lockfile.c: introduce 'hold_lock_file_for_update_mode'

We use 'hold_lock_file_for_update' (and the '_timeout') variant to
acquire a lock when updating references, the commit-graph file, and so
on.

In particular, the commit-graph machinery uses this to acquire a
temporary file that is used to write a non-split commit-graph. In a
subsequent commit, an issue in the commit-graph machinery produces
graph files that have a different permission based on whether or not
they are part of a multi-layer graph will be addressed.

To do so, the commit-graph machinery will need a version of
'hold_lock_file_for_update' that takes the permission bits from the
caller.

Introduce such a function in this patch for both the
'hold_lock_file_for_update' and 'hold_lock_file_for_update_timeout'
functions, and leave the existing functions alone by inlining their
definitions in terms of the new mode variants.

Note that, like in the previous commit, 'hold_lock_file_for_update_mode'
is not guarenteed to set the given mode, since it may be modified by
both the umask and 'core.sharedRepository'.

Note also that even though the commit-graph machinery only calls
'hold_lock_file_for_update', that this is defined in terms of
'hold_lock_file_for_update_timeout', and so both need an additional mode
parameter here.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

lockfile.c

@@ -70,7 +70,8 @@ static void resolve_symlink(struct strbuf *path)
 }
 
 /* Make sure errno contains a meaningful value on error */
-static int lock_file(struct lock_file *lk, const char *path, int flags)
+static int lock_file(struct lock_file *lk, const char *path, int flags,
+		     int mode)
 {
 	struct strbuf filename = STRBUF_INIT;
 
@@ -79,7 +80,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 		resolve_symlink(&filename);
 
 	strbuf_addstr(&filename, LOCK_SUFFIX);
-	lk->tempfile = create_tempfile(filename.buf);
+	lk->tempfile = create_tempfile_mode(filename.buf, mode);
 	strbuf_release(&filename);
 	return lk->tempfile ? lk->tempfile->fd : -1;
 }
@@ -99,7 +100,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
  * exactly once. If timeout_ms is -1, try indefinitely.
  */
 static int lock_file_timeout(struct lock_file *lk, const char *path,
-			     int flags, long timeout_ms)
+			     int flags, long timeout_ms, int mode)
 {
 	int n = 1;
 	int multiplier = 1;
@@ -107,7 +108,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
 	static int random_initialized = 0;
 
 	if (timeout_ms == 0)
-		return lock_file(lk, path, flags);
+		return lock_file(lk, path, flags, mode);
 
 	if (!random_initialized) {
 		srand((unsigned int)getpid());
@@ -121,7 +122,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
 		long backoff_ms, wait_ms;
 		int fd;
 
-		fd = lock_file(lk, path, flags);
+		fd = lock_file(lk, path, flags, mode);
 
 		if (fd >= 0)
 			return fd; /* success */
@@ -169,10 +170,11 @@ NORETURN void unable_to_lock_die(const char *path, int err)
 }
 
 /* This should return a meaningful errno on failure */
-int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
+int hold_lock_file_for_update_timeout_mode(struct lock_file *lk,
-				      int flags, long timeout_ms)
+					   const char *path, int flags,
+					   long timeout_ms, int mode)
 {
-	int fd = lock_file_timeout(lk, path, flags, timeout_ms);
+	int fd = lock_file_timeout(lk, path, flags, timeout_ms, mode);
 	if (fd < 0) {
 		if (flags & LOCK_DIE_ON_ERROR)
 			unable_to_lock_die(path, errno);

lockfile.h

@@ -90,6 +90,15 @@
  * functions. In particular, the state diagram and the cleanup
  * machinery are all implemented in the tempfile module.
  *
+ * Permission bits
+ * ---------------
+ *
+ * If you call either `hold_lock_file_for_update_mode` or
+ * `hold_lock_file_for_update_timeout_mode`, you can specify a suggested
+ * mode for the underlying temporary file. Note that the file isn't
+ * guaranteed to have this exact mode, since it may be limited by either
+ * the umask, 'core.sharedRepository', or both. See `adjust_shared_perm`
+ * for more.
  *
  * Error handling
  * --------------
@@ -156,12 +165,20 @@ struct lock_file {
  * file descriptor for writing to it, or -1 on error. If the file is
  * currently locked, retry with quadratic backoff for at least
  * timeout_ms milliseconds. If timeout_ms is 0, try exactly once; if
- * timeout_ms is -1, retry indefinitely. The flags argument and error
+ * timeout_ms is -1, retry indefinitely. The flags argument, error
- * handling are described above.
+ * handling, and mode are described above.
  */
-int hold_lock_file_for_update_timeout(
+int hold_lock_file_for_update_timeout_mode(
 		struct lock_file *lk, const char *path,
-		int flags, long timeout_ms);
+		int flags, long timeout_ms, int mode);
+
+static inline int hold_lock_file_for_update_timeout(
+		struct lock_file *lk, const char *path,
+		int flags, long timeout_ms)
+{
+	return hold_lock_file_for_update_timeout_mode(lk, path, flags,
+						      timeout_ms, 0666);
+}
 
 /*
  * Attempt to create a lockfile for the file at `path` and return a
@@ -175,6 +192,13 @@ static inline int hold_lock_file_for_update(
 	return hold_lock_file_for_update_timeout(lk, path, flags, 0);
 }
 
+static inline int hold_lock_file_for_update_mode(
+		struct lock_file *lk, const char *path,
+		int flags, int mode)
+{
+	return hold_lock_file_for_update_timeout_mode(lk, path, flags, 0, mode);
+}
+
 /*
  * Return a nonzero value iff `lk` is currently locked.
  */