5 static const char git_update_ref_usage[] = "git-update-ref <refname> <value> [<oldval>]";
7 static int re_verify(const char *path, unsigned char *oldsha1, unsigned char *currsha1)
10 int fd = open(path, O_RDONLY), nr;
13 nr = read(fd, buf, 40);
15 if (nr != 40 || get_sha1_hex(buf, currsha1) < 0)
17 return memcmp(oldsha1, currsha1, 20) ? -1 : 0;
20 int main(int argc, char **argv)
23 const char *refname, *value, *oldval, *path, *lockpath;
24 unsigned char sha1[20], oldsha1[20], currsha1[20];
27 setup_git_directory();
28 if (argc < 3 || argc > 4)
29 usage(git_update_ref_usage);
34 if (get_sha1(value, sha1) < 0)
35 die("%s: not a valid SHA1", value);
36 memset(oldsha1, 0, 20);
37 if (oldval && get_sha1(oldval, oldsha1) < 0)
38 die("%s: not a valid old SHA1", oldval);
40 path = resolve_ref(git_path("%s", refname), currsha1, !!oldval);
42 die("No such ref: %s", refname);
45 if (memcmp(currsha1, oldsha1, 20))
46 die("Ref %s changed to %s", refname, sha1_to_hex(currsha1));
48 if (!memcmp(oldsha1, sha1, 20))
52 lockpath = mkpath("%s.lock", path);
54 fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
56 die("Unable to create %s", lockpath);
57 hex = sha1_to_hex(sha1);
59 written = write(fd, hex, 41);
63 die("Unable to write to %s", lockpath);
67 * Re-read the ref after getting the lock to verify
69 if (oldval && re_verify(path, oldsha1, currsha1) < 0) {
71 die("Ref lock failed");
75 * Finally, replace the old ref with the new one
77 if (rename(lockpath, path) < 0) {
79 die("Unable to create %s", path);