Add a library function to add an alternate to the alternates file

This is in the core so that, if the alternates file has already been
read, the addition can be parsed and put into effect for the current
process.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/sha1_file.c b/sha1_file.c
index 3516777bc7..d21e23b464 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -380,6 +380,18 @@ static void read_info_alternates(const char * relative_base, int depth)
 	munmap(map, mapsz);
 }
 
+void add_to_alternates_file(const char *reference)
+{
+	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
+	int fd = hold_lock_file_for_append(lock, git_path("objects/info/alternates"), 1);
+	char *alt = mkpath("%s/objects\n", reference);
+	write_or_die(fd, alt, strlen(alt));
+	if (commit_lock_file(lock))
+		die("could not close alternates file");
+	if (alt_odb_tail)
+		link_alt_odb_entries(alt, alt + strlen(alt), '\n', NULL, 0);
+}
+
 void prepare_alt_odb(void)
 {
 	const char *alt;