read-tree.c

   1 /*
   2  * GIT - The information manager from hell
   3  *
   4  * Copyright (C) Linus Torvalds, 2005
   5  */
   6 #define DBRT_DEBUG 1
   7
   8 #include "cache.h"
   9
  10 #include "object.h"
  11 #include "tree.h"
  12 #include "cache-tree.h"
  13 #include <sys/time.h>
  14 #include <signal.h>
  15
  16 static int merge = 0;
  17 static int update = 0;
  18 static int index_only = 0;
  19 static int nontrivial_merge = 0;
  20 static int trivial_merges_only = 0;
  21 static int aggressive = 0;
  22 static int verbose_update = 0;
  23 static volatile int progress_update = 0;
  24 static const char *prefix = NULL;
  25
  26 static int head_idx = -1;
  27 static int merge_size = 0;
  28
  29 static struct object_list *trees = NULL;
  30
  31 static struct cache_entry df_conflict_entry = {
  32 };
  33
  34 static struct tree_entry_list df_conflict_list = {
  35         .name = NULL,
  36         .next = &df_conflict_list
  37 };
  38
  39 typedef int (*merge_fn_t)(struct cache_entry **src);
  40
  41 static int entcmp(char *name1, int dir1, char *name2, int dir2)
  42 {
  43         int len1 = strlen(name1);
  44         int len2 = strlen(name2);
  45         int len = len1 < len2 ? len1 : len2;
  46         int ret = memcmp(name1, name2, len);
  47         unsigned char c1, c2;
  48         if (ret)
  49                 return ret;
  50         c1 = name1[len];
  51         c2 = name2[len];
  52         if (!c1 && dir1)
  53                 c1 = '/';
  54         if (!c2 && dir2)
  55                 c2 = '/';
  56         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  57         if (c1 && c2 && !ret)
  58                 ret = len1 - len2;
  59         return ret;
  60 }
  61
  62 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  63                             const char *base, merge_fn_t fn, int *indpos)
  64 {
  65         int baselen = strlen(base);
  66         int src_size = len + 1;
  67         do {
  68                 int i;
  69                 char *first;
  70                 int firstdir = 0;
  71                 int pathlen;
  72                 unsigned ce_size;
  73                 struct tree_entry_list **subposns;
  74                 struct cache_entry **src;
  75                 int any_files = 0;
  76                 int any_dirs = 0;
  77                 char *cache_name;
  78                 int ce_stage;
  79
  80                 /* Find the first name in the input. */
  81
  82                 first = NULL;
  83                 cache_name = NULL;
  84
  85                 /* Check the cache */
  86                 if (merge && *indpos < active_nr) {
  87                         /* This is a bit tricky: */
  88                         /* If the index has a subdirectory (with
  89                          * contents) as the first name, it'll get a
  90                          * filename like "foo/bar". But that's after
  91                          * "foo", so the entry in trees will get
  92                          * handled first, at which point we'll go into
  93                          * "foo", and deal with "bar" from the index,
  94                          * because the base will be "foo/". The only
  95                          * way we can actually have "foo/bar" first of
  96                          * all the things is if the trees don't
  97                          * contain "foo" at all, in which case we'll
  98                          * handle "foo/bar" without going into the
  99                          * directory, but that's fine (and will return
 100                          * an error anyway, with the added unknown
 101                          * file case.
 102                          */
 103
 104                         cache_name = active_cache[*indpos]->name;
 105                         if (strlen(cache_name) > baselen &&
 106                             !memcmp(cache_name, base, baselen)) {
 107                                 cache_name += baselen;
 108                                 first = cache_name;
 109                         } else {
 110                                 cache_name = NULL;
 111                         }
 112                 }
 113
 114 #if DBRT_DEBUG > 1
 115                 if (first)
 116                         printf("index %s\n", first);
 117 #endif
 118                 for (i = 0; i < len; i++) {
 119                         if (!posns[i] || posns[i] == &df_conflict_list)
 120                                 continue;
 121 #if DBRT_DEBUG > 1
 122                         printf("%d %s\n", i + 1, posns[i]->name);
 123 #endif
 124                         if (!first || entcmp(first, firstdir,
 125                                              posns[i]->name,
 126                                              posns[i]->directory) > 0) {
 127                                 first = posns[i]->name;
 128                                 firstdir = posns[i]->directory;
 129                         }
 130                 }
 131                 /* No name means we're done */
 132                 if (!first)
 133                         return 0;
 134
 135                 pathlen = strlen(first);
 136                 ce_size = cache_entry_size(baselen + pathlen);
 137
 138                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 139
 140                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 141
 142                 if (cache_name && !strcmp(cache_name, first)) {
 143                         any_files = 1;
 144                         src[0] = active_cache[*indpos];
 145                         remove_cache_entry_at(*indpos);
 146                 }
 147
 148                 for (i = 0; i < len; i++) {
 149                         struct cache_entry *ce;
 150
 151                         if (!posns[i] ||
 152                             (posns[i] != &df_conflict_list &&
 153                              strcmp(first, posns[i]->name))) {
 154                                 continue;
 155                         }
 156
 157                         if (posns[i] == &df_conflict_list) {
 158                                 src[i + merge] = &df_conflict_entry;
 159                                 continue;
 160                         }
 161
 162                         if (posns[i]->directory) {
 163                                 any_dirs = 1;
 164                                 parse_tree(posns[i]->item.tree);
 165                                 subposns[i] = posns[i]->item.tree->entries;
 166                                 posns[i] = posns[i]->next;
 167                                 src[i + merge] = &df_conflict_entry;
 168                                 continue;
 169                         }
 170
 171                         if (!merge)
 172                                 ce_stage = 0;
 173                         else if (i + 1 < head_idx)
 174                                 ce_stage = 1;
 175                         else if (i + 1 > head_idx)
 176                                 ce_stage = 3;
 177                         else
 178                                 ce_stage = 2;
 179
 180                         ce = xcalloc(1, ce_size);
 181                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 182                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 183                                                        ce_stage);
 184                         memcpy(ce->name, base, baselen);
 185                         memcpy(ce->name + baselen, first, pathlen + 1);
 186
 187                         any_files = 1;
 188
 189                         memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
 190                         src[i + merge] = ce;
 191                         subposns[i] = &df_conflict_list;
 192                         posns[i] = posns[i]->next;
 193                 }
 194                 if (any_files) {
 195                         if (merge) {
 196                                 int ret;
 197
 198 #if DBRT_DEBUG > 1
 199                                 printf("%s:\n", first);
 200                                 for (i = 0; i < src_size; i++) {
 201                                         printf(" %d ", i);
 202                                         if (src[i])
 203                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 204                                         else
 205                                                 printf("\n");
 206                                 }
 207 #endif
 208                                 ret = fn(src);
 209
 210 #if DBRT_DEBUG > 1
 211                                 printf("Added %d entries\n", ret);
 212 #endif
 213                                 *indpos += ret;
 214                         } else {
 215                                 for (i = 0; i < src_size; i++) {
 216                                         if (src[i]) {
 217                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 218                                         }
 219                                 }
 220                         }
 221                 }
 222                 if (any_dirs) {
 223                         char *newbase = xmalloc(baselen + 2 + pathlen);
 224                         memcpy(newbase, base, baselen);
 225                         memcpy(newbase + baselen, first, pathlen);
 226                         newbase[baselen + pathlen] = '/';
 227                         newbase[baselen + pathlen + 1] = '\0';
 228                         if (unpack_trees_rec(subposns, len, newbase, fn,
 229                                              indpos))
 230                                 return -1;
 231                         free(newbase);
 232                 }
 233                 free(subposns);
 234                 free(src);
 235         } while (1);
 236 }
 237
 238 static void reject_merge(struct cache_entry *ce)
 239 {
 240         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 241             ce->name);
 242 }
 243
 244 /* Unlink the last component and attempt to remove leading
 245  * directories, in case this unlink is the removal of the
 246  * last entry in the directory -- empty directories are removed.
 247  */
 248 static void unlink_entry(char *name)
 249 {
 250         char *cp, *prev;
 251
 252         if (unlink(name))
 253                 return;
 254         prev = NULL;
 255         while (1) {
 256                 int status;
 257                 cp = strrchr(name, '/');
 258                 if (prev)
 259                         *prev = '/';
 260                 if (!cp)
 261                         break;
 262
 263                 *cp = 0;
 264                 status = rmdir(name);
 265                 if (status) {
 266                         *cp = '/';
 267                         break;
 268                 }
 269                 prev = cp;
 270         }
 271 }
 272
 273 static void progress_interval(int signum)
 274 {
 275         progress_update = 1;
 276 }
 277
 278 static void setup_progress_signal(void)
 279 {
 280         struct sigaction sa;
 281         struct itimerval v;
 282
 283         memset(&sa, 0, sizeof(sa));
 284         sa.sa_handler = progress_interval;
 285         sigemptyset(&sa.sa_mask);
 286         sa.sa_flags = SA_RESTART;
 287         sigaction(SIGALRM, &sa, NULL);
 288
 289         v.it_interval.tv_sec = 1;
 290         v.it_interval.tv_usec = 0;
 291         v.it_value = v.it_interval;
 292         setitimer(ITIMER_REAL, &v, NULL);
 293 }
 294
 295 static void check_updates(struct cache_entry **src, int nr)
 296 {
 297         static struct checkout state = {
 298                 .base_dir = "",
 299                 .force = 1,
 300                 .quiet = 1,
 301                 .refresh_cache = 1,
 302         };
 303         unsigned short mask = htons(CE_UPDATE);
 304         unsigned last_percent = 200, cnt = 0, total = 0;
 305
 306         if (update && verbose_update) {
 307                 for (total = cnt = 0; cnt < nr; cnt++) {
 308                         struct cache_entry *ce = src[cnt];
 309                         if (!ce->ce_mode || ce->ce_flags & mask)
 310                                 total++;
 311                 }
 312
 313                 /* Don't bother doing this for very small updates */
 314                 if (total < 250)
 315                         total = 0;
 316
 317                 if (total) {
 318                         fprintf(stderr, "Checking files out...\n");
 319                         setup_progress_signal();
 320                         progress_update = 1;
 321                 }
 322                 cnt = 0;
 323         }
 324
 325         while (nr--) {
 326                 struct cache_entry *ce = *src++;
 327
 328                 if (total) {
 329                         if (!ce->ce_mode || ce->ce_flags & mask) {
 330                                 unsigned percent;
 331                                 cnt++;
 332                                 percent = (cnt * 100) / total;
 333                                 if (percent != last_percent ||
 334                                     progress_update) {
 335                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 336                                                 percent, cnt, total);
 337                                         last_percent = percent;
 338                                 }
 339                         }
 340                 }
 341                 if (!ce->ce_mode) {
 342                         if (update)
 343                                 unlink_entry(ce->name);
 344                         continue;
 345                 }
 346                 if (ce->ce_flags & mask) {
 347                         ce->ce_flags &= ~mask;
 348                         if (update)
 349                                 checkout_entry(ce, &state, NULL);
 350                 }
 351         }
 352         if (total) {
 353                 signal(SIGALRM, SIG_IGN);
 354                 fputc('\n', stderr);
 355         }
 356 }
 357
 358 static int unpack_trees(merge_fn_t fn)
 359 {
 360         int indpos = 0;
 361         unsigned len = object_list_length(trees);
 362         struct tree_entry_list **posns;
 363         int i;
 364         struct object_list *posn = trees;
 365         merge_size = len;
 366
 367         if (len) {
 368                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 369                 for (i = 0; i < len; i++) {
 370                         posns[i] = ((struct tree *) posn->item)->entries;
 371                         posn = posn->next;
 372                 }
 373                 if (unpack_trees_rec(posns, len, prefix ? prefix : "",
 374                                      fn, &indpos))
 375                         return -1;
 376         }
 377
 378         if (trivial_merges_only && nontrivial_merge)
 379                 die("Merge requires file-level merging");
 380
 381         check_updates(active_cache, active_nr);
 382         return 0;
 383 }
 384
 385 static int list_tree(unsigned char *sha1)
 386 {
 387         struct tree *tree = parse_tree_indirect(sha1);
 388         if (!tree)
 389                 return -1;
 390         object_list_append(&tree->object, &trees);
 391         return 0;
 392 }
 393
 394 static int same(struct cache_entry *a, struct cache_entry *b)
 395 {
 396         if (!!a != !!b)
 397                 return 0;
 398         if (!a && !b)
 399                 return 1;
 400         return a->ce_mode == b->ce_mode &&
 401                 !memcmp(a->sha1, b->sha1, 20);
 402 }
 403
 404
 405 /*
 406  * When a CE gets turned into an unmerged entry, we
 407  * want it to be up-to-date
 408  */
 409 static void verify_uptodate(struct cache_entry *ce)
 410 {
 411         struct stat st;
 412
 413         if (index_only)
 414                 return;
 415
 416         if (!lstat(ce->name, &st)) {
 417                 unsigned changed = ce_match_stat(ce, &st, 1);
 418                 if (!changed)
 419                         return;
 420                 errno = 0;
 421         }
 422         if (errno == ENOENT)
 423                 return;
 424         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 425 }
 426
 427 static void invalidate_ce_path(struct cache_entry *ce)
 428 {
 429         if (ce)
 430                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 431 }
 432
 433 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 434 {
 435         merge->ce_flags |= htons(CE_UPDATE);
 436         if (old) {
 437                 /*
 438                  * See if we can re-use the old CE directly?
 439                  * That way we get the uptodate stat info.
 440                  *
 441                  * This also removes the UPDATE flag on
 442                  * a match.
 443                  */
 444                 if (same(old, merge)) {
 445                         *merge = *old;
 446                 } else {
 447                         verify_uptodate(old);
 448                         invalidate_ce_path(old);
 449                 }
 450         }
 451         else
 452                 invalidate_ce_path(merge);
 453         merge->ce_flags &= ~htons(CE_STAGEMASK);
 454         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 455         return 1;
 456 }
 457
 458 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 459 {
 460         if (old)
 461                 verify_uptodate(old);
 462         ce->ce_mode = 0;
 463         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 464         invalidate_ce_path(ce);
 465         return 1;
 466 }
 467
 468 static int keep_entry(struct cache_entry *ce)
 469 {
 470         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 471         return 1;
 472 }
 473
 474 #if DBRT_DEBUG
 475 static void show_stage_entry(FILE *o,
 476                              const char *label, const struct cache_entry *ce)
 477 {
 478         if (!ce)
 479                 fprintf(o, "%s (missing)\n", label);
 480         else
 481                 fprintf(o, "%s%06o %s %d\t%s\n",
 482                         label,
 483                         ntohl(ce->ce_mode),
 484                         sha1_to_hex(ce->sha1),
 485                         ce_stage(ce),
 486                         ce->name);
 487 }
 488 #endif
 489
 490 static int threeway_merge(struct cache_entry **stages)
 491 {
 492         struct cache_entry *index;
 493         struct cache_entry *head;
 494         struct cache_entry *remote = stages[head_idx + 1];
 495         int count;
 496         int head_match = 0;
 497         int remote_match = 0;
 498
 499         int df_conflict_head = 0;
 500         int df_conflict_remote = 0;
 501
 502         int any_anc_missing = 0;
 503         int no_anc_exists = 1;
 504         int i;
 505
 506         for (i = 1; i < head_idx; i++) {
 507                 if (!stages[i])
 508                         any_anc_missing = 1;
 509                 else
 510                         no_anc_exists = 0;
 511         }
 512
 513         index = stages[0];
 514         head = stages[head_idx];
 515
 516         if (head == &df_conflict_entry) {
 517                 df_conflict_head = 1;
 518                 head = NULL;
 519         }
 520
 521         if (remote == &df_conflict_entry) {
 522                 df_conflict_remote = 1;
 523                 remote = NULL;
 524         }
 525
 526         /* First, if there's a #16 situation, note that to prevent #13
 527          * and #14.
 528          */
 529         if (!same(remote, head)) {
 530                 for (i = 1; i < head_idx; i++) {
 531                         if (same(stages[i], head)) {
 532                                 head_match = i;
 533                         }
 534                         if (same(stages[i], remote)) {
 535                                 remote_match = i;
 536                         }
 537                 }
 538         }
 539
 540         /* We start with cases where the index is allowed to match
 541          * something other than the head: #14(ALT) and #2ALT, where it
 542          * is permitted to match the result instead.
 543          */
 544         /* #14, #14ALT, #2ALT */
 545         if (remote && !df_conflict_head && head_match && !remote_match) {
 546                 if (index && !same(index, remote) && !same(index, head))
 547                         reject_merge(index);
 548                 return merged_entry(remote, index);
 549         }
 550         /*
 551          * If we have an entry in the index cache, then we want to
 552          * make sure that it matches head.
 553          */
 554         if (index && !same(index, head)) {
 555                 reject_merge(index);
 556         }
 557
 558         if (head) {
 559                 /* #5ALT, #15 */
 560                 if (same(head, remote))
 561                         return merged_entry(head, index);
 562                 /* #13, #3ALT */
 563                 if (!df_conflict_remote && remote_match && !head_match)
 564                         return merged_entry(head, index);
 565         }
 566
 567         /* #1 */
 568         if (!head && !remote && any_anc_missing)
 569                 return 0;
 570
 571         /* Under the new "aggressive" rule, we resolve mostly trivial
 572          * cases that we historically had git-merge-one-file resolve.
 573          */
 574         if (aggressive) {
 575                 int head_deleted = !head && !df_conflict_head;
 576                 int remote_deleted = !remote && !df_conflict_remote;
 577                 /*
 578                  * Deleted in both.
 579                  * Deleted in one and unchanged in the other.
 580                  */
 581                 if ((head_deleted && remote_deleted) ||
 582                     (head_deleted && remote && remote_match) ||
 583                     (remote_deleted && head && head_match)) {
 584                         if (index)
 585                                 return deleted_entry(index, index);
 586                         return 0;
 587                 }
 588                 /*
 589                  * Added in both, identically.
 590                  */
 591                 if (no_anc_exists && head && remote && same(head, remote))
 592                         return merged_entry(head, index);
 593
 594         }
 595
 596         /* Below are "no merge" cases, which require that the index be
 597          * up-to-date to avoid the files getting overwritten with
 598          * conflict resolution files.
 599          */
 600         if (index) {
 601                 verify_uptodate(index);
 602         }
 603
 604         nontrivial_merge = 1;
 605
 606         /* #2, #3, #4, #6, #7, #9, #11. */
 607         count = 0;
 608         if (!head_match || !remote_match) {
 609                 for (i = 1; i < head_idx; i++) {
 610                         if (stages[i]) {
 611                                 keep_entry(stages[i]);
 612                                 count++;
 613                                 break;
 614                         }
 615                 }
 616         }
 617 #if DBRT_DEBUG
 618         else {
 619                 fprintf(stderr, "read-tree: warning #16 detected\n");
 620                 show_stage_entry(stderr, "head   ", stages[head_match]);
 621                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 622         }
 623 #endif
 624         if (head) { count += keep_entry(head); }
 625         if (remote) { count += keep_entry(remote); }
 626         return count;
 627 }
 628
 629 /*
 630  * Two-way merge.
 631  *
 632  * The rule is to "carry forward" what is in the index without losing
 633  * information across a "fast forward", favoring a successful merge
 634  * over a merge failure when it makes sense.  For details of the
 635  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 636  *
 637  */
 638 static int twoway_merge(struct cache_entry **src)
 639 {
 640         struct cache_entry *current = src[0];
 641         struct cache_entry *oldtree = src[1], *newtree = src[2];
 642
 643         if (merge_size != 2)
 644                 return error("Cannot do a twoway merge of %d trees",
 645                              merge_size);
 646
 647         if (current) {
 648                 if ((!oldtree && !newtree) || /* 4 and 5 */
 649                     (!oldtree && newtree &&
 650                      same(current, newtree)) || /* 6 and 7 */
 651                     (oldtree && newtree &&
 652                      same(oldtree, newtree)) || /* 14 and 15 */
 653                     (oldtree && newtree &&
 654                      !same(oldtree, newtree) && /* 18 and 19*/
 655                      same(current, newtree))) {
 656                         return keep_entry(current);
 657                 }
 658                 else if (oldtree && !newtree && same(current, oldtree)) {
 659                         /* 10 or 11 */
 660                         return deleted_entry(oldtree, current);
 661                 }
 662                 else if (oldtree && newtree &&
 663                          same(current, oldtree) && !same(current, newtree)) {
 664                         /* 20 or 21 */
 665                         return merged_entry(newtree, current);
 666                 }
 667                 else {
 668                         /* all other failures */
 669                         if (oldtree)
 670                                 reject_merge(oldtree);
 671                         if (current)
 672                                 reject_merge(current);
 673                         if (newtree)
 674                                 reject_merge(newtree);
 675                         return -1;
 676                 }
 677         }
 678         else if (newtree)
 679                 return merged_entry(newtree, current);
 680         else
 681                 return deleted_entry(oldtree, current);
 682 }
 683
 684 /*
 685  * Bind merge.
 686  *
 687  * Keep the index entries at stage0, collapse stage1 but make sure
 688  * stage0 does not have anything in prefix.
 689  */
 690 static int bind_merge(struct cache_entry **src)
 691 {
 692         struct cache_entry *old = src[0];
 693         struct cache_entry *a = src[1];
 694
 695         if (merge_size != 1)
 696                 return error("Cannot do a bind merge of %d trees\n",
 697                              merge_size);
 698         if (!a)
 699                 return merged_entry(old, NULL);
 700         if (old)
 701                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 702
 703         return merged_entry(a, NULL);
 704 }
 705
 706 /*
 707  * One-way merge.
 708  *
 709  * The rule is:
 710  * - take the stat information from stage0, take the data from stage1
 711  */
 712 static int oneway_merge(struct cache_entry **src)
 713 {
 714         struct cache_entry *old = src[0];
 715         struct cache_entry *a = src[1];
 716
 717         if (merge_size != 1)
 718                 return error("Cannot do a oneway merge of %d trees",
 719                              merge_size);
 720
 721         if (!a) {
 722                 invalidate_ce_path(old);
 723                 return 0;
 724         }
 725         if (old && same(old, a)) {
 726                 return keep_entry(old);
 727         }
 728         return merged_entry(a, NULL);
 729 }
 730
 731 static int read_cache_unmerged(void)
 732 {
 733         int i, deleted;
 734         struct cache_entry **dst;
 735
 736         read_cache();
 737         dst = active_cache;
 738         deleted = 0;
 739         for (i = 0; i < active_nr; i++) {
 740                 struct cache_entry *ce = active_cache[i];
 741                 if (ce_stage(ce)) {
 742                         deleted++;
 743                         invalidate_ce_path(ce);
 744                         continue;
 745                 }
 746                 if (deleted)
 747                         *dst = ce;
 748                 dst++;
 749         }
 750         active_nr -= deleted;
 751         return deleted;
 752 }
 753
 754 static void prime_cache_tree_rec(struct cache_tree *it, struct tree *tree)
 755 {
 756         struct tree_entry_list *ent;
 757         int cnt;
 758
 759         memcpy(it->sha1, tree->object.sha1, 20);
 760         for (cnt = 0, ent = tree->entries; ent; ent = ent->next) {
 761                 if (!ent->directory)
 762                         cnt++;
 763                 else {
 764                         struct cache_tree_sub *sub;
 765                         struct tree *subtree = (struct tree *)ent->item.tree;
 766                         if (!subtree->object.parsed)
 767                                 parse_tree(subtree);
 768                         sub = cache_tree_sub(it, ent->name);
 769                         sub->cache_tree = cache_tree();
 770                         prime_cache_tree_rec(sub->cache_tree, subtree);
 771                         cnt += sub->cache_tree->entry_count;
 772                 }
 773         }
 774         it->entry_count = cnt;
 775 }
 776
 777 static void prime_cache_tree(void)
 778 {
 779         struct tree *tree = (struct tree *)trees->item;
 780         if (!tree)
 781                 return;
 782         active_cache_tree = cache_tree();
 783         prime_cache_tree_rec(active_cache_tree, tree);
 784
 785 }
 786
 787 static const char read_tree_usage[] = "git-read-tree (<sha> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <sha1> [<sha2> [<sha3>]])";
 788
 789 static struct cache_file cache_file;
 790
 791 int main(int argc, char **argv)
 792 {
 793         int i, newfd, reset, stage = 0;
 794         unsigned char sha1[20];
 795         merge_fn_t fn = NULL;
 796
 797         setup_git_directory();
 798         git_config(git_default_config);
 799
 800         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 801         if (newfd < 0)
 802                 die("unable to create new cachefile");
 803
 804         git_config(git_default_config);
 805
 806         merge = 0;
 807         reset = 0;
 808         for (i = 1; i < argc; i++) {
 809                 const char *arg = argv[i];
 810
 811                 /* "-u" means "update", meaning that a merge will update
 812                  * the working tree.
 813                  */
 814                 if (!strcmp(arg, "-u")) {
 815                         update = 1;
 816                         continue;
 817                 }
 818
 819                 if (!strcmp(arg, "-v")) {
 820                         verbose_update = 1;
 821                         continue;
 822                 }
 823
 824                 /* "-i" means "index only", meaning that a merge will
 825                  * not even look at the working tree.
 826                  */
 827                 if (!strcmp(arg, "-i")) {
 828                         index_only = 1;
 829                         continue;
 830                 }
 831
 832                 /* "--prefix=<subdirectory>/" means keep the current index
 833                  *  entries and put the entries from the tree under the
 834                  * given subdirectory.
 835                  */
 836                 if (!strncmp(arg, "--prefix=", 9)) {
 837                         if (stage || merge || prefix)
 838                                 usage(read_tree_usage);
 839                         prefix = arg + 9;
 840                         merge = 1;
 841                         stage = 1;
 842                         if (read_cache_unmerged())
 843                                 die("you need to resolve your current index first");
 844                         continue;
 845                 }
 846
 847                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 848                 if (!strcmp(arg, "--reset")) {
 849                         if (stage || merge || prefix)
 850                                 usage(read_tree_usage);
 851                         reset = 1;
 852                         merge = 1;
 853                         stage = 1;
 854                         read_cache_unmerged();
 855                         continue;
 856                 }
 857
 858                 if (!strcmp(arg, "--trivial")) {
 859                         trivial_merges_only = 1;
 860                         continue;
 861                 }
 862
 863                 if (!strcmp(arg, "--aggressive")) {
 864                         aggressive = 1;
 865                         continue;
 866                 }
 867
 868                 /* "-m" stands for "merge", meaning we start in stage 1 */
 869                 if (!strcmp(arg, "-m")) {
 870                         if (stage || merge || prefix)
 871                                 usage(read_tree_usage);
 872                         if (read_cache_unmerged())
 873                                 die("you need to resolve your current index first");
 874                         stage = 1;
 875                         merge = 1;
 876                         continue;
 877                 }
 878
 879                 /* using -u and -i at the same time makes no sense */
 880                 if (1 < index_only + update)
 881                         usage(read_tree_usage);
 882
 883                 if (get_sha1(arg, sha1) < 0)
 884                         usage(read_tree_usage);
 885                 if (list_tree(sha1) < 0)
 886                         die("failed to unpack tree object %s", arg);
 887                 stage++;
 888         }
 889         if ((update||index_only) && !merge)
 890                 usage(read_tree_usage);
 891
 892         if (prefix) {
 893                 int pfxlen = strlen(prefix);
 894                 int pos;
 895                 if (prefix[pfxlen-1] != '/')
 896                         die("prefix must end with /");
 897                 if (stage != 2)
 898                         die("binding merge takes only one tree");
 899                 pos = cache_name_pos(prefix, pfxlen);
 900                 if (0 <= pos)
 901                         die("corrupt index file");
 902                 pos = -pos-1;
 903                 if (pos < active_nr &&
 904                     !strncmp(active_cache[pos]->name, prefix, pfxlen))
 905                         die("subdirectory '%s' already exists.", prefix);
 906                 pos = cache_name_pos(prefix, pfxlen-1);
 907                 if (0 <= pos)
 908                         die("file '%.*s' already exists.", pfxlen-1, prefix);
 909         }
 910
 911         if (merge) {
 912                 if (stage < 2)
 913                         die("just how do you expect me to merge %d trees?", stage-1);
 914                 switch (stage - 1) {
 915                 case 1:
 916                         fn = prefix ? bind_merge : oneway_merge;
 917                         break;
 918                 case 2:
 919                         fn = twoway_merge;
 920                         break;
 921                 case 3:
 922                 default:
 923                         fn = threeway_merge;
 924                         cache_tree_free(&active_cache_tree);
 925                         break;
 926                 }
 927
 928                 if (stage - 1 >= 3)
 929                         head_idx = stage - 2;
 930                 else
 931                         head_idx = 1;
 932         }
 933
 934         unpack_trees(fn);
 935
 936         /*
 937          * When reading only one tree (either the most basic form,
 938          * "-m ent" or "--reset ent" form), we can obtain a fully
 939          * valid cache-tree because the index must match exactly
 940          * what came from the tree.
 941          */
 942         if (trees && trees->item && (!merge || (stage == 2))) {
 943                 cache_tree_free(&active_cache_tree);
 944                 prime_cache_tree();
 945         }
 946
 947         if (write_cache(newfd, active_cache, active_nr) ||
 948             commit_index_file(&cache_file))
 949                 die("unable to write new index file");
 950         return 0;
 951 }