update-ref.c

   1 #include "cache.h"
   2 #include "refs.h"
   3
   4 static const char git_update_ref_usage[] = "git-update-ref <refname> <value> [<oldval>]";
   5
   6 static int re_verify(const char *path, unsigned char *oldsha1, unsigned char *currsha1)
   7 {
   8         char buf[40];
   9         int fd = open(path, O_RDONLY), nr;
  10         if (fd < 0)
  11                 return -1;
  12         nr = read(fd, buf, 40);
  13         close(fd);
  14         if (nr != 40 || get_sha1_hex(buf, currsha1) < 0)
  15                 return -1;
  16         return memcmp(oldsha1, currsha1, 20) ? -1 : 0;
  17 }
  18
  19 int main(int argc, char **argv)
  20 {
  21         char *hex;
  22         const char *refname, *value, *oldval, *path;
  23         char *lockpath;
  24         unsigned char sha1[20], oldsha1[20], currsha1[20];
  25         int fd, written;
  26
  27         setup_git_directory();
  28         git_config(git_default_config);
  29         if (argc < 3 || argc > 4)
  30                 usage(git_update_ref_usage);
  31
  32         refname = argv[1];
  33         value = argv[2];
  34         oldval = argv[3];
  35         if (get_sha1(value, sha1) < 0)
  36                 die("%s: not a valid SHA1", value);
  37         memset(oldsha1, 0, 20);
  38         if (oldval && get_sha1(oldval, oldsha1) < 0)
  39                 die("%s: not a valid old SHA1", oldval);
  40
  41         path = resolve_ref(git_path("%s", refname), currsha1, !!oldval);
  42         if (!path)
  43                 die("No such ref: %s", refname);
  44
  45         if (oldval) {
  46                 if (memcmp(currsha1, oldsha1, 20))
  47                         die("Ref %s is at %s but expected %s", refname, sha1_to_hex(currsha1), sha1_to_hex(oldsha1));
  48                 /* Nothing to do? */
  49                 if (!memcmp(oldsha1, sha1, 20))
  50                         exit(0);
  51         }
  52         path = strdup(path);
  53         lockpath = mkpath("%s.lock", path);
  54         if (safe_create_leading_directories(lockpath) < 0)
  55                 die("Unable to create all of %s", lockpath);
  56
  57         fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
  58         if (fd < 0)
  59                 die("Unable to create %s", lockpath);
  60         hex = sha1_to_hex(sha1);
  61         hex[40] = '\n';
  62         written = write(fd, hex, 41);
  63         close(fd);
  64         if (written != 41) {
  65                 unlink(lockpath);
  66                 die("Unable to write to %s", lockpath);
  67         }
  68
  69         /*
  70          * Re-read the ref after getting the lock to verify
  71          */
  72         if (oldval && re_verify(path, oldsha1, currsha1) < 0) {
  73                 unlink(lockpath);
  74                 die("Ref lock failed");
  75         }
  76
  77         /*
  78          * Finally, replace the old ref with the new one
  79          */
  80         if (rename(lockpath, path) < 0) {
  81                 unlink(lockpath);
  82                 die("Unable to create %s", path);
  83         }
  84         return 0;
  85 }