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