read-cache.c

   1 /*
   2  * GIT - The information manager from hell
   3  *
   4  * Copyright (C) Linus Torvalds, 2005
   5  */
   6 #include "cache.h"
   7 #include "cache-tree.h"
   8
   9 /* Index extensions.
  10  *
  11  * The first letter should be 'A'..'Z' for extensions that are not
  12  * necessary for a correct operation (i.e. optimization data).
  13  * When new extensions are added that _needs_ to be understood in
  14  * order to correctly interpret the index file, pick character that
  15  * is outside the range, to cause the reader to abort.
  16  */
  17
  18 #define CACHE_EXT(s) ( (s[0]<<24)|(s[1]<<16)|(s[2]<<8)|(s[3]) )
  19 #define CACHE_EXT_TREE 0x54524545       /* "TREE" */
  20
  21 struct cache_entry **active_cache = NULL;
  22 static time_t index_file_timestamp;
  23 unsigned int active_nr = 0, active_alloc = 0, active_cache_changed = 0;
  24
  25 struct cache_tree *active_cache_tree = NULL;
  26
  27 /*
  28  * This only updates the "non-critical" parts of the directory
  29  * cache, ie the parts that aren't tracked by GIT, and only used
  30  * to validate the cache.
  31  */
  32 void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
  33 {
  34         ce->ce_ctime.sec = htonl(st->st_ctime);
  35         ce->ce_mtime.sec = htonl(st->st_mtime);
  36 #ifdef USE_NSEC
  37         ce->ce_ctime.nsec = htonl(st->st_ctim.tv_nsec);
  38         ce->ce_mtime.nsec = htonl(st->st_mtim.tv_nsec);
  39 #endif
  40         ce->ce_dev = htonl(st->st_dev);
  41         ce->ce_ino = htonl(st->st_ino);
  42         ce->ce_uid = htonl(st->st_uid);
  43         ce->ce_gid = htonl(st->st_gid);
  44         ce->ce_size = htonl(st->st_size);
  45
  46         if (assume_unchanged)
  47                 ce->ce_flags |= htons(CE_VALID);
  48 }
  49
  50 static int ce_compare_data(struct cache_entry *ce, struct stat *st)
  51 {
  52         int match = -1;
  53         int fd = open(ce->name, O_RDONLY);
  54
  55         if (fd >= 0) {
  56                 unsigned char sha1[20];
  57                 if (!index_fd(sha1, fd, st, 0, NULL))
  58                         match = memcmp(sha1, ce->sha1, 20);
  59                 close(fd);
  60         }
  61         return match;
  62 }
  63
  64 static int ce_compare_link(struct cache_entry *ce, unsigned long expected_size)
  65 {
  66         int match = -1;
  67         char *target;
  68         void *buffer;
  69         unsigned long size;
  70         char type[10];
  71         int len;
  72
  73         target = xmalloc(expected_size);
  74         len = readlink(ce->name, target, expected_size);
  75         if (len != expected_size) {
  76                 free(target);
  77                 return -1;
  78         }
  79         buffer = read_sha1_file(ce->sha1, type, &size);
  80         if (!buffer) {
  81                 free(target);
  82                 return -1;
  83         }
  84         if (size == expected_size)
  85                 match = memcmp(buffer, target, size);
  86         free(buffer);
  87         free(target);
  88         return match;
  89 }
  90
  91 static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
  92 {
  93         switch (st->st_mode & S_IFMT) {
  94         case S_IFREG:
  95                 if (ce_compare_data(ce, st))
  96                         return DATA_CHANGED;
  97                 break;
  98         case S_IFLNK:
  99                 if (ce_compare_link(ce, st->st_size))
 100                         return DATA_CHANGED;
 101                 break;
 102         default:
 103                 return TYPE_CHANGED;
 104         }
 105         return 0;
 106 }
 107
 108 static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
 109 {
 110         unsigned int changed = 0;
 111
 112         switch (ntohl(ce->ce_mode) & S_IFMT) {
 113         case S_IFREG:
 114                 changed |= !S_ISREG(st->st_mode) ? TYPE_CHANGED : 0;
 115                 /* We consider only the owner x bit to be relevant for
 116                  * "mode changes"
 117                  */
 118                 if (trust_executable_bit &&
 119                     (0100 & (ntohl(ce->ce_mode) ^ st->st_mode)))
 120                         changed |= MODE_CHANGED;
 121                 break;
 122         case S_IFLNK:
 123                 changed |= !S_ISLNK(st->st_mode) ? TYPE_CHANGED : 0;
 124                 break;
 125         default:
 126                 die("internal error: ce_mode is %o", ntohl(ce->ce_mode));
 127         }
 128         if (ce->ce_mtime.sec != htonl(st->st_mtime))
 129                 changed |= MTIME_CHANGED;
 130         if (ce->ce_ctime.sec != htonl(st->st_ctime))
 131                 changed |= CTIME_CHANGED;
 132
 133 #ifdef USE_NSEC
 134         /*
 135          * nsec seems unreliable - not all filesystems support it, so
 136          * as long as it is in the inode cache you get right nsec
 137          * but after it gets flushed, you get zero nsec.
 138          */
 139         if (ce->ce_mtime.nsec != htonl(st->st_mtim.tv_nsec))
 140                 changed |= MTIME_CHANGED;
 141         if (ce->ce_ctime.nsec != htonl(st->st_ctim.tv_nsec))
 142                 changed |= CTIME_CHANGED;
 143 #endif
 144
 145         if (ce->ce_uid != htonl(st->st_uid) ||
 146             ce->ce_gid != htonl(st->st_gid))
 147                 changed |= OWNER_CHANGED;
 148         if (ce->ce_ino != htonl(st->st_ino))
 149                 changed |= INODE_CHANGED;
 150
 151 #ifdef USE_STDEV
 152         /*
 153          * st_dev breaks on network filesystems where different
 154          * clients will have different views of what "device"
 155          * the filesystem is on
 156          */
 157         if (ce->ce_dev != htonl(st->st_dev))
 158                 changed |= INODE_CHANGED;
 159 #endif
 160
 161         if (ce->ce_size != htonl(st->st_size))
 162                 changed |= DATA_CHANGED;
 163
 164         return changed;
 165 }
 166
 167 int ce_match_stat(struct cache_entry *ce, struct stat *st, int ignore_valid)
 168 {
 169         unsigned int changed;
 170
 171         /*
 172          * If it's marked as always valid in the index, it's
 173          * valid whatever the checked-out copy says.
 174          */
 175         if (!ignore_valid && (ce->ce_flags & htons(CE_VALID)))
 176                 return 0;
 177
 178         changed = ce_match_stat_basic(ce, st);
 179
 180         /*
 181          * Within 1 second of this sequence:
 182          *      echo xyzzy >file && git-update-index --add file
 183          * running this command:
 184          *      echo frotz >file
 185          * would give a falsely clean cache entry.  The mtime and
 186          * length match the cache, and other stat fields do not change.
 187          *
 188          * We could detect this at update-index time (the cache entry
 189          * being registered/updated records the same time as "now")
 190          * and delay the return from git-update-index, but that would
 191          * effectively mean we can make at most one commit per second,
 192          * which is not acceptable.  Instead, we check cache entries
 193          * whose mtime are the same as the index file timestamp more
 194          * carefully than others.
 195          */
 196         if (!changed &&
 197             index_file_timestamp &&
 198             index_file_timestamp <= ntohl(ce->ce_mtime.sec))
 199                 changed |= ce_modified_check_fs(ce, st);
 200
 201         return changed;
 202 }
 203
 204 int ce_modified(struct cache_entry *ce, struct stat *st, int really)
 205 {
 206         int changed, changed_fs;
 207         changed = ce_match_stat(ce, st, really);
 208         if (!changed)
 209                 return 0;
 210         /*
 211          * If the mode or type has changed, there's no point in trying
 212          * to refresh the entry - it's not going to match
 213          */
 214         if (changed & (MODE_CHANGED | TYPE_CHANGED))
 215                 return changed;
 216
 217         /* Immediately after read-tree or update-index --cacheinfo,
 218          * the length field is zero.  For other cases the ce_size
 219          * should match the SHA1 recorded in the index entry.
 220          */
 221         if ((changed & DATA_CHANGED) && ce->ce_size != htonl(0))
 222                 return changed;
 223
 224         changed_fs = ce_modified_check_fs(ce, st);
 225         if (changed_fs)
 226                 return changed | changed_fs;
 227         return 0;
 228 }
 229
 230 int base_name_compare(const char *name1, int len1, int mode1,
 231                       const char *name2, int len2, int mode2)
 232 {
 233         unsigned char c1, c2;
 234         int len = len1 < len2 ? len1 : len2;
 235         int cmp;
 236
 237         cmp = memcmp(name1, name2, len);
 238         if (cmp)
 239                 return cmp;
 240         c1 = name1[len];
 241         c2 = name2[len];
 242         if (!c1 && S_ISDIR(mode1))
 243                 c1 = '/';
 244         if (!c2 && S_ISDIR(mode2))
 245                 c2 = '/';
 246         return (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
 247 }
 248
 249 int cache_name_compare(const char *name1, int flags1, const char *name2, int flags2)
 250 {
 251         int len1 = flags1 & CE_NAMEMASK;
 252         int len2 = flags2 & CE_NAMEMASK;
 253         int len = len1 < len2 ? len1 : len2;
 254         int cmp;
 255
 256         cmp = memcmp(name1, name2, len);
 257         if (cmp)
 258                 return cmp;
 259         if (len1 < len2)
 260                 return -1;
 261         if (len1 > len2)
 262                 return 1;
 263
 264         /* Compare stages  */
 265         flags1 &= CE_STAGEMASK;
 266         flags2 &= CE_STAGEMASK;
 267
 268         if (flags1 < flags2)
 269                 return -1;
 270         if (flags1 > flags2)
 271                 return 1;
 272         return 0;
 273 }
 274
 275 int cache_name_pos(const char *name, int namelen)
 276 {
 277         int first, last;
 278
 279         first = 0;
 280         last = active_nr;
 281         while (last > first) {
 282                 int next = (last + first) >> 1;
 283                 struct cache_entry *ce = active_cache[next];
 284                 int cmp = cache_name_compare(name, namelen, ce->name, ntohs(ce->ce_flags));
 285                 if (!cmp)
 286                         return next;
 287                 if (cmp < 0) {
 288                         last = next;
 289                         continue;
 290                 }
 291                 first = next+1;
 292         }
 293         return -first-1;
 294 }
 295
 296 /* Remove entry, return true if there are more entries to go.. */
 297 int remove_cache_entry_at(int pos)
 298 {
 299         active_cache_changed = 1;
 300         active_nr--;
 301         if (pos >= active_nr)
 302                 return 0;
 303         memmove(active_cache + pos, active_cache + pos + 1, (active_nr - pos) * sizeof(struct cache_entry *));
 304         return 1;
 305 }
 306
 307 int remove_file_from_cache(const char *path)
 308 {
 309         int pos = cache_name_pos(path, strlen(path));
 310         if (pos < 0)
 311                 pos = -pos-1;
 312         while (pos < active_nr && !strcmp(active_cache[pos]->name, path))
 313                 remove_cache_entry_at(pos);
 314         return 0;
 315 }
 316
 317 int ce_same_name(struct cache_entry *a, struct cache_entry *b)
 318 {
 319         int len = ce_namelen(a);
 320         return ce_namelen(b) == len && !memcmp(a->name, b->name, len);
 321 }
 322
 323 int ce_path_match(const struct cache_entry *ce, const char **pathspec)
 324 {
 325         const char *match, *name;
 326         int len;
 327
 328         if (!pathspec)
 329                 return 1;
 330
 331         len = ce_namelen(ce);
 332         name = ce->name;
 333         while ((match = *pathspec++) != NULL) {
 334                 int matchlen = strlen(match);
 335                 if (matchlen > len)
 336                         continue;
 337                 if (memcmp(name, match, matchlen))
 338                         continue;
 339                 if (matchlen && name[matchlen-1] == '/')
 340                         return 1;
 341                 if (name[matchlen] == '/' || !name[matchlen])
 342                         return 1;
 343                 if (!matchlen)
 344                         return 1;
 345         }
 346         return 0;
 347 }
 348
 349 /*
 350  * Do we have another file that has the beginning components being a
 351  * proper superset of the name we're trying to add?
 352  */
 353 static int has_file_name(const struct cache_entry *ce, int pos, int ok_to_replace)
 354 {
 355         int retval = 0;
 356         int len = ce_namelen(ce);
 357         int stage = ce_stage(ce);
 358         const char *name = ce->name;
 359
 360         while (pos < active_nr) {
 361                 struct cache_entry *p = active_cache[pos++];
 362
 363                 if (len >= ce_namelen(p))
 364                         break;
 365                 if (memcmp(name, p->name, len))
 366                         break;
 367                 if (ce_stage(p) != stage)
 368                         continue;
 369                 if (p->name[len] != '/')
 370                         continue;
 371                 retval = -1;
 372                 if (!ok_to_replace)
 373                         break;
 374                 remove_cache_entry_at(--pos);
 375         }
 376         return retval;
 377 }
 378
 379 /*
 380  * Do we have another file with a pathname that is a proper
 381  * subset of the name we're trying to add?
 382  */
 383 static int has_dir_name(const struct cache_entry *ce, int pos, int ok_to_replace)
 384 {
 385         int retval = 0;
 386         int stage = ce_stage(ce);
 387         const char *name = ce->name;
 388         const char *slash = name + ce_namelen(ce);
 389
 390         for (;;) {
 391                 int len;
 392
 393                 for (;;) {
 394                         if (*--slash == '/')
 395                                 break;
 396                         if (slash <= ce->name)
 397                                 return retval;
 398                 }
 399                 len = slash - name;
 400
 401                 pos = cache_name_pos(name, ntohs(create_ce_flags(len, stage)));
 402                 if (pos >= 0) {
 403                         retval = -1;
 404                         if (ok_to_replace)
 405                                 break;
 406                         remove_cache_entry_at(pos);
 407                         continue;
 408                 }
 409
 410                 /*
 411                  * Trivial optimization: if we find an entry that
 412                  * already matches the sub-directory, then we know
 413                  * we're ok, and we can exit.
 414                  */
 415                 pos = -pos-1;
 416                 while (pos < active_nr) {
 417                         struct cache_entry *p = active_cache[pos];
 418                         if ((ce_namelen(p) <= len) ||
 419                             (p->name[len] != '/') ||
 420                             memcmp(p->name, name, len))
 421                                 break; /* not our subdirectory */
 422                         if (ce_stage(p) == stage)
 423                                 /* p is at the same stage as our entry, and
 424                                  * is a subdirectory of what we are looking
 425                                  * at, so we cannot have conflicts at our
 426                                  * level or anything shorter.
 427                                  */
 428                                 return retval;
 429                         pos++;
 430                 }
 431         }
 432         return retval;
 433 }
 434
 435 /* We may be in a situation where we already have path/file and path
 436  * is being added, or we already have path and path/file is being
 437  * added.  Either one would result in a nonsense tree that has path
 438  * twice when git-write-tree tries to write it out.  Prevent it.
 439  *
 440  * If ok-to-replace is specified, we remove the conflicting entries
 441  * from the cache so the caller should recompute the insert position.
 442  * When this happens, we return non-zero.
 443  */
 444 static int check_file_directory_conflict(const struct cache_entry *ce, int pos, int ok_to_replace)
 445 {
 446         /*
 447          * We check if the path is a sub-path of a subsequent pathname
 448          * first, since removing those will not change the position
 449          * in the array
 450          */
 451         int retval = has_file_name(ce, pos, ok_to_replace);
 452         /*
 453          * Then check if the path might have a clashing sub-directory
 454          * before it.
 455          */
 456         return retval + has_dir_name(ce, pos, ok_to_replace);
 457 }
 458
 459 int add_cache_entry(struct cache_entry *ce, int option)
 460 {
 461         int pos;
 462         int ok_to_add = option & ADD_CACHE_OK_TO_ADD;
 463         int ok_to_replace = option & ADD_CACHE_OK_TO_REPLACE;
 464         int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
 465
 466         pos = cache_name_pos(ce->name, ntohs(ce->ce_flags));
 467
 468         /* existing match? Just replace it. */
 469         if (pos >= 0) {
 470                 active_cache_changed = 1;
 471                 active_cache[pos] = ce;
 472                 return 0;
 473         }
 474         pos = -pos-1;
 475
 476         /*
 477          * Inserting a merged entry ("stage 0") into the index
 478          * will always replace all non-merged entries..
 479          */
 480         if (pos < active_nr && ce_stage(ce) == 0) {
 481                 while (ce_same_name(active_cache[pos], ce)) {
 482                         ok_to_add = 1;
 483                         if (!remove_cache_entry_at(pos))
 484                                 break;
 485                 }
 486         }
 487
 488         if (!ok_to_add)
 489                 return -1;
 490
 491         if (!skip_df_check &&
 492             check_file_directory_conflict(ce, pos, ok_to_replace)) {
 493                 if (!ok_to_replace)
 494                         return -1;
 495                 pos = cache_name_pos(ce->name, ntohs(ce->ce_flags));
 496                 pos = -pos-1;
 497         }
 498
 499         /* Make sure the array is big enough .. */
 500         if (active_nr == active_alloc) {
 501                 active_alloc = alloc_nr(active_alloc);
 502                 active_cache = xrealloc(active_cache, active_alloc * sizeof(struct cache_entry *));
 503         }
 504
 505         /* Add it in.. */
 506         active_nr++;
 507         if (active_nr > pos)
 508                 memmove(active_cache + pos + 1, active_cache + pos, (active_nr - pos - 1) * sizeof(ce));
 509         active_cache[pos] = ce;
 510         active_cache_changed = 1;
 511         return 0;
 512 }
 513
 514 static int verify_hdr(struct cache_header *hdr, unsigned long size)
 515 {
 516         SHA_CTX c;
 517         unsigned char sha1[20];
 518
 519         if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
 520                 return error("bad signature");
 521         if (hdr->hdr_version != htonl(2))
 522                 return error("bad index version");
 523         SHA1_Init(&c);
 524         SHA1_Update(&c, hdr, size - 20);
 525         SHA1_Final(sha1, &c);
 526         if (memcmp(sha1, (void *)hdr + size - 20, 20))
 527                 return error("bad index file sha1 signature");
 528         return 0;
 529 }
 530
 531 static int read_index_extension(const char *ext, void *data, unsigned long sz)
 532 {
 533         switch (CACHE_EXT(ext)) {
 534         case CACHE_EXT_TREE:
 535                 active_cache_tree = cache_tree_read(data, sz);
 536                 break;
 537         default:
 538                 if (*ext < 'A' || 'Z' < *ext)
 539                         return error("index uses %.4s extension, which we do not understand",
 540                                      ext);
 541                 fprintf(stderr, "ignoring %.4s extension\n", ext);
 542                 break;
 543         }
 544         return 0;
 545 }
 546
 547 int read_cache(void)
 548 {
 549         int fd, i;
 550         struct stat st;
 551         unsigned long size, offset;
 552         void *map;
 553         struct cache_header *hdr;
 554
 555         errno = EBUSY;
 556         if (active_cache)
 557                 return active_nr;
 558
 559         errno = ENOENT;
 560         index_file_timestamp = 0;
 561         fd = open(get_index_file(), O_RDONLY);
 562         if (fd < 0) {
 563                 if (errno == ENOENT)
 564                         return 0;
 565                 die("index file open failed (%s)", strerror(errno));
 566         }
 567
 568         size = 0; // avoid gcc warning
 569         map = MAP_FAILED;
 570         if (!fstat(fd, &st)) {
 571                 size = st.st_size;
 572                 errno = EINVAL;
 573                 if (size >= sizeof(struct cache_header) + 20)
 574                         map = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
 575         }
 576         close(fd);
 577         if (map == MAP_FAILED)
 578                 die("index file mmap failed (%s)", strerror(errno));
 579
 580         hdr = map;
 581         if (verify_hdr(hdr, size) < 0)
 582                 goto unmap;
 583
 584         active_nr = ntohl(hdr->hdr_entries);
 585         active_alloc = alloc_nr(active_nr);
 586         active_cache = xcalloc(active_alloc, sizeof(struct cache_entry *));
 587
 588         offset = sizeof(*hdr);
 589         for (i = 0; i < active_nr; i++) {
 590                 struct cache_entry *ce = map + offset;
 591                 offset = offset + ce_size(ce);
 592                 active_cache[i] = ce;
 593         }
 594         index_file_timestamp = st.st_mtime;
 595         while (offset <= size - 20 - 8) {
 596                 /* After an array of active_nr index entries,
 597                  * there can be arbitrary number of extended
 598                  * sections, each of which is prefixed with
 599                  * extension name (4-byte) and section length
 600                  * in 4-byte network byte order.
 601                  */
 602                 unsigned long extsize;
 603                 memcpy(&extsize, map + offset + 4, 4);
 604                 extsize = ntohl(extsize);
 605                 if (read_index_extension(map + offset,
 606                                          map + offset + 8, extsize) < 0)
 607                         goto unmap;
 608                 offset += 8;
 609                 offset += extsize;
 610         }
 611         return active_nr;
 612
 613 unmap:
 614         munmap(map, size);
 615         errno = EINVAL;
 616         die("index file corrupt");
 617 }
 618
 619 #define WRITE_BUFFER_SIZE 8192
 620 static unsigned char write_buffer[WRITE_BUFFER_SIZE];
 621 static unsigned long write_buffer_len;
 622
 623 static int ce_write(SHA_CTX *context, int fd, void *data, unsigned int len)
 624 {
 625         while (len) {
 626                 unsigned int buffered = write_buffer_len;
 627                 unsigned int partial = WRITE_BUFFER_SIZE - buffered;
 628                 if (partial > len)
 629                         partial = len;
 630                 memcpy(write_buffer + buffered, data, partial);
 631                 buffered += partial;
 632                 if (buffered == WRITE_BUFFER_SIZE) {
 633                         SHA1_Update(context, write_buffer, WRITE_BUFFER_SIZE);
 634                         if (write(fd, write_buffer, WRITE_BUFFER_SIZE) != WRITE_BUFFER_SIZE)
 635                                 return -1;
 636                         buffered = 0;
 637                 }
 638                 write_buffer_len = buffered;
 639                 len -= partial;
 640                 data += partial;
 641         }
 642         return 0;
 643 }
 644
 645 static int write_index_ext_header(SHA_CTX *context, int fd,
 646                                   unsigned long ext, unsigned long sz)
 647 {
 648         ext = htonl(ext);
 649         sz = htonl(sz);
 650         if ((ce_write(context, fd, &ext, 4) < 0) ||
 651             (ce_write(context, fd, &sz, 4) < 0))
 652                 return -1;
 653         return 0;
 654 }
 655
 656 static int ce_flush(SHA_CTX *context, int fd)
 657 {
 658         unsigned int left = write_buffer_len;
 659
 660         if (left) {
 661                 write_buffer_len = 0;
 662                 SHA1_Update(context, write_buffer, left);
 663         }
 664
 665         /* Flush first if not enough space for SHA1 signature */
 666         if (left + 20 > WRITE_BUFFER_SIZE) {
 667                 if (write(fd, write_buffer, left) != left)
 668                         return -1;
 669                 left = 0;
 670         }
 671
 672         /* Append the SHA1 signature at the end */
 673         SHA1_Final(write_buffer + left, context);
 674         left += 20;
 675         if (write(fd, write_buffer, left) != left)
 676                 return -1;
 677         return 0;
 678 }
 679
 680 static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
 681 {
 682         /*
 683          * The only thing we care about in this function is to smudge the
 684          * falsely clean entry due to touch-update-touch race, so we leave
 685          * everything else as they are.  We are called for entries whose
 686          * ce_mtime match the index file mtime.
 687          */
 688         struct stat st;
 689
 690         if (lstat(ce->name, &st) < 0)
 691                 return;
 692         if (ce_match_stat_basic(ce, &st))
 693                 return;
 694         if (ce_modified_check_fs(ce, &st)) {
 695                 /* This is "racily clean"; smudge it.  Note that this
 696                  * is a tricky code.  At first glance, it may appear
 697                  * that it can break with this sequence:
 698                  *
 699                  * $ echo xyzzy >frotz
 700                  * $ git-update-index --add frotz
 701                  * $ : >frotz
 702                  * $ sleep 3
 703                  * $ echo filfre >nitfol
 704                  * $ git-update-index --add nitfol
 705                  *
 706                  * but it does not.  Whe the second update-index runs,
 707                  * it notices that the entry "frotz" has the same timestamp
 708                  * as index, and if we were to smudge it by resetting its
 709                  * size to zero here, then the object name recorded
 710                  * in index is the 6-byte file but the cached stat information
 711                  * becomes zero --- which would then match what we would
 712                  * obtain from the filesystem next time we stat("frotz").
 713                  *
 714                  * However, the second update-index, before calling
 715                  * this function, notices that the cached size is 6
 716                  * bytes and what is on the filesystem is an empty
 717                  * file, and never calls us, so the cached size information
 718                  * for "frotz" stays 6 which does not match the filesystem.
 719                  */
 720                 ce->ce_size = htonl(0);
 721         }
 722 }
 723
 724 int write_cache(int newfd, struct cache_entry **cache, int entries)
 725 {
 726         SHA_CTX c;
 727         struct cache_header hdr;
 728         int i, removed;
 729
 730         for (i = removed = 0; i < entries; i++)
 731                 if (!cache[i]->ce_mode)
 732                         removed++;
 733
 734         hdr.hdr_signature = htonl(CACHE_SIGNATURE);
 735         hdr.hdr_version = htonl(2);
 736         hdr.hdr_entries = htonl(entries - removed);
 737
 738         SHA1_Init(&c);
 739         if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
 740                 return -1;
 741
 742         for (i = 0; i < entries; i++) {
 743                 struct cache_entry *ce = cache[i];
 744                 if (!ce->ce_mode)
 745                         continue;
 746                 if (index_file_timestamp &&
 747                     index_file_timestamp <= ntohl(ce->ce_mtime.sec))
 748                         ce_smudge_racily_clean_entry(ce);
 749                 if (ce_write(&c, newfd, ce, ce_size(ce)) < 0)
 750                         return -1;
 751         }
 752
 753         /* Write extension data here */
 754         if (active_cache_tree) {
 755                 unsigned long sz;
 756                 void *data = cache_tree_write(active_cache_tree, &sz);
 757                 if (data &&
 758                     !write_index_ext_header(&c, newfd, CACHE_EXT_TREE, sz) &&
 759                     !ce_write(&c, newfd, data, sz))
 760                         ;
 761                 else {
 762                         free(data);
 763                         return -1;
 764                 }
 765         }
 766         return ce_flush(&c, newfd);
 767 }