv)++;
 			(*argc)--;
 		} else if (skip_prefix(cmd, "--list-cmds=", &cmd)) {
+			trace2_cmd_name("_query_");
 			if (!strcmp(cmd, "parseopt")) {
 				struct string_list list = STRING_LIST_INIT_DUP;
 				int i;
@@ -332,9 +337,14 @@ static int handle_alias(int *argcp, const char ***argv)
 			commit_pager_choice();
 
 			child.use_shell = 1;
+			child.trace2_child_class = "shell_alias";
 			argv_array_push(&child.args, alias_string + 1);
 			argv_array_pushv(&child.args, (*argv) + 1);
 
+			trace2_cmd_alias(alias_command, child.args.argv);
+			trace2_cmd_list_config();
+			trace2_cmd_name("_run_shell_alias_");
+
 			ret = run_command(&child);
 			if (ret >= 0)   /* normal exit */
 				exit(ret);
@@ -369,6 +379,9 @@ static int handle_alias(int *argcp, const char ***argv)
 		/* insert after command name */
 		memcpy(new_argv + count, *argv + 1, sizeof(char *) * *argcp);
 
+		trace2_cmd_alias(alias_command, new_argv);
+		trace2_cmd_list_config();
+
 		*argv = new_argv;
 		*argcp += count - 1;
 
@@ -417,6 +430,8 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 		setup_work_tree();
 
 	trace_argv_printf(argv, "trace: built-in: git");
+	trace2_cmd_name(p->cmd);
+	trace2_cmd_list_config();
 
 	validate_cache_entries(the_repository->index);
 	status = p->fn(argc, argv, prefix);
@@ -666,7 +681,14 @@ static void execv_dashed_external(const char **argv)
 	cmd.clean_on_exit = 1;
 	cmd.wait_after_clean = 1;
 	cmd.silent_exec_failure = 1;
+	cmd.trace2_child_class = "dashed";
 
+	trace2_cmd_name("_run_dashed_");
+
+	/*
+	 * The code in run_command() logs trace2 child_start/child_exit
+	 * events, so we do not need to report exec/exec_result events here.
+	 */
 	trace_argv_printf(cmd.args.argv, "trace: exec:");
 
 	/*
@@ -676,6 +698,12 @@ static void execv_dashed_external(const char **argv)
 	 * the program.
 	 */
 	status = run_command(&cmd);
+
+	/*
+	 * If the child process ran and we are now going to exit, emit a
+	 * generic string as our trace2 command verb to indicate that we
+	 * launched a dashed command.
+	 */
 	if (status >= 0)
 		exit(status);
 	else if (errno != ENOENT)
@@ -701,6 +729,43 @@ static int run_argv(int *argcp, const char ***argv)
 		if (!done_alias)
 			handle_builtin(*argcp, *argv);
 
+#if 0 // TODO In GFW, need to amend a7924b655e940b06cb547c235d6bed9767929673 to include trace2_ and _tr2 lines.
+		else if (get_builtin(**argv)) {
+			struct argv_array args = ARGV_ARRAY_INIT;
+			int i;
+
+			/*
+			 * The current process is committed to launching a
+			 * child process to run the command named in (**argv)
+			 * and exiting.  Log a generic string as the trace2
+			 * command verb to indicate this.  Note that the child
+			 * process will log the actual verb when it runs.
+			 */
+			trace2_cmd_name("_run_git_alias_");
+
+			if (get_super_prefix())
+				die("%s doesn't support --super-prefix", **argv);
+
+			commit_pager_choice();
+
+			argv_array_push(&args, "git");
+			for (i = 0; i < *argcp; i++)
+				argv_array_push(&args, (*argv)[i]);
+
+			trace_argv_printf(args.argv, "trace: exec:");
+
+			/*
+			 * if we fail because the command is not found, it is
+			 * OK to return. Otherwise, we just pass along the status code.
+			 */
+			i = run_command_v_opt_tr2(args.argv, RUN_SILENT_EXEC_FAILURE |
+						  RUN_CLEAN_ON_EXIT, "git_alias");
+			if (i >= 0 || errno != ENOENT)
+				exit(i);
+			die("could not execute builtin %s", **argv);
+		}
+#endif // a7924b655e940b06cb547c235d6bed9767929673
+
 		/* .. then try the external ones */
 		execv_dashed_external(*argv);
 

pager.c

@@ -100,6 +100,7 @@ void prepare_pager_args(struct child_process *pager_process, const char *pager)
 	argv_array_push(&pager_process->args, pager);
 	pager_process->use_shell = 1;
 	setup_pager_env(&pager_process->env_array);
+	pager_process->trace2_child_class = "pager";
 }
 
 void setup_pager(void)

read-cache.c

@@ -2226,6 +2226,16 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		load_index_extensions(&p);
 	}
 	munmap((void *)mmap, mmap_size);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "read/version",
+			   istate->version);
+	trace2_data_intmax("index", the_repository, "read/cache_nr",
+			   istate->cache_nr);
+
 	return istate->cache_nr;
 
 unmap:
@@ -2257,9 +2267,17 @@ int read_index_from(struct index_state *istate, const char *path,
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 	trace_performance_enter();
 	ret = do_read_index(istate, path, 0);
 	trace_performance_leave("read cache %s", path);
+	trace2_region_leave_printf("index", "do_read_index", the_repository,
+				   "%s", path);
 
 	split_index = istate->split_index;
 	if (!split_index || is_null_oid(&split_index->base_oid)) {
@@ -2275,7 +2293,11 @@ int read_index_from(struct index_state *istate, const char *path,
 
 	base_oid_hex = oid_to_hex(&split_index->base_oid);
 	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
+	trace2_region_enter_printf("index", "shared/do_read_index",
+				   the_repository, "%s", base_path);
 	ret = do_read_index(split_index->base, base_path, 1);
+	trace2_region_leave_printf("index", "shared/do_read_index",
+				   the_repository, "%s", base_path);
 	if (!oideq(&split_index->base_oid, &split_index->base->oid))
 		die(_("broken index, expect %s in %s, got %s"),
 		    base_oid_hex, base_path,
@@ -2983,6 +3005,16 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	istate->timestamp.sec = (unsigned int)st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 	trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_data_intmax("index", the_repository, "write/version",
+			   istate->version);
+	trace2_data_intmax("index", the_repository, "write/cache_nr",
+			   istate->cache_nr);
+
 	return 0;
 }
 
@@ -3002,7 +3034,18 @@ static int commit_locked_index(struct lock_file *lk)
 static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
 				 unsigned flags)
 {
-	int ret = do_write_index(istate, lock->tempfile, 0);
+	int ret;
+
+	/*
+	 * TODO trace2: replace "the_repository" with the actual repo instance
+	 * that is associated with the given "istate".
+	 */
+	trace2_region_enter_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+	ret = do_write_index(istate, lock->tempfile, 0);
+	trace2_region_leave_printf("index", "do_write_index", the_repository,
+				   "%s", lock->tempfile->filename.buf);
+
 	if (ret)
 		return ret;
 	if (flags & COMMIT_LOCK)
@@ -3087,7 +3130,13 @@ static int write_shared_index(struct index_state *istate,
 	int ret;
 
 	move_cache_to_base_index(istate);
+
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
 	ret = do_write_index(si->base, *temp, 1);
+	trace2_region_enter_printf("index", "shared/do_write_index",
+				   the_repository, "%s", (*temp)->filename.buf);
+
 	if (ret)
 		return ret;
 	ret = adjust_shared_perm(get_tempfile_path(*temp));

remote-curl.c

@@ -1385,6 +1385,13 @@ int cmd_main(int argc, const char **argv)
 	string_list_init(&options.deepen_not, 1);
 	string_list_init(&options.push_options, 1);
 
+	/*
+	 * Just report "remote-curl" here (folding all the various aliases
+	 * ("git-remote-http", "git-remote-https", and etc.) here since they
+	 * are all just copies of the same actual executable.
+	 */
+	trace2_cmd_name("remote-curl");
+
 	remote = remote_get(argv[1]);
 
 	if (argc > 2) {

repository.c

@@ -126,6 +126,8 @@ out:
 void repo_set_worktree(struct repository *repo, const char *path)
 {
 	repo->worktree = real_pathdup(path, 1);
+
+	trace2_def_repo(repo);
 }
 
 static int read_and_verify_repository_format(struct repository_format *format,

repository.h

@@ -92,6 +92,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* A unique-id for tracing purposes. */
+	int trace2_repo_id;
+
 	/* Configurations */
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */

run-command.c

@@ -219,9 +219,29 @@ static int exists_in_PATH(const char *file)
 
 int sane_execvp(const char *file, char * const argv[])
 {
+#ifndef GIT_WINDOWS_NATIVE
+	/*
+	 * execvp() doesn't return, so we all we can do is tell trace2
+	 * what we are about to do and let it leave a hint in the log
+	 * (unless of course the execvp() fails).
+	 *
+	 * we skip this for Windows because the compat layer already
+	 * has to emulate the execvp() call anyway.
+	 */
+	int exec_id = trace2_exec(file, (const char **)argv);
+#endif
+
 	if (!execvp(file, argv))
 		return 0; /* cannot happen ;-) */
 
+#ifndef GIT_WINDOWS_NATIVE
+	{
+		int ec = errno;
+		trace2_exec_result(exec_id, ec);
+		errno = ec;
+	}
+#endif
+
 	/*
 	 * When a command can't be found because one of the directories
 	 * listed in $PATH is unsearchable, execvp reports EACCES, but
@@ -712,6 +732,7 @@ fail_pipe:
 		cmd->err = fderr[0];
 	}
 
+	trace2_child_start(cmd);
 	trace_run_command(cmd);
 
 	fflush(NULL);
@@ -926,6 +947,8 @@ end_of_spawn:
 #endif
 
 	if (cmd->pid < 0) {
+		trace2_child_exit(cmd, -1);
+
 		if (need_in)
 			close_pair(fdin);
 		else if (cmd->in)
@@ -964,13 +987,16 @@ end_of_spawn:
 int finish_command(struct child_process *cmd)
 {
 	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 0);
+	trace2_child_exit(cmd, ret);
 	child_process_clear(cmd);
 	return ret;
 }
 
 int finish_command_in_signal(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 1);
+	trace2_child_exit(cmd, ret);
+	return ret;
 }
 
 
@@ -992,7 +1018,18 @@ int run_command_v_opt(const char **argv, int opt)
 	return run_command_v_opt_cd_env(argv, opt, NULL, NULL);
 }
 
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, NULL, NULL, tr2_class);
+}
+
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env)
+{
+	return run_command_v_opt_cd_env_tr2(argv, opt, dir, env, NULL);
+}
+
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir,
+				 const char *const *env, const char *tr2_class)
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	cmd.argv = argv;
@@ -1004,6 +1041,7 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
 	cmd.clean_on_exit = opt & RUN_CLEAN_ON_EXIT ? 1 : 0;
 	cmd.dir = dir;
 	cmd.env = env;
+	cmd.trace2_child_class = tr2_class;
 	return run_command(&cmd);
 }
 
@@ -1319,6 +1357,7 @@ int run_hook_ve(const char *const *env, const char *name, va_list args)
 	hook.env = env;
 	hook.no_stdin = 1;
 	hook.stdout_to_stderr = 1;
+	hook.trace2_hook_name = name;
 
 	return run_command(&hook);
 }
@@ -1807,3 +1846,21 @@ int run_processes_parallel(int n,
 	pp_cleanup(&pp);
 	return 0;
 }
+
+int run_processes_parallel_tr2(int n, get_next_task_fn get_next_task,
+			       start_failure_fn start_failure,
+			       task_finished_fn task_finished, void *pp_cb,
+			       const char *tr2_category, const char *tr2_label)
+{
+	int result;
+
+	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d",
+				   ((n < 1) ? online_cpus() : n));
+
+	result = run_processes_parallel(n, get_next_task, start_failure,
+					task_finished, pp_cb);
+
+	trace2_region_leave(tr2_category, tr2_label, NULL);
+
+	return result;
+}

run-command.h

@@ -10,6 +10,12 @@ struct child_process {
 	struct argv_array args;
 	struct argv_array env_array;
 	pid_t pid;
+
+	int trace2_child_id;
+	uint64_t trace2_child_us_start;
+	const char *trace2_child_class;
+	const char *trace2_hook_name;
+
 	/*
 	 * Using .in, .out, .err:
 	 * - Specify 0 for no redirections (child inherits stdin, stdout,
@@ -73,12 +79,14 @@ extern int run_hook_ve(const char *const *env, const char *name, va_list args);
 #define RUN_USING_SHELL 16
 #define RUN_CLEAN_ON_EXIT 32
 int run_command_v_opt(const char **argv, int opt);
-
+int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class);
 /*
  * env (the environment) is to be formatted like environ: "VAR=VALUE".
  * To unset an environment variable use just "VAR".
  */
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
+int run_command_v_opt_cd_env_tr2(const char **argv, int opt, const char *dir,
+				 const char *const *env, const char *tr2_class);
 
 /**
  * Execute the given command, sending "in" to its stdin, and capturing its
@@ -220,5 +228,8 @@ int run_processes_parallel(int n,
 			   start_failure_fn,
 			   task_finished_fn,
 			   void *pp_cb);
+int run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
+			       task_finished_fn, void *pp_cb,
+			       const char *tr2_category, const char *tr2_label);
 
 #endif

sequencer.c

@@ -1103,6 +1103,7 @@ static int run_rewrite_hook(const struct object_id *oldoid,
 	proc.argv = argv;
 	proc.in = -1;
 	proc.stdout_to_stderr = 1;
+	proc.trace2_hook_name = "post-rewrite";
 
 	code = start_command(&proc);
 	if (code)
@@ -3786,6 +3787,7 @@ cleanup_head_ref:
 				hook.in = open(rebase_path_rewritten_list(),
 					O_RDONLY);
 				hook.stdout_to_stderr = 1;
+				hook.trace2_hook_name = "post-rewrite";
 				argv_array_push(&hook.args, post_rewrite_hook);
 				argv_array_push(&hook.args, "rebase");
 				/* we don't care if this hook failed */

sh-i18n--envsubst.c

@@ -14,6 +14,7 @@
  */
 
 #include "git-compat-util.h"
+#include "trace2.h"
 
 /* Substitution of environment variables in shell format strings.
    Copyright (C) 2003-2007 Free Software Foundation, Inc.
@@ -67,6 +68,8 @@ cmd_main (int argc, const char *argv[])
   /* Default values for command line options.  */
   /* unsigned short int show_variables = 0; */
 
+  trace2_cmd_name("sh-i18n--envsubst");
+
   switch (argc)
 	{
 	case 1:

sub-process.c

@@ -88,6 +88,7 @@ int subprocess_start(struct hashmap *hashmap, struct subprocess_entry *entry, co
 	process->out = -1;
 	process->clean_on_exit = 1;
 	process->clean_on_exit_handler = subprocess_exit_handler;
+	process->trace2_child_class = "subprocess";
 
 	err = start_command(process);
 	if (err) {

submodule.c

@@ -1609,11 +1609,12 @@ int fetch_populated_submodules(struct repository *r,
 
 	calculate_changed_submodule_paths(r, &spf.changed_submodule_names);
 	string_list_sort(&spf.changed_submodule_names);
-	run_processes_parallel(max_parallel_jobs,
-			       get_next_submodule,
-			       fetch_start_failure,
-			       fetch_finish,
-			       &spf);
+	run_processes_parallel_tr2(max_parallel_jobs,
+				   get_next_submodule,
+				   fetch_start_failure,
+				   fetch_finish,
+				   &spf,
+				   "submodule", "parallel/fetch");
 
 	argv_array_clear(&spf.args);
 out:

t/helper/test-parse-options.c

@@ -2,6 +2,7 @@
 #include "cache.h"
 #include "parse-options.h"
 #include "string-list.h"
+#include "trace2.h"
 
 static int boolean = 0;
 static int integer = 0;
@@ -153,6 +154,8 @@ int cmd__parse_options(int argc, const char **argv)
 	int i;
 	int ret = 0;
 
+	trace2_cmd_name("_parse_");
+
 	argc = parse_options(argc, (const char **)argv, prefix, options, usage, 0);
 
 	if (length_cb.called) {

t/helper/test-tool.c

@@ -1,5 +1,6 @@
 #include "git-compat-util.h"
 #include "test-tool.h"
+#include "trace2.h"
 
 struct test_cmd {
 	const char *name;
@@ -51,6 +52,7 @@ static struct test_cmd cmds[] = {
 	{ "submodule-config", cmd__submodule_config },
 	{ "submodule-nested-repo-config", cmd__submodule_nested_repo_config },
 	{ "subprocess", cmd__subprocess },
+	{ "trace2", cmd__trace2 },
 	{ "urlmatch-normalization", cmd__urlmatch_normalization },
 	{ "xml-encode", cmd__xml_encode },
 	{ "wildmatch", cmd__wildmatch },
@@ -82,6 +84,8 @@ int cmd_main(int argc, const char **argv)
 		if (!strcmp(cmds[i].name, argv[1])) {
 			argv++;
 			argc--;
+			trace2_cmd_name(cmds[i].name);
+			trace2_cmd_list_config();
 			return cmds[i].fn(argc, argv);
 		}
 	}

t/helper/test-tool.h

@@ -48,6 +48,7 @@ int cmd__string_list(int argc, const char **argv);
 int cmd__submodule_config(int argc, const char **argv);
 int cmd__submodule_nested_repo_config(int argc, const char **argv);
 int cmd__subprocess(int argc, const char **argv);
+int cmd__trace2(int argc, const char **argv);
 int cmd__urlmatch_normalization(int argc, const char **argv);
 int cmd__xml_encode(int argc, const char **argv);
 int cmd__wildmatch(int argc, const char **argv);

t/helper/test-trace2.c

@@ -0,0 +1,273 @@
+#include "test-tool.h"
+#include "cache.h"
+#include "argv-array.h"
+#include "run-command.h"
+#include "exec-cmd.h"
+#include "config.h"
+
+typedef int(fn_unit_test)(int argc, const char **argv);
+
+struct unit_test {
+	fn_unit_test *ut_fn;
+	const char *ut_name;
+	const char *ut_usage;
+};
+
+#define MyOk 0
+#define MyError 1
+
+static int get_i(int *p_value, const char *data)
+{
+	char *endptr;
+
+	if (!data || !*data)
+		return MyError;
+
+	*p_value = strtol(data, &endptr, 10);
+	if (*endptr || errno == ERANGE)
+		return MyError;
+
+	return MyOk;
+}
+
+/*
+ * Cause process to exit with the requested value via "return".
+ *
+ * Rely on test-tool.c:cmd_main() to call trace2_cmd_exit()
+ * with our result.
+ *
+ * Test harness can confirm:
+ * [] the process-exit value.
+ * [] the "code" field in the "exit" trace2 event.
+ * [] the "code" field in the "atexit" trace2 event.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] "def_param" events for all of the "interesting" pre-defined
+ * config settings.
+ */
+static int ut_001return(int argc, const char **argv)
+{
+	int rc;
+
+	if (get_i(&rc, argv[0]))
+		die("expect <exit_code>");
+
+	return rc;
+}
+
+/*
+ * Cause the process to exit with the requested value via "exit()".
+ *
+ * Test harness can confirm:
+ * [] the "code" field in the "exit" trace2 event.
+ * [] the "code" field in the "atexit" trace2 event.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] "def_param" events for all of the "interesting" pre-defined
+ * config settings.
+ */
+static int ut_002exit(int argc, const char **argv)
+{
+	int rc;
+
+	if (get_i(&rc, argv[0]))
+		die("expect <exit_code>");
+
+	exit(rc);
+}
+
+/*
+ * Send an "error" event with each value in argv.  Normally, git only issues
+ * a single "error" event immediately before issuing an "exit" event (such
+ * as in die() or BUG()), but multiple "error" events are allowed.
+ *
+ * Test harness can confirm:
+ * [] a trace2 "error" event for each value in argv.
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] (optional) the file:line in the "exit" event refers to this function.
+ */
+static int ut_003error(int argc, const char **argv)
+{
+	int k;
+
+	if (!argv[0] || !*argv[0])
+		die("expect <error_message>");
+
+	for (k = 0; k < argc; k++)
+		error("%s", argv[k]);
+
+	return 0;
+}
+
+/*
+ * Run a child process and wait for it to finish and exit with its return code.
+ * test-tool trace2 004child [<child-command-line>]
+ *
+ * For example:
+ * test-tool trace2 004child git version
+ * test-tool trace2 004child test-tool trace2 001return 0
+ * test-tool trace2 004child test-tool trace2 004child test-tool trace2 004child
+ * test-tool trace2 004child git -c alias.xyz=version xyz
+ *
+ * Test harness can confirm:
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] that the outer process has a single component SID (or depth "d0" in
+ *    the PERF stream).
+ * [] that "child_start" and "child_exit" events are generated for the child.
+ * [] if the child process is an instrumented executable:
+ *    [] that "version", "start", ..., "exit", and "atexit" events are
+ *       generated by the child process.
+ *    [] that the child process events have a multiple component SID (or
+ *       depth "dN+1" in the PERF stream).
+ * [] that the child exit code is propagated to the parent process "exit"
+ *    and "atexit" events..
+ * [] (optional) that the "t_abs" field in the child process "atexit" event
+ *    is less than the "t_rel" field in the "child_exit" event of the parent
+ *    process.
+ * [] if the child process is like the alias example above,
+ *    [] (optional) the child process attempts to run "git-xyx" as a dashed
+ *       command.
+ *    [] the child process emits an "alias" event with "xyz" => "version"
+ *    [] the child process runs "git version" as a child process.
+ *    [] the child process has a 3 component SID (or depth "d2" in the PERF
+ *       stream).
+ */
+static int ut_004child(int argc, const char **argv)
+{
+	int result;
+
+	/*
+	 * Allow empty <child_command_line> so we can do arbitrarily deep
+	 * command nesting and let the last one be null.
+	 */
+	if (!argc)
+		return 0;
+
+	result = run_command_v_opt(argv, 0);
+	exit(result);
+}
+
+/*
+ * Exec a git command.  This may either create a child process (Windows)
+ * or replace the existing process.
+ * test-tool trace2 005exec <git_command_args>
+ *
+ * For example:
+ * test-tool trace2 005exec version
+ *
+ * Test harness can confirm (on Windows):
+ * [] the "name" field in the "cmd_name" trace2 event.
+ * [] that the outer process has a single component SID (or depth "d0" in
+ *    the PERF stream).
+ * [] that "exec" and "exec_result" events are generated for the child
+ *    process (since the Windows compatibility layer fakes an exec() with
+ *    a CreateProcess(), WaitForSingleObject(), and exit()).
+ * [] that the child process has multiple component SID (or depth "dN+1"
+ *    in the PERF stream).
+ *
+ * Test harness can confirm (on platforms with a real exec() function):
+ * [] TODO talk about process replacement and how it affects SID.
+ */
+static int ut_005exec(int argc, const char **argv)
+{
+	int result;
+
+	if (!argc)
+		return 0;
+
+	result = execv_git_cmd(argv);
+	return result;
+}
+
+static int ut_006data(int argc, const char **argv)
+{
+	const char *usage_error =
+		"expect <cat0> <k0> <v0> [<cat1> <k1> <v1> [...]]";
+
+	if (argc % 3 != 0)
+		die("%s", usage_error);
+
+	while (argc) {
+		if (!argv[0] || !*argv[0] || !argv[1] || !*argv[1] ||
+		    !argv[2] || !*argv[2])
+			die("%s", usage_error);
+
+		trace2_data_string(argv[0], the_repository, argv[1], argv[2]);
+		argv += 3;
+		argc -= 3;
+	}
+
+	return 0;
+}
+
+/*
+ * Usage:
+ *     test-tool trace2 <ut_name_1> <ut_usage_1>
+ *     test-tool trace2 <ut_name_2> <ut_usage_2>
+ *     ...
+ */
+#define USAGE_PREFIX "test-tool trace2"
+
+/* clang-format off */
+static struct unit_test ut_table[] = {
+	{ ut_001return,   "001return", "<exit_code>" },
+	{ ut_002exit,     "002exit",   "<exit_code>" },
+	{ ut_003error,    "003error",  "<error_message>+" },
+	{ ut_004child,    "004child",  "[<child_command_line>]" },
+	{ ut_005exec,     "005exec",   "<git_command_args>" },
+	{ ut_006data,     "006data",   "[<category> <key> <value>]+" },
+};
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_ut(k, ut_k)			\
+	for (k = 0, ut_k = &ut_table[k];	\
+	     k < ARRAY_SIZE(ut_table);		\
+	     k++, ut_k = &ut_table[k])
+/* clang-format on */
+
+static int print_usage(void)
+{
+	int k;
+	struct unit_test *ut_k;
+
+	fprintf(stderr, "usage:\n");
+	for_each_ut (k, ut_k)
+		fprintf(stderr, "\t%s %s %s\n", USAGE_PREFIX, ut_k->ut_name,
+			ut_k->ut_usage);
+
+	return 129;
+}
+
+/*
+ * Issue various trace2 events for testing.
+ *
+ * We assume that these trace2 routines has already been called:
+ *    [] trace2_initialize()      [common-main.c:main()]
+ *    [] trace2_cmd_start()       [common-main.c:main()]
+ *    [] trace2_cmd_name()        [test-tool.c:cmd_main()]
+ *    [] tracd2_cmd_list_config() [test-tool.c:cmd_main()]
+ * So that:
+ *    [] the various trace2 streams are open.
+ *    [] the process SID has been created.
+ *    [] the "version" event has been generated.
+ *    [] the "start" event has been generated.
+ *    [] the "cmd_name" event has been generated.
+ *    [] this writes various "def_param" events for interesting config values.
+ *
+ * We further assume that if we return (rather than exit()), trace2_cmd_exit()
+ * will be called by test-tool.c:cmd_main().
+ */
+int cmd__trace2(int argc, const char **argv)
+{
+	int k;
+	struct unit_test *ut_k;
+
+	argc--; /* skip over "trace2" arg */
+	argv++;
+
+	if (argc)
+		for_each_ut (k, ut_k)
+			if (!strcmp(argv[0], ut_k->ut_name))
+				return ut_k->ut_fn(argc - 1, argv + 1);
+
+	return print_usage();
+}

t/t0001-init.sh

@@ -93,6 +93,7 @@ test_expect_success 'No extra GIT_* on alias scripts' '
 		sed -n \
 			-e "/^GIT_PREFIX=/d" \
 			-e "/^GIT_TEXTDOMAINDIR=/d" \
+			-e "/^GIT_TR2_PARENT/d" \
 			-e "/^GIT_/s/=.*//p" |
 		sort
 	EOF

t/t0210-trace2-normal.sh

@@ -0,0 +1,135 @@
+#!/bin/sh
+
+test_description='test trace2 facility (normal target)'
+. ./test-lib.sh
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+# Turn off any inherited trace2 settings for this test.
+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+unset GIT_TR2_BRIEF
+unset GIT_TR2_CONFIG_PARAMS
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# This script tests the normal target in isolation.
+#
+# Defer setting GIT_TR2 until the actual command line we want to test
+# because hidden git and test-tool commands run by the test harness
+# can contaminate our output.
+
+# Enable "brief" feature which turns off "<clock> <file>:<line> " prefix.
+GIT_TR2_BRIEF=1 && export GIT_TR2_BRIEF
+
+# Basic tests of the trace2 normal stream.  Since this stream is used
+# primarily with printf-style debugging/tracing, we do limited testing
+# here.
+#
+# We do confirm the following API features:
+# [] the 'version <v>' event
+# [] the 'start <argv>' event
+# [] the 'cmd_name <name>' event
+# [] the 'exit <time> code:<code>' event
+# [] the 'atexit <time> code:<code>' event
+#
+# Fields of the form _FIELD_ are tokens that have been replaced (such
+# as the elapsed time).
+
+# Verb 001return
+#
+# Implicit return from cmd_<verb> function propagates <code>.
+
+test_expect_success 'normal stream, return code 0' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'normal stream, return code 1' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_must_fail env GIT_TR2="$(pwd)/trace.normal" test-tool trace2 001return 1 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 001return 1
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:1
+		atexit elapsed:_TIME_ code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 002exit
+#
+# Explicit exit(code) from within cmd_<verb> propagates <code>.
+
+test_expect_success 'normal stream, exit code 0' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 002exit 0 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 002exit 0
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'normal stream, exit code 1' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_must_fail env GIT_TR2="$(pwd)/trace.normal" test-tool trace2 002exit 1 &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 002exit 1
+		cmd_name trace2 (trace2)
+		exit elapsed:_TIME_ code:1
+		atexit elapsed:_TIME_ code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success 'normal stream, error event' '
+	test_when_finished "rm trace.normal actual expect" &&
+	GIT_TR2="$(pwd)/trace.normal" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 003error '\''hello world'\'' '\''this is a test'\''
+		cmd_name trace2 (trace2)
+		error hello world
+		error this is a test
+		exit elapsed:_TIME_ code:0
+		atexit elapsed:_TIME_ code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_done

t/t0210/scrub_normal.perl

@@ -0,0 +1,48 @@
+#!/usr/bin/perl
+#
+# Scrub the variable fields from the normal trace2 output to
+# make testing easier.
+
+use strict;
+use warnings;
+
+my $float = '[0-9]*\.[0-9]+([eE][-+]?[0-9]+)?';
+
+# This code assumes that the trace2 data was written with bare
+# turned on (which omits the "<clock> <file>:<line>" prefix.
+
+while (<>) {
+    # Various messages include an elapsed time in the middle
+    # of the message.  Replace the time with a placeholder to
+    # simplify our HEREDOC in the test script.
+    s/elapsed:$float/elapsed:_TIME_/g;
+
+    my $line = $_;
+
+    # we expect:
+    #    start <argv0> [<argv1> [<argv2> [...]]]
+    #
+    # where argv0 might be a relative or absolute path, with
+    # or without quotes, and platform dependent.  Replace argv0
+    # with a token for HEREDOC matching in the test script.
+
+    if ($line =~ m/^start/) {
+	$line =~ /^start\s+(.*)/;
+	my $argv = $1;
+	$argv =~ m/(\'[^\']*\'|[^ ]+)\s+(.*)/;
+	my $argv_0 = $1;
+	my $argv_rest = $2;
+
+	print "start _EXE_ $argv_rest\n";
+    }
+    elsif ($line =~ m/^cmd_path/) {
+	# Likewise, the 'cmd_path' message breaks out argv[0].
+	#
+	# This line is only emitted when RUNTIME_PREFIX is defined,
+	# so just omit it for testing purposes.
+	# print "cmd_path _EXE_\n";
+    }
+    else {
+	print "$line";
+    }
+}

t/t0211-trace2-perf.sh

@@ -0,0 +1,153 @@
+#!/bin/sh
+
+test_description='test trace2 facility (perf target)'
+. ./test-lib.sh
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+# Turn off any inherited trace2 settings for this test.
+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+unset GIT_TR2_PERF_BRIEF
+unset GIT_TR2_CONFIG_PARAMS
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# Test each target independently.
+#
+# Defer setting GIT_TR2_PERF until the actual command we want to
+# test because hidden git and test-tool commands in the test
+# harness can contaminate our output.
+
+# Enable "brief" feature which turns off the prefix:
+#     "<clock> <file>:<line> | <nr_parents> | "
+GIT_TR2_PERF_BRIEF=1 && export GIT_TR2_PERF_BRIEF
+
+# Repeat some of the t0210 tests using the perf target stream instead of
+# the normal stream.
+#
+# Tokens here of the form _FIELD_ have been replaced in the observed output.
+
+# Verb 001return
+#
+# Implicit return from cmd_<verb> function propagates <code>.
+
+test_expect_success 'perf stream, return code 0' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start|||||_EXE_ trace2 001return 0
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'perf stream, return code 1' '
+	test_when_finished "rm trace.perf actual expect" &&
+	test_must_fail env GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 001return 1 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start|||||_EXE_ trace2 001return 1
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|exit||_T_ABS_|||code:1
+		d0|main|atexit||_T_ABS_|||code:1
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success 'perf stream, error event' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start|||||_EXE_ trace2 003error '\''hello world'\'' '\''this is a test'\''
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|error|||||hello world
+		d0|main|error|||||this is a test
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 004child
+#
+# Test nested spawning of child processes.
+#
+# Conceptually, this looks like:
+#    P1: TT trace2 004child
+#    P2: |--- TT trace2 004child
+#    P3:      |--- TT trace2 001return 0
+#
+# Which should generate events:
+#    P1: version
+#    P1: start
+#    P1: cmd_name
+#    P1: child_start
+#        P2: version
+#        P2: start
+#        P2: cmd_name
+#        P2: child_start
+#            P3: version
+#            P3: start
+#            P3: cmd_name
+#            P3: exit
+#            P3: atexit
+#        P2: child_exit
+#        P2: exit
+#        P2: atexit
+#    P1: child_exit
+#    P1: exit
+#    P1: atexit
+
+test_expect_success 'perf stream, child processes' '
+	test_when_finished "rm trace.perf actual expect" &&
+	GIT_TR2_PERF="$(pwd)/trace.perf" test-tool trace2 004child test-tool trace2 004child test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0211/scrub_perf.perl" <trace.perf >actual &&
+	cat >expect <<-EOF &&
+		d0|main|version|||||$V
+		d0|main|start|||||_EXE_ trace2 004child test-tool trace2 004child test-tool trace2 001return 0
+		d0|main|cmd_name|||||trace2 (trace2)
+		d0|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 004child test-tool trace2 001return 0
+		d1|main|version|||||$V
+		d1|main|start|||||_EXE_ trace2 004child test-tool trace2 001return 0
+		d1|main|cmd_name|||||trace2 (trace2/trace2)
+		d1|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 001return 0
+		d2|main|version|||||$V
+		d2|main|start|||||_EXE_ trace2 001return 0
+		d2|main|cmd_name|||||trace2 (trace2/trace2/trace2)
+		d2|main|exit||_T_ABS_|||code:0
+		d2|main|atexit||_T_ABS_|||code:0
+		d1|main|child_exit||_T_ABS_|_T_REL_||[ch0] pid:_PID_ code:0
+		d1|main|exit||_T_ABS_|||code:0
+		d1|main|atexit||_T_ABS_|||code:0
+		d0|main|child_exit||_T_ABS_|_T_REL_||[ch0] pid:_PID_ code:0
+		d0|main|exit||_T_ABS_|||code:0
+		d0|main|atexit||_T_ABS_|||code:0
+	EOF
+	test_cmp expect actual
+'
+
+test_done

t/t0211/scrub_perf.perl

@@ -0,0 +1,76 @@
+#!/usr/bin/perl
+#
+# Scrub the variable fields from the perf trace2 output to
+# make testing easier.
+
+use strict;
+use warnings;
+
+my $qpath = '\'[^\']*\'|[^ ]*';
+
+my $col_depth=0;
+my $col_thread=1;
+my $col_event=2;
+my $col_repo=3;
+my $col_t_abs=4;
+my $col_t_rel=5;
+my $col_category=6;
+my $col_rest=7;
+
+# This code assumes that the trace2 data was written with bare
+# turned on (which omits the "<clock> <file>:<line> | <parents>"
+# prefix.
+
+while (<>) {
+    my @tokens = split /\|/;
+
+    foreach my $col (@tokens) { $col =~ s/^\s+|\s+$//g; }
+
+    if ($tokens[$col_event] =~ m/^start/) {
+	# The 'start' message lists the contents of argv in $col_rest.
+	# On some platforms (Windows), argv[0] is *sometimes* a canonical
+	# absolute path to the EXE rather than the value passed in the
+	# shell script.  Replace it with a placeholder to simplify our
+	# HEREDOC in the test script.
+	my $argv0;
+	my $argvRest;
+	$tokens[$col_rest] =~ s/^($qpath)\W*(.*)/_EXE_ $2/;
+    }
+    elsif ($tokens[$col_event] =~ m/cmd_path/) {
+	# Likewise, the 'cmd_path' message breaks out argv[0].
+	#
+	# This line is only emitted when RUNTIME_PREFIX is defined,
+	# so just omit it for testing purposes.
+	# $tokens[$col_rest] = "_EXE_";
+	goto SKIP_LINE;
+    }
+    elsif ($tokens[$col_event] =~ m/child_exit/) {
+	$tokens[$col_rest] =~ s/ pid:\d* / pid:_PID_ /;
+    }
+    elsif ($tokens[$col_event] =~ m/data/) {
+	if ($tokens[$col_category] =~ m/process/) {
+	    # 'data' and 'data_json' events containing 'process'
+	    # category data are assumed to be platform-specific
+	    # and highly variable.  Just omit them.
+	    goto SKIP_LINE;
+	}
+    }
+
+    # t_abs and t_rel are either blank or a float.  Replace the float
+    # with a constant for matching the HEREDOC in the test script.
+    if ($tokens[$col_t_abs] =~ m/\d/) {
+	$tokens[$col_t_abs] = "_T_ABS_";
+    }
+    if ($tokens[$col_t_rel] =~ m/\d/) {
+	$tokens[$col_t_rel] = "_T_REL_";
+    }
+
+    my $out;
+
+    $out = join('|', @tokens);
+    print "$out\n";
+
+  SKIP_LINE:
+}
+
+

t/t0212-trace2-event.sh

@@ -0,0 +1,236 @@
+#!/bin/sh
+
+test_description='test trace2 facility'
+. ./test-lib.sh
+
+perl -MJSON::PP -e 0 >/dev/null 2>&1 && test_set_prereq JSON_PP
+
+# Add t/helper directory to PATH so that we can use a relative
+# path to run nested instances of test-tool.exe (see 004child).
+# This helps with HEREDOC comparisons later.
+TTDIR="$GIT_BUILD_DIR/t/helper/" && export TTDIR
+PATH="$TTDIR:$PATH" && export PATH
+
+# Warning: use of 'test_cmp' may run test-tool.exe and/or git.exe
+# Warning: to do the actual diff/comparison, so the HEREDOCs here
+# Warning: only cover our actual calls to test-tool and/or git.
+# Warning: So you may see extra lines in artifact files when
+# Warning: interactively debugging.
+
+# Turn off any inherited trace2 settings for this test.
+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT
+unset GIT_TR2_BARE
+unset GIT_TR2_CONFIG_PARAMS
+
+V=$(git version | sed -e 's/^git version //') && export V
+
+# There are multiple trace2 targets: normal, perf, and event.
+# Trace2 events will/can be written to each active target (subject
+# to whatever filtering that target decides to do).
+# Test each target independently.
+#
+# Defer setting GIT_TR2_PERF until the actual command we want to
+# test because hidden git and test-tool commands in the test
+# harness can contaminate our output.
+
+# We don't bother repeating the 001return and 002exit tests, since they
+# have coverage in the normal and perf targets.
+
+# Verb 003error
+#
+# To the above, add multiple 'error <msg>' events
+
+test_expect_success JSON_PP 'event stream, error event' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 003error "hello world" "this is a test" &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "003error",
+	|      "hello world",
+	|      "this is a test"
+	|    ],
+	|    "errors":[
+	|      "%s",
+	|      "%s"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+# Verb 004child
+#
+# Test nested spawning of child processes.
+#
+# Conceptually, this looks like:
+#    P1: TT trace2 004child
+#    P2: |--- TT trace2 004child
+#    P3:      |--- TT trace2 001return 0
+
+test_expect_success JSON_PP 'event stream, return code 0' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 004child test-tool trace2 004child test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "child":{
+	|      "0":{
+	|        "child_argv":[
+	|          "_EXE_",
+	|          "trace2",
+	|          "004child",
+	|          "test-tool",
+	|          "trace2",
+	|          "001return",
+	|          "0"
+	|        ],
+	|        "child_class":"?",
+	|        "child_code":0,
+	|        "use_shell":0
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  },
+	|  "_SID0_/_SID1_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "004child",
+	|      "test-tool",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "child":{
+	|      "0":{
+	|        "child_argv":[
+	|          "_EXE_",
+	|          "trace2",
+	|          "001return",
+	|          "0"
+	|        ],
+	|        "child_class":"?",
+	|        "child_code":0,
+	|        "use_shell":0
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2/trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  },
+	|  "_SID0_/_SID1_/_SID2_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2/trace2/trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+# Test listing of all "interesting" config settings.
+
+test_expect_success JSON_PP 'event stream, list config' '
+	test_when_finished "rm trace.event actual expect" &&
+	git config --local t0212.abc 1 &&
+	git config --local t0212.def "hello world" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" GIT_TR2_CONFIG_PARAMS="t0212.*" test-tool trace2 001return 0 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "001return",
+	|      "0"
+	|    ],
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "params":[
+	|      {
+	|        "param":"t0212.abc",
+	|        "value":"1"
+	|      },
+	|      {
+	|        "param":"t0212.def",
+	|        "value":"hello world"
+	|      }
+	|    ],
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success JSON_PP 'basic trace2_data' '
+	test_when_finished "rm trace.event actual expect" &&
+	GIT_TR2_EVENT="$(pwd)/trace.event" test-tool trace2 006data test_category k1 v1 test_category k2 v2 &&
+	perl "$TEST_DIRECTORY/t0212/parse_events.perl" <trace.event >actual &&
+	sed -e "s/^|//" >expect <<-EOF &&
+	|VAR1 = {
+	|  "_SID0_":{
+	|    "argv":[
+	|      "_EXE_",
+	|      "trace2",
+	|      "006data",
+	|      "test_category",
+	|      "k1",
+	|      "v1",
+	|      "test_category",
+	|      "k2",
+	|      "v2"
+	|    ],
+	|    "data":{
+	|      "test_category":{
+	|        "k1":"v1",
+	|        "k2":"v2"
+	|      }
+	|    },
+	|    "exit_code":0,
+	|    "hierarchy":"trace2",
+	|    "name":"trace2",
+	|    "version":"$V"
+	|  }
+	|};
+	EOF
+	test_cmp expect actual
+'
+
+test_done

t/t0212/parse_events.perl

@@ -0,0 +1,251 @@
+#!/usr/bin/perl
+#
+# Parse event stream and convert individual events into a summary
+# record for the process.
+#
+# Git.exe generates one or more "event" records for each API method,
+# such as "start <argv>" and "exit <code>", during the life of the git
+# process.  Additionally, the input may contain interleaved events
+# from multiple concurrent git processes and/or multiple threads from
+# within a git process.
+#
+# Accumulate events for each process (based on its unique SID) in a
+# dictionary and emit process summary records.
+#
+# Convert some of the variable fields (such as elapsed time) into
+# placeholders (or omit them) to make HEREDOC comparisons easier in
+# the test scripts.
+#
+# We may also omit fields not (currently) useful for testing purposes.
+
+use strict;
+use warnings;
+use JSON::PP;
+use Data::Dumper;
+use Getopt::Long;
+
+# The version of the trace2 event target format that we understand.
+# This is reported in the 'version' event in the 'evt' field.
+# It comes from the GIT_TR2_EVENT_VERSION macro in trace2/tr2_tgt_event.c
+my $evt_version = '1';
+
+my $show_children = 1;
+my $show_exec     = 1;
+my $show_threads  = 1;
+
+# A hack to generate test HEREDOC data for pasting into the test script.
+# Usage:
+#    cd "t/trash directory.t0212-trace2-event"
+#    $TT trace ... >trace.event
+#    VV=$(../../git.exe version | sed -e 's/^git version //')
+#    perl ../t0212/parse_events.perl --HEREDOC --VERSION=$VV <trace.event >heredoc
+# Then paste heredoc into your new test.
+
+my $gen_heredoc = 0;
+my $gen_version = '';
+
+GetOptions("children!" => \$show_children,
+	   "exec!"     => \$show_exec,
+	   "threads!"  => \$show_threads,
+	   "HEREDOC!"  => \$gen_heredoc,
+	   "VERSION=s" => \$gen_version    )
+    or die("Error in command line arguments\n");
+
+
+# SIDs contains timestamps and PIDs of the process and its parents.
+# This makes it difficult to match up in a HEREDOC in the test script.
+# Build a map from actual SIDs to predictable constant values and yet
+# keep the parent/child relationships.  For example:
+# {..., "sid":"1539706952458276-8652", ...}
+# {..., "sid":"1539706952458276-8652/1539706952649493-15452", ...}
+# becomes:
+# {..., "sid":"_SID1_", ...}
+# {..., "sid":"_SID1_/_SID2_", ...}
+my $sid_map;
+my $sid_count = 0;
+
+my $processes;
+
+while (<>) {
+    my $line = decode_json( $_ );
+
+    my $sid = "";
+    my $sid_sep = "";
+
+    my $raw_sid = $line->{'sid'};
+    my @raw_sid_parts = split /\//, $raw_sid;
+    foreach my $raw_sid_k (@raw_sid_parts) {
+	if (!exists $sid_map->{$raw_sid_k}) {
+	    $sid_map->{$raw_sid_k} = '_SID' . $sid_count . '_';
+	    $sid_count++;
+	}
+	$sid = $sid . $sid_sep . $sid_map->{$raw_sid_k};
+	$sid_sep = '/';
+    }
+    
+    my $event = $line->{'event'};
+
+    if ($event eq 'version') {
+	$processes->{$sid}->{'version'} = $line->{'exe'};
+	if ($gen_heredoc == 1 && $gen_version eq $line->{'exe'}) {
+	    # If we are generating data FOR the test script, replace
+	    # the reported git.exe version with a reference to an
+	    # environment variable.  When our output is pasted into
+	    # the test script, it will then be expanded in future
+	    # test runs to the THEN current version of git.exe.
+	    # We assume that the test script uses env var $V.
+	    $processes->{$sid}->{'version'} = "\$V";
+	}
+    }
+
+    elsif ($event eq 'start') {
+	$processes->{$sid}->{'argv'} = $line->{'argv'};
+	$processes->{$sid}->{'argv'}[0] = "_EXE_";
+    }
+
+    elsif ($event eq 'exit') {
+	$processes->{$sid}->{'exit_code'} = $line->{'code'};
+    }
+
+    elsif ($event eq 'atexit') {
+	$processes->{$sid}->{'exit_code'} = $line->{'code'};
+    }
+
+    elsif ($event eq 'error') {
+	# For HEREDOC purposes, use the error message format string if
+	# available, rather than the formatted message (which probably
+	# has an absolute pathname).
+	if (exists $line->{'fmt'}) {
+	    push( @{$processes->{$sid}->{'errors'}}, $line->{'fmt'} );
+	}
+	elsif (exists $line->{'msg'}) {
+	    push( @{$processes->{$sid}->{'errors'}}, $line->{'msg'} );
+	}
+    }
+
+    elsif ($event eq 'cmd_path') {
+	## $processes->{$sid}->{'path'} = $line->{'path'};
+	#
+	# Like in the 'start' event, we need to replace the value of
+	# argv[0] with a token for HEREDOC purposes.  However, the
+	# event is only emitted when RUNTIME_PREFIX is defined, so
+	# just omit it for testing purposes.
+	# $processes->{$sid}->{'path'} = "_EXE_";
+    }
+    
+    elsif ($event eq 'cmd_name') {
+	$processes->{$sid}->{'name'} = $line->{'name'};
+	$processes->{$sid}->{'hierarchy'} = $line->{'hierarchy'};
+    }
+
+    elsif ($event eq 'alias') {
+	$processes->{$sid}->{'alias'}->{'key'} = $line->{'alias'};
+	$processes->{$sid}->{'alias'}->{'argv'} = $line->{'argv'};
+    }
+
+    elsif ($event eq 'def_param') {
+	my $kv;
+	$kv->{'param'} = $line->{'param'};
+	$kv->{'value'} = $line->{'value'};
+	push( @{$processes->{$sid}->{'params'}}, $kv );
+    }
+
+    elsif ($event eq 'child_start') {
+	if ($show_children == 1) {
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_class'} = $line->{'child_class'};
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_argv'} = $line->{'argv'};
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_argv'}[0] = "_EXE_";
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'use_shell'} = $line->{'use_shell'} ? 1 : 0;
+	}
+    }
+
+    elsif ($event eq 'child_exit') {
+	if ($show_children == 1) {
+	    $processes->{$sid}->{'child'}->{$line->{'child_id'}}->{'child_code'} = $line->{'code'};
+	}
+    }
+
+    # TODO decide what information we want to test from thread events.
+
+    elsif ($event eq 'thread_start') {
+	if ($show_threads == 1) {
+	}
+    }
+
+    elsif ($event eq 'thread_exit') {
+	if ($show_threads == 1) {
+	}
+    }
+
+    # TODO decide what information we want to test from exec events.
+
+    elsif ($event eq 'exec') {
+	if ($show_exec == 1) {
+	}
+    }
+
+    elsif ($event eq 'exec_result') {
+	if ($show_exec == 1) {
+	}
+    }
+
+    elsif ($event eq 'def_param') {
+	# Accumulate parameter key/value pairs by key rather than in an array
+	# so that we get overwrite (last one wins) effects.
+	$processes->{$sid}->{'params'}->{$line->{'param'}} = $line->{'value'};
+    }
+
+    elsif ($event eq 'def_repo') {
+	# $processes->{$sid}->{'repos'}->{$line->{'repo'}} = $line->{'worktree'};
+	$processes->{$sid}->{'repos'}->{$line->{'repo'}} = "_WORKTREE_";
+    }
+
+    # A series of potentially nested and threaded region and data events
+    # is fundamentally incompatibile with the type of summary record we
+    # are building in this script.  Since they are intended for
+    # perf-trace-like analysis rather than a result summary, we ignore
+    # most of them here.
+
+    # elsif ($event eq 'region_enter') {
+    # }
+    # elsif ($event eq 'region_leave') {
+    # }
+
+    elsif ($event eq 'data') {
+	my $cat = $line->{'category'};
+	if ($cat eq 'test_category') {
+	    
+	    my $key = $line->{'key'};
+	    my $value = $line->{'value'};
+	    $processes->{$sid}->{'data'}->{$cat}->{$key} = $value;
+	}
+    }
+
+    # This trace2 target does not emit 'printf' events.
+    #
+    # elsif ($event eq 'printf') {
+    # }
+}
+
+# Dump the resulting hash into something that we can compare against
+# in the test script.  These options make Dumper output look a little
+# bit like JSON.  Also convert variable references of the form "$VAR*"
+# so that the matching HEREDOC doesn't need to escape it.
+
+$Data::Dumper::Sortkeys = 1;
+$Data::Dumper::Indent = 1;
+$Data::Dumper::Purity = 1;
+$Data::Dumper::Pair = ':';
+
+my $out = Dumper($processes);
+$out =~ s/'/"/g;
+$out =~ s/\$VAR/VAR/g;
+
+# Finally, if we're running this script to generate (manually confirmed)
+# data to add to the test script, guard the indentation.
+
+if ($gen_heredoc == 1) {
+    $out =~ s/^/\t\|/gms;
+}
+
+print $out;

trace2.c

@@ -0,0 +1,761 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "quote.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "thread-utils.h"
+#include "version.h"
+#include "trace2/tr2_cfg.h"
+#include "trace2/tr2_cmd_name.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static int trace2_enabled;
+
+static int tr2_next_child_id; /* modify under lock */
+static int tr2_next_exec_id; /* modify under lock */
+static int tr2_next_repo_id = 1; /* modify under lock. zero is reserved */
+
+/*
+ * A table of the builtin TRACE2 targets.  Each of these may be independently
+ * enabled or disabled.  Each TRACE2 API method will try to write an event to
+ * *each* of the enabled targets.
+ */
+/* clang-format off */
+static struct tr2_tgt *tr2_tgt_builtins[] =
+{
+	&tr2_tgt_normal,
+	&tr2_tgt_perf,
+	&tr2_tgt_event,
+	NULL
+};
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_builtin(j, tgt_j)			\
+	for (j = 0, tgt_j = tr2_tgt_builtins[j];	\
+	     tgt_j;					\
+	     j++, tgt_j = tr2_tgt_builtins[j])
+/* clang-format on */
+
+/* clang-format off */
+#define for_each_wanted_builtin(j, tgt_j)            \
+	for_each_builtin(j, tgt_j)                   \
+		if (tr2_dst_trace_want(tgt_j->pdst))
+/* clang-format on */
+
+/*
+ * Force (rather than lazily) initialize any of the requested
+ * builtin TRACE2 targets at startup (and before we've seen an
+ * actual TRACE2 event call) so we can see if we need to setup
+ * the TR2 and TLS machinery.
+ *
+ * Return the number of builtin targets enabled.
+ */
+static int tr2_tgt_want_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	int sum = 0;
+
+	for_each_builtin (j, tgt_j)
+		if (tgt_j->pfn_init())
+			sum++;
+
+	return sum;
+}
+
+/*
+ * Properly terminate each builtin target.  Give each target
+ * a chance to write a summary event and/or flush if necessary
+ * and then close the fd.
+ */
+static void tr2_tgt_disable_builtins(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	for_each_builtin (j, tgt_j)
+		tgt_j->pfn_term();
+}
+
+static int tr2main_exit_code;
+
+/*
+ * Our atexit routine should run after everything has finished.
+ *
+ * Note that events generated here might not actually appear if
+ * we are writing to fd 1 or 2 and our atexit routine runs after
+ * the pager's atexit routine (since it closes them to shutdown
+ * the pipes).
+ */
+static void tr2main_atexit_handler(void)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions so that our atexit message
+	 * does not appear nested.  This improves the appearance of
+	 * the trace output if someone calls die(), for example.
+	 */
+	tr2tls_pop_unwind_self();
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_atexit)
+			tgt_j->pfn_atexit(us_elapsed_absolute,
+					  tr2main_exit_code);
+
+	tr2_tgt_disable_builtins();
+
+	tr2tls_release();
+	tr2_sid_release();
+	tr2_cmd_name_release();
+	tr2_cfg_free_patterns();
+
+	trace2_enabled = 0;
+}
+
+static void tr2main_signal_handler(int signo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_signal)
+			tgt_j->pfn_signal(us_elapsed_absolute, signo);
+
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+void trace2_initialize_fl(const char *file, int line)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (trace2_enabled)
+		return;
+
+	if (!tr2_tgt_want_builtins())
+		return;
+	trace2_enabled = 1;
+
+	tr2_sid_get();
+
+	atexit(tr2main_atexit_handler);
+	sigchain_push(SIGPIPE, tr2main_signal_handler);
+	tr2tls_init();
+
+	/*
+	 * Emit 'version' message on each active builtin target.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_version_fl)
+			tgt_j->pfn_version_fl(file, line);
+}
+
+int trace2_is_enabled(void)
+{
+	return trace2_enabled;
+}
+
+void trace2_cmd_start_fl(const char *file, int line, const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_start_fl)
+			tgt_j->pfn_start_fl(file, line, argv);
+}
+
+int trace2_cmd_exit_fl(const char *file, int line, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	code &= 0xff;
+
+	if (!trace2_enabled)
+		return code;
+
+	tr2main_exit_code = code;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exit_fl)
+			tgt_j->pfn_exit_fl(file, line, us_elapsed_absolute,
+					   code);
+
+	return code;
+}
+
+void trace2_cmd_error_va_fl(const char *file, int line, const char *fmt,
+			    va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy (because an 'ap' can only be walked once).
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_error_va_fl)
+			tgt_j->pfn_error_va_fl(file, line, fmt, ap);
+}
+
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_path_fl)
+			tgt_j->pfn_command_path_fl(file, line, pathname);
+}
+
+void trace2_cmd_name_fl(const char *file, int line, const char *name)
+{
+	struct tr2_tgt *tgt_j;
+	const char *hierarchy;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	tr2_cmd_name_append_hierarchy(name);
+	hierarchy = tr2_cmd_name_get_hierarchy();
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_name_fl)
+			tgt_j->pfn_command_name_fl(file, line, name, hierarchy);
+}
+
+void trace2_cmd_mode_fl(const char *file, int line, const char *mode)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_command_mode_fl)
+			tgt_j->pfn_command_mode_fl(file, line, mode);
+}
+
+void trace2_cmd_alias_fl(const char *file, int line, const char *alias,
+			 const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_alias_fl)
+			tgt_j->pfn_alias_fl(file, line, alias, argv);
+}
+
+void trace2_cmd_list_config_fl(const char *file, int line)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_list_config_fl(file, line);
+}
+
+void trace2_cmd_set_config_fl(const char *file, int line, const char *key,
+			      const char *value)
+{
+	if (!trace2_enabled)
+		return;
+
+	tr2_cfg_set_fl(file, line, key, value);
+}
+
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	cmd->trace2_child_id = tr2tls_locked_increment(&tr2_next_child_id);
+	cmd->trace2_child_us_start = us_now;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_child_start_fl)
+			tgt_j->pfn_child_start_fl(file, line,
+						  us_elapsed_absolute, cmd);
+}
+
+void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
+			  int child_exit_code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_child;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	if (cmd->trace2_child_us_start)
+		us_elapsed_child = us_now - cmd->trace2_child_us_start;
+	else
+		us_elapsed_child = 0;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_child_exit_fl)
+			tgt_j->pfn_child_exit_fl(file, line,
+						 us_elapsed_absolute,
+						 cmd->trace2_child_id, cmd->pid,
+						 child_exit_code,
+						 us_elapsed_child);
+}
+
+int trace2_exec_fl(const char *file, int line, const char *exe,
+		   const char **argv)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	int exec_id;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return -1;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	exec_id = tr2tls_locked_increment(&tr2_next_exec_id);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exec_fl)
+			tgt_j->pfn_exec_fl(file, line, us_elapsed_absolute,
+					   exec_id, exe, argv);
+
+	return exec_id;
+}
+
+void trace2_exec_result_fl(const char *file, int line, int exec_id, int code)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_exec_result_fl)
+			tgt_j->pfn_exec_result_fl(
+				file, line, us_elapsed_absolute, exec_id, code);
+}
+
+void trace2_thread_start_fl(const char *file, int line, const char *thread_name)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread()) {
+		/*
+		 * We should only be called from the new thread's thread-proc,
+		 * so this is technically a bug.  But in those cases where the
+		 * main thread also runs the thread-proc function (or when we
+		 * are built with threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-enter so the nesting looks
+		 * correct.
+		 */
+		trace2_region_enter_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main: %s",
+					      thread_name);
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	tr2tls_create_self(thread_name);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_thread_start_fl)
+			tgt_j->pfn_thread_start_fl(file, line,
+						   us_elapsed_absolute);
+}
+
+void trace2_thread_exit_fl(const char *file, int line)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_thread;
+
+	if (!trace2_enabled)
+		return;
+
+	if (tr2tls_is_main_thread()) {
+		/*
+		 * We should only be called from the exiting thread's
+		 * thread-proc, so this is technically a bug.  But in
+		 * those cases where the main thread also runs the
+		 * thread-proc function (or when we are built with
+		 * threading disabled), we need to allow it.
+		 *
+		 * Convert this call to a region-leave so the nesting
+		 * looks correct.
+		 */
+		trace2_region_leave_printf_fl(file, line, NULL, NULL, NULL,
+					      "thread-proc on main");
+		return;
+	}
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Clear any unbalanced regions and then get the relative time
+	 * for the outer-most region (which we pushed when the thread
+	 * started).  This gives us the run time of the thread.
+	 */
+	tr2tls_pop_unwind_self();
+	us_elapsed_thread = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_thread_exit_fl)
+			tgt_j->pfn_thread_exit_fl(file, line,
+						  us_elapsed_absolute,
+						  us_elapsed_thread);
+
+	tr2tls_unset_self();
+}
+
+void trace2_def_param_fl(const char *file, int line, const char *param,
+			 const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_param_fl)
+			tgt_j->pfn_param_fl(file, line, param, value);
+}
+
+void trace2_def_repo_fl(const char *file, int line, struct repository *repo)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+
+	if (!trace2_enabled)
+		return;
+
+	if (repo->trace2_repo_id)
+		return;
+
+	repo->trace2_repo_id = tr2tls_locked_increment(&tr2_next_repo_id);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_repo_fl)
+			tgt_j->pfn_repo_fl(file, line, repo);
+}
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Print the region-enter message at the current nesting
+	 * (indentation) level and then push a new level.
+	 *
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_region_enter_printf_va_fl)
+			tgt_j->pfn_region_enter_printf_va_fl(
+				file, line, us_elapsed_absolute, category,
+				label, repo, fmt, ap);
+
+	tr2tls_push_self(us_now);
+}
+
+void trace2_region_enter_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo)
+{
+	trace2_region_enter_printf_va_fl(file, line, category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(file, line, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_enter_printf_va_fl(NULL, 0, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * Get the elapsed time in the current region before we
+	 * pop it off the stack.  Pop the stack.  And then print
+	 * the perf message at the new (shallower) level so that
+	 * it lines up with the corresponding push/enter.
+	 */
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	tr2tls_pop_self();
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_region_leave_printf_va_fl)
+			tgt_j->pfn_region_leave_printf_va_fl(
+				file, line, us_elapsed_absolute,
+				us_elapsed_region, category, label, repo, fmt,
+				ap);
+}
+
+void trace2_region_leave_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo)
+{
+	trace2_region_leave_printf_va_fl(file, line, category, label, repo,
+					 NULL, NULL);
+}
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(file, line, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_region_leave_printf_va_fl(NULL, 0, category, label, repo, fmt,
+					 ap);
+	va_end(ap);
+}
+#endif
+
+void trace2_data_string_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   const char *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_data_fl)
+			tgt_j->pfn_data_fl(file, line, us_elapsed_absolute,
+					   us_elapsed_region, category, repo,
+					   key, value);
+}
+
+void trace2_data_intmax_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   intmax_t value)
+{
+	struct strbuf buf_string = STRBUF_INIT;
+
+	if (!trace2_enabled)
+		return;
+
+	strbuf_addf(&buf_string, "%" PRIdMAX, value);
+	trace2_data_string_fl(file, line, category, repo, key, buf_string.buf);
+	strbuf_release(&buf_string);
+}
+
+void trace2_data_json_fl(const char *file, int line, const char *category,
+			 const struct repository *repo, const char *key,
+			 const struct json_writer *value)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_region;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+	us_elapsed_region = tr2tls_region_elasped_self(us_now);
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_data_fl)
+			tgt_j->pfn_data_json_fl(file, line, us_elapsed_absolute,
+						us_elapsed_region, category,
+						repo, key, value);
+}
+
+void trace2_printf_va_fl(const char *file, int line, const char *fmt,
+			 va_list ap)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	/*
+	 * We expect each target function to treat 'ap' as constant
+	 * and use va_copy.
+	 */
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_printf_va_fl)
+			tgt_j->pfn_printf_va_fl(file, line, us_elapsed_absolute,
+						fmt, ap);
+}
+
+void trace2_printf_fl(const char *file, int line, const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(file, line, fmt, ap);
+	va_end(ap);
+}
+
+#ifndef HAVE_VARIADIC_MACROS
+void trace2_printf(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace2_printf_va_fl(NULL, 0, fmt, ap);
+	va_end(ap);
+}
+#endif

trace2.h

@@ -0,0 +1,385 @@
+#ifndef TRACE2_H
+#define TRACE2_H
+
+struct child_process;
+struct repository;
+struct json_writer;
+
+/*
+ * The public TRACE2 routines are grouped into the following groups:
+ *
+ * [] trace2_initialize -- initialization.
+ * [] trace2_cmd_*      -- emit command/control messages.
+ * [] trace2_child*     -- emit child start/stop messages.
+ * [] trace2_exec*      -- emit exec start/stop messages.
+ * [] trace2_thread*    -- emit thread start/stop messages.
+ * [] trace2_def*       -- emit definition/parameter mesasges.
+ * [] trace2_region*    -- emit region nesting messages.
+ * [] trace2_data*      -- emit region/thread/repo data messages.
+ * [] trace2_printf*    -- legacy trace[1] messages.
+ */
+
+/*
+ * Initialize TRACE2 tracing facility if any of the builtin TRACE2
+ * targets are enabled in the environment.  Emits a 'version' event.
+ *
+ * Cleanup/Termination is handled automatically by a registered
+ * atexit() routine.
+ */
+void trace2_initialize_fl(const char *file, int line);
+
+#define trace2_initialize() trace2_initialize_fl(__FILE__, __LINE__)
+
+/*
+ * Return true if trace2 is enabled.
+ */
+int trace2_is_enabled(void);
+
+/*
+ * Emit a 'start' event with the original (unmodified) argv.
+ */
+void trace2_cmd_start_fl(const char *file, int line, const char **argv);
+
+#define trace2_cmd_start(argv) trace2_cmd_start_fl(__FILE__, __LINE__, (argv))
+
+/*
+ * Emit an 'exit' event.
+ *
+ * Write the exit-code that will be passed to exit() or returned
+ * from main().
+ *
+ * Use this prior to actually calling exit().
+ * See "#define exit()" in git-compat-util.h
+ */
+int trace2_cmd_exit_fl(const char *file, int line, int code);
+
+#define trace2_cmd_exit(code) (trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+
+/*
+ * Emit an 'error' event.
+ *
+ * Write an error message to the TRACE2 targets.
+ */
+void trace2_cmd_error_va_fl(const char *file, int line, const char *fmt,
+			    va_list ap);
+
+#define trace2_cmd_error_va(fmt, ap) \
+	trace2_cmd_error_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+/*
+ * Emit a 'pathname' event with the canonical pathname of the current process
+ * This gives post-processors a simple field to identify the command without
+ * having to parse the argv.  For example, to distinguish invocations from
+ * installed versus debug executables.
+ */
+void trace2_cmd_path_fl(const char *file, int line, const char *pathname);
+
+#define trace2_cmd_path(p) trace2_cmd_path_fl(__FILE__, __LINE__, (p))
+
+/*
+ * Emit a 'cmd_name' event with the canonical name of the command.
+ * This gives post-processors a simple field to identify the command
+ * without having to parse the argv.
+ */
+void trace2_cmd_name_fl(const char *file, int line, const char *name);
+
+#define trace2_cmd_name(v) trace2_cmd_name_fl(__FILE__, __LINE__, (v))
+
+/*
+ * Emit a 'cmd_mode' event to further describe the command being run.
+ * For example, "checkout" can checkout a single file or can checkout a
+ * different branch.  This gives post-processors a simple field to compare
+ * equivalent commands without having to parse the argv.
+ */
+void trace2_cmd_mode_fl(const char *file, int line, const char *mode);
+
+#define trace2_cmd_mode(sv) trace2_cmd_mode_fl(__FILE__, __LINE__, (sv))
+
+/*
+ * Emit an 'alias' expansion event.
+ */
+void trace2_cmd_alias_fl(const char *file, int line, const char *alias,
+			 const char **argv);
+
+#define trace2_cmd_alias(alias, argv) \
+	trace2_cmd_alias_fl(__FILE__, __LINE__, (alias), (argv))
+
+/*
+ * Emit one or more 'def_param' events for "interesting" configuration
+ * settings.
+ *
+ * The environment variable "GIT_TR2_CONFIG_PARAMS" can be set to a
+ * list of patterns considered important.  For example:
+ *
+ *    GIT_TR2_CONFIG_PARAMS="core.*,remote.*.url"
+ *
+ * Note: this routine does a read-only iteration on the config data
+ * (using read_early_config()), so it must not be called until enough
+ * of the process environment has been established.  This includes the
+ * location of the git and worktree directories, expansion of any "-c"
+ * and "-C" command line options, and etc.
+ */
+void trace2_cmd_list_config_fl(const char *file, int line);
+
+#define trace2_cmd_list_config() trace2_cmd_list_config_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a "def_param" event for the given config key/value pair IF
+ * we consider the key to be "interesting".
+ *
+ * Use this for new/updated config settings created/updated after
+ * trace2_cmd_list_config() is called.
+ */
+void trace2_cmd_set_config_fl(const char *file, int line, const char *key,
+			      const char *value);
+
+#define trace2_cmd_set_config(k, v) \
+	trace2_cmd_set_config_fl(__FILE__, __LINE__, (k), (v))
+
+/*
+ * Emit a 'child_start' event prior to spawning a child process.
+ *
+ * Before calling optionally set "cmd->trace2_child_class" to a string
+ * describing the type of the child process.  For example, "editor" or
+ * "pager".
+ */
+void trace2_child_start_fl(const char *file, int line,
+			   struct child_process *cmd);
+
+#define trace2_child_start(cmd) trace2_child_start_fl(__FILE__, __LINE__, (cmd))
+
+/*
+ * Emit a 'child_exit' event after the child process completes.
+ */
+void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
+			  int child_exit_code);
+
+#define trace2_child_exit(cmd, code) \
+	trace2_child_exit_fl(__FILE__, __LINE__, (cmd), (code))
+
+/*
+ * Emit an 'exec' event prior to calling one of exec(), execv(),
+ * execvp(), and etc.  On Unix-derived systems, this will be the
+ * last event emitted for the current process, unless the exec
+ * fails.  On Windows, exec() behaves like 'child_start' and a
+ * waitpid(), so additional events may be emitted.
+ *
+ * Returns the "exec_id".
+ */
+int trace2_exec_fl(const char *file, int line, const char *exe,
+		   const char **argv);
+
+#define trace2_exec(exe, argv) trace2_exec_fl(__FILE__, __LINE__, (exe), (argv))
+
+/*
+ * Emit an 'exec_result' when possible.  On Unix-derived systems,
+ * this should be called after exec() returns (which only happens
+ * when there is an error starting the new process).  On Windows,
+ * this should be called after the waitpid().
+ *
+ * The "exec_id" should be the value returned from trace2_exec().
+ */
+void trace2_exec_result_fl(const char *file, int line, int exec_id, int code);
+
+#define trace2_exec_result(id, code) \
+	trace2_exec_result_fl(__FILE__, __LINE__, (id), (code))
+
+/*
+ * Emit a 'thread_start' event.  This must be called from inside the
+ * thread-proc to set up the trace2 TLS data for the thread.
+ *
+ * Thread names should be descriptive, like "preload_index".
+ * Thread names will be decorated with an instance number automatically.
+ */
+void trace2_thread_start_fl(const char *file, int line,
+			    const char *thread_name);
+
+#define trace2_thread_start(thread_name) \
+	trace2_thread_start_fl(__FILE__, __LINE__, (thread_name))
+
+/*
+ * Emit a 'thread_exit' event.  This must be called from inside the
+ * thread-proc to report thread-specific data and cleanup TLS data
+ * for the thread.
+ */
+void trace2_thread_exit_fl(const char *file, int line);
+
+#define trace2_thread_exit() trace2_thread_exit_fl(__FILE__, __LINE__)
+
+/*
+ * Emit a 'param' event.
+ *
+ * Write a "<param> = <value>" pair describing some aspect of the
+ * run such as an important configuration setting or command line
+ * option that significantly changes command behavior.
+ */
+void trace2_def_param_fl(const char *file, int line, const char *param,
+			 const char *value);
+
+#define trace2_def_param(param, value) \
+	trace2_def_param_fl(__FILE__, __LINE__, (param), (value))
+
+/*
+ * Tell trace2 about a newly instantiated repo object and assign
+ * a trace2-repo-id to be used in subsequent activity events.
+ *
+ * Emits a 'worktree' event for this repo instance.
+ */
+void trace2_def_repo_fl(const char *file, int line, struct repository *repo);
+
+#define trace2_def_repo(repo) trace2_def_repo_fl(__FILE__, __LINE__, repo)
+
+/*
+ * Emit a 'region_enter' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Enter a new nesting level on the current thread and remember the
+ * current time.  This controls the indenting of all subsequent events
+ * on this thread.
+ */
+void trace2_region_enter_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo);
+
+#define trace2_region_enter(category, label, repo) \
+	trace2_region_enter_fl(__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_enter_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_enter_printf_va(category, label, repo, fmt, ap)    \
+	trace2_region_enter_printf_va_fl(__FILE__, __LINE__, (category), \
+					 (label), (repo), (fmt), (ap))
+
+void trace2_region_enter_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_enter_printf(category, label, repo, ...)                 \
+	trace2_region_enter_printf_fl(__FILE__, __LINE__, (category), (label), \
+				      (repo), __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (region_enter_printf, 4, 5)))
+void trace2_region_enter_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...);
+/* clang-format on */
+#endif
+
+/*
+ * Emit a 'region_leave' event for <category>.<label> with optional
+ * repo-id and printf message.
+ *
+ * Leave current nesting level and report the elapsed time spent
+ * in this nesting level.
+ */
+void trace2_region_leave_fl(const char *file, int line, const char *category,
+			    const char *label, const struct repository *repo);
+
+#define trace2_region_leave(category, label, repo) \
+	trace2_region_leave_fl(__FILE__, __LINE__, (category), (label), (repo))
+
+void trace2_region_leave_printf_va_fl(const char *file, int line,
+				      const char *category, const char *label,
+				      const struct repository *repo,
+				      const char *fmt, va_list ap);
+
+#define trace2_region_leave_printf_va(category, label, repo, fmt, ap)    \
+	trace2_region_leave_printf_va_fl(__FILE__, __LINE__, (category), \
+					 (label), (repo), (fmt), (ap))
+
+void trace2_region_leave_printf_fl(const char *file, int line,
+				   const char *category, const char *label,
+				   const struct repository *repo,
+				   const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_region_leave_printf(category, label, repo, ...)                 \
+	trace2_region_leave_printf_fl(__FILE__, __LINE__, (category), (label), \
+				      (repo), __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (region_leave_printf, 4, 5)))
+void trace2_region_leave_printf(const char *category, const char *label,
+				const struct repository *repo, const char *fmt,
+				...);
+/* clang-format on */
+#endif
+
+/*
+ * Emit a key-value pair 'data' event of the form <category>.<key> = <value>.
+ * This event implicitly contains information about thread, nesting region,
+ * and optional repo-id.
+ *
+ * On event-based TRACE2 targets, this generates a 'data' event suitable
+ * for post-processing.  On printf-based TRACE2 targets, this is converted
+ * into a fixed-format printf message.
+ */
+void trace2_data_string_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   const char *value);
+
+#define trace2_data_string(category, repo, key, value)                       \
+	trace2_data_string_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			      (value))
+
+void trace2_data_intmax_fl(const char *file, int line, const char *category,
+			   const struct repository *repo, const char *key,
+			   intmax_t value);
+
+#define trace2_data_intmax(category, repo, key, value)                       \
+	trace2_data_intmax_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			      (value))
+
+void trace2_data_json_fl(const char *file, int line, const char *category,
+			 const struct repository *repo, const char *key,
+			 const struct json_writer *jw);
+
+#define trace2_data_json(category, repo, key, value)                       \
+	trace2_data_json_fl(__FILE__, __LINE__, (category), (repo), (key), \
+			    (value))
+
+/*
+ * Emit a 'printf' event.
+ *
+ * Write an arbitrary formatted message to the TRACE2 targets.  These
+ * text messages should be considered as human-readable strings without
+ * any formatting guidelines.  Post-processors may choose to ignore
+ * them.
+ */
+void trace2_printf_va_fl(const char *file, int line, const char *fmt,
+			 va_list ap);
+
+#define trace2_printf_va(fmt, ap) \
+	trace2_printf_va_fl(__FILE__, __LINE__, (fmt), (ap))
+
+void trace2_printf_fl(const char *file, int line, const char *fmt, ...);
+
+#ifdef HAVE_VARIADIC_MACROS
+#define trace2_printf(...) trace2_printf_fl(__FILE__, __LINE__, __VA_ARGS__)
+#else
+/* clang-format off */
+__attribute__((format (printf, 1, 2)))
+void trace2_printf(const char *fmt, ...);
+/* clang-format on */
+#endif
+
+/*
+ * Optional platform-specific code to dump information about the
+ * current and any parent process(es).  This is intended to allow
+ * post-processors to know who spawned this git instance and anything
+ * else the platform may be able to tell us about the current process.
+ */
+#if defined(GIT_WINDOWS_NATIVE)
+void trace2_collect_process_info(void);
+#else
+#define trace2_collect_process_info() \
+	do {                          \
+	} while (0)
+#endif
+
+#endif /* TRACE2_H */

trace2/tr2_cfg.c

@@ -0,0 +1,90 @@
+#include "cache.h"
+#include "config.h"
+#include "tr2_cfg.h"
+
+#define TR2_ENVVAR_CFG_PARAM "GIT_TR2_CONFIG_PARAMS"
+
+static struct strbuf **tr2_cfg_patterns;
+static int tr2_cfg_count_patterns;
+static int tr2_cfg_loaded;
+
+/*
+ * Parse a string containing a comma-delimited list of config keys
+ * or wildcard patterns into a list of strbufs.
+ */
+static int tr2_cfg_load_patterns(void)
+{
+	struct strbuf **s;
+	const char *envvar;
+
+	if (tr2_cfg_loaded)
+		return tr2_cfg_count_patterns;
+	tr2_cfg_loaded = 1;
+
+	envvar = getenv(TR2_ENVVAR_CFG_PARAM);
+	if (!envvar || !*envvar)
+		return tr2_cfg_count_patterns;
+
+	tr2_cfg_patterns = strbuf_split_buf(envvar, strlen(envvar), ',', -1);
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+
+		if (buf->len && buf->buf[buf->len - 1] == ',')
+			strbuf_setlen(buf, buf->len - 1);
+		strbuf_trim_trailing_newline(*s);
+		strbuf_trim(*s);
+	}
+
+	tr2_cfg_count_patterns = s - tr2_cfg_patterns;
+	return tr2_cfg_count_patterns;
+}
+
+void tr2_cfg_free_patterns(void)
+{
+	if (tr2_cfg_patterns)
+		strbuf_list_free(tr2_cfg_patterns);
+	tr2_cfg_count_patterns = 0;
+	tr2_cfg_loaded = 0;
+}
+
+struct tr2_cfg_data {
+	const char *file;
+	int line;
+};
+
+/*
+ * See if the given config key matches any of our patterns of interest.
+ */
+static int tr2_cfg_cb(const char *key, const char *value, void *d)
+{
+	struct strbuf **s;
+	struct tr2_cfg_data *data = (struct tr2_cfg_data *)d;
+
+	for (s = tr2_cfg_patterns; *s; s++) {
+		struct strbuf *buf = *s;
+		int wm = wildmatch(buf->buf, key, WM_CASEFOLD);
+		if (wm == WM_MATCH) {
+			trace2_def_param_fl(data->file, data->line, key, value);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+void tr2_cfg_list_config_fl(const char *file, int line)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		read_early_config(tr2_cfg_cb, &data);
+}
+
+void tr2_cfg_set_fl(const char *file, int line, const char *key,
+		    const char *value)
+{
+	struct tr2_cfg_data data = { file, line };
+
+	if (tr2_cfg_load_patterns() > 0)
+		tr2_cfg_cb(key, value, &data);
+}

trace2/tr2_cfg.h

@@ -0,0 +1,19 @@
+#ifndef TR2_CFG_H
+#define TR2_CFG_H
+
+/*
+ * Iterate over all config settings and emit 'def_param' events for the
+ * "interesting" ones to TRACE2.
+ */
+void tr2_cfg_list_config_fl(const char *file, int line);
+
+/*
+ * Emit a "def_param" event for the given key/value pair IF we consider
+ * the key to be "interesting".
+ */
+void tr2_cfg_set_fl(const char *file, int line, const char *key,
+		    const char *value);
+
+void tr2_cfg_free_patterns(void);
+
+#endif /* TR2_CFG_H */

trace2/tr2_cmd_name.c

@@ -0,0 +1,30 @@
+#include "cache.h"
+#include "trace2/tr2_cmd_name.h"
+
+#define TR2_ENVVAR_PARENT_NAME "GIT_TR2_PARENT_NAME"
+
+static struct strbuf tr2cmdname_hierarchy = STRBUF_INIT;
+
+void tr2_cmd_name_append_hierarchy(const char *name)
+{
+	const char *parent_name = getenv(TR2_ENVVAR_PARENT_NAME);
+
+	strbuf_reset(&tr2cmdname_hierarchy);
+	if (parent_name && *parent_name) {
+		strbuf_addstr(&tr2cmdname_hierarchy, parent_name);
+		strbuf_addch(&tr2cmdname_hierarchy, '/');
+	}
+	strbuf_addstr(&tr2cmdname_hierarchy, name);
+
+	setenv(TR2_ENVVAR_PARENT_NAME, tr2cmdname_hierarchy.buf, 1);
+}
+
+const char *tr2_cmd_name_get_hierarchy(void)
+{
+	return tr2cmdname_hierarchy.buf;
+}
+
+void tr2_cmd_name_release(void)
+{
+	strbuf_release(&tr2cmdname_hierarchy);
+}

trace2/tr2_cmd_name.h

@@ -0,0 +1,24 @@
+#ifndef TR2_CMD_NAME_H
+#define TR2_CMD_NAME_H
+
+/*
+ * Append the current command name to the list being maintained
+ * in the environment.
+ *
+ * The hierarchy for a top-level git command is just the current
+ * command name.  For a child git process, the hierarchy includes the
+ * names of the parent processes.
+ *
+ * The hierarchy for the current process will be exported to the
+ * environment and inherited by child processes.
+ */
+void tr2_cmd_name_append_hierarchy(const char *name);
+
+/*
+ * Get the command name hierarchy for the current process.
+ */
+const char *tr2_cmd_name_get_hierarchy(void);
+
+void tr2_cmd_name_release(void);
+
+#endif /* TR2_CMD_NAME_H */

trace2/tr2_dst.c

@@ -0,0 +1,252 @@
+#include "cache.h"
+#include "trace2/tr2_dst.h"
+
+/*
+ * If a Trace2 target cannot be opened for writing, we should issue a
+ * warning to stderr, but this is very annoying if the target is a pipe
+ * or socket and beyond the user's control -- especially since every
+ * git command (and sub-command) will print the message.  So we silently
+ * eat these warnings and just discard the trace data.
+ *
+ * Enable the following environment variable to see these warnings.
+ */
+#define TR2_ENVVAR_DST_DEBUG "GIT_TR2_DST_DEBUG"
+
+static int tr2_dst_want_warning(void)
+{
+	static int tr2env_dst_debug = -1;
+
+	if (tr2env_dst_debug == -1) {
+		const char *env_value = getenv(TR2_ENVVAR_DST_DEBUG);
+		if (!env_value || !*env_value)
+			tr2env_dst_debug = 0;
+		else
+			tr2env_dst_debug = atoi(env_value) > 0;
+	}
+
+	return tr2env_dst_debug;
+}
+
+void tr2_dst_trace_disable(struct tr2_dst *dst)
+{
+	if (dst->need_close)
+		close(dst->fd);
+	dst->fd = 0;
+	dst->initialized = 1;
+	dst->need_close = 0;
+}
+
+static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value)
+{
+	int fd = open(tgt_value, O_WRONLY | O_APPEND | O_CREAT, 0666);
+	if (fd == -1) {
+		if (tr2_dst_want_warning())
+			warning("trace2: could not open '%s' for '%s' tracing: %s",
+				tgt_value, dst->env_var_name, strerror(errno));
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	dst->fd = fd;
+	dst->need_close = 1;
+	dst->initialized = 1;
+
+	return dst->fd;
+}
+
+#ifndef NO_UNIX_SOCKETS
+#define PREFIX_AF_UNIX "af_unix:"
+#define PREFIX_AF_UNIX_STREAM "af_unix:stream:"
+#define PREFIX_AF_UNIX_DGRAM "af_unix:dgram:"
+
+static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd)
+{
+	int fd;
+	struct sockaddr_un sa;
+
+	fd = socket(AF_UNIX, sock_type, 0);
+	if (fd == -1)
+		return errno;
+
+	sa.sun_family = AF_UNIX;
+	strlcpy(sa.sun_path, path, sizeof(sa.sun_path));
+
+	if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
+		int e = errno;
+		close(fd);
+		return e;
+	}
+
+	*out_fd = fd;
+	return 0;
+}
+
+#define TR2_DST_UDS_TRY_STREAM (1 << 0)
+#define TR2_DST_UDS_TRY_DGRAM  (1 << 1)
+
+static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
+					  const char *tgt_value)
+{
+	unsigned int uds_try = 0;
+	int fd;
+	int e;
+	const char *path = NULL;
+
+	/*
+	 * Allow "af_unix:[<type>:]<absolute_path>"
+	 *
+	 * Trace2 always writes complete individual messages (without
+	 * chunking), so we can talk to either DGRAM or STREAM type sockets.
+	 *
+	 * Allow the user to explicitly request the socket type.
+	 *
+	 * If they omit the socket type, try one and then the other.
+	 */
+
+	if (skip_prefix(tgt_value, PREFIX_AF_UNIX_STREAM, &path))
+		uds_try |= TR2_DST_UDS_TRY_STREAM;
+
+	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX_DGRAM, &path))
+		uds_try |= TR2_DST_UDS_TRY_DGRAM;
+
+	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX, &path))
+		uds_try |= TR2_DST_UDS_TRY_STREAM | TR2_DST_UDS_TRY_DGRAM;
+
+	if (!path || !*path) {
+		if (tr2_dst_want_warning())
+			warning("trace2: invalid AF_UNIX value '%s' for '%s' tracing",
+				tgt_value, dst->env_var_name);
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	if (!is_absolute_path(path) ||
+	    strlen(path) >= sizeof(((struct sockaddr_un *)0)->sun_path)) {
+		if (tr2_dst_want_warning())
+			warning("trace2: invalid AF_UNIX path '%s' for '%s' tracing",
+				path, dst->env_var_name);
+
+		tr2_dst_trace_disable(dst);
+		return 0;
+	}
+
+	if (uds_try & TR2_DST_UDS_TRY_STREAM) {
+		e = tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd);
+		if (!e)
+			goto connected;
+		if (e != EPROTOTYPE)
+			goto error;
+	}
+	if (uds_try & TR2_DST_UDS_TRY_DGRAM) {
+		e = tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd);
+		if (!e)
+			goto connected;
+	}
+
+error:
+	if (tr2_dst_want_warning())
+		warning("trace2: could not connect to socket '%s' for '%s' tracing: %s",
+			path, dst->env_var_name, strerror(e));
+
+	tr2_dst_trace_disable(dst);
+	return 0;
+
+connected:
+	dst->fd = fd;
+	dst->need_close = 1;
+	dst->initialized = 1;
+
+	return dst->fd;
+}
+#endif
+
+static void tr2_dst_malformed_warning(struct tr2_dst *dst,
+				      const char *tgt_value)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_addf(&buf, "trace2: unknown value for '%s': '%s'",
+		    dst->env_var_name, tgt_value);
+	warning("%s", buf.buf);
+
+	strbuf_release(&buf);
+}
+
+int tr2_dst_get_trace_fd(struct tr2_dst *dst)
+{
+	const char *tgt_value;
+
+	/* don't open twice */
+	if (dst->initialized)
+		return dst->fd;
+
+	dst->initialized = 1;
+
+	tgt_value = getenv(dst->env_var_name);
+
+	if (!tgt_value || !strcmp(tgt_value, "") || !strcmp(tgt_value, "0") ||
+	    !strcasecmp(tgt_value, "false")) {
+		dst->fd = 0;
+		return dst->fd;
+	}
+
+	if (!strcmp(tgt_value, "1") || !strcasecmp(tgt_value, "true")) {
+		dst->fd = STDERR_FILENO;
+		return dst->fd;
+	}
+
+	if (strlen(tgt_value) == 1 && isdigit(*tgt_value)) {
+		dst->fd = atoi(tgt_value);
+		return dst->fd;
+	}
+
+	if (is_absolute_path(tgt_value))
+		return tr2_dst_try_path(dst, tgt_value);
+
+#ifndef NO_UNIX_SOCKETS
+	if (starts_with(tgt_value, PREFIX_AF_UNIX))
+		return tr2_dst_try_unix_domain_socket(dst, tgt_value);
+#endif
+
+	/* Always warn about malformed values. */
+	tr2_dst_malformed_warning(dst, tgt_value);
+	tr2_dst_trace_disable(dst);
+	return 0;
+}
+
+int tr2_dst_trace_want(struct tr2_dst *dst)
+{
+	return !!tr2_dst_get_trace_fd(dst);
+}
+
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line)
+{
+	int fd = tr2_dst_get_trace_fd(dst);
+
+	strbuf_complete_line(buf_line); /* ensure final NL on buffer */
+
+	/*
+	 * We do not use write_in_full() because we do not want
+	 * a short-write to try again.  We are using O_APPEND mode
+	 * files and the kernel handles the atomic seek+write. If
+	 * another thread or git process is concurrently writing to
+	 * this fd or file, our remainder-write may not be contiguous
+	 * with our initial write of this message.  And that will
+	 * confuse readers.  So just don't bother.
+	 *
+	 * It is assumed that TRACE2 messages are short enough that
+	 * the system can write them in 1 attempt and we won't see
+	 * a short-write.
+	 *
+	 * If we get an IO error, just close the trace dst.
+	 */
+	if (write(fd, buf_line->buf, buf_line->len) >= 0)
+		return;
+
+	if (tr2_dst_want_warning())
+		warning("unable to write trace to '%s': %s", dst->env_var_name,
+			strerror(errno));
+	tr2_dst_trace_disable(dst);
+}

trace2/tr2_dst.h

@@ -0,0 +1,36 @@
+#ifndef TR2_DST_H
+#define TR2_DST_H
+
+struct strbuf;
+
+struct tr2_dst {
+	const char *const env_var_name;
+	int fd;
+	unsigned int initialized : 1;
+	unsigned int need_close : 1;
+};
+
+/*
+ * Disable TRACE2 on the destination.  In TRACE2 a destination (DST)
+ * wraps a file descriptor; it is associated with a TARGET which
+ * defines the formatting.
+ */
+void tr2_dst_trace_disable(struct tr2_dst *dst);
+
+/*
+ * Return the file descriptor for the DST.
+ * If 0, the dst is closed or disabled.
+ */
+int tr2_dst_get_trace_fd(struct tr2_dst *dst);
+
+/*
+ * Return true if the DST is opened for writing.
+ */
+int tr2_dst_trace_want(struct tr2_dst *dst);
+
+/*
+ * Write a single line/message to the trace file.
+ */
+void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line);
+
+#endif /* TR2_DST_H */

trace2/tr2_sid.c

@@ -0,0 +1,67 @@
+#include "cache.h"
+#include "trace2/tr2_sid.h"
+
+#define TR2_ENVVAR_PARENT_SID "GIT_TR2_PARENT_SID"
+
+static struct strbuf tr2sid_buf = STRBUF_INIT;
+static int tr2sid_nr_git_parents;
+
+/*
+ * Compute a "unique" session id (SID) for the current process.  This allows
+ * all events from this process to have a single label (much like a PID).
+ *
+ * Export this into our environment so that all child processes inherit it.
+ *
+ * If we were started by another git instance, use our parent's SID as a
+ * prefix.  (This lets us track parent/child relationships even if there
+ * is an intermediate shell process.)
+ *
+ * Additionally, count the number of nested git processes.
+ */
+static void tr2_sid_compute(void)
+{
+	uint64_t us_now;
+	const char *parent_sid;
+
+	if (tr2sid_buf.len)
+		return;
+
+	parent_sid = getenv(TR2_ENVVAR_PARENT_SID);
+	if (parent_sid && *parent_sid) {
+		const char *p;
+		for (p = parent_sid; *p; p++)
+			if (*p == '/')
+				tr2sid_nr_git_parents++;
+
+		strbuf_addstr(&tr2sid_buf, parent_sid);
+		strbuf_addch(&tr2sid_buf, '/');
+		tr2sid_nr_git_parents++;
+	}
+
+	us_now = getnanotime() / 1000;
+	strbuf_addf(&tr2sid_buf, "%" PRIuMAX "-%" PRIdMAX, (uintmax_t)us_now,
+		    (intmax_t)getpid());
+
+	setenv(TR2_ENVVAR_PARENT_SID, tr2sid_buf.buf, 1);
+}
+
+const char *tr2_sid_get(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_buf.buf;
+}
+
+int tr2_sid_depth(void)
+{
+	if (!tr2sid_buf.len)
+		tr2_sid_compute();
+
+	return tr2sid_nr_git_parents;
+}
+
+void tr2_sid_release(void)
+{
+	strbuf_release(&tr2sid_buf);
+}

trace2/tr2_sid.h

@@ -0,0 +1,18 @@
+#ifndef TR2_SID_H
+#define TR2_SID_H
+
+/*
+ * Get our session id. Compute if necessary.
+ */
+const char *tr2_sid_get(void);
+
+/*
+ * Get our process depth.  A top-level git process invoked from the
+ * command line will have depth=0.  A child git process will have
+ * depth=1 and so on.
+ */
+int tr2_sid_depth(void);
+
+void tr2_sid_release(void);
+
+#endif /* TR2_SID_H */

trace2/tr2_tbuf.c

@@ -0,0 +1,32 @@
+#include "cache.h"
+#include "tr2_tbuf.h"
+
+void tr2_tbuf_local_time(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	localtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf), "%02d:%02d:%02d.%06ld", tm.tm_hour,
+		  tm.tm_min, tm.tm_sec, (long)tv.tv_usec);
+}
+
+void tr2_tbuf_utc_time(struct tr2_tbuf *tb)
+{
+	struct timeval tv;
+	struct tm tm;
+	time_t secs;
+
+	gettimeofday(&tv, NULL);
+	secs = tv.tv_sec;
+	gmtime_r(&secs, &tm);
+
+	xsnprintf(tb->buf, sizeof(tb->buf),
+		  "%4d-%02d-%02d %02d:%02d:%02d.%06ld", tm.tm_year + 1900,
+		  tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec,
+		  (long)tv.tv_usec);
+}

trace2/tr2_tbuf.h

@@ -0,0 +1,23 @@
+#ifndef TR2_TBUF_H
+#define TR2_TBUF_H
+
+/*
+ * A simple wrapper around a fixed buffer to avoid C syntax
+ * quirks and the need to pass around an additional size_t
+ * argument.
+ */
+struct tr2_tbuf {
+	char buf[32];
+};
+
+/*
+ * Fill buffer with formatted local time string.
+ */
+void tr2_tbuf_local_time(struct tr2_tbuf *tb);
+
+/*
+ * Fill buffer with formatted UTC time string.
+ */
+void tr2_tbuf_utc_time(struct tr2_tbuf *tb);
+
+#endif /* TR2_TBUF_H */

trace2/tr2_tgt.h

@@ -0,0 +1,133 @@
+#ifndef TR2_TGT_H
+#define TR2_TGT_H
+
+struct child_process;
+struct repository;
+struct json_writer;
+
+/*
+ * Function prototypes for a TRACE2 "target" vtable.
+ */
+
+typedef int(tr2_tgt_init_t)(void);
+typedef void(tr2_tgt_term_t)(void);
+
+typedef void(tr2_tgt_evt_version_fl_t)(const char *file, int line);
+
+typedef void(tr2_tgt_evt_start_fl_t)(const char *file, int line,
+				     const char **argv);
+typedef void(tr2_tgt_evt_exit_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute, int code);
+typedef void(tr2_tgt_evt_signal_t)(uint64_t us_elapsed_absolute, int signo);
+typedef void(tr2_tgt_evt_atexit_t)(uint64_t us_elapsed_absolute, int code);
+
+typedef void(tr2_tgt_evt_error_va_fl_t)(const char *file, int line,
+					const char *fmt, va_list ap);
+
+typedef void(tr2_tgt_evt_command_path_fl_t)(const char *file, int line,
+					    const char *command_path);
+typedef void(tr2_tgt_evt_command_name_fl_t)(const char *file, int line,
+					    const char *name,
+					    const char *hierarchy);
+typedef void(tr2_tgt_evt_command_mode_fl_t)(const char *file, int line,
+					    const char *mode);
+
+typedef void(tr2_tgt_evt_alias_fl_t)(const char *file, int line,
+				     const char *alias, const char **argv);
+
+typedef void(tr2_tgt_evt_child_start_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   const struct child_process *cmd);
+typedef void(tr2_tgt_evt_child_exit_fl_t)(const char *file, int line,
+					  uint64_t us_elapsed_absolute, int cid,
+					  int pid, int code,
+					  uint64_t us_elapsed_child);
+
+typedef void(tr2_tgt_evt_thread_start_fl_t)(const char *file, int line,
+					    uint64_t us_elapsed_absolute);
+typedef void(tr2_tgt_evt_thread_exit_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   uint64_t us_elapsed_thread);
+
+typedef void(tr2_tgt_evt_exec_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute, int exec_id,
+				    const char *exe, const char **argv);
+typedef void(tr2_tgt_evt_exec_result_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   int exec_id, int code);
+
+typedef void(tr2_tgt_evt_param_fl_t)(const char *file, int line,
+				     const char *param, const char *value);
+
+typedef void(tr2_tgt_evt_repo_fl_t)(const char *file, int line,
+				    const struct repository *repo);
+
+typedef void(tr2_tgt_evt_region_enter_printf_va_fl_t)(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	const char *category, const char *label, const struct repository *repo,
+	const char *fmt, va_list ap);
+typedef void(tr2_tgt_evt_region_leave_printf_va_fl_t)(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap);
+
+typedef void(tr2_tgt_evt_data_fl_t)(const char *file, int line,
+				    uint64_t us_elapsed_absolute,
+				    uint64_t us_elapsed_region,
+				    const char *category,
+				    const struct repository *repo,
+				    const char *key, const char *value);
+typedef void(tr2_tgt_evt_data_json_fl_t)(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 uint64_t us_elapsed_region,
+					 const char *category,
+					 const struct repository *repo,
+					 const char *key,
+					 const struct json_writer *value);
+
+typedef void(tr2_tgt_evt_printf_va_fl_t)(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *fmt, va_list ap);
+
+/*
+ * "vtable" for a TRACE2 target.  Use NULL if a target does not want
+ * to emit that message.
+ */
+/* clang-format off */
+struct tr2_tgt {
+	struct tr2_dst                          *pdst;
+
+	tr2_tgt_init_t                          *pfn_init;
+	tr2_tgt_term_t                          *pfn_term;
+
+	tr2_tgt_evt_version_fl_t                *pfn_version_fl;
+	tr2_tgt_evt_start_fl_t                  *pfn_start_fl;
+	tr2_tgt_evt_exit_fl_t                   *pfn_exit_fl;
+	tr2_tgt_evt_signal_t                    *pfn_signal;
+	tr2_tgt_evt_atexit_t                    *pfn_atexit;
+	tr2_tgt_evt_error_va_fl_t               *pfn_error_va_fl;
+	tr2_tgt_evt_command_path_fl_t           *pfn_command_path_fl;
+	tr2_tgt_evt_command_name_fl_t           *pfn_command_name_fl;
+	tr2_tgt_evt_command_mode_fl_t           *pfn_command_mode_fl;
+	tr2_tgt_evt_alias_fl_t                  *pfn_alias_fl;
+	tr2_tgt_evt_child_start_fl_t            *pfn_child_start_fl;
+	tr2_tgt_evt_child_exit_fl_t             *pfn_child_exit_fl;
+	tr2_tgt_evt_thread_start_fl_t           *pfn_thread_start_fl;
+	tr2_tgt_evt_thread_exit_fl_t            *pfn_thread_exit_fl;
+	tr2_tgt_evt_exec_fl_t                   *pfn_exec_fl;
+	tr2_tgt_evt_exec_result_fl_t            *pfn_exec_result_fl;
+	tr2_tgt_evt_param_fl_t                  *pfn_param_fl;
+	tr2_tgt_evt_repo_fl_t                   *pfn_repo_fl;
+	tr2_tgt_evt_region_enter_printf_va_fl_t *pfn_region_enter_printf_va_fl;
+	tr2_tgt_evt_region_leave_printf_va_fl_t *pfn_region_leave_printf_va_fl;
+	tr2_tgt_evt_data_fl_t                   *pfn_data_fl;
+	tr2_tgt_evt_data_json_fl_t              *pfn_data_json_fl;
+	tr2_tgt_evt_printf_va_fl_t              *pfn_printf_va_fl;
+};
+/* clang-format on */
+
+extern struct tr2_tgt tr2_tgt_event;
+extern struct tr2_tgt tr2_tgt_normal;
+extern struct tr2_tgt tr2_tgt_perf;
+
+#endif /* TR2_TGT_H */

trace2/tr2_tgt_event.c

@@ -0,0 +1,588 @@
+#include "cache.h"
+#include "config.h"
+#include "json-writer.h"
+#include "run-command.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_event = { "GIT_TR2_EVENT", 0, 0, 0 };
+
+/*
+ * The version number of the JSON data generated by the EVENT target
+ * in this source file.  Update this if you make a significant change
+ * to the JSON fields or message structure.  You probably do not need
+ * to update this if you just add another call to one of the existing
+ * TRACE2 API methods.
+ */
+#define TR2_EVENT_VERSION "1"
+
+/*
+ * Region nesting limit for messages written to the event target.
+ *
+ * The "region_enter" and "region_leave" messages (especially recursive
+ * messages such as those produced while diving the worktree or index)
+ * are primarily intended for the performance target during debugging.
+ *
+ * Some of the outer-most messages, however, may be of interest to the
+ * event target.  Set this environment variable to a larger integer for
+ * more detail in the event target.
+ */
+#define TR2_ENVVAR_EVENT_NESTING "GIT_TR2_EVENT_NESTING"
+static int tr2env_event_nesting_wanted = 2;
+
+/*
+ * Set this environment variable to true to omit the <time>, <file>, and
+ * <line> fields from most events.
+ */
+#define TR2_ENVVAR_EVENT_BRIEF "GIT_TR2_EVENT_BRIEF"
+static int tr2env_event_brief;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_event);
+	int want_nesting;
+	int want_brief;
+	char *nesting;
+	char *brief;
+
+	if (!want)
+		return want;
+
+	nesting = getenv(TR2_ENVVAR_EVENT_NESTING);
+	if (nesting && ((want_nesting = atoi(nesting)) > 0))
+		tr2env_event_nesting_wanted = want_nesting;
+
+	brief = getenv(TR2_ENVVAR_EVENT_BRIEF);
+	if (brief && ((want_brief = atoi(brief)) > 0))
+		tr2env_event_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_event);
+}
+
+/*
+ * Append common key-value pairs to the currently open JSON object.
+ *     "event:"<event_name>"
+ *      "sid":"<sid>"
+ *   "thread":"<thread_name>"
+ *     "time":"<time>"
+ *     "file":"<filename>"
+ *     "line":<line_number>
+ *     "repo":<repo_id>
+ */
+static void event_fmt_prepare(const char *event_name, const char *file,
+			      int line, const struct repository *repo,
+			      struct json_writer *jw)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct tr2_tbuf tb_now;
+
+	jw_object_string(jw, "event", event_name);
+	jw_object_string(jw, "sid", tr2_sid_get());
+	jw_object_string(jw, "thread", ctx->thread_name.buf);
+
+	/*
+	 * In brief mode, only emit <time> on these 2 event types.
+	 */
+	if (!tr2env_event_brief || !strcmp(event_name, "version") ||
+	    !strcmp(event_name, "atexit")) {
+		tr2_tbuf_utc_time(&tb_now);
+		jw_object_string(jw, "time", tb_now.buf);
+	}
+
+	if (!tr2env_event_brief && file && *file) {
+		jw_object_string(jw, "file", file);
+		jw_object_intmax(jw, "line", line);
+	}
+
+	if (repo)
+		jw_object_intmax(jw, "repo", repo->trace2_repo_id);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "evt", TR2_EVENT_VERSION);
+	jw_object_string(&jw, "exe", git_version_string);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	const char *event_name = "start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	const char *event_name = "exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "signo", signo);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void maybe_add_string_va(struct json_writer *jw, const char *field_name,
+				const char *fmt, va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+		struct strbuf buf = STRBUF_INIT;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(&buf, fmt, copy_ap);
+		va_end(copy_ap);
+
+		jw_object_string(jw, field_name, buf.buf);
+		strbuf_release(&buf);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		jw_object_string(jw, field_name, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	const char *event_name = "error";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	maybe_add_string_va(&jw, "msg", fmt, ap);
+	/*
+	 * Also emit the format string as a field in case
+	 * post-processors want to aggregate common error
+	 * messages by type without argument fields (such
+	 * as pathnames or branch names) cluttering it up.
+	 */
+	if (fmt && *fmt)
+		jw_object_string(&jw, "fmt", fmt);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "path", pathname);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	const char *event_name = "cmd_name";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "name", name);
+	if (hierarchy && *hierarchy)
+		jw_object_string(&jw, "hierarchy", hierarchy);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	const char *event_name = "cmd_mode";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "name", mode);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	const char *event_name = "alias";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "alias", alias);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cmd->trace2_child_id);
+	if (cmd->trace2_hook_name) {
+		jw_object_string(&jw, "child_class", "hook");
+		jw_object_string(&jw, "hook_name", cmd->trace2_hook_name);
+	} else {
+		const char *child_class =
+			cmd->trace2_child_class ? cmd->trace2_child_class : "?";
+		jw_object_string(&jw, "child_class", child_class);
+	}
+	if (cmd->dir)
+		jw_object_string(&jw, "cd", cmd->dir);
+	jw_object_bool(&jw, "use_shell", cmd->use_shell);
+	jw_object_inline_begin_array(&jw, "argv");
+	if (cmd->git_cmd)
+		jw_array_string(&jw, "git");
+	jw_array_argv(&jw, cmd->argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_child / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cid);
+	jw_object_intmax(&jw, "pid", pid);
+	jw_object_intmax(&jw, "code", code);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+
+	jw_release(&jw);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+			       uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_thread / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "exec_id", exec_id);
+	if (exe)
+		jw_object_string(&jw, "exe", exe);
+	jw_object_inline_begin_array(&jw, "argv");
+	jw_array_argv(&jw, argv);
+	jw_end(&jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	const char *event_name = "exec_result";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "exec_id", exec_id);
+	jw_object_intmax(&jw, "code", code);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	const char *event_name = "def_param";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_string(&jw, "param", param);
+	jw_object_string(&jw, "value", value);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, repo, &jw);
+	jw_object_string(&jw, "worktree", repo->worktree);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_region_leave_printf_va_fl(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		if (category)
+			jw_object_string(&jw, "category", category);
+		if (label)
+			jw_object_string(&jw, "label", label);
+		maybe_add_string_va(&jw, "msg", fmt, ap);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_data_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region, const char *category,
+		       const struct repository *repo, const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_abs = (double)us_elapsed_absolute / 1000000.0;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_abs", 6, t_abs);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		jw_object_string(&jw, "category", category);
+		jw_object_string(&jw, "key", key);
+		jw_object_string(&jw, "value", value);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+static void fn_data_json_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    uint64_t us_elapsed_region, const char *category,
+			    const struct repository *repo, const char *key,
+			    const struct json_writer *value)
+{
+	const char *event_name = "data_json";
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	if (ctx->nr_open_regions <= tr2env_event_nesting_wanted) {
+		struct json_writer jw = JSON_WRITER_INIT;
+		double t_abs = (double)us_elapsed_absolute / 1000000.0;
+		double t_rel = (double)us_elapsed_region / 1000000.0;
+
+		jw_object_begin(&jw, 0);
+		event_fmt_prepare(event_name, file, line, repo, &jw);
+		jw_object_double(&jw, "t_abs", 6, t_abs);
+		jw_object_double(&jw, "t_rel", 6, t_rel);
+		jw_object_intmax(&jw, "nesting", ctx->nr_open_regions);
+		jw_object_string(&jw, "category", category);
+		jw_object_string(&jw, "key", key);
+		jw_object_sub_jw(&jw, "value", value);
+		jw_end(&jw);
+
+		tr2_dst_write_line(&tr2dst_event, &jw.json);
+		jw_release(&jw);
+	}
+}
+
+struct tr2_tgt tr2_tgt_event = {
+	&tr2dst_event,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	fn_data_json_fl,
+	NULL, /* printf */
+};

trace2/tr2_tgt_normal.c

@@ -0,0 +1,323 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_normal = { "GIT_TR2", 0, 0, 0 };
+
+/*
+ * Set this environment variable to true to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin normal target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+#define TR2_ENVVAR_NORMAL_BRIEF "GIT_TR2_BRIEF"
+static int tr2env_normal_brief;
+
+#define TR2FMT_NORMAL_FL_WIDTH (50)
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_normal);
+	int want_brief;
+	char *brief;
+
+	if (!want)
+		return want;
+
+	brief = getenv(TR2_ENVVAR_NORMAL_BRIEF);
+	if (brief && *brief &&
+	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
+		tr2env_normal_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_normal);
+}
+
+static void normal_fmt_prepare(const char *file, int line, struct strbuf *buf)
+{
+	strbuf_setlen(buf, 0);
+
+	if (!tr2env_normal_brief) {
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_local_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_NORMAL_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+	}
+}
+
+static void normal_io_write_fl(const char *file, int line,
+			       const struct strbuf *buf_payload)
+{
+	struct strbuf buf_line = STRBUF_INIT;
+
+	normal_fmt_prepare(file, line, &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_normal, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "version %s", git_version_string);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "start ");
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "exit elapsed:%.6f code:%d", elapsed, code);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "signal elapsed:%.6f code:%d", elapsed,
+		    signo);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_absolute / 1000000.0;
+
+	strbuf_addf(&buf_payload, "atexit elapsed:%.6f code:%d", elapsed, code);
+	normal_io_write_fl(__FILE__, __LINE__, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
+				   va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "error ");
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_path %s", pathname);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_name %s", name);
+	if (hierarchy && *hierarchy)
+		strbuf_addf(&buf_payload, " (%s)", hierarchy);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "cmd_mode %s", mode);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias %s ->", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "child_start[%d] ", cmd->trace2_child_id);
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+		strbuf_addstr(&buf_payload, "; ");
+	}
+
+	/*
+	 * TODO if (cmd->env) { Consider dumping changes to environment. }
+	 * See trace_add_env() in run-command.c as used by original trace.c
+	 */
+
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, "git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_child / 1000000.0;
+
+	strbuf_addf(&buf_payload, "child_exit[%d] pid:%d code:%d elapsed:%.6f",
+		    cid, pid, code, elapsed);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "exec[%d] ", exec_id);
+	if (exe)
+		strbuf_addstr(&buf_payload, exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "exec_result[%d] code:%d", exec_id, code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "def_param %s=%s", param, value);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree ");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute, const char *fmt,
+			    va_list ap)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_normal = {
+	&tr2dst_normal,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	NULL, /* thread_start */
+	NULL, /* thread_exit */
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	NULL, /* region_enter */
+	NULL, /* region_leave */
+	NULL, /* data */
+	NULL, /* data_json */
+	fn_printf_va_fl,
+};

trace2/tr2_tgt_perf.c

@@ -0,0 +1,534 @@
+#include "cache.h"
+#include "config.h"
+#include "run-command.h"
+#include "quote.h"
+#include "version.h"
+#include "json-writer.h"
+#include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
+#include "trace2/tr2_tbuf.h"
+#include "trace2/tr2_tgt.h"
+#include "trace2/tr2_tls.h"
+
+static struct tr2_dst tr2dst_perf = { "GIT_TR2_PERF", 0, 0, 0 };
+
+/*
+ * Set this environment variable to true to omit the "<time> <file>:<line>"
+ * fields from each line written to the builtin performance target.
+ *
+ * Unit tests may want to use this to help with testing.
+ */
+#define TR2_ENVVAR_PERF_BRIEF "GIT_TR2_PERF_BRIEF"
+static int tr2env_perf_brief;
+
+#define TR2FMT_PERF_FL_WIDTH (50)
+#define TR2FMT_PERF_MAX_EVENT_NAME (12)
+#define TR2FMT_PERF_REPO_WIDTH (4)
+#define TR2FMT_PERF_CATEGORY_WIDTH (10)
+
+#define TR2_DOTS_BUFFER_SIZE (100)
+#define TR2_INDENT (2)
+#define TR2_INDENT_LENGTH(ctx) (((ctx)->nr_open_regions - 1) * TR2_INDENT)
+
+static struct strbuf dots = STRBUF_INIT;
+
+static int fn_init(void)
+{
+	int want = tr2_dst_trace_want(&tr2dst_perf);
+	int want_brief;
+	char *brief;
+
+	if (!want)
+		return want;
+
+	strbuf_addchars(&dots, '.', TR2_DOTS_BUFFER_SIZE);
+
+	brief = getenv(TR2_ENVVAR_PERF_BRIEF);
+	if (brief && *brief &&
+	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
+		tr2env_perf_brief = want_brief;
+
+	return want;
+}
+
+static void fn_term(void)
+{
+	tr2_dst_trace_disable(&tr2dst_perf);
+
+	strbuf_release(&dots);
+}
+
+/*
+ * Format trace line prefix in human-readable classic format for
+ * the performance target:
+ *     "[<time> [<file>:<line>] <bar>] <nr_parents> <bar>
+ *         <thread_name> <bar> <event_name> <bar> [<repo>] <bar>
+ *         [<elapsed_absolute>] [<elapsed_relative>] <bar>
+ *         [<category>] <bar> [<dots>] "
+ */
+static void perf_fmt_prepare(const char *event_name,
+			     struct tr2tls_thread_ctx *ctx, const char *file,
+			     int line, const struct repository *repo,
+			     uint64_t *p_us_elapsed_absolute,
+			     uint64_t *p_us_elapsed_relative,
+			     const char *category, struct strbuf *buf)
+{
+	int len;
+
+	strbuf_setlen(buf, 0);
+
+	if (!tr2env_perf_brief) {
+		struct tr2_tbuf tb_now;
+
+		tr2_tbuf_local_time(&tb_now);
+		strbuf_addstr(buf, tb_now.buf);
+		strbuf_addch(buf, ' ');
+
+		if (file && *file)
+			strbuf_addf(buf, "%s:%d ", file, line);
+		while (buf->len < TR2FMT_PERF_FL_WIDTH)
+			strbuf_addch(buf, ' ');
+
+		strbuf_addstr(buf, "| ");
+	}
+
+	strbuf_addf(buf, "d%d | ", tr2_sid_depth());
+	strbuf_addf(buf, "%-*s | %-*s | ", TR2_MAX_THREAD_NAME,
+		    ctx->thread_name.buf, TR2FMT_PERF_MAX_EVENT_NAME,
+		    event_name);
+
+	len = buf->len + TR2FMT_PERF_REPO_WIDTH;
+	if (repo)
+		strbuf_addf(buf, "r%d ", repo->trace2_repo_id);
+	while (buf->len < len)
+		strbuf_addch(buf, ' ');
+	strbuf_addstr(buf, "| ");
+
+	if (p_us_elapsed_absolute)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_absolute)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+
+	if (p_us_elapsed_relative)
+		strbuf_addf(buf, "%9.6f | ",
+			    ((double)(*p_us_elapsed_relative)) / 1000000.0);
+	else
+		strbuf_addf(buf, "%9s | ", " ");
+
+	strbuf_addf(buf, "%-*s | ", TR2FMT_PERF_CATEGORY_WIDTH,
+		    (category ? category : ""));
+
+	if (ctx->nr_open_regions > 0) {
+		int len_indent = TR2_INDENT_LENGTH(ctx);
+		while (len_indent > dots.len) {
+			strbuf_addbuf(buf, &dots);
+			len_indent -= dots.len;
+		}
+		strbuf_addf(buf, "%.*s", len_indent, dots.buf);
+	}
+}
+
+static void perf_io_write_fl(const char *file, int line, const char *event_name,
+			     const struct repository *repo,
+			     uint64_t *p_us_elapsed_absolute,
+			     uint64_t *p_us_elapsed_relative,
+			     const char *category,
+			     const struct strbuf *buf_payload)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+	struct strbuf buf_line = STRBUF_INIT;
+
+	perf_fmt_prepare(event_name, ctx, file, line, repo,
+			 p_us_elapsed_absolute, p_us_elapsed_relative, category,
+			 &buf_line);
+	strbuf_addbuf(&buf_line, buf_payload);
+	tr2_dst_write_line(&tr2dst_perf, &buf_line);
+	strbuf_release(&buf_line);
+}
+
+static void fn_version_fl(const char *file, int line)
+{
+	const char *event_name = "version";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, git_version_string);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_start_fl(const char *file, int line, const char **argv)
+{
+	const char *event_name = "start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exit_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int code)
+{
+	const char *event_name = "exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_signal(uint64_t us_elapsed_absolute, int signo)
+{
+	const char *event_name = "signal";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "signo:%d", signo);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_atexit(uint64_t us_elapsed_absolute, int code)
+{
+	const char *event_name = "atexit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "code:%d", code);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
+				   va_list ap)
+{
+	if (fmt && *fmt && ap) {
+		va_list copy_ap;
+
+		va_copy(copy_ap, ap);
+		strbuf_vaddf(buf, fmt, copy_ap);
+		va_end(copy_ap);
+		return;
+	}
+
+	if (fmt && *fmt) {
+		strbuf_addstr(buf, fmt);
+		return;
+	}
+}
+
+static void fn_error_va_fl(const char *file, int line, const char *fmt,
+			   va_list ap)
+{
+	const char *event_name = "error";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_path_fl(const char *file, int line, const char *pathname)
+{
+	const char *event_name = "cmd_path";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, pathname);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_name_fl(const char *file, int line, const char *name,
+			       const char *hierarchy)
+{
+	const char *event_name = "cmd_name";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, name);
+	if (hierarchy && *hierarchy)
+		strbuf_addf(&buf_payload, " (%s)", hierarchy);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_command_mode_fl(const char *file, int line, const char *mode)
+{
+	const char *event_name = "cmd_mode";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, mode);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_alias_fl(const char *file, int line, const char *alias,
+			const char **argv)
+{
+	const char *event_name = "alias";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "alias:%s argv:", alias);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_start_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      const struct child_process *cmd)
+{
+	const char *event_name = "child_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (cmd->trace2_hook_name) {
+		strbuf_addf(&buf_payload, "[ch%d] class:hook hook:%s",
+			    cmd->trace2_child_id, cmd->trace2_hook_name);
+	} else {
+		const char *child_class =
+			cmd->trace2_child_class ? cmd->trace2_child_class : "?";
+		strbuf_addf(&buf_payload, "[ch%d] class:%s",
+			    cmd->trace2_child_id, child_class);
+	}
+
+	if (cmd->dir) {
+		strbuf_addstr(&buf_payload, " cd:");
+		sq_quote_buf_pretty(&buf_payload, cmd->dir);
+	}
+
+	strbuf_addstr(&buf_payload, " argv:");
+	if (cmd->git_cmd)
+		strbuf_addstr(&buf_payload, " git");
+	sq_quote_argv_pretty(&buf_payload, cmd->argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_child_exit_fl(const char *file, int line,
+			     uint64_t us_elapsed_absolute, int cid, int pid,
+			     int code, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "[ch%d] pid:%d code:%d", cid, pid, code);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 &us_elapsed_child, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_start_fl(const char *file, int line,
+			       uint64_t us_elapsed_absolute)
+{
+	const char *event_name = "thread_start";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_thread_exit_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute,
+			      uint64_t us_elapsed_thread)
+{
+	const char *event_name = "thread_exit";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 &us_elapsed_thread, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       int exec_id, const char *exe, const char **argv)
+{
+	const char *event_name = "exec";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "id:%d ", exec_id);
+	strbuf_addstr(&buf_payload, "argv:");
+	if (exe)
+		strbuf_addf(&buf_payload, " %s", exe);
+	sq_quote_argv_pretty(&buf_payload, argv);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_exec_result_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int exec_id,
+			      int code)
+{
+	const char *event_name = "exec_result";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "id:%d code:%d", exec_id, code);
+	if (code > 0)
+		strbuf_addf(&buf_payload, " err:%s", strerror(code));
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_param_fl(const char *file, int line, const char *param,
+			const char *value)
+{
+	const char *event_name = "def_param";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", param, value);
+
+	perf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_repo_fl(const char *file, int line,
+		       const struct repository *repo)
+{
+	const char *event_name = "def_repo";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addstr(&buf_payload, "worktree:");
+	sq_quote_buf_pretty(&buf_payload, repo->worktree);
+
+	perf_io_write_fl(file, line, event_name, repo, NULL, NULL, NULL,
+			 &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_enter_printf_va_fl(const char *file, int line,
+					 uint64_t us_elapsed_absolute,
+					 const char *category,
+					 const char *label,
+					 const struct repository *repo,
+					 const char *fmt, va_list ap)
+{
+	const char *event_name = "region_enter";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 NULL, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_region_leave_printf_va_fl(
+	const char *file, int line, uint64_t us_elapsed_absolute,
+	uint64_t us_elapsed_region, const char *category, const char *label,
+	const struct repository *repo, const char *fmt, va_list ap)
+{
+	const char *event_name = "region_leave";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	if (label)
+		strbuf_addf(&buf_payload, "label:%s ", label);
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_data_fl(const char *file, int line, uint64_t us_elapsed_absolute,
+		       uint64_t us_elapsed_region, const char *category,
+		       const struct repository *repo, const char *key,
+		       const char *value)
+{
+	const char *event_name = "data";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", key, value);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_data_json_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute,
+			    uint64_t us_elapsed_region, const char *category,
+			    const struct repository *repo, const char *key,
+			    const struct json_writer *value)
+{
+	const char *event_name = "data_json";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "%s:%s", key, value->json.buf);
+
+	perf_io_write_fl(file, line, event_name, repo, &us_elapsed_absolute,
+			 &us_elapsed_region, category, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+static void fn_printf_va_fl(const char *file, int line,
+			    uint64_t us_elapsed_absolute, const char *fmt,
+			    va_list ap)
+{
+	const char *event_name = "printf";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	maybe_append_string_va(&buf_payload, fmt, ap);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 NULL, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
+struct tr2_tgt tr2_tgt_perf = {
+	&tr2dst_perf,
+
+	fn_init,
+	fn_term,
+
+	fn_version_fl,
+	fn_start_fl,
+	fn_exit_fl,
+	fn_signal,
+	fn_atexit,
+	fn_error_va_fl,
+	fn_command_path_fl,
+	fn_command_name_fl,
+	fn_command_mode_fl,
+	fn_alias_fl,
+	fn_child_start_fl,
+	fn_child_exit_fl,
+	fn_thread_start_fl,
+	fn_thread_exit_fl,
+	fn_exec_fl,
+	fn_exec_result_fl,
+	fn_param_fl,
+	fn_repo_fl,
+	fn_region_enter_printf_va_fl,
+	fn_region_leave_printf_va_fl,
+	fn_data_fl,
+	fn_data_json_fl,
+	fn_printf_va_fl,
+};

trace2/tr2_tls.c

@@ -0,0 +1,164 @@
+#include "cache.h"
+#include "thread-utils.h"
+#include "trace2/tr2_tls.h"
+
+/*
+ * Initialize size of the thread stack for nested regions.
+ * This is used to store nested region start times.  Note that
+ * this stack is per-thread and not per-trace-key.
+ */
+#define TR2_REGION_NESTING_INITIAL_SIZE (100)
+
+static struct tr2tls_thread_ctx *tr2tls_thread_main;
+static uint64_t tr2tls_us_start_main;
+
+static pthread_mutex_t tr2tls_mutex;
+static pthread_key_t tr2tls_key;
+
+static int tr2_next_thread_id; /* modify under lock */
+
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name)
+{
+	uint64_t us_now = getnanotime() / 1000;
+	struct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));
+
+	/*
+	 * Implicitly "tr2tls_push_self()" to capture the thread's start
+	 * time in array_us_start[0].  For the main thread this gives us the
+	 * application run time.
+	 */
+	ctx->alloc = TR2_REGION_NESTING_INITIAL_SIZE;
+	ctx->array_us_start = (uint64_t *)xcalloc(ctx->alloc, sizeof(uint64_t));
+	ctx->array_us_start[ctx->nr_open_regions++] = us_now;
+
+	ctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
+
+	strbuf_init(&ctx->thread_name, 0);
+	if (ctx->thread_id)
+		strbuf_addf(&ctx->thread_name, "th%02d:", ctx->thread_id);
+	strbuf_addstr(&ctx->thread_name, thread_name);
+	if (ctx->thread_name.len > TR2_MAX_THREAD_NAME)
+		strbuf_setlen(&ctx->thread_name, TR2_MAX_THREAD_NAME);
+
+	pthread_setspecific(tr2tls_key, ctx);
+
+	return ctx;
+}
+
+struct tr2tls_thread_ctx *tr2tls_get_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = pthread_getspecific(tr2tls_key);
+
+	/*
+	 * If the thread-proc did not call trace2_thread_start(), we won't
+	 * have any TLS data associated with the current thread.  Fix it
+	 * here and silently continue.
+	 */
+	if (!ctx)
+		ctx = tr2tls_create_self("unknown");
+
+	return ctx;
+}
+
+int tr2tls_is_main_thread(void)
+{
+	struct tr2tls_thread_ctx *ctx = pthread_getspecific(tr2tls_key);
+
+	return ctx == tr2tls_thread_main;
+}
+
+void tr2tls_unset_self(void)
+{
+	struct tr2tls_thread_ctx *ctx;
+
+	ctx = tr2tls_get_self();
+
+	pthread_setspecific(tr2tls_key, NULL);
+
+	free(ctx->array_us_start);
+	free(ctx);
+}
+
+void tr2tls_push_self(uint64_t us_now)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	ALLOC_GROW(ctx->array_us_start, ctx->nr_open_regions + 1, ctx->alloc);
+	ctx->array_us_start[ctx->nr_open_regions++] = us_now;
+}
+
+void tr2tls_pop_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	if (!ctx->nr_open_regions)
+		BUG("no open regions in thread '%s'", ctx->thread_name.buf);
+
+	ctx->nr_open_regions--;
+}
+
+void tr2tls_pop_unwind_self(void)
+{
+	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
+
+	while (ctx->nr_open_regions > 1)
+		tr2tls_pop_self();
+}
+
+uint64_t tr2tls_region_elasped_self(uint64_t us)
+{
+	struct tr2tls_thread_ctx *ctx;
+	uint64_t us_start;
+
+	ctx = tr2tls_get_self();
+	if (!ctx->nr_open_regions)
+		return 0;
+
+	us_start = ctx->array_us_start[ctx->nr_open_regions - 1];
+
+	return us - us_start;
+}
+
+uint64_t tr2tls_absolute_elapsed(uint64_t us)
+{
+	if (!tr2tls_thread_main)
+		return 0;
+
+	return us - tr2tls_us_start_main;
+}
+
+void tr2tls_init(void)
+{
+	pthread_key_create(&tr2tls_key, NULL);
+	init_recursive_mutex(&tr2tls_mutex);
+
+	tr2tls_thread_main = tr2tls_create_self("main");
+	/*
+	 * Keep a copy of the absolute start time of the main thread
+	 * in a fixed variable since other threads need to access it.
+	 * This also eliminates the need to lock accesses to the main
+	 * thread's array (because of reallocs).
+	 */
+	tr2tls_us_start_main = tr2tls_thread_main->array_us_start[0];
+}
+
+void tr2tls_release(void)
+{
+	tr2tls_unset_self();
+	tr2tls_thread_main = NULL;
+
+	pthread_mutex_destroy(&tr2tls_mutex);
+	pthread_key_delete(tr2tls_key);
+}
+
+int tr2tls_locked_increment(int *p)
+{
+	int current_value;
+
+	pthread_mutex_lock(&tr2tls_mutex);
+	current_value = *p;
+	*p = current_value + 1;
+	pthread_mutex_unlock(&tr2tls_mutex);
+
+	return current_value;
+}

trace2/tr2_tls.h

@@ -0,0 +1,97 @@
+#ifndef TR2_TLS_H
+#define TR2_TLS_H
+
+#include "strbuf.h"
+
+/*
+ * Arbitry limit for thread names for column alignment.
+ */
+#define TR2_MAX_THREAD_NAME (24)
+
+struct tr2tls_thread_ctx {
+	struct strbuf thread_name;
+	uint64_t *array_us_start;
+	int alloc;
+	int nr_open_regions; /* plays role of "nr" in ALLOC_GROW */
+	int thread_id;
+};
+
+/*
+ * Create TLS data for the current thread.  This gives us a place to
+ * put per-thread data, such as thread start time, function nesting
+ * and a per-thread label for our messages.
+ *
+ * We assume the first thread is "main".  Other threads are given
+ * non-zero thread-ids to help distinguish messages from concurrent
+ * threads.
+ *
+ * Truncate the thread name if necessary to help with column alignment
+ * in printf-style messages.
+ *
+ * In this and all following functions the term "self" refers to the
+ * current thread.
+ */
+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name);
+
+/*
+ * Get our TLS data.
+ */
+struct tr2tls_thread_ctx *tr2tls_get_self(void);
+
+/*
+ * return true if the current thread is the main thread.
+ */
+int tr2tls_is_main_thread(void);
+
+/*
+ * Free our TLS data.
+ */
+void tr2tls_unset_self(void);
+
+/*
+ * Begin a new nested region and remember the start time.
+ */
+void tr2tls_push_self(uint64_t us_now);
+
+/*
+ * End the innermost nested region.
+ */
+void tr2tls_pop_self(void);
+
+/*
+ * Pop any extra (above the first) open regions on the current
+ * thread and discard.  During a thread-exit, we should only
+ * have region[0] that was pushed in trace2_thread_start() if
+ * the thread exits normally.
+ */
+void tr2tls_pop_unwind_self(void);
+
+/*
+ * Compute the elapsed time since the innermost region in the
+ * current thread started and the given time (usually now).
+ */
+uint64_t tr2tls_region_elasped_self(uint64_t us);
+
+/*
+ * Compute the elapsed time since the main thread started
+ * and the given time (usually now).  This is assumed to
+ * be the absolute run time of the process.
+ */
+uint64_t tr2tls_absolute_elapsed(uint64_t us);
+
+/*
+ * Initialize the tr2 TLS system.
+ */
+void tr2tls_init(void);
+
+/*
+ * Free all tr2 TLS resources.
+ */
+void tr2tls_release(void);
+
+/*
+ * Protected increment of an integer.
+ */
+int tr2tls_locked_increment(int *p);
+
+#endif /* TR2_TLS_H */

transport-helper.c

@@ -127,6 +127,8 @@ static struct child_process *get_helper(struct transport *transport)
 		argv_array_pushf(&helper->env_array, "%s=%s",
 				 GIT_DIR_ENVIRONMENT, get_git_dir());
 
+	helper->trace2_child_class = helper->args.argv[0]; /* "remote-<name>" */
+
 	code = start_command(helper);
 	if (code < 0 && errno == ENOENT)
 		die(_("unable to find remote helper for '%s'"), data->name);

transport.c

@@ -1062,6 +1062,7 @@ static int run_pre_push_hook(struct transport *transport,
 
 	proc.argv = argv;
 	proc.in = -1;
+	proc.trace2_hook_name = "pre-push";
 
 	if (start_command(&proc)) {
 		finish_command(&proc);

usage.c

@@ -22,17 +22,48 @@ void vreportf(const char *prefix, const char *err, va_list params)
 static NORETURN void usage_builtin(const char *err, va_list params)
 {
 	vreportf("usage: ", err, params);
+
+	/*
+	 * When we detect a usage error *before* the command dispatch in
+	 * cmd_main(), we don't know what verb to report.  Force it to this
+	 * to facilitate post-processing.
+	 */
+	trace2_cmd_name("_usage_");
+
+	/*
+	 * Currently, the (err, params) are usually just the static usage
+	 * string which isn't very useful here.  Usually, the call site
+	 * manually calls fprintf(stderr,...) with the actual detailed
+	 * syntax error before calling usage().
+	 *
+	 * TODO It would be nice to update the call sites to pass both
+	 * the static usage string and the detailed error message.
+	 */
+
 	exit(129);
 }
 
 static NORETURN void die_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("fatal: ", err, params);
+
 	exit(128);
 }
 
 static void error_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("error: ", err, params);
 }
 

wt-status.c

@@ -748,12 +748,23 @@ static int has_unmerged(struct wt_status *s)
 
 void wt_status_collect(struct wt_status *s)
 {
+	trace2_region_enter("status", "worktrees", s->repo);
 	wt_status_collect_changes_worktree(s);
-	if (s->is_initial)
+	trace2_region_leave("status", "worktrees", s->repo);
+
+	if (s->is_initial) {
+		trace2_region_enter("status", "initial", s->repo);
 		wt_status_collect_changes_initial(s);
-	else
+		trace2_region_leave("status", "initial", s->repo);
+	} else {
+		trace2_region_enter("status", "index", s->repo);
 		wt_status_collect_changes_index(s);
+		trace2_region_leave("status", "index", s->repo);
+	}
+
+	trace2_region_enter("status", "untracked", s->repo);
 	wt_status_collect_untracked(s);
+	trace2_region_leave("status", "untracked", s->repo);
 
 	wt_status_get_state(s->repo, &s->state, s->branch && !strcmp(s->branch, "HEAD"));
 	if (s->state.merge_in_progress && !has_unmerged(s))
@@ -2291,6 +2302,13 @@ static void wt_porcelain_v2_print(struct wt_status *s)
 
 void wt_status_print(struct wt_status *s)
 {
+	trace2_data_intmax("status", s->repo, "count/changed", s->change.nr);
+	trace2_data_intmax("status", s->repo, "count/untracked",
+			   s->untracked.nr);
+	trace2_data_intmax("status", s->repo, "count/ignored", s->ignored.nr);
+
+	trace2_region_enter("status", "print", s->repo);
+
 	switch (s->status_format) {
 	case STATUS_FORMAT_SHORT:
 		wt_shortstatus_print(s);
@@ -2309,6 +2327,8 @@ void wt_status_print(struct wt_status *s)
 		wt_longstatus_print(s);
 		break;
 	}
+
+	trace2_region_leave("status", "print", s->repo);
 }
 
 /**