shallow.c

   1 #include "cache.h"
   2 #include "tempfile.h"
   3 #include "lockfile.h"
   4 #include "commit.h"
   5 #include "tag.h"
   6 #include "pkt-line.h"
   7 #include "remote.h"
   8 #include "refs.h"
   9 #include "sha1-array.h"
  10 #include "diff.h"
  11 #include "revision.h"
  12 #include "commit-slab.h"
  13 #include "sigchain.h"
  14
  15 static int is_shallow = -1;
  16 static struct stat_validity shallow_stat;
  17 static char *alternate_shallow_file;
  18
  19 void set_alternate_shallow_file(const char *path, int override)
  20 {
  21         if (is_shallow != -1)
  22                 die("BUG: is_repository_shallow must not be called before set_alternate_shallow_file");
  23         if (alternate_shallow_file && !override)
  24                 return;
  25         free(alternate_shallow_file);
  26         alternate_shallow_file = xstrdup_or_null(path);
  27 }
  28
  29 int register_shallow(const unsigned char *sha1)
  30 {
  31         struct commit_graft *graft =
  32                 xmalloc(sizeof(struct commit_graft));
  33         struct commit *commit = lookup_commit(sha1);
  34
  35         hashcpy(graft->oid.hash, sha1);
  36         graft->nr_parent = -1;
  37         if (commit && commit->object.parsed)
  38                 commit->parents = NULL;
  39         return register_commit_graft(graft, 0);
  40 }
  41
  42 int is_repository_shallow(void)
  43 {
  44         FILE *fp;
  45         char buf[1024];
  46         const char *path = alternate_shallow_file;
  47
  48         if (is_shallow >= 0)
  49                 return is_shallow;
  50
  51         if (!path)
  52                 path = git_path_shallow();
  53         /*
  54          * fetch-pack sets '--shallow-file ""' as an indicator that no
  55          * shallow file should be used. We could just open it and it
  56          * will likely fail. But let's do an explicit check instead.
  57          */
  58         if (!*path || (fp = fopen(path, "r")) == NULL) {
  59                 stat_validity_clear(&shallow_stat);
  60                 is_shallow = 0;
  61                 return is_shallow;
  62         }
  63         stat_validity_update(&shallow_stat, fileno(fp));
  64         is_shallow = 1;
  65
  66         while (fgets(buf, sizeof(buf), fp)) {
  67                 unsigned char sha1[20];
  68                 if (get_sha1_hex(buf, sha1))
  69                         die("bad shallow line: %s", buf);
  70                 register_shallow(sha1);
  71         }
  72         fclose(fp);
  73         return is_shallow;
  74 }
  75
  76 struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
  77                 int shallow_flag, int not_shallow_flag)
  78 {
  79         int i = 0, cur_depth = 0;
  80         struct commit_list *result = NULL;
  81         struct object_array stack = OBJECT_ARRAY_INIT;
  82         struct commit *commit = NULL;
  83         struct commit_graft *graft;
  84
  85         while (commit || i < heads->nr || stack.nr) {
  86                 struct commit_list *p;
  87                 if (!commit) {
  88                         if (i < heads->nr) {
  89                                 commit = (struct commit *)
  90                                         deref_tag(heads->objects[i++].item, NULL, 0);
  91                                 if (!commit || commit->object.type != OBJ_COMMIT) {
  92                                         commit = NULL;
  93                                         continue;
  94                                 }
  95                                 if (!commit->util)
  96                                         commit->util = xmalloc(sizeof(int));
  97                                 *(int *)commit->util = 0;
  98                                 cur_depth = 0;
  99                         } else {
 100                                 commit = (struct commit *)
 101                                         stack.objects[--stack.nr].item;
 102                                 cur_depth = *(int *)commit->util;
 103                         }
 104                 }
 105                 parse_commit_or_die(commit);
 106                 cur_depth++;
 107                 if ((depth != INFINITE_DEPTH && cur_depth >= depth) ||
 108                     (is_repository_shallow() && !commit->parents &&
 109                      (graft = lookup_commit_graft(commit->object.sha1)) != NULL &&
 110                      graft->nr_parent < 0)) {
 111                         commit_list_insert(commit, &result);
 112                         commit->object.flags |= shallow_flag;
 113                         commit = NULL;
 114                         continue;
 115                 }
 116                 commit->object.flags |= not_shallow_flag;
 117                 for (p = commit->parents, commit = NULL; p; p = p->next) {
 118                         if (!p->item->util) {
 119                                 int *pointer = xmalloc(sizeof(int));
 120                                 p->item->util = pointer;
 121                                 *pointer =  cur_depth;
 122                         } else {
 123                                 int *pointer = p->item->util;
 124                                 if (cur_depth >= *pointer)
 125                                         continue;
 126                                 *pointer = cur_depth;
 127                         }
 128                         if (p->next)
 129                                 add_object_array(&p->item->object,
 130                                                 NULL, &stack);
 131                         else {
 132                                 commit = p->item;
 133                                 cur_depth = *(int *)commit->util;
 134                         }
 135                 }
 136         }
 137
 138         return result;
 139 }
 140
 141 static void check_shallow_file_for_update(void)
 142 {
 143         if (is_shallow == -1)
 144                 die("BUG: shallow must be initialized by now");
 145
 146         if (!stat_validity_check(&shallow_stat, git_path_shallow()))
 147                 die("shallow file has changed since we read it");
 148 }
 149
 150 #define SEEN_ONLY 1
 151 #define VERBOSE   2
 152
 153 struct write_shallow_data {
 154         struct strbuf *out;
 155         int use_pack_protocol;
 156         int count;
 157         unsigned flags;
 158 };
 159
 160 static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 161 {
 162         struct write_shallow_data *data = cb_data;
 163         const char *hex = oid_to_hex(&graft->oid);
 164         if (graft->nr_parent != -1)
 165                 return 0;
 166         if (data->flags & SEEN_ONLY) {
 167                 struct commit *c = lookup_commit(graft->oid.hash);
 168                 if (!c || !(c->object.flags & SEEN)) {
 169                         if (data->flags & VERBOSE)
 170                                 printf("Removing %s from .git/shallow\n",
 171                                        sha1_to_hex(c->object.sha1));
 172                         return 0;
 173                 }
 174         }
 175         data->count++;
 176         if (data->use_pack_protocol)
 177                 packet_buf_write(data->out, "shallow %s", hex);
 178         else {
 179                 strbuf_addstr(data->out, hex);
 180                 strbuf_addch(data->out, '\n');
 181         }
 182         return 0;
 183 }
 184
 185 static int write_shallow_commits_1(struct strbuf *out, int use_pack_protocol,
 186                                    const struct sha1_array *extra,
 187                                    unsigned flags)
 188 {
 189         struct write_shallow_data data;
 190         int i;
 191         data.out = out;
 192         data.use_pack_protocol = use_pack_protocol;
 193         data.count = 0;
 194         data.flags = flags;
 195         for_each_commit_graft(write_one_shallow, &data);
 196         if (!extra)
 197                 return data.count;
 198         for (i = 0; i < extra->nr; i++) {
 199                 strbuf_addstr(out, sha1_to_hex(extra->sha1[i]));
 200                 strbuf_addch(out, '\n');
 201                 data.count++;
 202         }
 203         return data.count;
 204 }
 205
 206 int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 207                           const struct sha1_array *extra)
 208 {
 209         return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
 210 }
 211
 212 static struct tempfile temporary_shallow;
 213
 214 const char *setup_temporary_shallow(const struct sha1_array *extra)
 215 {
 216         struct strbuf sb = STRBUF_INIT;
 217         int fd;
 218
 219         if (write_shallow_commits(&sb, 0, extra)) {
 220                 fd = xmks_tempfile(&temporary_shallow, git_path("shallow_XXXXXX"));
 221
 222                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 223                         die_errno("failed to write to %s",
 224                                   get_tempfile_path(&temporary_shallow));
 225                 close_tempfile(&temporary_shallow);
 226                 strbuf_release(&sb);
 227                 return get_tempfile_path(&temporary_shallow);
 228         }
 229         /*
 230          * is_repository_shallow() sees empty string as "no shallow
 231          * file".
 232          */
 233         return get_tempfile_path(&temporary_shallow);
 234 }
 235
 236 void setup_alternate_shallow(struct lock_file *shallow_lock,
 237                              const char **alternate_shallow_file,
 238                              const struct sha1_array *extra)
 239 {
 240         struct strbuf sb = STRBUF_INIT;
 241         int fd;
 242
 243         fd = hold_lock_file_for_update(shallow_lock, git_path_shallow(),
 244                                        LOCK_DIE_ON_ERROR);
 245         check_shallow_file_for_update();
 246         if (write_shallow_commits(&sb, 0, extra)) {
 247                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 248                         die_errno("failed to write to %s",
 249                                   get_lock_file_path(shallow_lock));
 250                 *alternate_shallow_file = get_lock_file_path(shallow_lock);
 251         } else
 252                 /*
 253                  * is_repository_shallow() sees empty string as "no
 254                  * shallow file".
 255                  */
 256                 *alternate_shallow_file = "";
 257         strbuf_release(&sb);
 258 }
 259
 260 static int advertise_shallow_grafts_cb(const struct commit_graft *graft, void *cb)
 261 {
 262         int fd = *(int *)cb;
 263         if (graft->nr_parent == -1)
 264                 packet_write(fd, "shallow %s\n", oid_to_hex(&graft->oid));
 265         return 0;
 266 }
 267
 268 void advertise_shallow_grafts(int fd)
 269 {
 270         if (!is_repository_shallow())
 271                 return;
 272         for_each_commit_graft(advertise_shallow_grafts_cb, &fd);
 273 }
 274
 275 /*
 276  * mark_reachable_objects() should have been run prior to this and all
 277  * reachable commits marked as "SEEN".
 278  */
 279 void prune_shallow(int show_only)
 280 {
 281         static struct lock_file shallow_lock;
 282         struct strbuf sb = STRBUF_INIT;
 283         int fd;
 284
 285         if (show_only) {
 286                 write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY | VERBOSE);
 287                 strbuf_release(&sb);
 288                 return;
 289         }
 290         fd = hold_lock_file_for_update(&shallow_lock, git_path_shallow(),
 291                                        LOCK_DIE_ON_ERROR);
 292         check_shallow_file_for_update();
 293         if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
 294                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 295                         die_errno("failed to write to %s",
 296                                   get_lock_file_path(&shallow_lock));
 297                 commit_lock_file(&shallow_lock);
 298         } else {
 299                 unlink(git_path_shallow());
 300                 rollback_lock_file(&shallow_lock);
 301         }
 302         strbuf_release(&sb);
 303 }
 304
 305 struct trace_key trace_shallow = TRACE_KEY_INIT(SHALLOW);
 306
 307 /*
 308  * Step 1, split sender shallow commits into "ours" and "theirs"
 309  * Step 2, clean "ours" based on .git/shallow
 310  */
 311 void prepare_shallow_info(struct shallow_info *info, struct sha1_array *sa)
 312 {
 313         int i;
 314         trace_printf_key(&trace_shallow, "shallow: prepare_shallow_info\n");
 315         memset(info, 0, sizeof(*info));
 316         info->shallow = sa;
 317         if (!sa)
 318                 return;
 319         info->ours = xmalloc(sizeof(*info->ours) * sa->nr);
 320         info->theirs = xmalloc(sizeof(*info->theirs) * sa->nr);
 321         for (i = 0; i < sa->nr; i++) {
 322                 if (has_sha1_file(sa->sha1[i])) {
 323                         struct commit_graft *graft;
 324                         graft = lookup_commit_graft(sa->sha1[i]);
 325                         if (graft && graft->nr_parent < 0)
 326                                 continue;
 327                         info->ours[info->nr_ours++] = i;
 328                 } else
 329                         info->theirs[info->nr_theirs++] = i;
 330         }
 331 }
 332
 333 void clear_shallow_info(struct shallow_info *info)
 334 {
 335         free(info->ours);
 336         free(info->theirs);
 337 }
 338
 339 /* Step 4, remove non-existent ones in "theirs" after getting the pack */
 340
 341 void remove_nonexistent_theirs_shallow(struct shallow_info *info)
 342 {
 343         unsigned char (*sha1)[20] = info->shallow->sha1;
 344         int i, dst;
 345         trace_printf_key(&trace_shallow, "shallow: remove_nonexistent_theirs_shallow\n");
 346         for (i = dst = 0; i < info->nr_theirs; i++) {
 347                 if (i != dst)
 348                         info->theirs[dst] = info->theirs[i];
 349                 if (has_sha1_file(sha1[info->theirs[i]]))
 350                         dst++;
 351         }
 352         info->nr_theirs = dst;
 353 }
 354
 355 define_commit_slab(ref_bitmap, uint32_t *);
 356
 357 struct paint_info {
 358         struct ref_bitmap ref_bitmap;
 359         unsigned nr_bits;
 360         char **slab;
 361         char *free, *end;
 362         unsigned slab_count;
 363 };
 364
 365 static uint32_t *paint_alloc(struct paint_info *info)
 366 {
 367         unsigned nr = (info->nr_bits + 31) / 32;
 368         unsigned size = nr * sizeof(uint32_t);
 369         void *p;
 370         if (!info->slab_count || info->free + size > info->end) {
 371                 info->slab_count++;
 372                 REALLOC_ARRAY(info->slab, info->slab_count);
 373                 info->free = xmalloc(COMMIT_SLAB_SIZE);
 374                 info->slab[info->slab_count - 1] = info->free;
 375                 info->end = info->free + COMMIT_SLAB_SIZE;
 376         }
 377         p = info->free;
 378         info->free += size;
 379         return p;
 380 }
 381
 382 /*
 383  * Given a commit SHA-1, walk down to parents until either SEEN,
 384  * UNINTERESTING or BOTTOM is hit. Set the id-th bit in ref_bitmap for
 385  * all walked commits.
 386  */
 387 static void paint_down(struct paint_info *info, const unsigned char *sha1,
 388                        int id)
 389 {
 390         unsigned int i, nr;
 391         struct commit_list *head = NULL;
 392         int bitmap_nr = (info->nr_bits + 31) / 32;
 393         int bitmap_size = bitmap_nr * sizeof(uint32_t);
 394         uint32_t *tmp = xmalloc(bitmap_size); /* to be freed before return */
 395         uint32_t *bitmap = paint_alloc(info);
 396         struct commit *c = lookup_commit_reference_gently(sha1, 1);
 397         if (!c)
 398                 return;
 399         memset(bitmap, 0, bitmap_size);
 400         bitmap[id / 32] |= (1 << (id % 32));
 401         commit_list_insert(c, &head);
 402         while (head) {
 403                 struct commit_list *p;
 404                 struct commit *c = pop_commit(&head);
 405                 uint32_t **refs = ref_bitmap_at(&info->ref_bitmap, c);
 406
 407                 /* XXX check "UNINTERESTING" from pack bitmaps if available */
 408                 if (c->object.flags & (SEEN | UNINTERESTING))
 409                         continue;
 410                 else
 411                         c->object.flags |= SEEN;
 412
 413                 if (*refs == NULL)
 414                         *refs = bitmap;
 415                 else {
 416                         memcpy(tmp, *refs, bitmap_size);
 417                         for (i = 0; i < bitmap_nr; i++)
 418                                 tmp[i] |= bitmap[i];
 419                         if (memcmp(tmp, *refs, bitmap_size)) {
 420                                 *refs = paint_alloc(info);
 421                                 memcpy(*refs, tmp, bitmap_size);
 422                         }
 423                 }
 424
 425                 if (c->object.flags & BOTTOM)
 426                         continue;
 427
 428                 if (parse_commit(c))
 429                         die("unable to parse commit %s",
 430                             sha1_to_hex(c->object.sha1));
 431
 432                 for (p = c->parents; p; p = p->next) {
 433                         uint32_t **p_refs = ref_bitmap_at(&info->ref_bitmap,
 434                                                           p->item);
 435                         if (p->item->object.flags & SEEN)
 436                                 continue;
 437                         if (*p_refs == NULL || *p_refs == *refs)
 438                                 *p_refs = *refs;
 439                         commit_list_insert(p->item, &head);
 440                 }
 441         }
 442
 443         nr = get_max_object_index();
 444         for (i = 0; i < nr; i++) {
 445                 struct object *o = get_indexed_object(i);
 446                 if (o && o->type == OBJ_COMMIT)
 447                         o->flags &= ~SEEN;
 448         }
 449
 450         free(tmp);
 451 }
 452
 453 static int mark_uninteresting(const char *refname, const struct object_id *oid,
 454                               int flags, void *cb_data)
 455 {
 456         struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
 457         if (!commit)
 458                 return 0;
 459         commit->object.flags |= UNINTERESTING;
 460         mark_parents_uninteresting(commit);
 461         return 0;
 462 }
 463
 464 static void post_assign_shallow(struct shallow_info *info,
 465                                 struct ref_bitmap *ref_bitmap,
 466                                 int *ref_status);
 467 /*
 468  * Step 6(+7), associate shallow commits with new refs
 469  *
 470  * info->ref must be initialized before calling this function.
 471  *
 472  * If used is not NULL, it's an array of info->shallow->nr
 473  * bitmaps. The n-th bit set in the m-th bitmap if ref[n] needs the
 474  * m-th shallow commit from info->shallow.
 475  *
 476  * If used is NULL, "ours" and "theirs" are updated. And if ref_status
 477  * is not NULL it's an array of ref->nr ints. ref_status[i] is true if
 478  * the ref needs some shallow commits from either info->ours or
 479  * info->theirs.
 480  */
 481 void assign_shallow_commits_to_refs(struct shallow_info *info,
 482                                     uint32_t **used, int *ref_status)
 483 {
 484         unsigned char (*sha1)[20] = info->shallow->sha1;
 485         struct sha1_array *ref = info->ref;
 486         unsigned int i, nr;
 487         int *shallow, nr_shallow = 0;
 488         struct paint_info pi;
 489
 490         trace_printf_key(&trace_shallow, "shallow: assign_shallow_commits_to_refs\n");
 491         shallow = xmalloc(sizeof(*shallow) * (info->nr_ours + info->nr_theirs));
 492         for (i = 0; i < info->nr_ours; i++)
 493                 shallow[nr_shallow++] = info->ours[i];
 494         for (i = 0; i < info->nr_theirs; i++)
 495                 shallow[nr_shallow++] = info->theirs[i];
 496
 497         /*
 498          * Prepare the commit graph to track what refs can reach what
 499          * (new) shallow commits.
 500          */
 501         nr = get_max_object_index();
 502         for (i = 0; i < nr; i++) {
 503                 struct object *o = get_indexed_object(i);
 504                 if (!o || o->type != OBJ_COMMIT)
 505                         continue;
 506
 507                 o->flags &= ~(UNINTERESTING | BOTTOM | SEEN);
 508         }
 509
 510         memset(&pi, 0, sizeof(pi));
 511         init_ref_bitmap(&pi.ref_bitmap);
 512         pi.nr_bits = ref->nr;
 513
 514         /*
 515          * "--not --all" to cut short the traversal if new refs
 516          * connect to old refs. If not (e.g. force ref updates) it'll
 517          * have to go down to the current shallow commits.
 518          */
 519         head_ref(mark_uninteresting, NULL);
 520         for_each_ref(mark_uninteresting, NULL);
 521
 522         /* Mark potential bottoms so we won't go out of bound */
 523         for (i = 0; i < nr_shallow; i++) {
 524                 struct commit *c = lookup_commit(sha1[shallow[i]]);
 525                 c->object.flags |= BOTTOM;
 526         }
 527
 528         for (i = 0; i < ref->nr; i++)
 529                 paint_down(&pi, ref->sha1[i], i);
 530
 531         if (used) {
 532                 int bitmap_size = ((pi.nr_bits + 31) / 32) * sizeof(uint32_t);
 533                 memset(used, 0, sizeof(*used) * info->shallow->nr);
 534                 for (i = 0; i < nr_shallow; i++) {
 535                         const struct commit *c = lookup_commit(sha1[shallow[i]]);
 536                         uint32_t **map = ref_bitmap_at(&pi.ref_bitmap, c);
 537                         if (*map)
 538                                 used[shallow[i]] = xmemdupz(*map, bitmap_size);
 539                 }
 540                 /*
 541                  * unreachable shallow commits are not removed from
 542                  * "ours" and "theirs". The user is supposed to run
 543                  * step 7 on every ref separately and not trust "ours"
 544                  * and "theirs" any more.
 545                  */
 546         } else
 547                 post_assign_shallow(info, &pi.ref_bitmap, ref_status);
 548
 549         clear_ref_bitmap(&pi.ref_bitmap);
 550         for (i = 0; i < pi.slab_count; i++)
 551                 free(pi.slab[i]);
 552         free(pi.slab);
 553         free(shallow);
 554 }
 555
 556 struct commit_array {
 557         struct commit **commits;
 558         int nr, alloc;
 559 };
 560
 561 static int add_ref(const char *refname, const struct object_id *oid,
 562                    int flags, void *cb_data)
 563 {
 564         struct commit_array *ca = cb_data;
 565         ALLOC_GROW(ca->commits, ca->nr + 1, ca->alloc);
 566         ca->commits[ca->nr] = lookup_commit_reference_gently(oid->hash, 1);
 567         if (ca->commits[ca->nr])
 568                 ca->nr++;
 569         return 0;
 570 }
 571
 572 static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)
 573 {
 574         int i;
 575         if (!ref_status)
 576                 return;
 577         for (i = 0; i < nr; i++)
 578                 if (bitmap[i / 32] & (1 << (i % 32)))
 579                         ref_status[i]++;
 580 }
 581
 582 /*
 583  * Step 7, reachability test on "ours" at commit level
 584  */
 585 static void post_assign_shallow(struct shallow_info *info,
 586                                 struct ref_bitmap *ref_bitmap,
 587                                 int *ref_status)
 588 {
 589         unsigned char (*sha1)[20] = info->shallow->sha1;
 590         struct commit *c;
 591         uint32_t **bitmap;
 592         int dst, i, j;
 593         int bitmap_nr = (info->ref->nr + 31) / 32;
 594         struct commit_array ca;
 595
 596         trace_printf_key(&trace_shallow, "shallow: post_assign_shallow\n");
 597         if (ref_status)
 598                 memset(ref_status, 0, sizeof(*ref_status) * info->ref->nr);
 599
 600         /* Remove unreachable shallow commits from "theirs" */
 601         for (i = dst = 0; i < info->nr_theirs; i++) {
 602                 if (i != dst)
 603                         info->theirs[dst] = info->theirs[i];
 604                 c = lookup_commit(sha1[info->theirs[i]]);
 605                 bitmap = ref_bitmap_at(ref_bitmap, c);
 606                 if (!*bitmap)
 607                         continue;
 608                 for (j = 0; j < bitmap_nr; j++)
 609                         if (bitmap[0][j]) {
 610                                 update_refstatus(ref_status, info->ref->nr, *bitmap);
 611                                 dst++;
 612                                 break;
 613                         }
 614         }
 615         info->nr_theirs = dst;
 616
 617         memset(&ca, 0, sizeof(ca));
 618         head_ref(add_ref, &ca);
 619         for_each_ref(add_ref, &ca);
 620
 621         /* Remove unreachable shallow commits from "ours" */
 622         for (i = dst = 0; i < info->nr_ours; i++) {
 623                 if (i != dst)
 624                         info->ours[dst] = info->ours[i];
 625                 c = lookup_commit(sha1[info->ours[i]]);
 626                 bitmap = ref_bitmap_at(ref_bitmap, c);
 627                 if (!*bitmap)
 628                         continue;
 629                 for (j = 0; j < bitmap_nr; j++)
 630                         if (bitmap[0][j] &&
 631                             /* Step 7, reachability test at commit level */
 632                             !in_merge_bases_many(c, ca.nr, ca.commits)) {
 633                                 update_refstatus(ref_status, info->ref->nr, *bitmap);
 634                                 dst++;
 635                                 break;
 636                         }
 637         }
 638         info->nr_ours = dst;
 639
 640         free(ca.commits);
 641 }
 642
 643 /* (Delayed) step 7, reachability test at commit level */
 644 int delayed_reachability_test(struct shallow_info *si, int c)
 645 {
 646         if (si->need_reachability_test[c]) {
 647                 struct commit *commit = lookup_commit(si->shallow->sha1[c]);
 648
 649                 if (!si->commits) {
 650                         struct commit_array ca;
 651
 652                         memset(&ca, 0, sizeof(ca));
 653                         head_ref(add_ref, &ca);
 654                         for_each_ref(add_ref, &ca);
 655                         si->commits = ca.commits;
 656                         si->nr_commits = ca.nr;
 657                 }
 658
 659                 si->reachable[c] = in_merge_bases_many(commit,
 660                                                        si->nr_commits,
 661                                                        si->commits);
 662                 si->need_reachability_test[c] = 0;
 663         }
 664         return si->reachable[c];
 665 }