refs.c

   1 #include "refs.h"
   2 #include "cache.h"
   3
   4 #include <errno.h>
   5
   6 struct ref_list {
   7         struct ref_list *next;
   8         unsigned char flag; /* ISSYMREF? ISPACKED? */
   9         unsigned char sha1[20];
  10         char name[FLEX_ARRAY];
  11 };
  12
  13 static const char *parse_ref_line(char *line, unsigned char *sha1)
  14 {
  15         /*
  16          * 42: the answer to everything.
  17          *
  18          * In this case, it happens to be the answer to
  19          *  40 (length of sha1 hex representation)
  20          *  +1 (space in between hex and name)
  21          *  +1 (newline at the end of the line)
  22          */
  23         int len = strlen(line) - 42;
  24
  25         if (len <= 0)
  26                 return NULL;
  27         if (get_sha1_hex(line, sha1) < 0)
  28                 return NULL;
  29         if (!isspace(line[40]))
  30                 return NULL;
  31         line += 41;
  32         if (isspace(*line))
  33                 return NULL;
  34         if (line[len] != '\n')
  35                 return NULL;
  36         line[len] = 0;
  37         return line;
  38 }
  39
  40 static struct ref_list *add_ref(const char *name, const unsigned char *sha1,
  41                                 int flag, struct ref_list *list)
  42 {
  43         int len;
  44         struct ref_list **p = &list, *entry;
  45
  46         /* Find the place to insert the ref into.. */
  47         while ((entry = *p) != NULL) {
  48                 int cmp = strcmp(entry->name, name);
  49                 if (cmp > 0)
  50                         break;
  51
  52                 /* Same as existing entry? */
  53                 if (!cmp)
  54                         return list;
  55                 p = &entry->next;
  56         }
  57
  58         /* Allocate it and add it in.. */
  59         len = strlen(name) + 1;
  60         entry = xmalloc(sizeof(struct ref_list) + len);
  61         hashcpy(entry->sha1, sha1);
  62         memcpy(entry->name, name, len);
  63         entry->flag = flag;
  64         entry->next = *p;
  65         *p = entry;
  66         return list;
  67 }
  68
  69 /*
  70  * Future: need to be in "struct repository"
  71  * when doing a full libification.
  72  */
  73 struct cached_refs {
  74         char did_loose;
  75         char did_packed;
  76         struct ref_list *loose;
  77         struct ref_list *packed;
  78 } cached_refs;
  79
  80 static void free_ref_list(struct ref_list *list)
  81 {
  82         struct ref_list *next;
  83         for ( ; list; list = next) {
  84                 next = list->next;
  85                 free(list);
  86         }
  87 }
  88
  89 static void invalidate_cached_refs(void)
  90 {
  91         struct cached_refs *ca = &cached_refs;
  92
  93         if (ca->did_loose && ca->loose)
  94                 free_ref_list(ca->loose);
  95         if (ca->did_packed && ca->packed)
  96                 free_ref_list(ca->packed);
  97         ca->loose = ca->packed = NULL;
  98         ca->did_loose = ca->did_packed = 0;
  99 }
 100
 101 static struct ref_list *get_packed_refs(void)
 102 {
 103         if (!cached_refs.did_packed) {
 104                 struct ref_list *refs = NULL;
 105                 FILE *f = fopen(git_path("packed-refs"), "r");
 106                 if (f) {
 107                         struct ref_list *list = NULL;
 108                         char refline[PATH_MAX];
 109                         while (fgets(refline, sizeof(refline), f)) {
 110                                 unsigned char sha1[20];
 111                                 const char *name = parse_ref_line(refline, sha1);
 112                                 if (!name)
 113                                         continue;
 114                                 list = add_ref(name, sha1, REF_ISPACKED, list);
 115                         }
 116                         fclose(f);
 117                         refs = list;
 118                 }
 119                 cached_refs.packed = refs;
 120                 cached_refs.did_packed = 1;
 121         }
 122         return cached_refs.packed;
 123 }
 124
 125 static struct ref_list *get_ref_dir(const char *base, struct ref_list *list)
 126 {
 127         DIR *dir = opendir(git_path("%s", base));
 128
 129         if (dir) {
 130                 struct dirent *de;
 131                 int baselen = strlen(base);
 132                 char *ref = xmalloc(baselen + 257);
 133
 134                 memcpy(ref, base, baselen);
 135                 if (baselen && base[baselen-1] != '/')
 136                         ref[baselen++] = '/';
 137
 138                 while ((de = readdir(dir)) != NULL) {
 139                         unsigned char sha1[20];
 140                         struct stat st;
 141                         int flag;
 142                         int namelen;
 143
 144                         if (de->d_name[0] == '.')
 145                                 continue;
 146                         namelen = strlen(de->d_name);
 147                         if (namelen > 255)
 148                                 continue;
 149                         if (has_extension(de->d_name, ".lock"))
 150                                 continue;
 151                         memcpy(ref + baselen, de->d_name, namelen+1);
 152                         if (stat(git_path("%s", ref), &st) < 0)
 153                                 continue;
 154                         if (S_ISDIR(st.st_mode)) {
 155                                 list = get_ref_dir(ref, list);
 156                                 continue;
 157                         }
 158                         if (!resolve_ref(ref, sha1, 1, &flag)) {
 159                                 error("%s points nowhere!", ref);
 160                                 continue;
 161                         }
 162                         list = add_ref(ref, sha1, flag, list);
 163                 }
 164                 free(ref);
 165                 closedir(dir);
 166         }
 167         return list;
 168 }
 169
 170 static struct ref_list *get_loose_refs(void)
 171 {
 172         if (!cached_refs.did_loose) {
 173                 cached_refs.loose = get_ref_dir("refs", NULL);
 174                 cached_refs.did_loose = 1;
 175         }
 176         return cached_refs.loose;
 177 }
 178
 179 /* We allow "recursive" symbolic refs. Only within reason, though */
 180 #define MAXDEPTH 5
 181
 182 const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *flag)
 183 {
 184         int depth = MAXDEPTH, len;
 185         char buffer[256];
 186         static char ref_buffer[256];
 187
 188         if (flag)
 189                 *flag = 0;
 190
 191         for (;;) {
 192                 const char *path = git_path("%s", ref);
 193                 struct stat st;
 194                 char *buf;
 195                 int fd;
 196
 197                 if (--depth < 0)
 198                         return NULL;
 199
 200                 /* Special case: non-existing file.
 201                  * Not having the refs/heads/new-branch is OK
 202                  * if we are writing into it, so is .git/HEAD
 203                  * that points at refs/heads/master still to be
 204                  * born.  It is NOT OK if we are resolving for
 205                  * reading.
 206                  */
 207                 if (lstat(path, &st) < 0) {
 208                         struct ref_list *list = get_packed_refs();
 209                         while (list) {
 210                                 if (!strcmp(ref, list->name)) {
 211                                         hashcpy(sha1, list->sha1);
 212                                         if (flag)
 213                                                 *flag |= REF_ISPACKED;
 214                                         return ref;
 215                                 }
 216                                 list = list->next;
 217                         }
 218                         if (reading || errno != ENOENT)
 219                                 return NULL;
 220                         hashclr(sha1);
 221                         return ref;
 222                 }
 223
 224                 /* Follow "normalized" - ie "refs/.." symlinks by hand */
 225                 if (S_ISLNK(st.st_mode)) {
 226                         len = readlink(path, buffer, sizeof(buffer)-1);
 227                         if (len >= 5 && !memcmp("refs/", buffer, 5)) {
 228                                 buffer[len] = 0;
 229                                 strcpy(ref_buffer, buffer);
 230                                 ref = ref_buffer;
 231                                 if (flag)
 232                                         *flag |= REF_ISSYMREF;
 233                                 continue;
 234                         }
 235                 }
 236
 237                 /*
 238                  * Anything else, just open it and try to use it as
 239                  * a ref
 240                  */
 241                 fd = open(path, O_RDONLY);
 242                 if (fd < 0)
 243                         return NULL;
 244                 len = read(fd, buffer, sizeof(buffer)-1);
 245                 close(fd);
 246
 247                 /*
 248                  * Is it a symbolic ref?
 249                  */
 250                 if (len < 4 || memcmp("ref:", buffer, 4))
 251                         break;
 252                 buf = buffer + 4;
 253                 len -= 4;
 254                 while (len && isspace(*buf))
 255                         buf++, len--;
 256                 while (len && isspace(buf[len-1]))
 257                         len--;
 258                 buf[len] = 0;
 259                 memcpy(ref_buffer, buf, len + 1);
 260                 ref = ref_buffer;
 261                 if (flag)
 262                         *flag |= REF_ISSYMREF;
 263         }
 264         if (len < 40 || get_sha1_hex(buffer, sha1))
 265                 return NULL;
 266         return ref;
 267 }
 268
 269 int create_symref(const char *ref_target, const char *refs_heads_master)
 270 {
 271         const char *lockpath;
 272         char ref[1000];
 273         int fd, len, written;
 274         const char *git_HEAD = git_path("%s", ref_target);
 275
 276 #ifndef NO_SYMLINK_HEAD
 277         if (prefer_symlink_refs) {
 278                 unlink(git_HEAD);
 279                 if (!symlink(refs_heads_master, git_HEAD))
 280                         return 0;
 281                 fprintf(stderr, "no symlink - falling back to symbolic ref\n");
 282         }
 283 #endif
 284
 285         len = snprintf(ref, sizeof(ref), "ref: %s\n", refs_heads_master);
 286         if (sizeof(ref) <= len) {
 287                 error("refname too long: %s", refs_heads_master);
 288                 return -1;
 289         }
 290         lockpath = mkpath("%s.lock", git_HEAD);
 291         fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
 292         written = write(fd, ref, len);
 293         close(fd);
 294         if (written != len) {
 295                 unlink(lockpath);
 296                 error("Unable to write to %s", lockpath);
 297                 return -2;
 298         }
 299         if (rename(lockpath, git_HEAD) < 0) {
 300                 unlink(lockpath);
 301                 error("Unable to create %s", git_HEAD);
 302                 return -3;
 303         }
 304         if (adjust_shared_perm(git_HEAD)) {
 305                 unlink(lockpath);
 306                 error("Unable to fix permissions on %s", lockpath);
 307                 return -4;
 308         }
 309         return 0;
 310 }
 311
 312 int read_ref(const char *ref, unsigned char *sha1)
 313 {
 314         if (resolve_ref(ref, sha1, 1, NULL))
 315                 return 0;
 316         return -1;
 317 }
 318
 319 static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
 320                            void *cb_data)
 321 {
 322         int retval;
 323         struct ref_list *packed = get_packed_refs();
 324         struct ref_list *loose = get_loose_refs();
 325
 326         while (packed && loose) {
 327                 struct ref_list *entry;
 328                 int cmp = strcmp(packed->name, loose->name);
 329                 if (!cmp) {
 330                         packed = packed->next;
 331                         continue;
 332                 }
 333                 if (cmp > 0) {
 334                         entry = loose;
 335                         loose = loose->next;
 336                 } else {
 337                         entry = packed;
 338                         packed = packed->next;
 339                 }
 340                 if (strncmp(base, entry->name, trim))
 341                         continue;
 342                 if (is_null_sha1(entry->sha1))
 343                         continue;
 344                 if (!has_sha1_file(entry->sha1)) {
 345                         error("%s does not point to a valid object!", entry->name);
 346                         continue;
 347                 }
 348                 retval = fn(entry->name + trim, entry->sha1,
 349                             entry->flag, cb_data);
 350                 if (retval)
 351                         return retval;
 352         }
 353
 354         packed = packed ? packed : loose;
 355         while (packed) {
 356                 if (!strncmp(base, packed->name, trim)) {
 357                         retval = fn(packed->name + trim, packed->sha1,
 358                                     packed->flag, cb_data);
 359                         if (retval)
 360                                 return retval;
 361                 }
 362                 packed = packed->next;
 363         }
 364         return 0;
 365 }
 366
 367 int head_ref(each_ref_fn fn, void *cb_data)
 368 {
 369         unsigned char sha1[20];
 370         int flag;
 371
 372         if (resolve_ref("HEAD", sha1, 1, &flag))
 373                 return fn("HEAD", sha1, flag, cb_data);
 374         return 0;
 375 }
 376
 377 int for_each_ref(each_ref_fn fn, void *cb_data)
 378 {
 379         return do_for_each_ref("refs/", fn, 0, cb_data);
 380 }
 381
 382 int for_each_tag_ref(each_ref_fn fn, void *cb_data)
 383 {
 384         return do_for_each_ref("refs/tags/", fn, 10, cb_data);
 385 }
 386
 387 int for_each_branch_ref(each_ref_fn fn, void *cb_data)
 388 {
 389         return do_for_each_ref("refs/heads/", fn, 11, cb_data);
 390 }
 391
 392 int for_each_remote_ref(each_ref_fn fn, void *cb_data)
 393 {
 394         return do_for_each_ref("refs/remotes/", fn, 13, cb_data);
 395 }
 396
 397 /* NEEDSWORK: This is only used by ssh-upload and it should go; the
 398  * caller should do resolve_ref or read_ref like everybody else.  Or
 399  * maybe everybody else should use get_ref_sha1() instead of doing
 400  * read_ref().
 401  */
 402 int get_ref_sha1(const char *ref, unsigned char *sha1)
 403 {
 404         if (check_ref_format(ref))
 405                 return -1;
 406         return read_ref(mkpath("refs/%s", ref), sha1);
 407 }
 408
 409 int delete_ref(const char *refname, unsigned char *sha1)
 410 {
 411         struct ref_lock *lock;
 412         int err, i, ret = 0;
 413
 414         lock = lock_any_ref_for_update(refname, sha1);
 415         if (!lock)
 416                 return 1;
 417         i = strlen(lock->lk->filename) - 5; /* .lock */
 418         lock->lk->filename[i] = 0;
 419         err = unlink(lock->lk->filename);
 420         if (err) {
 421                 ret = 1;
 422                 error("unlink(%s) failed: %s",
 423                       lock->lk->filename, strerror(errno));
 424         }
 425         lock->lk->filename[i] = '.';
 426
 427         err = unlink(lock->log_file);
 428         if (err && errno != ENOENT)
 429                 fprintf(stderr, "warning: unlink(%s) failed: %s",
 430                         lock->log_file, strerror(errno));
 431
 432         invalidate_cached_refs();
 433         return ret;
 434 }
 435
 436 /*
 437  * Make sure "ref" is something reasonable to have under ".git/refs/";
 438  * We do not like it if:
 439  *
 440  * - any path component of it begins with ".", or
 441  * - it has double dots "..", or
 442  * - it has ASCII control character, "~", "^", ":" or SP, anywhere, or
 443  * - it ends with a "/".
 444  */
 445
 446 static inline int bad_ref_char(int ch)
 447 {
 448         return (((unsigned) ch) <= ' ' ||
 449                 ch == '~' || ch == '^' || ch == ':' ||
 450                 /* 2.13 Pattern Matching Notation */
 451                 ch == '?' || ch == '*' || ch == '[');
 452 }
 453
 454 int check_ref_format(const char *ref)
 455 {
 456         int ch, level;
 457         const char *cp = ref;
 458
 459         level = 0;
 460         while (1) {
 461                 while ((ch = *cp++) == '/')
 462                         ; /* tolerate duplicated slashes */
 463                 if (!ch)
 464                         return -1; /* should not end with slashes */
 465
 466                 /* we are at the beginning of the path component */
 467                 if (ch == '.' || bad_ref_char(ch))
 468                         return -1;
 469
 470                 /* scan the rest of the path component */
 471                 while ((ch = *cp++) != 0) {
 472                         if (bad_ref_char(ch))
 473                                 return -1;
 474                         if (ch == '/')
 475                                 break;
 476                         if (ch == '.' && *cp == '.')
 477                                 return -1;
 478                 }
 479                 level++;
 480                 if (!ch) {
 481                         if (level < 2)
 482                                 return -1; /* at least of form "heads/blah" */
 483                         return 0;
 484                 }
 485         }
 486 }
 487
 488 static struct ref_lock *verify_lock(struct ref_lock *lock,
 489         const unsigned char *old_sha1, int mustexist)
 490 {
 491         if (!resolve_ref(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
 492                 error("Can't verify ref %s", lock->ref_name);
 493                 unlock_ref(lock);
 494                 return NULL;
 495         }
 496         if (hashcmp(lock->old_sha1, old_sha1)) {
 497                 error("Ref %s is at %s but expected %s", lock->ref_name,
 498                         sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
 499                 unlock_ref(lock);
 500                 return NULL;
 501         }
 502         return lock;
 503 }
 504
 505 static int remove_empty_dir_recursive(char *path, int len)
 506 {
 507         DIR *dir = opendir(path);
 508         struct dirent *e;
 509         int ret = 0;
 510
 511         if (!dir)
 512                 return -1;
 513         if (path[len-1] != '/')
 514                 path[len++] = '/';
 515         while ((e = readdir(dir)) != NULL) {
 516                 struct stat st;
 517                 int namlen;
 518                 if ((e->d_name[0] == '.') &&
 519                     ((e->d_name[1] == 0) ||
 520                      ((e->d_name[1] == '.') && e->d_name[2] == 0)))
 521                         continue; /* "." and ".." */
 522
 523                 namlen = strlen(e->d_name);
 524                 if ((len + namlen < PATH_MAX) &&
 525                     strcpy(path + len, e->d_name) &&
 526                     !lstat(path, &st) &&
 527                     S_ISDIR(st.st_mode) &&
 528                     remove_empty_dir_recursive(path, len + namlen))
 529                         continue; /* happy */
 530
 531                 /* path too long, stat fails, or non-directory still exists */
 532                 ret = -1;
 533                 break;
 534         }
 535         closedir(dir);
 536         if (!ret) {
 537                 path[len] = 0;
 538                 ret = rmdir(path);
 539         }
 540         return ret;
 541 }
 542
 543 static int remove_empty_directories(char *file)
 544 {
 545         /* we want to create a file but there is a directory there;
 546          * if that is an empty directory (or a directory that contains
 547          * only empty directories), remove them.
 548          */
 549         char path[PATH_MAX];
 550         int len = strlen(file);
 551
 552         if (len >= PATH_MAX) /* path too long ;-) */
 553                 return -1;
 554         strcpy(path, file);
 555         return remove_empty_dir_recursive(path, len);
 556 }
 557
 558 static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char *old_sha1)
 559 {
 560         char *ref_file;
 561         const char *orig_ref = ref;
 562         struct ref_lock *lock;
 563         struct stat st;
 564         int last_errno = 0;
 565         int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
 566
 567         lock = xcalloc(1, sizeof(struct ref_lock));
 568         lock->lock_fd = -1;
 569
 570         ref = resolve_ref(ref, lock->old_sha1, mustexist, NULL);
 571         if (!ref && errno == EISDIR) {
 572                 /* we are trying to lock foo but we used to
 573                  * have foo/bar which now does not exist;
 574                  * it is normal for the empty directory 'foo'
 575                  * to remain.
 576                  */
 577                 ref_file = git_path("%s", orig_ref);
 578                 if (remove_empty_directories(ref_file)) {
 579                         last_errno = errno;
 580                         error("there are still refs under '%s'", orig_ref);
 581                         goto error_return;
 582                 }
 583                 ref = resolve_ref(orig_ref, lock->old_sha1, mustexist, NULL);
 584         }
 585         if (!ref) {
 586                 last_errno = errno;
 587                 error("unable to resolve reference %s: %s",
 588                         orig_ref, strerror(errno));
 589                 goto error_return;
 590         }
 591         if (is_null_sha1(lock->old_sha1)) {
 592                 /* The ref did not exist and we are creating it.
 593                  * Make sure there is no existing ref that is packed
 594                  * whose name begins with our refname, nor a ref whose
 595                  * name is a proper prefix of our refname.
 596                  */
 597                 int namlen = strlen(ref); /* e.g. 'foo/bar' */
 598                 struct ref_list *list = get_packed_refs();
 599                 while (list) {
 600                         /* list->name could be 'foo' or 'foo/bar/baz' */
 601                         int len = strlen(list->name);
 602                         int cmplen = (namlen < len) ? namlen : len;
 603                         const char *lead = (namlen < len) ? list->name : ref;
 604
 605                         if (!strncmp(ref, list->name, cmplen) &&
 606                             lead[cmplen] == '/') {
 607                                 error("'%s' exists; cannot create '%s'",
 608                                       list->name, ref);
 609                                 goto error_return;
 610                         }
 611                         list = list->next;
 612                 }
 613         }
 614
 615         lock->lk = xcalloc(1, sizeof(struct lock_file));
 616
 617         lock->ref_name = xstrdup(ref);
 618         lock->log_file = xstrdup(git_path("logs/%s", ref));
 619         ref_file = git_path("%s", ref);
 620         lock->force_write = lstat(ref_file, &st) && errno == ENOENT;
 621
 622         if (safe_create_leading_directories(ref_file)) {
 623                 last_errno = errno;
 624                 error("unable to create directory for %s", ref_file);
 625                 goto error_return;
 626         }
 627         lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, 1);
 628
 629         return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
 630
 631  error_return:
 632         unlock_ref(lock);
 633         errno = last_errno;
 634         return NULL;
 635 }
 636
 637 struct ref_lock *lock_ref_sha1(const char *ref, const unsigned char *old_sha1)
 638 {
 639         char refpath[PATH_MAX];
 640         if (check_ref_format(ref))
 641                 return NULL;
 642         strcpy(refpath, mkpath("refs/%s", ref));
 643         return lock_ref_sha1_basic(refpath, old_sha1);
 644 }
 645
 646 struct ref_lock *lock_any_ref_for_update(const char *ref, const unsigned char *old_sha1)
 647 {
 648         return lock_ref_sha1_basic(ref, old_sha1);
 649 }
 650
 651 void unlock_ref(struct ref_lock *lock)
 652 {
 653         if (lock->lock_fd >= 0) {
 654                 close(lock->lock_fd);
 655                 /* Do not free lock->lk -- atexit() still looks at them */
 656                 if (lock->lk)
 657                         rollback_lock_file(lock->lk);
 658         }
 659         free(lock->ref_name);
 660         free(lock->log_file);
 661         free(lock);
 662 }
 663
 664 static int log_ref_write(struct ref_lock *lock,
 665         const unsigned char *sha1, const char *msg)
 666 {
 667         int logfd, written, oflags = O_APPEND | O_WRONLY;
 668         unsigned maxlen, len;
 669         char *logrec;
 670         const char *committer;
 671
 672         if (log_all_ref_updates) {
 673                 if (safe_create_leading_directories(lock->log_file) < 0)
 674                         return error("unable to create directory for %s",
 675                                 lock->log_file);
 676                 oflags |= O_CREAT;
 677         }
 678
 679         logfd = open(lock->log_file, oflags, 0666);
 680         if (logfd < 0) {
 681                 if (!log_all_ref_updates && errno == ENOENT)
 682                         return 0;
 683                 return error("Unable to append to %s: %s",
 684                         lock->log_file, strerror(errno));
 685         }
 686
 687         committer = git_committer_info(1);
 688         if (msg) {
 689                 maxlen = strlen(committer) + strlen(msg) + 2*40 + 5;
 690                 logrec = xmalloc(maxlen);
 691                 len = snprintf(logrec, maxlen, "%s %s %s\t%s\n",
 692                         sha1_to_hex(lock->old_sha1),
 693                         sha1_to_hex(sha1),
 694                         committer,
 695                         msg);
 696         }
 697         else {
 698                 maxlen = strlen(committer) + 2*40 + 4;
 699                 logrec = xmalloc(maxlen);
 700                 len = snprintf(logrec, maxlen, "%s %s %s\n",
 701                         sha1_to_hex(lock->old_sha1),
 702                         sha1_to_hex(sha1),
 703                         committer);
 704         }
 705         written = len <= maxlen ? write(logfd, logrec, len) : -1;
 706         free(logrec);
 707         close(logfd);
 708         if (written != len)
 709                 return error("Unable to append to %s", lock->log_file);
 710         return 0;
 711 }
 712
 713 int write_ref_sha1(struct ref_lock *lock,
 714         const unsigned char *sha1, const char *logmsg)
 715 {
 716         static char term = '\n';
 717
 718         if (!lock)
 719                 return -1;
 720         if (!lock->force_write && !hashcmp(lock->old_sha1, sha1)) {
 721                 unlock_ref(lock);
 722                 return 0;
 723         }
 724         if (write(lock->lock_fd, sha1_to_hex(sha1), 40) != 40 ||
 725             write(lock->lock_fd, &term, 1) != 1
 726                 || close(lock->lock_fd) < 0) {
 727                 error("Couldn't write %s", lock->lk->filename);
 728                 unlock_ref(lock);
 729                 return -1;
 730         }
 731         invalidate_cached_refs();
 732         if (log_ref_write(lock, sha1, logmsg) < 0) {
 733                 unlock_ref(lock);
 734                 return -1;
 735         }
 736         if (commit_lock_file(lock->lk)) {
 737                 error("Couldn't set %s", lock->ref_name);
 738                 unlock_ref(lock);
 739                 return -1;
 740         }
 741         lock->lock_fd = -1;
 742         unlock_ref(lock);
 743         return 0;
 744 }
 745
 746 int read_ref_at(const char *ref, unsigned long at_time, unsigned char *sha1)
 747 {
 748         const char *logfile, *logdata, *logend, *rec, *lastgt, *lastrec;
 749         char *tz_c;
 750         int logfd, tz;
 751         struct stat st;
 752         unsigned long date;
 753         unsigned char logged_sha1[20];
 754
 755         logfile = git_path("logs/%s", ref);
 756         logfd = open(logfile, O_RDONLY, 0);
 757         if (logfd < 0)
 758                 die("Unable to read log %s: %s", logfile, strerror(errno));
 759         fstat(logfd, &st);
 760         if (!st.st_size)
 761                 die("Log %s is empty.", logfile);
 762         logdata = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, logfd, 0);
 763         close(logfd);
 764
 765         lastrec = NULL;
 766         rec = logend = logdata + st.st_size;
 767         while (logdata < rec) {
 768                 if (logdata < rec && *(rec-1) == '\n')
 769                         rec--;
 770                 lastgt = NULL;
 771                 while (logdata < rec && *(rec-1) != '\n') {
 772                         rec--;
 773                         if (*rec == '>')
 774                                 lastgt = rec;
 775                 }
 776                 if (!lastgt)
 777                         die("Log %s is corrupt.", logfile);
 778                 date = strtoul(lastgt + 1, &tz_c, 10);
 779                 if (date <= at_time) {
 780                         if (lastrec) {
 781                                 if (get_sha1_hex(lastrec, logged_sha1))
 782                                         die("Log %s is corrupt.", logfile);
 783                                 if (get_sha1_hex(rec + 41, sha1))
 784                                         die("Log %s is corrupt.", logfile);
 785                                 if (hashcmp(logged_sha1, sha1)) {
 786                                         tz = strtoul(tz_c, NULL, 10);
 787                                         fprintf(stderr,
 788                                                 "warning: Log %s has gap after %s.\n",
 789                                                 logfile, show_rfc2822_date(date, tz));
 790                                 }
 791                         }
 792                         else if (date == at_time) {
 793                                 if (get_sha1_hex(rec + 41, sha1))
 794                                         die("Log %s is corrupt.", logfile);
 795                         }
 796                         else {
 797                                 if (get_sha1_hex(rec + 41, logged_sha1))
 798                                         die("Log %s is corrupt.", logfile);
 799                                 if (hashcmp(logged_sha1, sha1)) {
 800                                         tz = strtoul(tz_c, NULL, 10);
 801                                         fprintf(stderr,
 802                                                 "warning: Log %s unexpectedly ended on %s.\n",
 803                                                 logfile, show_rfc2822_date(date, tz));
 804                                 }
 805                         }
 806                         munmap((void*)logdata, st.st_size);
 807                         return 0;
 808                 }
 809                 lastrec = rec;
 810         }
 811
 812         rec = logdata;
 813         while (rec < logend && *rec != '>' && *rec != '\n')
 814                 rec++;
 815         if (rec == logend || *rec == '\n')
 816                 die("Log %s is corrupt.", logfile);
 817         date = strtoul(rec + 1, &tz_c, 10);
 818         tz = strtoul(tz_c, NULL, 10);
 819         if (get_sha1_hex(logdata, sha1))
 820                 die("Log %s is corrupt.", logfile);
 821         munmap((void*)logdata, st.st_size);
 822         fprintf(stderr, "warning: Log %s only goes back to %s.\n",
 823                 logfile, show_rfc2822_date(date, tz));
 824         return 0;
 825 }