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, *lockpath;
  23         unsigned char sha1[20], oldsha1[20], currsha1[20];
  24         int fd, written;
  25
  26         setup_git_directory();
  27         if (argc < 3 || argc > 4)
  28                 usage(git_update_ref_usage);
  29
  30         refname = argv[1];
  31         value = argv[2];
  32         oldval = argv[3];
  33         if (get_sha1(value, sha1) < 0)
  34                 die("%s: not a valid SHA1", value);
  35         memset(oldsha1, 0, 20);
  36         if (oldval && get_sha1(oldval, oldsha1) < 0)
  37                 die("%s: not a valid old SHA1", oldval);
  38
  39         path = resolve_ref(git_path("%s", refname), currsha1, !!oldval);
  40         if (!path)
  41                 die("No such ref: %s", refname);
  42
  43         if (oldval) {
  44                 if (memcmp(currsha1, oldsha1, 20))
  45                         die("Ref %s changed to %s", refname, sha1_to_hex(currsha1));
  46                 /* Nothing to do? */
  47                 if (!memcmp(oldsha1, sha1, 20))
  48                         exit(0);
  49         }
  50         path = strdup(path);
  51         lockpath = mkpath("%s.lock", path);
  52
  53         fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
  54         if (fd < 0)
  55                 die("Unable to create %s", lockpath);
  56         hex = sha1_to_hex(sha1);
  57         hex[40] = '\n';
  58         written = write(fd, hex, 41);
  59         close(fd);
  60         if (written != 41) {
  61                 unlink(lockpath);
  62                 die("Unable to write to %s", lockpath);
  63         }
  64
  65         /*
  66          * Re-read the ref after getting the lock to verify
  67          */
  68         if (oldval && re_verify(path, oldsha1, currsha1) < 0) {
  69                 unlink(lockpath);
  70                 die("Ref lock failed");
  71         }
  72
  73         /*
  74          * Finally, replace the old ref with the new one
  75          */
  76         if (rename(lockpath, path) < 0) {
  77                 unlink(lockpath);
  78                 die("Unable to create %s", path);
  79         }
  80         return 0;
  81 }