builtin-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 #include "builtin.h"
  16
  17 static int reset = 0;
  18 static int merge = 0;
  19 static int update = 0;
  20 static int index_only = 0;
  21 static int nontrivial_merge = 0;
  22 static int trivial_merges_only = 0;
  23 static int aggressive = 0;
  24 static int verbose_update = 0;
  25 static volatile int progress_update = 0;
  26 static const char *prefix = NULL;
  27
  28 static int head_idx = -1;
  29 static int merge_size = 0;
  30
  31 static struct object_list *trees = NULL;
  32
  33 static struct cache_entry df_conflict_entry = {
  34 };
  35
  36 static struct tree_entry_list df_conflict_list = {
  37         .name = NULL,
  38         .next = &df_conflict_list
  39 };
  40
  41 typedef int (*merge_fn_t)(struct cache_entry **src);
  42
  43 static int entcmp(char *name1, int dir1, char *name2, int dir2)
  44 {
  45         int len1 = strlen(name1);
  46         int len2 = strlen(name2);
  47         int len = len1 < len2 ? len1 : len2;
  48         int ret = memcmp(name1, name2, len);
  49         unsigned char c1, c2;
  50         if (ret)
  51                 return ret;
  52         c1 = name1[len];
  53         c2 = name2[len];
  54         if (!c1 && dir1)
  55                 c1 = '/';
  56         if (!c2 && dir2)
  57                 c2 = '/';
  58         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
  59         if (c1 && c2 && !ret)
  60                 ret = len1 - len2;
  61         return ret;
  62 }
  63
  64 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
  65                             const char *base, merge_fn_t fn, int *indpos)
  66 {
  67         int baselen = strlen(base);
  68         int src_size = len + 1;
  69         do {
  70                 int i;
  71                 char *first;
  72                 int firstdir = 0;
  73                 int pathlen;
  74                 unsigned ce_size;
  75                 struct tree_entry_list **subposns;
  76                 struct cache_entry **src;
  77                 int any_files = 0;
  78                 int any_dirs = 0;
  79                 char *cache_name;
  80                 int ce_stage;
  81
  82                 /* Find the first name in the input. */
  83
  84                 first = NULL;
  85                 cache_name = NULL;
  86
  87                 /* Check the cache */
  88                 if (merge && *indpos < active_nr) {
  89                         /* This is a bit tricky: */
  90                         /* If the index has a subdirectory (with
  91                          * contents) as the first name, it'll get a
  92                          * filename like "foo/bar". But that's after
  93                          * "foo", so the entry in trees will get
  94                          * handled first, at which point we'll go into
  95                          * "foo", and deal with "bar" from the index,
  96                          * because the base will be "foo/". The only
  97                          * way we can actually have "foo/bar" first of
  98                          * all the things is if the trees don't
  99                          * contain "foo" at all, in which case we'll
 100                          * handle "foo/bar" without going into the
 101                          * directory, but that's fine (and will return
 102                          * an error anyway, with the added unknown
 103                          * file case.
 104                          */
 105
 106                         cache_name = active_cache[*indpos]->name;
 107                         if (strlen(cache_name) > baselen &&
 108                             !memcmp(cache_name, base, baselen)) {
 109                                 cache_name += baselen;
 110                                 first = cache_name;
 111                         } else {
 112                                 cache_name = NULL;
 113                         }
 114                 }
 115
 116 #if DBRT_DEBUG > 1
 117                 if (first)
 118                         printf("index %s\n", first);
 119 #endif
 120                 for (i = 0; i < len; i++) {
 121                         if (!posns[i] || posns[i] == &df_conflict_list)
 122                                 continue;
 123 #if DBRT_DEBUG > 1
 124                         printf("%d %s\n", i + 1, posns[i]->name);
 125 #endif
 126                         if (!first || entcmp(first, firstdir,
 127                                              posns[i]->name,
 128                                              posns[i]->directory) > 0) {
 129                                 first = posns[i]->name;
 130                                 firstdir = posns[i]->directory;
 131                         }
 132                 }
 133                 /* No name means we're done */
 134                 if (!first)
 135                         return 0;
 136
 137                 pathlen = strlen(first);
 138                 ce_size = cache_entry_size(baselen + pathlen);
 139
 140                 src = xcalloc(src_size, sizeof(struct cache_entry *));
 141
 142                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 143
 144                 if (cache_name && !strcmp(cache_name, first)) {
 145                         any_files = 1;
 146                         src[0] = active_cache[*indpos];
 147                         remove_cache_entry_at(*indpos);
 148                 }
 149
 150                 for (i = 0; i < len; i++) {
 151                         struct cache_entry *ce;
 152
 153                         if (!posns[i] ||
 154                             (posns[i] != &df_conflict_list &&
 155                              strcmp(first, posns[i]->name))) {
 156                                 continue;
 157                         }
 158
 159                         if (posns[i] == &df_conflict_list) {
 160                                 src[i + merge] = &df_conflict_entry;
 161                                 continue;
 162                         }
 163
 164                         if (posns[i]->directory) {
 165                                 any_dirs = 1;
 166                                 parse_tree(posns[i]->item.tree);
 167                                 subposns[i] = posns[i]->item.tree->entries;
 168                                 posns[i] = posns[i]->next;
 169                                 src[i + merge] = &df_conflict_entry;
 170                                 continue;
 171                         }
 172
 173                         if (!merge)
 174                                 ce_stage = 0;
 175                         else if (i + 1 < head_idx)
 176                                 ce_stage = 1;
 177                         else if (i + 1 > head_idx)
 178                                 ce_stage = 3;
 179                         else
 180                                 ce_stage = 2;
 181
 182                         ce = xcalloc(1, ce_size);
 183                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 184                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 185                                                        ce_stage);
 186                         memcpy(ce->name, base, baselen);
 187                         memcpy(ce->name + baselen, first, pathlen + 1);
 188
 189                         any_files = 1;
 190
 191                         memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
 192                         src[i + merge] = ce;
 193                         subposns[i] = &df_conflict_list;
 194                         posns[i] = posns[i]->next;
 195                 }
 196                 if (any_files) {
 197                         if (merge) {
 198                                 int ret;
 199
 200 #if DBRT_DEBUG > 1
 201                                 printf("%s:\n", first);
 202                                 for (i = 0; i < src_size; i++) {
 203                                         printf(" %d ", i);
 204                                         if (src[i])
 205                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 206                                         else
 207                                                 printf("\n");
 208                                 }
 209 #endif
 210                                 ret = fn(src);
 211
 212 #if DBRT_DEBUG > 1
 213                                 printf("Added %d entries\n", ret);
 214 #endif
 215                                 *indpos += ret;
 216                         } else {
 217                                 for (i = 0; i < src_size; i++) {
 218                                         if (src[i]) {
 219                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 220                                         }
 221                                 }
 222                         }
 223                 }
 224                 if (any_dirs) {
 225                         char *newbase = xmalloc(baselen + 2 + pathlen);
 226                         memcpy(newbase, base, baselen);
 227                         memcpy(newbase + baselen, first, pathlen);
 228                         newbase[baselen + pathlen] = '/';
 229                         newbase[baselen + pathlen + 1] = '\0';
 230                         if (unpack_trees_rec(subposns, len, newbase, fn,
 231                                              indpos))
 232                                 return -1;
 233                         free(newbase);
 234                 }
 235                 free(subposns);
 236                 free(src);
 237         } while (1);
 238 }
 239
 240 static void reject_merge(struct cache_entry *ce)
 241 {
 242         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 243             ce->name);
 244 }
 245
 246 /* Unlink the last component and attempt to remove leading
 247  * directories, in case this unlink is the removal of the
 248  * last entry in the directory -- empty directories are removed.
 249  */
 250 static void unlink_entry(char *name)
 251 {
 252         char *cp, *prev;
 253
 254         if (unlink(name))
 255                 return;
 256         prev = NULL;
 257         while (1) {
 258                 int status;
 259                 cp = strrchr(name, '/');
 260                 if (prev)
 261                         *prev = '/';
 262                 if (!cp)
 263                         break;
 264
 265                 *cp = 0;
 266                 status = rmdir(name);
 267                 if (status) {
 268                         *cp = '/';
 269                         break;
 270                 }
 271                 prev = cp;
 272         }
 273 }
 274
 275 static void progress_interval(int signum)
 276 {
 277         progress_update = 1;
 278 }
 279
 280 static void setup_progress_signal(void)
 281 {
 282         struct sigaction sa;
 283         struct itimerval v;
 284
 285         memset(&sa, 0, sizeof(sa));
 286         sa.sa_handler = progress_interval;
 287         sigemptyset(&sa.sa_mask);
 288         sa.sa_flags = SA_RESTART;
 289         sigaction(SIGALRM, &sa, NULL);
 290
 291         v.it_interval.tv_sec = 1;
 292         v.it_interval.tv_usec = 0;
 293         v.it_value = v.it_interval;
 294         setitimer(ITIMER_REAL, &v, NULL);
 295 }
 296
 297 static void check_updates(struct cache_entry **src, int nr)
 298 {
 299         static struct checkout state = {
 300                 .base_dir = "",
 301                 .force = 1,
 302                 .quiet = 1,
 303                 .refresh_cache = 1,
 304         };
 305         unsigned short mask = htons(CE_UPDATE);
 306         unsigned last_percent = 200, cnt = 0, total = 0;
 307
 308         if (update && verbose_update) {
 309                 for (total = cnt = 0; cnt < nr; cnt++) {
 310                         struct cache_entry *ce = src[cnt];
 311                         if (!ce->ce_mode || ce->ce_flags & mask)
 312                                 total++;
 313                 }
 314
 315                 /* Don't bother doing this for very small updates */
 316                 if (total < 250)
 317                         total = 0;
 318
 319                 if (total) {
 320                         fprintf(stderr, "Checking files out...\n");
 321                         setup_progress_signal();
 322                         progress_update = 1;
 323                 }
 324                 cnt = 0;
 325         }
 326
 327         while (nr--) {
 328                 struct cache_entry *ce = *src++;
 329
 330                 if (total) {
 331                         if (!ce->ce_mode || ce->ce_flags & mask) {
 332                                 unsigned percent;
 333                                 cnt++;
 334                                 percent = (cnt * 100) / total;
 335                                 if (percent != last_percent ||
 336                                     progress_update) {
 337                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 338                                                 percent, cnt, total);
 339                                         last_percent = percent;
 340                                 }
 341                         }
 342                 }
 343                 if (!ce->ce_mode) {
 344                         if (update)
 345                                 unlink_entry(ce->name);
 346                         continue;
 347                 }
 348                 if (ce->ce_flags & mask) {
 349                         ce->ce_flags &= ~mask;
 350                         if (update)
 351                                 checkout_entry(ce, &state, NULL);
 352                 }
 353         }
 354         if (total) {
 355                 signal(SIGALRM, SIG_IGN);
 356                 fputc('\n', stderr);
 357         }
 358 }
 359
 360 static int unpack_trees(merge_fn_t fn)
 361 {
 362         int indpos = 0;
 363         unsigned len = object_list_length(trees);
 364         struct tree_entry_list **posns;
 365         int i;
 366         struct object_list *posn = trees;
 367         merge_size = len;
 368
 369         if (len) {
 370                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 371                 for (i = 0; i < len; i++) {
 372                         posns[i] = ((struct tree *) posn->item)->entries;
 373                         posn = posn->next;
 374                 }
 375                 if (unpack_trees_rec(posns, len, prefix ? prefix : "",
 376                                      fn, &indpos))
 377                         return -1;
 378         }
 379
 380         if (trivial_merges_only && nontrivial_merge)
 381                 die("Merge requires file-level merging");
 382
 383         check_updates(active_cache, active_nr);
 384         return 0;
 385 }
 386
 387 static int list_tree(unsigned char *sha1)
 388 {
 389         struct tree *tree = parse_tree_indirect(sha1);
 390         if (!tree)
 391                 return -1;
 392         object_list_append(&tree->object, &trees);
 393         return 0;
 394 }
 395
 396 static int same(struct cache_entry *a, struct cache_entry *b)
 397 {
 398         if (!!a != !!b)
 399                 return 0;
 400         if (!a && !b)
 401                 return 1;
 402         return a->ce_mode == b->ce_mode &&
 403                 !memcmp(a->sha1, b->sha1, 20);
 404 }
 405
 406
 407 /*
 408  * When a CE gets turned into an unmerged entry, we
 409  * want it to be up-to-date
 410  */
 411 static void verify_uptodate(struct cache_entry *ce)
 412 {
 413         struct stat st;
 414
 415         if (index_only || reset)
 416                 return;
 417
 418         if (!lstat(ce->name, &st)) {
 419                 unsigned changed = ce_match_stat(ce, &st, 1);
 420                 if (!changed)
 421                         return;
 422                 errno = 0;
 423         }
 424         if (reset) {
 425                 ce->ce_flags |= htons(CE_UPDATE);
 426                 return;
 427         }
 428         if (errno == ENOENT)
 429                 return;
 430         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 431 }
 432
 433 static void invalidate_ce_path(struct cache_entry *ce)
 434 {
 435         if (ce)
 436                 cache_tree_invalidate_path(active_cache_tree, ce->name);
 437 }
 438
 439 /*
 440  * We do not want to remove or overwrite a working tree file that
 441  * is not tracked.
 442  */
 443 static void verify_absent(const char *path, const char *action)
 444 {
 445         struct stat st;
 446
 447         if (index_only || reset || !update)
 448                 return;
 449         if (!lstat(path, &st))
 450                 die("Untracked working tree file '%s' "
 451                     "would be %s by merge.", path, action);
 452 }
 453
 454 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 455 {
 456         merge->ce_flags |= htons(CE_UPDATE);
 457         if (old) {
 458                 /*
 459                  * See if we can re-use the old CE directly?
 460                  * That way we get the uptodate stat info.
 461                  *
 462                  * This also removes the UPDATE flag on
 463                  * a match.
 464                  */
 465                 if (same(old, merge)) {
 466                         *merge = *old;
 467                 } else {
 468                         verify_uptodate(old);
 469                         invalidate_ce_path(old);
 470                 }
 471         }
 472         else {
 473                 verify_absent(merge->name, "overwritten");
 474                 invalidate_ce_path(merge);
 475         }
 476
 477         merge->ce_flags &= ~htons(CE_STAGEMASK);
 478         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 479         return 1;
 480 }
 481
 482 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 483 {
 484         if (old)
 485                 verify_uptodate(old);
 486         else
 487                 verify_absent(ce->name, "removed");
 488         ce->ce_mode = 0;
 489         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 490         invalidate_ce_path(ce);
 491         return 1;
 492 }
 493
 494 static int keep_entry(struct cache_entry *ce)
 495 {
 496         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 497         return 1;
 498 }
 499
 500 #if DBRT_DEBUG
 501 static void show_stage_entry(FILE *o,
 502                              const char *label, const struct cache_entry *ce)
 503 {
 504         if (!ce)
 505                 fprintf(o, "%s (missing)\n", label);
 506         else
 507                 fprintf(o, "%s%06o %s %d\t%s\n",
 508                         label,
 509                         ntohl(ce->ce_mode),
 510                         sha1_to_hex(ce->sha1),
 511                         ce_stage(ce),
 512                         ce->name);
 513 }
 514 #endif
 515
 516 static int threeway_merge(struct cache_entry **stages)
 517 {
 518         struct cache_entry *index;
 519         struct cache_entry *head;
 520         struct cache_entry *remote = stages[head_idx + 1];
 521         int count;
 522         int head_match = 0;
 523         int remote_match = 0;
 524         const char *path = NULL;
 525
 526         int df_conflict_head = 0;
 527         int df_conflict_remote = 0;
 528
 529         int any_anc_missing = 0;
 530         int no_anc_exists = 1;
 531         int i;
 532
 533         for (i = 1; i < head_idx; i++) {
 534                 if (!stages[i])
 535                         any_anc_missing = 1;
 536                 else {
 537                         if (!path)
 538                                 path = stages[i]->name;
 539                         no_anc_exists = 0;
 540                 }
 541         }
 542
 543         index = stages[0];
 544         head = stages[head_idx];
 545
 546         if (head == &df_conflict_entry) {
 547                 df_conflict_head = 1;
 548                 head = NULL;
 549         }
 550
 551         if (remote == &df_conflict_entry) {
 552                 df_conflict_remote = 1;
 553                 remote = NULL;
 554         }
 555
 556         if (!path && index)
 557                 path = index->name;
 558         if (!path && head)
 559                 path = head->name;
 560         if (!path && remote)
 561                 path = remote->name;
 562
 563         /* First, if there's a #16 situation, note that to prevent #13
 564          * and #14.
 565          */
 566         if (!same(remote, head)) {
 567                 for (i = 1; i < head_idx; i++) {
 568                         if (same(stages[i], head)) {
 569                                 head_match = i;
 570                         }
 571                         if (same(stages[i], remote)) {
 572                                 remote_match = i;
 573                         }
 574                 }
 575         }
 576
 577         /* We start with cases where the index is allowed to match
 578          * something other than the head: #14(ALT) and #2ALT, where it
 579          * is permitted to match the result instead.
 580          */
 581         /* #14, #14ALT, #2ALT */
 582         if (remote && !df_conflict_head && head_match && !remote_match) {
 583                 if (index && !same(index, remote) && !same(index, head))
 584                         reject_merge(index);
 585                 return merged_entry(remote, index);
 586         }
 587         /*
 588          * If we have an entry in the index cache, then we want to
 589          * make sure that it matches head.
 590          */
 591         if (index && !same(index, head)) {
 592                 reject_merge(index);
 593         }
 594
 595         if (head) {
 596                 /* #5ALT, #15 */
 597                 if (same(head, remote))
 598                         return merged_entry(head, index);
 599                 /* #13, #3ALT */
 600                 if (!df_conflict_remote && remote_match && !head_match)
 601                         return merged_entry(head, index);
 602         }
 603
 604         /* #1 */
 605         if (!head && !remote && any_anc_missing)
 606                 return 0;
 607
 608         /* Under the new "aggressive" rule, we resolve mostly trivial
 609          * cases that we historically had git-merge-one-file resolve.
 610          */
 611         if (aggressive) {
 612                 int head_deleted = !head && !df_conflict_head;
 613                 int remote_deleted = !remote && !df_conflict_remote;
 614                 /*
 615                  * Deleted in both.
 616                  * Deleted in one and unchanged in the other.
 617                  */
 618                 if ((head_deleted && remote_deleted) ||
 619                     (head_deleted && remote && remote_match) ||
 620                     (remote_deleted && head && head_match)) {
 621                         if (index)
 622                                 return deleted_entry(index, index);
 623                         else if (path)
 624                                 verify_absent(path, "removed");
 625                         return 0;
 626                 }
 627                 /*
 628                  * Added in both, identically.
 629                  */
 630                 if (no_anc_exists && head && remote && same(head, remote))
 631                         return merged_entry(head, index);
 632
 633         }
 634
 635         /* Below are "no merge" cases, which require that the index be
 636          * up-to-date to avoid the files getting overwritten with
 637          * conflict resolution files.
 638          */
 639         if (index) {
 640                 verify_uptodate(index);
 641         }
 642         else if (path)
 643                 verify_absent(path, "overwritten");
 644
 645         nontrivial_merge = 1;
 646
 647         /* #2, #3, #4, #6, #7, #9, #11. */
 648         count = 0;
 649         if (!head_match || !remote_match) {
 650                 for (i = 1; i < head_idx; i++) {
 651                         if (stages[i]) {
 652                                 keep_entry(stages[i]);
 653                                 count++;
 654                                 break;
 655                         }
 656                 }
 657         }
 658 #if DBRT_DEBUG
 659         else {
 660                 fprintf(stderr, "read-tree: warning #16 detected\n");
 661                 show_stage_entry(stderr, "head   ", stages[head_match]);
 662                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 663         }
 664 #endif
 665         if (head) { count += keep_entry(head); }
 666         if (remote) { count += keep_entry(remote); }
 667         return count;
 668 }
 669
 670 /*
 671  * Two-way merge.
 672  *
 673  * The rule is to "carry forward" what is in the index without losing
 674  * information across a "fast forward", favoring a successful merge
 675  * over a merge failure when it makes sense.  For details of the
 676  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 677  *
 678  */
 679 static int twoway_merge(struct cache_entry **src)
 680 {
 681         struct cache_entry *current = src[0];
 682         struct cache_entry *oldtree = src[1], *newtree = src[2];
 683
 684         if (merge_size != 2)
 685                 return error("Cannot do a twoway merge of %d trees",
 686                              merge_size);
 687
 688         if (current) {
 689                 if ((!oldtree && !newtree) || /* 4 and 5 */
 690                     (!oldtree && newtree &&
 691                      same(current, newtree)) || /* 6 and 7 */
 692                     (oldtree && newtree &&
 693                      same(oldtree, newtree)) || /* 14 and 15 */
 694                     (oldtree && newtree &&
 695                      !same(oldtree, newtree) && /* 18 and 19*/
 696                      same(current, newtree))) {
 697                         return keep_entry(current);
 698                 }
 699                 else if (oldtree && !newtree && same(current, oldtree)) {
 700                         /* 10 or 11 */
 701                         return deleted_entry(oldtree, current);
 702                 }
 703                 else if (oldtree && newtree &&
 704                          same(current, oldtree) && !same(current, newtree)) {
 705                         /* 20 or 21 */
 706                         return merged_entry(newtree, current);
 707                 }
 708                 else {
 709                         /* all other failures */
 710                         if (oldtree)
 711                                 reject_merge(oldtree);
 712                         if (current)
 713                                 reject_merge(current);
 714                         if (newtree)
 715                                 reject_merge(newtree);
 716                         return -1;
 717                 }
 718         }
 719         else if (newtree)
 720                 return merged_entry(newtree, current);
 721         else
 722                 return deleted_entry(oldtree, current);
 723 }
 724
 725 /*
 726  * Bind merge.
 727  *
 728  * Keep the index entries at stage0, collapse stage1 but make sure
 729  * stage0 does not have anything there.
 730  */
 731 static int bind_merge(struct cache_entry **src)
 732 {
 733         struct cache_entry *old = src[0];
 734         struct cache_entry *a = src[1];
 735
 736         if (merge_size != 1)
 737                 return error("Cannot do a bind merge of %d trees\n",
 738                              merge_size);
 739         if (a && old)
 740                 die("Entry '%s' overlaps.  Cannot bind.", a->name);
 741         if (!a)
 742                 return keep_entry(old);
 743         else
 744                 return merged_entry(a, NULL);
 745 }
 746
 747 /*
 748  * One-way merge.
 749  *
 750  * The rule is:
 751  * - take the stat information from stage0, take the data from stage1
 752  */
 753 static int oneway_merge(struct cache_entry **src)
 754 {
 755         struct cache_entry *old = src[0];
 756         struct cache_entry *a = src[1];
 757
 758         if (merge_size != 1)
 759                 return error("Cannot do a oneway merge of %d trees",
 760                              merge_size);
 761
 762         if (!a) {
 763                 invalidate_ce_path(old);
 764                 return deleted_entry(old, old);
 765         }
 766         if (old && same(old, a)) {
 767                 if (reset) {
 768                         struct stat st;
 769                         if (lstat(old->name, &st) ||
 770                             ce_match_stat(old, &st, 1))
 771                                 old->ce_flags |= htons(CE_UPDATE);
 772                 }
 773                 return keep_entry(old);
 774         }
 775         return merged_entry(a, old);
 776 }
 777
 778 static int read_cache_unmerged(void)
 779 {
 780         int i, deleted;
 781         struct cache_entry **dst;
 782
 783         read_cache();
 784         dst = active_cache;
 785         deleted = 0;
 786         for (i = 0; i < active_nr; i++) {
 787                 struct cache_entry *ce = active_cache[i];
 788                 if (ce_stage(ce)) {
 789                         deleted++;
 790                         invalidate_ce_path(ce);
 791                         continue;
 792                 }
 793                 if (deleted)
 794                         *dst = ce;
 795                 dst++;
 796         }
 797         active_nr -= deleted;
 798         return deleted;
 799 }
 800
 801 static void prime_cache_tree_rec(struct cache_tree *it, struct tree *tree)
 802 {
 803         struct tree_entry_list *ent;
 804         int cnt;
 805
 806         memcpy(it->sha1, tree->object.sha1, 20);
 807         for (cnt = 0, ent = tree->entries; ent; ent = ent->next) {
 808                 if (!ent->directory)
 809                         cnt++;
 810                 else {
 811                         struct cache_tree_sub *sub;
 812                         struct tree *subtree = (struct tree *)ent->item.tree;
 813                         if (!subtree->object.parsed)
 814                                 parse_tree(subtree);
 815                         sub = cache_tree_sub(it, ent->name);
 816                         sub->cache_tree = cache_tree();
 817                         prime_cache_tree_rec(sub->cache_tree, subtree);
 818                         cnt += sub->cache_tree->entry_count;
 819                 }
 820         }
 821         it->entry_count = cnt;
 822 }
 823
 824 static void prime_cache_tree(void)
 825 {
 826         struct tree *tree = (struct tree *)trees->item;
 827         if (!tree)
 828                 return;
 829         active_cache_tree = cache_tree();
 830         prime_cache_tree_rec(active_cache_tree, tree);
 831
 832 }
 833
 834 static const char read_tree_usage[] = "git-read-tree (<sha> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <sha1> [<sha2> [<sha3>]])";
 835
 836 static struct cache_file cache_file;
 837
 838 int cmd_read_tree(int argc, const char **argv, char **envp)
 839 {
 840         int i, newfd, stage = 0;
 841         unsigned char sha1[20];
 842         merge_fn_t fn = NULL;
 843
 844         setup_git_directory();
 845         git_config(git_default_config);
 846
 847         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 848         if (newfd < 0)
 849                 die("unable to create new cachefile");
 850
 851         git_config(git_default_config);
 852
 853         merge = 0;
 854         reset = 0;
 855         for (i = 1; i < argc; i++) {
 856                 const char *arg = argv[i];
 857
 858                 /* "-u" means "update", meaning that a merge will update
 859                  * the working tree.
 860                  */
 861                 if (!strcmp(arg, "-u")) {
 862                         update = 1;
 863                         continue;
 864                 }
 865
 866                 if (!strcmp(arg, "-v")) {
 867                         verbose_update = 1;
 868                         continue;
 869                 }
 870
 871                 /* "-i" means "index only", meaning that a merge will
 872                  * not even look at the working tree.
 873                  */
 874                 if (!strcmp(arg, "-i")) {
 875                         index_only = 1;
 876                         continue;
 877                 }
 878
 879                 /* "--prefix=<subdirectory>/" means keep the current index
 880                  *  entries and put the entries from the tree under the
 881                  * given subdirectory.
 882                  */
 883                 if (!strncmp(arg, "--prefix=", 9)) {
 884                         if (stage || merge || prefix)
 885                                 usage(read_tree_usage);
 886                         prefix = arg + 9;
 887                         merge = 1;
 888                         stage = 1;
 889                         if (read_cache_unmerged())
 890                                 die("you need to resolve your current index first");
 891                         continue;
 892                 }
 893
 894                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 895                 if (!strcmp(arg, "--reset")) {
 896                         if (stage || merge || prefix)
 897                                 usage(read_tree_usage);
 898                         reset = 1;
 899                         merge = 1;
 900                         stage = 1;
 901                         read_cache_unmerged();
 902                         continue;
 903                 }
 904
 905                 if (!strcmp(arg, "--trivial")) {
 906                         trivial_merges_only = 1;
 907                         continue;
 908                 }
 909
 910                 if (!strcmp(arg, "--aggressive")) {
 911                         aggressive = 1;
 912                         continue;
 913                 }
 914
 915                 /* "-m" stands for "merge", meaning we start in stage 1 */
 916                 if (!strcmp(arg, "-m")) {
 917                         if (stage || merge || prefix)
 918                                 usage(read_tree_usage);
 919                         if (read_cache_unmerged())
 920                                 die("you need to resolve your current index first");
 921                         stage = 1;
 922                         merge = 1;
 923                         continue;
 924                 }
 925
 926                 /* using -u and -i at the same time makes no sense */
 927                 if (1 < index_only + update)
 928                         usage(read_tree_usage);
 929
 930                 if (get_sha1(arg, sha1))
 931                         die("Not a valid object name %s", arg);
 932                 if (list_tree(sha1) < 0)
 933                         die("failed to unpack tree object %s", arg);
 934                 stage++;
 935         }
 936         if ((update||index_only) && !merge)
 937                 usage(read_tree_usage);
 938
 939         if (prefix) {
 940                 int pfxlen = strlen(prefix);
 941                 int pos;
 942                 if (prefix[pfxlen-1] != '/')
 943                         die("prefix must end with /");
 944                 if (stage != 2)
 945                         die("binding merge takes only one tree");
 946                 pos = cache_name_pos(prefix, pfxlen);
 947                 if (0 <= pos)
 948                         die("corrupt index file");
 949                 pos = -pos-1;
 950                 if (pos < active_nr &&
 951                     !strncmp(active_cache[pos]->name, prefix, pfxlen))
 952                         die("subdirectory '%s' already exists.", prefix);
 953                 pos = cache_name_pos(prefix, pfxlen-1);
 954                 if (0 <= pos)
 955                         die("file '%.*s' already exists.", pfxlen-1, prefix);
 956         }
 957
 958         if (merge) {
 959                 if (stage < 2)
 960                         die("just how do you expect me to merge %d trees?", stage-1);
 961                 switch (stage - 1) {
 962                 case 1:
 963                         fn = prefix ? bind_merge : oneway_merge;
 964                         break;
 965                 case 2:
 966                         fn = twoway_merge;
 967                         break;
 968                 case 3:
 969                 default:
 970                         fn = threeway_merge;
 971                         cache_tree_free(&active_cache_tree);
 972                         break;
 973                 }
 974
 975                 if (stage - 1 >= 3)
 976                         head_idx = stage - 2;
 977                 else
 978                         head_idx = 1;
 979         }
 980
 981         unpack_trees(fn);
 982
 983         /*
 984          * When reading only one tree (either the most basic form,
 985          * "-m ent" or "--reset ent" form), we can obtain a fully
 986          * valid cache-tree because the index must match exactly
 987          * what came from the tree.
 988          */
 989         if (trees && trees->item && (!merge || (stage == 2))) {
 990                 cache_tree_free(&active_cache_tree);
 991                 prime_cache_tree();
 992         }
 993
 994         if (write_cache(newfd, active_cache, active_nr) ||
 995             commit_index_file(&cache_file))
 996                 die("unable to write new index file");
 997         return 0;
 998 }