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 <sys/time.h>
  13 #include <signal.h>
  14 #include "builtin.h"
  15
  16 static int reset = 0;
  17 static int merge = 0;
  18 static int update = 0;
  19 static int index_only = 0;
  20 static int nontrivial_merge = 0;
  21 static int trivial_merges_only = 0;
  22 static int aggressive = 0;
  23 static int verbose_update = 0;
  24 static volatile int progress_update = 0;
  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(const char *name1, int dir1, const 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                 const 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                                 struct tree *tree = lookup_tree(posns[i]->sha1);
 164                                 any_dirs = 1;
 165                                 parse_tree(tree);
 166                                 subposns[i] = create_tree_entry_list(tree);
 167                                 posns[i] = posns[i]->next;
 168                                 src[i + merge] = &df_conflict_entry;
 169                                 continue;
 170                         }
 171
 172                         if (!merge)
 173                                 ce_stage = 0;
 174                         else if (i + 1 < head_idx)
 175                                 ce_stage = 1;
 176                         else if (i + 1 > head_idx)
 177                                 ce_stage = 3;
 178                         else
 179                                 ce_stage = 2;
 180
 181                         ce = xcalloc(1, ce_size);
 182                         ce->ce_mode = create_ce_mode(posns[i]->mode);
 183                         ce->ce_flags = create_ce_flags(baselen + pathlen,
 184                                                        ce_stage);
 185                         memcpy(ce->name, base, baselen);
 186                         memcpy(ce->name + baselen, first, pathlen + 1);
 187
 188                         any_files = 1;
 189
 190                         memcpy(ce->sha1, posns[i]->sha1, 20);
 191                         src[i + merge] = ce;
 192                         subposns[i] = &df_conflict_list;
 193                         posns[i] = posns[i]->next;
 194                 }
 195                 if (any_files) {
 196                         if (merge) {
 197                                 int ret;
 198
 199 #if DBRT_DEBUG > 1
 200                                 printf("%s:\n", first);
 201                                 for (i = 0; i < src_size; i++) {
 202                                         printf(" %d ", i);
 203                                         if (src[i])
 204                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
 205                                         else
 206                                                 printf("\n");
 207                                 }
 208 #endif
 209                                 ret = fn(src);
 210
 211 #if DBRT_DEBUG > 1
 212                                 printf("Added %d entries\n", ret);
 213 #endif
 214                                 *indpos += ret;
 215                         } else {
 216                                 for (i = 0; i < src_size; i++) {
 217                                         if (src[i]) {
 218                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
 219                                         }
 220                                 }
 221                         }
 222                 }
 223                 if (any_dirs) {
 224                         char *newbase = xmalloc(baselen + 2 + pathlen);
 225                         memcpy(newbase, base, baselen);
 226                         memcpy(newbase + baselen, first, pathlen);
 227                         newbase[baselen + pathlen] = '/';
 228                         newbase[baselen + pathlen + 1] = '\0';
 229                         if (unpack_trees_rec(subposns, len, newbase, fn,
 230                                              indpos))
 231                                 return -1;
 232                         free(newbase);
 233                 }
 234                 free(subposns);
 235                 free(src);
 236         } while (1);
 237 }
 238
 239 static void reject_merge(struct cache_entry *ce)
 240 {
 241         die("Entry '%s' would be overwritten by merge. Cannot merge.",
 242             ce->name);
 243 }
 244
 245 /* Unlink the last component and attempt to remove leading
 246  * directories, in case this unlink is the removal of the
 247  * last entry in the directory -- empty directories are removed.
 248  */
 249 static void unlink_entry(char *name)
 250 {
 251         char *cp, *prev;
 252
 253         if (unlink(name))
 254                 return;
 255         prev = NULL;
 256         while (1) {
 257                 int status;
 258                 cp = strrchr(name, '/');
 259                 if (prev)
 260                         *prev = '/';
 261                 if (!cp)
 262                         break;
 263
 264                 *cp = 0;
 265                 status = rmdir(name);
 266                 if (status) {
 267                         *cp = '/';
 268                         break;
 269                 }
 270                 prev = cp;
 271         }
 272 }
 273
 274 static void progress_interval(int signum)
 275 {
 276         progress_update = 1;
 277 }
 278
 279 static void setup_progress_signal(void)
 280 {
 281         struct sigaction sa;
 282         struct itimerval v;
 283
 284         memset(&sa, 0, sizeof(sa));
 285         sa.sa_handler = progress_interval;
 286         sigemptyset(&sa.sa_mask);
 287         sa.sa_flags = SA_RESTART;
 288         sigaction(SIGALRM, &sa, NULL);
 289
 290         v.it_interval.tv_sec = 1;
 291         v.it_interval.tv_usec = 0;
 292         v.it_value = v.it_interval;
 293         setitimer(ITIMER_REAL, &v, NULL);
 294 }
 295
 296 static void check_updates(struct cache_entry **src, int nr)
 297 {
 298         static struct checkout state = {
 299                 .base_dir = "",
 300                 .force = 1,
 301                 .quiet = 1,
 302                 .refresh_cache = 1,
 303         };
 304         unsigned short mask = htons(CE_UPDATE);
 305         unsigned last_percent = 200, cnt = 0, total = 0;
 306
 307         if (update && verbose_update) {
 308                 for (total = cnt = 0; cnt < nr; cnt++) {
 309                         struct cache_entry *ce = src[cnt];
 310                         if (!ce->ce_mode || ce->ce_flags & mask)
 311                                 total++;
 312                 }
 313
 314                 /* Don't bother doing this for very small updates */
 315                 if (total < 250)
 316                         total = 0;
 317
 318                 if (total) {
 319                         fprintf(stderr, "Checking files out...\n");
 320                         setup_progress_signal();
 321                         progress_update = 1;
 322                 }
 323                 cnt = 0;
 324         }
 325
 326         while (nr--) {
 327                 struct cache_entry *ce = *src++;
 328
 329                 if (total) {
 330                         if (!ce->ce_mode || ce->ce_flags & mask) {
 331                                 unsigned percent;
 332                                 cnt++;
 333                                 percent = (cnt * 100) / total;
 334                                 if (percent != last_percent ||
 335                                     progress_update) {
 336                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
 337                                                 percent, cnt, total);
 338                                         last_percent = percent;
 339                                 }
 340                         }
 341                 }
 342                 if (!ce->ce_mode) {
 343                         if (update)
 344                                 unlink_entry(ce->name);
 345                         continue;
 346                 }
 347                 if (ce->ce_flags & mask) {
 348                         ce->ce_flags &= ~mask;
 349                         if (update)
 350                                 checkout_entry(ce, &state, NULL);
 351                 }
 352         }
 353         if (total) {
 354                 signal(SIGALRM, SIG_IGN);
 355                 fputc('\n', stderr);
 356         }
 357 }
 358
 359 static int unpack_trees(merge_fn_t fn)
 360 {
 361         int indpos = 0;
 362         unsigned len = object_list_length(trees);
 363         struct tree_entry_list **posns;
 364         int i;
 365         struct object_list *posn = trees;
 366         merge_size = len;
 367
 368         if (len) {
 369                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
 370                 for (i = 0; i < len; i++) {
 371                         posns[i] = create_tree_entry_list((struct tree *) posn->item);
 372                         posn = posn->next;
 373                 }
 374                 if (unpack_trees_rec(posns, len, "", 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 || reset)
 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 (reset) {
 423                 ce->ce_flags |= htons(CE_UPDATE);
 424                 return;
 425         }
 426         if (errno == ENOENT)
 427                 return;
 428         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 429 }
 430
 431 /*
 432  * We do not want to remove or overwrite a working tree file that
 433  * is not tracked.
 434  */
 435 static void verify_absent(const char *path, const char *action)
 436 {
 437         struct stat st;
 438
 439         if (index_only || reset || !update)
 440                 return;
 441         if (!lstat(path, &st))
 442                 die("Untracked working tree file '%s' "
 443                     "would be %s by merge.", path, action);
 444 }
 445
 446 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
 447 {
 448         merge->ce_flags |= htons(CE_UPDATE);
 449         if (old) {
 450                 /*
 451                  * See if we can re-use the old CE directly?
 452                  * That way we get the uptodate stat info.
 453                  *
 454                  * This also removes the UPDATE flag on
 455                  * a match.
 456                  */
 457                 if (same(old, merge)) {
 458                         *merge = *old;
 459                 } else {
 460                         verify_uptodate(old);
 461                 }
 462         }
 463         else
 464                 verify_absent(merge->name, "overwritten");
 465
 466         merge->ce_flags &= ~htons(CE_STAGEMASK);
 467         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
 468         return 1;
 469 }
 470
 471 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 472 {
 473         if (old)
 474                 verify_uptodate(old);
 475         else
 476                 verify_absent(ce->name, "removed");
 477         ce->ce_mode = 0;
 478         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 479         return 1;
 480 }
 481
 482 static int keep_entry(struct cache_entry *ce)
 483 {
 484         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
 485         return 1;
 486 }
 487
 488 #if DBRT_DEBUG
 489 static void show_stage_entry(FILE *o,
 490                              const char *label, const struct cache_entry *ce)
 491 {
 492         if (!ce)
 493                 fprintf(o, "%s (missing)\n", label);
 494         else
 495                 fprintf(o, "%s%06o %s %d\t%s\n",
 496                         label,
 497                         ntohl(ce->ce_mode),
 498                         sha1_to_hex(ce->sha1),
 499                         ce_stage(ce),
 500                         ce->name);
 501 }
 502 #endif
 503
 504 static int threeway_merge(struct cache_entry **stages)
 505 {
 506         struct cache_entry *index;
 507         struct cache_entry *head;
 508         struct cache_entry *remote = stages[head_idx + 1];
 509         int count;
 510         int head_match = 0;
 511         int remote_match = 0;
 512         const char *path = NULL;
 513
 514         int df_conflict_head = 0;
 515         int df_conflict_remote = 0;
 516
 517         int any_anc_missing = 0;
 518         int no_anc_exists = 1;
 519         int i;
 520
 521         for (i = 1; i < head_idx; i++) {
 522                 if (!stages[i])
 523                         any_anc_missing = 1;
 524                 else {
 525                         if (!path)
 526                                 path = stages[i]->name;
 527                         no_anc_exists = 0;
 528                 }
 529         }
 530
 531         index = stages[0];
 532         head = stages[head_idx];
 533
 534         if (head == &df_conflict_entry) {
 535                 df_conflict_head = 1;
 536                 head = NULL;
 537         }
 538
 539         if (remote == &df_conflict_entry) {
 540                 df_conflict_remote = 1;
 541                 remote = NULL;
 542         }
 543
 544         if (!path && index)
 545                 path = index->name;
 546         if (!path && head)
 547                 path = head->name;
 548         if (!path && remote)
 549                 path = remote->name;
 550
 551         /* First, if there's a #16 situation, note that to prevent #13
 552          * and #14.
 553          */
 554         if (!same(remote, head)) {
 555                 for (i = 1; i < head_idx; i++) {
 556                         if (same(stages[i], head)) {
 557                                 head_match = i;
 558                         }
 559                         if (same(stages[i], remote)) {
 560                                 remote_match = i;
 561                         }
 562                 }
 563         }
 564
 565         /* We start with cases where the index is allowed to match
 566          * something other than the head: #14(ALT) and #2ALT, where it
 567          * is permitted to match the result instead.
 568          */
 569         /* #14, #14ALT, #2ALT */
 570         if (remote && !df_conflict_head && head_match && !remote_match) {
 571                 if (index && !same(index, remote) && !same(index, head))
 572                         reject_merge(index);
 573                 return merged_entry(remote, index);
 574         }
 575         /*
 576          * If we have an entry in the index cache, then we want to
 577          * make sure that it matches head.
 578          */
 579         if (index && !same(index, head)) {
 580                 reject_merge(index);
 581         }
 582
 583         if (head) {
 584                 /* #5ALT, #15 */
 585                 if (same(head, remote))
 586                         return merged_entry(head, index);
 587                 /* #13, #3ALT */
 588                 if (!df_conflict_remote && remote_match && !head_match)
 589                         return merged_entry(head, index);
 590         }
 591
 592         /* #1 */
 593         if (!head && !remote && any_anc_missing)
 594                 return 0;
 595
 596         /* Under the new "aggressive" rule, we resolve mostly trivial
 597          * cases that we historically had git-merge-one-file resolve.
 598          */
 599         if (aggressive) {
 600                 int head_deleted = !head && !df_conflict_head;
 601                 int remote_deleted = !remote && !df_conflict_remote;
 602                 /*
 603                  * Deleted in both.
 604                  * Deleted in one and unchanged in the other.
 605                  */
 606                 if ((head_deleted && remote_deleted) ||
 607                     (head_deleted && remote && remote_match) ||
 608                     (remote_deleted && head && head_match)) {
 609                         if (index)
 610                                 return deleted_entry(index, index);
 611                         else if (path)
 612                                 verify_absent(path, "removed");
 613                         return 0;
 614                 }
 615                 /*
 616                  * Added in both, identically.
 617                  */
 618                 if (no_anc_exists && head && remote && same(head, remote))
 619                         return merged_entry(head, index);
 620
 621         }
 622
 623         /* Below are "no merge" cases, which require that the index be
 624          * up-to-date to avoid the files getting overwritten with
 625          * conflict resolution files.
 626          */
 627         if (index) {
 628                 verify_uptodate(index);
 629         }
 630         else if (path)
 631                 verify_absent(path, "overwritten");
 632
 633         nontrivial_merge = 1;
 634
 635         /* #2, #3, #4, #6, #7, #9, #11. */
 636         count = 0;
 637         if (!head_match || !remote_match) {
 638                 for (i = 1; i < head_idx; i++) {
 639                         if (stages[i]) {
 640                                 keep_entry(stages[i]);
 641                                 count++;
 642                                 break;
 643                         }
 644                 }
 645         }
 646 #if DBRT_DEBUG
 647         else {
 648                 fprintf(stderr, "read-tree: warning #16 detected\n");
 649                 show_stage_entry(stderr, "head   ", stages[head_match]);
 650                 show_stage_entry(stderr, "remote ", stages[remote_match]);
 651         }
 652 #endif
 653         if (head) { count += keep_entry(head); }
 654         if (remote) { count += keep_entry(remote); }
 655         return count;
 656 }
 657
 658 /*
 659  * Two-way merge.
 660  *
 661  * The rule is to "carry forward" what is in the index without losing
 662  * information across a "fast forward", favoring a successful merge
 663  * over a merge failure when it makes sense.  For details of the
 664  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 665  *
 666  */
 667 static int twoway_merge(struct cache_entry **src)
 668 {
 669         struct cache_entry *current = src[0];
 670         struct cache_entry *oldtree = src[1], *newtree = src[2];
 671
 672         if (merge_size != 2)
 673                 return error("Cannot do a twoway merge of %d trees",
 674                              merge_size);
 675
 676         if (current) {
 677                 if ((!oldtree && !newtree) || /* 4 and 5 */
 678                     (!oldtree && newtree &&
 679                      same(current, newtree)) || /* 6 and 7 */
 680                     (oldtree && newtree &&
 681                      same(oldtree, newtree)) || /* 14 and 15 */
 682                     (oldtree && newtree &&
 683                      !same(oldtree, newtree) && /* 18 and 19*/
 684                      same(current, newtree))) {
 685                         return keep_entry(current);
 686                 }
 687                 else if (oldtree && !newtree && same(current, oldtree)) {
 688                         /* 10 or 11 */
 689                         return deleted_entry(oldtree, current);
 690                 }
 691                 else if (oldtree && newtree &&
 692                          same(current, oldtree) && !same(current, newtree)) {
 693                         /* 20 or 21 */
 694                         return merged_entry(newtree, current);
 695                 }
 696                 else {
 697                         /* all other failures */
 698                         if (oldtree)
 699                                 reject_merge(oldtree);
 700                         if (current)
 701                                 reject_merge(current);
 702                         if (newtree)
 703                                 reject_merge(newtree);
 704                         return -1;
 705                 }
 706         }
 707         else if (newtree)
 708                 return merged_entry(newtree, current);
 709         else
 710                 return deleted_entry(oldtree, current);
 711 }
 712
 713 /*
 714  * One-way merge.
 715  *
 716  * The rule is:
 717  * - take the stat information from stage0, take the data from stage1
 718  */
 719 static int oneway_merge(struct cache_entry **src)
 720 {
 721         struct cache_entry *old = src[0];
 722         struct cache_entry *a = src[1];
 723
 724         if (merge_size != 1)
 725                 return error("Cannot do a oneway merge of %d trees",
 726                              merge_size);
 727
 728         if (!a)
 729                 return deleted_entry(old, old);
 730         if (old && same(old, a)) {
 731                 if (reset) {
 732                         struct stat st;
 733                         if (lstat(old->name, &st) ||
 734                             ce_match_stat(old, &st, 1))
 735                                 old->ce_flags |= htons(CE_UPDATE);
 736                 }
 737                 return keep_entry(old);
 738         }
 739         return merged_entry(a, old);
 740 }
 741
 742 static int read_cache_unmerged(void)
 743 {
 744         int i, deleted;
 745         struct cache_entry **dst;
 746
 747         read_cache();
 748         dst = active_cache;
 749         deleted = 0;
 750         for (i = 0; i < active_nr; i++) {
 751                 struct cache_entry *ce = active_cache[i];
 752                 if (ce_stage(ce)) {
 753                         deleted++;
 754                         continue;
 755                 }
 756                 if (deleted)
 757                         *dst = ce;
 758                 dst++;
 759         }
 760         active_nr -= deleted;
 761         return deleted;
 762 }
 763
 764 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
 765
 766 static struct cache_file cache_file;
 767
 768 int cmd_read_tree(int argc, const char **argv, char **envp)
 769 {
 770         int i, newfd, stage = 0;
 771         unsigned char sha1[20];
 772         merge_fn_t fn = NULL;
 773
 774         setup_git_directory();
 775         git_config(git_default_config);
 776
 777         newfd = hold_index_file_for_update(&cache_file, get_index_file());
 778         if (newfd < 0)
 779                 die("unable to create new cachefile");
 780
 781         git_config(git_default_config);
 782
 783         merge = 0;
 784         reset = 0;
 785         for (i = 1; i < argc; i++) {
 786                 const char *arg = argv[i];
 787
 788                 /* "-u" means "update", meaning that a merge will update
 789                  * the working tree.
 790                  */
 791                 if (!strcmp(arg, "-u")) {
 792                         update = 1;
 793                         continue;
 794                 }
 795
 796                 if (!strcmp(arg, "-v")) {
 797                         verbose_update = 1;
 798                         continue;
 799                 }
 800
 801                 /* "-i" means "index only", meaning that a merge will
 802                  * not even look at the working tree.
 803                  */
 804                 if (!strcmp(arg, "-i")) {
 805                         index_only = 1;
 806                         continue;
 807                 }
 808
 809                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
 810                 if (!strcmp(arg, "--reset")) {
 811                         if (stage || merge)
 812                                 usage(read_tree_usage);
 813                         reset = 1;
 814                         merge = 1;
 815                         stage = 1;
 816                         read_cache_unmerged();
 817                         continue;
 818                 }
 819
 820                 if (!strcmp(arg, "--trivial")) {
 821                         trivial_merges_only = 1;
 822                         continue;
 823                 }
 824
 825                 if (!strcmp(arg, "--aggressive")) {
 826                         aggressive = 1;
 827                         continue;
 828                 }
 829
 830                 /* "-m" stands for "merge", meaning we start in stage 1 */
 831                 if (!strcmp(arg, "-m")) {
 832                         if (stage || merge)
 833                                 usage(read_tree_usage);
 834                         if (read_cache_unmerged())
 835                                 die("you need to resolve your current index first");
 836                         stage = 1;
 837                         merge = 1;
 838                         continue;
 839                 }
 840
 841                 /* using -u and -i at the same time makes no sense */
 842                 if (1 < index_only + update)
 843                         usage(read_tree_usage);
 844
 845                 if (get_sha1(arg, sha1))
 846                         die("Not a valid object name %s", arg);
 847                 if (list_tree(sha1) < 0)
 848                         die("failed to unpack tree object %s", arg);
 849                 stage++;
 850         }
 851         if ((update||index_only) && !merge)
 852                 usage(read_tree_usage);
 853
 854         if (merge) {
 855                 if (stage < 2)
 856                         die("just how do you expect me to merge %d trees?", stage-1);
 857                 switch (stage - 1) {
 858                 case 1:
 859                         fn = oneway_merge;
 860                         break;
 861                 case 2:
 862                         fn = twoway_merge;
 863                         break;
 864                 case 3:
 865                         fn = threeway_merge;
 866                         break;
 867                 default:
 868                         fn = threeway_merge;
 869                         break;
 870                 }
 871
 872                 if (stage - 1 >= 3)
 873                         head_idx = stage - 2;
 874                 else
 875                         head_idx = 1;
 876         }
 877
 878         unpack_trees(fn);
 879         if (write_cache(newfd, active_cache, active_nr) ||
 880             commit_index_file(&cache_file))
 881                 die("unable to write new index file");
 882         return 0;
 883 }