Make sure objects/pack exists before creating a new pack

In a repository created with git older than f49fb35 (git-init-db: create
"pack" subdirectory under objects, 2005-06-27), objects/pack/ directory is
not created upon initialization.  It was Ok because subdirectories are
created as needed inside directories init-db creates, and back then,
packfiles were recent invention.

After the said commit, new codepaths started relying on the presense of
objects/pack/ directory in the repository.  This was exacerbated with
8b4eb6b (Do not perform cross-directory renames when creating packs,
2008-09-22) that moved the location temporary pack files are created from
objects/ directory to objects/pack/ directory, because moving temporary to
the final location was done carefully with lazy leading directory creation.

Many packfile related operations in such an old repository can fail
mysteriously because of this.

This commit introduces two helper functions to make things work better.

 - odb_mkstemp() is a specialized version of mkstemp() to refactor the
   code and teach it to create leading directories as needed;

 - odb_pack_keep() refactors the code to create a ".keep" file while
   create leading directories as needed.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -473,9 +473,8 @@ static void write_pack_file(void)
 		} else {
 			char tmpname[PATH_MAX];
 			int fd;
-			snprintf(tmpname, sizeof(tmpname),
-				 "%s/pack/tmp_pack_XXXXXX", get_object_directory());
-			fd = xmkstemp(tmpname);
+			fd = odb_mkstemp(tmpname, sizeof(tmpname),
+					 "pack/tmp_pack_XXXXXX");
 			pack_tmp_name = xstrdup(tmpname);
 			f = sha1fd(fd, pack_tmp_name);
 		}

fast-import.c

@@ -815,9 +815,8 @@ static void start_packfile(void)
 	struct pack_header hdr;
 	int pack_fd;
 
-	snprintf(tmpfile, sizeof(tmpfile),
-		"%s/pack/tmp_pack_XXXXXX", get_object_directory());
-	pack_fd = xmkstemp(tmpfile);
+	pack_fd = odb_mkstemp(tmpfile, sizeof(tmpfile),
+			      "pack/tmp_pack_XXXXXX");
 	p = xcalloc(1, sizeof(*p) + strlen(tmpfile) + 2);
 	strcpy(p->pack_name, tmpfile);
 	p->pack_fd = pack_fd;
@@ -877,9 +876,8 @@ static char *create_index(void)
 		c = next;
 	}
 
-	snprintf(tmpfile, sizeof(tmpfile),
-		"%s/pack/tmp_idx_XXXXXX", get_object_directory());
-	idx_fd = xmkstemp(tmpfile);
+	idx_fd = odb_mkstemp(tmpfile, sizeof(tmpfile),
+			     "pack/tmp_idx_XXXXXX");
 	f = sha1fd(idx_fd, tmpfile);
 	sha1write(f, array, 256 * sizeof(int));
 	SHA1_Init(&ctx);
@@ -905,9 +903,7 @@ static char *keep_pack(char *curr_index_name)
 	chmod(pack_data->pack_name, 0444);
 	chmod(curr_index_name, 0444);
 
-	snprintf(name, sizeof(name), "%s/pack/pack-%s.keep",
-		 get_object_directory(), sha1_to_hex(pack_data->sha1));
-	keep_fd = open(name, O_RDWR|O_CREAT|O_EXCL, 0600);
+	keep_fd = odb_pack_keep(name, sizeof(name), pack_data->sha1);
 	if (keep_fd < 0)
 		die("cannot create keep file");
 	write_or_die(keep_fd, keep_msg, strlen(keep_msg));

git-compat-util.h

@@ -294,6 +294,8 @@ extern ssize_t xwrite(int fd, const void *buf, size_t len);
 extern int xdup(int fd);
 extern FILE *xfdopen(int fd, const char *mode);
 extern int xmkstemp(char *template);
+extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
+extern int odb_pack_keep(char *name, size_t namesz, unsigned char *sha1);
 
 static inline size_t xsize_t(off_t len)
 {

index-pack.c

@@ -171,9 +171,8 @@ static char *open_pack_file(char *pack_name)
 		input_fd = 0;
 		if (!pack_name) {
 			static char tmpfile[PATH_MAX];
-			snprintf(tmpfile, sizeof(tmpfile),
-				 "%s/pack/tmp_pack_XXXXXX", get_object_directory());
-			output_fd = xmkstemp(tmpfile);
+			output_fd = odb_mkstemp(tmpfile, sizeof(tmpfile),
+						"pack/tmp_pack_XXXXXX");
 			pack_name = xstrdup(tmpfile);
 		} else
 			output_fd = open(pack_name, O_CREAT|O_EXCL|O_RDWR, 0600);
@@ -795,22 +794,24 @@ static void final(const char *final_pack_name, const char *curr_pack_name,
 
 	if (keep_msg) {
 		int keep_fd, keep_msg_len = strlen(keep_msg);
-		if (!keep_name) {
-			snprintf(name, sizeof(name), "%s/pack/pack-%s.keep",
-				 get_object_directory(), sha1_to_hex(sha1));
-			keep_name = name;
-		}
-		keep_fd = open(keep_name, O_RDWR|O_CREAT|O_EXCL, 0600);
+
+		if (!keep_name)
+			keep_fd = odb_pack_keep(name, sizeof(name), sha1);
+		else
+			keep_fd = open(keep_name, O_RDWR|O_CREAT|O_EXCL, 0600);
+
 		if (keep_fd < 0) {
 			if (errno != EEXIST)
-				die("cannot write keep file");
+				die("cannot write keep file '%s' (%s)",
+				    keep_name, strerror(errno));
 		} else {
 			if (keep_msg_len > 0) {
 				write_or_die(keep_fd, keep_msg, keep_msg_len);
 				write_or_die(keep_fd, "\n", 1);
 			}
 			if (close(keep_fd) != 0)
-				die("cannot write keep file");
+				die("cannot close written keep file '%s' (%s)",
+				    keep_name, strerror(errno));
 			report = "keep";
 		}
 	}

pack-write.c

@@ -44,9 +44,7 @@ char *write_idx_file(char *index_name, struct pack_idx_entry **objects,
 
 	if (!index_name) {
 		static char tmpfile[PATH_MAX];
-		snprintf(tmpfile, sizeof(tmpfile),
-			 "%s/pack/tmp_idx_XXXXXX", get_object_directory());
-		fd = xmkstemp(tmpfile);
+		fd = odb_mkstemp(tmpfile, sizeof(tmpfile), "pack/tmp_idx_XXXXXX");
 		index_name = xstrdup(tmpfile);
 	} else {
 		unlink(index_name);
@@ -239,7 +237,7 @@ char *index_pack_lockfile(int ip_out)
 	char packname[46];
 
 	/*
-	 * The first thing we expects from index-pack's output
+	 * The first thing we expect from index-pack's output
 	 * is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
 	 * %40s is the newly created pack SHA1 name.  In the "keep"
 	 * case, we need it to remove the corresponding .keep file

t/t5300-pack-object.sh

@@ -180,6 +180,23 @@ test_expect_success \
 
 unset GIT_OBJECT_DIRECTORY
 
+test_expect_success 'survive missing objects/pack directory' '
+	(
+		rm -fr missing-pack &&
+		mkdir missing-pack &&
+		cd missing-pack &&
+		git init &&
+		GOP=.git/objects/pack
+		rm -fr $GOP &&
+		git index-pack --stdin --keep=test <../test-3-${packname_3}.pack &&
+		test -f $GOP/pack-${packname_3}.pack &&
+		test_cmp $GOP/pack-${packname_3}.pack ../test-3-${packname_3}.pack &&
+		test -f $GOP/pack-${packname_3}.idx &&
+		test_cmp $GOP/pack-${packname_3}.idx ../test-3-${packname_3}.idx &&
+		test -f $GOP/pack-${packname_3}.keep
+	)
+'
+
 test_expect_success \
     'verify pack' \
     'git verify-pack	test-1-${packname_1}.idx \

wrapper.c

@@ -196,3 +196,35 @@ int xmkstemp(char *template)
 		die("Unable to create temporary file: %s", strerror(errno));
 	return fd;
 }
+
+int odb_mkstemp(char *template, size_t limit, const char *pattern)
+{
+	int fd;
+
+	snprintf(template, limit, "%s/%s",
+		 get_object_directory(), pattern);
+	fd = mkstemp(template);
+	if (0 <= fd)
+		return fd;
+
+	/* slow path */
+	safe_create_leading_directories(template);
+	snprintf(template, limit, "%s/%s",
+		 get_object_directory(), pattern);
+	return xmkstemp(template);
+}
+
+int odb_pack_keep(char *name, size_t namesz, unsigned char *sha1)
+{
+	int fd;
+
+	snprintf(name, namesz, "%s/pack/pack-%s.keep",
+		 get_object_directory(), sha1_to_hex(sha1));
+	fd = open(name, O_RDWR|O_CREAT|O_EXCL, 0600);
+	if (0 <= fd)
+		return fd;
+
+	/* slow path */
+	safe_create_leading_directories(name);
+	return open(name, O_RDWR|O_CREAT|O_EXCL, 0600);
+}