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         if (argc < 3 || argc > 4)
  29                 usage(git_update_ref_usage);
  30
  31         refname = argv[1];
  32         value = argv[2];
  33         oldval = argv[3];
  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);
  39
  40         path = resolve_ref(git_path("%s", refname), currsha1, !!oldval);
  41         if (!path)
  42                 die("No such ref: %s", refname);
  43
  44         if (oldval) {
  45                 if (memcmp(currsha1, oldsha1, 20))
  46                         die("Ref %s is at %s but expected %s", refname, sha1_to_hex(currsha1), sha1_to_hex(oldsha1));
  47                 /* Nothing to do? */
  48                 if (!memcmp(oldsha1, sha1, 20))
  49                         exit(0);
  50         }
  51         path = strdup(path);
  52         lockpath = mkpath("%s.lock", path);
  53         if (safe_create_leading_directories(lockpath) < 0)
  54                 die("Unable to create all of %s", lockpath);
  55
  56         fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
  57         if (fd < 0)
  58                 die("Unable to create %s", lockpath);
  59         hex = sha1_to_hex(sha1);
  60         hex[40] = '\n';
  61         written = write(fd, hex, 41);
  62         close(fd);
  63         if (written != 41) {
  64                 unlink(lockpath);
  65                 die("Unable to write to %s", lockpath);
  66         }
  67
  68         /*
  69          * Re-read the ref after getting the lock to verify
  70          */
  71         if (oldval && re_verify(path, oldsha1, currsha1) < 0) {
  72                 unlink(lockpath);
  73                 die("Ref lock failed");
  74         }
  75
  76         /*
  77          * Finally, replace the old ref with the new one
  78          */
  79         if (rename(lockpath, path) < 0) {
  80                 unlink(lockpath);
  81                 die("Unable to create %s", path);
  82         }
  83         return 0;
  84 }