1 files changed, 49 insertions, 19 deletions

diff --git a/sha1_file.c b/sha1_file.c
index 1cee438422..d295a3225a 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -377,15 +377,12 @@ void read_info_alternates(const char * relative_base, int depth)
 	char *map;
 	size_t mapsz;
 	struct stat st;
-	const char alt_file_name[] = "info/alternates";
-	/* Given that relative_base is no longer than PATH_MAX,
-	   ensure that "path" has enough space to append "/", the
-	   file name, "info/alternates", and a trailing NUL.  */
-	char path[PATH_MAX + 1 + sizeof alt_file_name];
+	char *path;
 	int fd;
 
-	sprintf(path, "%s/%s", relative_base, alt_file_name);
+	path = xstrfmt("%s/info/alternates", relative_base);
 	fd = git_open_noatime(path);
+	free(path);
 	if (fd < 0)
 		return;
 	if (fstat(fd, &st) || (st.st_size == 0)) {
@@ -404,13 +401,46 @@ void read_info_alternates(const char * relative_base, int depth)
 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"), LOCK_DIE_ON_ERROR);
-	const char *alt = mkpath("%s\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, strlen(alt), '\n', NULL, 0);
+	char *alts = git_pathdup("objects/info/alternates");
+	FILE *in, *out;
+
+	hold_lock_file_for_update(lock, alts, LOCK_DIE_ON_ERROR);
+	out = fdopen_lock_file(lock, "w");
+	if (!out)
+		die_errno("unable to fdopen alternates lockfile");
+
+	in = fopen(alts, "r");
+	if (in) {
+		struct strbuf line = STRBUF_INIT;
+		int found = 0;
+
+		while (strbuf_getline(&line, in, '\n') != EOF) {
+			if (!strcmp(reference, line.buf)) {
+				found = 1;
+				break;
+			}
+			fprintf_or_die(out, "%s\n", line.buf);
+		}
+
+		strbuf_release(&line);
+		fclose(in);
+
+		if (found) {
+			rollback_lock_file(lock);
+			lock = NULL;
+		}
+	}
+	else if (errno != ENOENT)
+		die_errno("unable to read alternates file");
+
+	if (lock) {
+		fprintf_or_die(out, "%s\n", reference);
+		if (commit_lock_file(lock))
+			die_errno("unable to move new alternates file into place");
+		if (alt_odb_tail)
+			link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+	}
+	free(alts);
 }
 
 int foreach_alt_odb(alt_odb_fn fn, void *cb)
@@ -1461,7 +1491,10 @@ int git_open_noatime(const char *name)
 	static int sha1_file_open_flag = O_NOATIME;
 
 	for (;;) {
-		int fd = open(name, O_RDONLY | sha1_file_open_flag);
+		int fd;
+
+		errno = 0;
+		fd = open(name, O_RDONLY | sha1_file_open_flag);
 		if (fd >= 0)
 			return fd;
 
@@ -2908,11 +2941,8 @@ static void write_sha1_file_prepare(const void *buf, unsigned long len,
 
 /*
  * Move the just written object into its final resting place.
- * NEEDSWORK: this should be renamed to finalize_temp_file() as
- * "moving" is only a part of what it does, when no patch between
- * master to pu changes the call sites of this function.
  */
-int move_temp_to_file(const char *tmpfile, const char *filename)
+int finalize_object_file(const char *tmpfile, const char *filename)
 {
 	int ret = 0;
 
@@ -3085,7 +3115,7 @@ static int write_loose_object(const unsigned char *sha1, char *hdr, int hdrlen,
 				tmp_file, strerror(errno));
 	}
 
-	return move_temp_to_file(tmp_file, filename);
+	return finalize_object_file(tmp_file, filename);
 }
 
 static int freshen_loose_object(const unsigned char *sha1)