read-cache.c

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