pack-objects.c

   1 #include "cache.h"
   2 #include "object.h"
   3 #include "delta.h"
   4 #include "pack.h"
   5 #include "csum-file.h"
   6 #include "diff.h"
   7 #include <sys/time.h>
   8
   9 static const char pack_usage[] = "git-pack-objects [-q] [--no-reuse-delta] [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
  10
  11 struct object_entry {
  12         unsigned char sha1[20];
  13         unsigned long size;     /* uncompressed size */
  14         unsigned long offset;   /* offset into the final pack file;
  15                                  * nonzero if already written.
  16                                  */
  17         unsigned int depth;     /* delta depth */
  18         unsigned int delta_limit;       /* base adjustment for in-pack delta */
  19         unsigned int hash;      /* name hint hash */
  20         enum object_type type;
  21         enum object_type in_pack_type;  /* could be delta */
  22         unsigned long delta_size;       /* delta data size (uncompressed) */
  23         struct object_entry *delta;     /* delta base object */
  24         struct packed_git *in_pack;     /* already in pack */
  25         unsigned int in_pack_offset;
  26         struct object_entry *delta_child; /* delitified objects who bases me */
  27         struct object_entry *delta_sibling; /* other deltified objects who
  28                                              * uses the same base as me
  29                                              */
  30         int preferred_base;     /* we do not pack this, but is encouraged to
  31                                  * be used as the base objectto delta huge
  32                                  * objects against.
  33                                  */
  34         int based_on_preferred; /* current delta candidate is a preferred
  35                                  * one, or delta against a preferred one.
  36                                  */
  37 };
  38
  39 /*
  40  * Objects we are going to pack are colected in objects array (dynamically
  41  * expanded).  nr_objects & nr_alloc controls this array.  They are stored
  42  * in the order we see -- typically rev-list --objects order that gives us
  43  * nice "minimum seek" order.
  44  *
  45  * sorted-by-sha ans sorted-by-type are arrays of pointers that point at
  46  * elements in the objects array.  The former is used to build the pack
  47  * index (lists object names in the ascending order to help offset lookup),
  48  * and the latter is used to group similar things together by try_delta()
  49  * heuristics.
  50  */
  51
  52 static unsigned char object_list_sha1[20];
  53 static int non_empty = 0;
  54 static int no_reuse_delta = 0;
  55 static int local = 0;
  56 static int incremental = 0;
  57 static struct object_entry **sorted_by_sha, **sorted_by_type;
  58 static struct object_entry *objects = NULL;
  59 static int nr_objects = 0, nr_alloc = 0, nr_result = 0;
  60 static const char *base_name;
  61 static unsigned char pack_file_sha1[20];
  62 static int progress = 1;
  63
  64 /*
  65  * The object names in objects array are hashed with this hashtable,
  66  * to help looking up the entry by object name.  Binary search from
  67  * sorted_by_sha is also possible but this was easier to code and faster.
  68  * This hashtable is built after all the objects are seen.
  69  */
  70 static int *object_ix = NULL;
  71 static int object_ix_hashsz = 0;
  72
  73 /*
  74  * Pack index for existing packs give us easy access to the offsets into
  75  * corresponding pack file where each object's data starts, but the entries
  76  * do not store the size of the compressed representation (uncompressed
  77  * size is easily available by examining the pack entry header).  We build
  78  * a hashtable of existing packs (pack_revindex), and keep reverse index
  79  * here -- pack index file is sorted by object name mapping to offset; this
  80  * pack_revindex[].revindex array is an ordered list of offsets, so if you
  81  * know the offset of an object, next offset is where its packed
  82  * representation ends.
  83  */
  84 struct pack_revindex {
  85         struct packed_git *p;
  86         unsigned long *revindex;
  87 } *pack_revindex = NULL;
  88 static int pack_revindex_hashsz = 0;
  89
  90 /*
  91  * stats
  92  */
  93 static int written = 0;
  94 static int written_delta = 0;
  95 static int reused = 0;
  96 static int reused_delta = 0;
  97
  98 static int pack_revindex_ix(struct packed_git *p)
  99 {
 100         unsigned int ui = (unsigned int) p;
 101         int i;
 102
 103         ui = ui ^ (ui >> 16); /* defeat structure alignment */
 104         i = (int)(ui % pack_revindex_hashsz);
 105         while (pack_revindex[i].p) {
 106                 if (pack_revindex[i].p == p)
 107                         return i;
 108                 if (++i == pack_revindex_hashsz)
 109                         i = 0;
 110         }
 111         return -1 - i;
 112 }
 113
 114 static void prepare_pack_ix(void)
 115 {
 116         int num;
 117         struct packed_git *p;
 118         for (num = 0, p = packed_git; p; p = p->next)
 119                 num++;
 120         if (!num)
 121                 return;
 122         pack_revindex_hashsz = num * 11;
 123         pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
 124         for (p = packed_git; p; p = p->next) {
 125                 num = pack_revindex_ix(p);
 126                 num = - 1 - num;
 127                 pack_revindex[num].p = p;
 128         }
 129         /* revindex elements are lazily initialized */
 130 }
 131
 132 static int cmp_offset(const void *a_, const void *b_)
 133 {
 134         unsigned long a = *(unsigned long *) a_;
 135         unsigned long b = *(unsigned long *) b_;
 136         if (a < b)
 137                 return -1;
 138         else if (a == b)
 139                 return 0;
 140         else
 141                 return 1;
 142 }
 143
 144 /*
 145  * Ordered list of offsets of objects in the pack.
 146  */
 147 static void prepare_pack_revindex(struct pack_revindex *rix)
 148 {
 149         struct packed_git *p = rix->p;
 150         int num_ent = num_packed_objects(p);
 151         int i;
 152         void *index = p->index_base + 256;
 153
 154         rix->revindex = xmalloc(sizeof(unsigned long) * (num_ent + 1));
 155         for (i = 0; i < num_ent; i++) {
 156                 long hl = *((long *)(index + 24 * i));
 157                 rix->revindex[i] = ntohl(hl);
 158         }
 159         /* This knows the pack format -- the 20-byte trailer
 160          * follows immediately after the last object data.
 161          */
 162         rix->revindex[num_ent] = p->pack_size - 20;
 163         qsort(rix->revindex, num_ent, sizeof(unsigned long), cmp_offset);
 164 }
 165
 166 static unsigned long find_packed_object_size(struct packed_git *p,
 167                                              unsigned long ofs)
 168 {
 169         int num;
 170         int lo, hi;
 171         struct pack_revindex *rix;
 172         unsigned long *revindex;
 173         num = pack_revindex_ix(p);
 174         if (num < 0)
 175                 die("internal error: pack revindex uninitialized");
 176         rix = &pack_revindex[num];
 177         if (!rix->revindex)
 178                 prepare_pack_revindex(rix);
 179         revindex = rix->revindex;
 180         lo = 0;
 181         hi = num_packed_objects(p) + 1;
 182         do {
 183                 int mi = (lo + hi) / 2;
 184                 if (revindex[mi] == ofs) {
 185                         return revindex[mi+1] - ofs;
 186                 }
 187                 else if (ofs < revindex[mi])
 188                         hi = mi;
 189                 else
 190                         lo = mi + 1;
 191         } while (lo < hi);
 192         die("internal error: pack revindex corrupt");
 193 }
 194
 195 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
 196 {
 197         unsigned long othersize, delta_size;
 198         char type[10];
 199         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
 200         void *delta_buf;
 201
 202         if (!otherbuf)
 203                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
 204         delta_buf = diff_delta(otherbuf, othersize,
 205                                buf, size, &delta_size, 0);
 206         if (!delta_buf || delta_size != entry->delta_size)
 207                 die("delta size changed");
 208         free(buf);
 209         free(otherbuf);
 210         return delta_buf;
 211 }
 212
 213 /*
 214  * The per-object header is a pretty dense thing, which is
 215  *  - first byte: low four bits are "size", then three bits of "type",
 216  *    and the high bit is "size continues".
 217  *  - each byte afterwards: low seven bits are size continuation,
 218  *    with the high bit being "size continues"
 219  */
 220 static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
 221 {
 222         int n = 1;
 223         unsigned char c;
 224
 225         if (type < OBJ_COMMIT || type > OBJ_DELTA)
 226                 die("bad type %d", type);
 227
 228         c = (type << 4) | (size & 15);
 229         size >>= 4;
 230         while (size) {
 231                 *hdr++ = c | 0x80;
 232                 c = size & 0x7f;
 233                 size >>= 7;
 234                 n++;
 235         }
 236         *hdr = c;
 237         return n;
 238 }
 239
 240 static unsigned long write_object(struct sha1file *f,
 241                                   struct object_entry *entry)
 242 {
 243         unsigned long size;
 244         char type[10];
 245         void *buf;
 246         unsigned char header[10];
 247         unsigned hdrlen, datalen;
 248         enum object_type obj_type;
 249         int to_reuse = 0;
 250
 251         if (entry->preferred_base)
 252                 return 0;
 253
 254         obj_type = entry->type;
 255         if (! entry->in_pack)
 256                 to_reuse = 0;   /* can't reuse what we don't have */
 257         else if (obj_type == OBJ_DELTA)
 258                 to_reuse = 1;   /* check_object() decided it for us */
 259         else if (obj_type != entry->in_pack_type)
 260                 to_reuse = 0;   /* pack has delta which is unusable */
 261         else if (entry->delta)
 262                 to_reuse = 0;   /* we want to pack afresh */
 263         else
 264                 to_reuse = 1;   /* we have it in-pack undeltified,
 265                                  * and we do not need to deltify it.
 266                                  */
 267
 268         if (! to_reuse) {
 269                 buf = read_sha1_file(entry->sha1, type, &size);
 270                 if (!buf)
 271                         die("unable to read %s", sha1_to_hex(entry->sha1));
 272                 if (size != entry->size)
 273                         die("object %s size inconsistency (%lu vs %lu)",
 274                             sha1_to_hex(entry->sha1), size, entry->size);
 275                 if (entry->delta) {
 276                         buf = delta_against(buf, size, entry);
 277                         size = entry->delta_size;
 278                         obj_type = OBJ_DELTA;
 279                 }
 280                 /*
 281                  * The object header is a byte of 'type' followed by zero or
 282                  * more bytes of length.  For deltas, the 20 bytes of delta
 283                  * sha1 follows that.
 284                  */
 285                 hdrlen = encode_header(obj_type, size, header);
 286                 sha1write(f, header, hdrlen);
 287
 288                 if (entry->delta) {
 289                         sha1write(f, entry->delta, 20);
 290                         hdrlen += 20;
 291                 }
 292                 datalen = sha1write_compressed(f, buf, size);
 293                 free(buf);
 294         }
 295         else {
 296                 struct packed_git *p = entry->in_pack;
 297                 use_packed_git(p);
 298
 299                 datalen = find_packed_object_size(p, entry->in_pack_offset);
 300                 buf = p->pack_base + entry->in_pack_offset;
 301                 sha1write(f, buf, datalen);
 302                 unuse_packed_git(p);
 303                 hdrlen = 0; /* not really */
 304                 if (obj_type == OBJ_DELTA)
 305                         reused_delta++;
 306                 reused++;
 307         }
 308         if (obj_type == OBJ_DELTA)
 309                 written_delta++;
 310         written++;
 311         return hdrlen + datalen;
 312 }
 313
 314 static unsigned long write_one(struct sha1file *f,
 315                                struct object_entry *e,
 316                                unsigned long offset)
 317 {
 318         if (e->offset)
 319                 /* offset starts from header size and cannot be zero
 320                  * if it is written already.
 321                  */
 322                 return offset;
 323         e->offset = offset;
 324         offset += write_object(f, e);
 325         /* if we are deltified, write out its base object. */
 326         if (e->delta)
 327                 offset = write_one(f, e->delta, offset);
 328         return offset;
 329 }
 330
 331 static void write_pack_file(void)
 332 {
 333         int i;
 334         struct sha1file *f;
 335         unsigned long offset;
 336         struct pack_header hdr;
 337
 338         if (!base_name)
 339                 f = sha1fd(1, "<stdout>");
 340         else
 341                 f = sha1create("%s-%s.%s", base_name,
 342                                sha1_to_hex(object_list_sha1), "pack");
 343         hdr.hdr_signature = htonl(PACK_SIGNATURE);
 344         hdr.hdr_version = htonl(PACK_VERSION);
 345         hdr.hdr_entries = htonl(nr_result);
 346         sha1write(f, &hdr, sizeof(hdr));
 347         offset = sizeof(hdr);
 348         for (i = 0; i < nr_objects; i++)
 349                 offset = write_one(f, objects + i, offset);
 350
 351         sha1close(f, pack_file_sha1, 1);
 352 }
 353
 354 static void write_index_file(void)
 355 {
 356         int i;
 357         struct sha1file *f = sha1create("%s-%s.%s", base_name,
 358                                         sha1_to_hex(object_list_sha1), "idx");
 359         struct object_entry **list = sorted_by_sha;
 360         struct object_entry **last = list + nr_result;
 361         unsigned int array[256];
 362
 363         /*
 364          * Write the first-level table (the list is sorted,
 365          * but we use a 256-entry lookup to be able to avoid
 366          * having to do eight extra binary search iterations).
 367          */
 368         for (i = 0; i < 256; i++) {
 369                 struct object_entry **next = list;
 370                 while (next < last) {
 371                         struct object_entry *entry = *next;
 372                         if (entry->sha1[0] != i)
 373                                 break;
 374                         next++;
 375                 }
 376                 array[i] = htonl(next - sorted_by_sha);
 377                 list = next;
 378         }
 379         sha1write(f, array, 256 * sizeof(int));
 380
 381         /*
 382          * Write the actual SHA1 entries..
 383          */
 384         list = sorted_by_sha;
 385         for (i = 0; i < nr_result; i++) {
 386                 struct object_entry *entry = *list++;
 387                 unsigned int offset = htonl(entry->offset);
 388                 sha1write(f, &offset, 4);
 389                 sha1write(f, entry->sha1, 20);
 390         }
 391         sha1write(f, pack_file_sha1, 20);
 392         sha1close(f, NULL, 1);
 393 }
 394
 395 static int locate_object_entry_hash(const unsigned char *sha1)
 396 {
 397         int i;
 398         unsigned int ui;
 399         memcpy(&ui, sha1, sizeof(unsigned int));
 400         i = ui % object_ix_hashsz;
 401         while (0 < object_ix[i]) {
 402                 if (!memcmp(sha1, objects[object_ix[i]-1].sha1, 20))
 403                         return i;
 404                 if (++i == object_ix_hashsz)
 405                         i = 0;
 406         }
 407         return -1 - i;
 408 }
 409
 410 static struct object_entry *locate_object_entry(const unsigned char *sha1)
 411 {
 412         int i;
 413
 414         if (!object_ix_hashsz)
 415                 return NULL;
 416
 417         i = locate_object_entry_hash(sha1);
 418         if (0 <= i)
 419                 return &objects[object_ix[i]-1];
 420         return NULL;
 421 }
 422
 423 static void rehash_objects(void)
 424 {
 425         int i;
 426         struct object_entry *oe;
 427
 428         object_ix_hashsz = nr_objects * 3;
 429         if (object_ix_hashsz < 1024)
 430                 object_ix_hashsz = 1024;
 431         object_ix = xrealloc(object_ix, sizeof(int) * object_ix_hashsz);
 432         object_ix = memset(object_ix, 0, sizeof(int) * object_ix_hashsz);
 433         for (i = 0, oe = objects; i < nr_objects; i++, oe++) {
 434                 int ix = locate_object_entry_hash(oe->sha1);
 435                 if (0 <= ix)
 436                         continue;
 437                 ix = -1 - ix;
 438                 object_ix[ix] = i + 1;
 439         }
 440 }
 441
 442 struct name_path {
 443         struct name_path *up;
 444         const char *elem;
 445         int len;
 446 };
 447
 448 #define DIRBITS 12
 449
 450 static unsigned name_hash(struct name_path *path, const char *name)
 451 {
 452         struct name_path *p = path;
 453         const char *n = name + strlen(name);
 454         unsigned hash = 0, name_hash = 0, name_done = 0;
 455
 456         if (n != name && n[-1] == '\n')
 457                 n--;
 458         while (name <= --n) {
 459                 unsigned char c = *n;
 460                 if (c == '/' && !name_done) {
 461                         name_hash = hash;
 462                         name_done = 1;
 463                         hash = 0;
 464                 }
 465                 hash = hash * 11 + c;
 466         }
 467         if (!name_done) {
 468                 name_hash = hash;
 469                 hash = 0;
 470         }
 471         for (p = path; p; p = p->up) {
 472                 hash = hash * 11 + '/';
 473                 n = p->elem + p->len;
 474                 while (p->elem <= --n) {
 475                         unsigned char c = *n;
 476                         hash = hash * 11 + c;
 477                 }
 478         }
 479         /*
 480          * Make sure "Makefile" and "t/Makefile" are hashed separately
 481          * but close enough.
 482          */
 483         hash = (name_hash<<DIRBITS) | (hash & ((1U<<DIRBITS )-1));
 484
 485         if (0) { /* debug */
 486                 n = name + strlen(name);
 487                 if (n != name && n[-1] == '\n')
 488                         n--;
 489                 while (name <= --n)
 490                         fputc(*n, stderr);
 491                 for (p = path; p; p = p->up) {
 492                         fputc('/', stderr);
 493                         n = p->elem + p->len;
 494                         while (p->elem <= --n)
 495                                 fputc(*n, stderr);
 496                 }
 497                 fprintf(stderr, "\t%08x\n", hash);
 498         }
 499         return hash;
 500 }
 501
 502 static int add_object_entry(const unsigned char *sha1, unsigned hash, int exclude)
 503 {
 504         unsigned int idx = nr_objects;
 505         struct object_entry *entry;
 506         struct packed_git *p;
 507         unsigned int found_offset = 0;
 508         struct packed_git *found_pack = NULL;
 509         int ix, status = 0;
 510
 511         if (!exclude) {
 512                 for (p = packed_git; p; p = p->next) {
 513                         struct pack_entry e;
 514                         if (find_pack_entry_one(sha1, &e, p)) {
 515                                 if (incremental)
 516                                         return 0;
 517                                 if (local && !p->pack_local)
 518                                         return 0;
 519                                 if (!found_pack) {
 520                                         found_offset = e.offset;
 521                                         found_pack = e.p;
 522                                 }
 523                         }
 524                 }
 525         }
 526         if ((entry = locate_object_entry(sha1)) != NULL)
 527                 goto already_added;
 528
 529         if (idx >= nr_alloc) {
 530                 unsigned int needed = (idx + 1024) * 3 / 2;
 531                 objects = xrealloc(objects, needed * sizeof(*entry));
 532                 nr_alloc = needed;
 533         }
 534         entry = objects + idx;
 535         nr_objects = idx + 1;
 536         memset(entry, 0, sizeof(*entry));
 537         memcpy(entry->sha1, sha1, 20);
 538         entry->hash = hash;
 539
 540         if (object_ix_hashsz * 3 <= nr_objects * 4)
 541                 rehash_objects();
 542         else {
 543                 ix = locate_object_entry_hash(entry->sha1);
 544                 if (0 <= ix)
 545                         die("internal error in object hashing.");
 546                 object_ix[-1 - ix] = idx + 1;
 547         }
 548         status = 1;
 549
 550  already_added:
 551         if (exclude)
 552                 entry->preferred_base = 1;
 553         else {
 554                 if (found_pack) {
 555                         entry->in_pack = found_pack;
 556                         entry->in_pack_offset = found_offset;
 557                 }
 558         }
 559         return status;
 560 }
 561
 562 static void add_pbase_tree(struct tree_desc *tree, struct name_path *up)
 563 {
 564         while (tree->size) {
 565                 const unsigned char *sha1;
 566                 const char *name;
 567                 unsigned mode, hash;
 568                 unsigned long size;
 569                 char type[20];
 570
 571                 sha1 = tree_entry_extract(tree, &name, &mode);
 572                 update_tree_entry(tree);
 573                 if (!has_sha1_file(sha1))
 574                         continue;
 575                 if (sha1_object_info(sha1, type, &size))
 576                         continue;
 577
 578                 hash = name_hash(up, name);
 579                 if (!add_object_entry(sha1, hash, 1))
 580                         continue;
 581
 582                 if (!strcmp(type, "tree")) {
 583                         struct tree_desc sub;
 584                         void *elem;
 585                         struct name_path me;
 586
 587                         elem = read_sha1_file(sha1, type, &sub.size);
 588                         sub.buf = elem;
 589                         if (sub.buf) {
 590                                 me.up = up;
 591                                 me.elem = name;
 592                                 me.len = strlen(name);
 593                                 add_pbase_tree(&sub, &me);
 594                                 free(elem);
 595                         }
 596                 }
 597         }
 598 }
 599
 600 static void add_preferred_base(unsigned char *sha1)
 601 {
 602         struct tree_desc tree;
 603         void *elem;
 604
 605         elem = read_object_with_reference(sha1, "tree", &tree.size, NULL);
 606         tree.buf = elem;
 607         if (!tree.buf)
 608                 return;
 609         if (add_object_entry(sha1, name_hash(NULL, ""), 1))
 610                 add_pbase_tree(&tree, NULL);
 611         free(elem);
 612 }
 613
 614 static void check_object(struct object_entry *entry)
 615 {
 616         char type[20];
 617
 618         if (entry->in_pack && !entry->preferred_base) {
 619                 unsigned char base[20];
 620                 unsigned long size;
 621                 struct object_entry *base_entry;
 622
 623                 /* We want in_pack_type even if we do not reuse delta.
 624                  * There is no point not reusing non-delta representations.
 625                  */
 626                 check_reuse_pack_delta(entry->in_pack,
 627                                        entry->in_pack_offset,
 628                                        base, &size,
 629                                        &entry->in_pack_type);
 630
 631                 /* Check if it is delta, and the base is also an object
 632                  * we are going to pack.  If so we will reuse the existing
 633                  * delta.
 634                  */
 635                 if (!no_reuse_delta &&
 636                     entry->in_pack_type == OBJ_DELTA &&
 637                     (base_entry = locate_object_entry(base)) &&
 638                     (!base_entry->preferred_base)) {
 639
 640                         /* Depth value does not matter - find_deltas()
 641                          * will never consider reused delta as the
 642                          * base object to deltify other objects
 643                          * against, in order to avoid circular deltas.
 644                          */
 645
 646                         /* uncompressed size of the delta data */
 647                         entry->size = entry->delta_size = size;
 648                         entry->delta = base_entry;
 649                         entry->type = OBJ_DELTA;
 650
 651                         entry->delta_sibling = base_entry->delta_child;
 652                         base_entry->delta_child = entry;
 653
 654                         return;
 655                 }
 656                 /* Otherwise we would do the usual */
 657         }
 658
 659         if (sha1_object_info(entry->sha1, type, &entry->size))
 660                 die("unable to get type of object %s",
 661                     sha1_to_hex(entry->sha1));
 662
 663         if (!strcmp(type, "commit")) {
 664                 entry->type = OBJ_COMMIT;
 665         } else if (!strcmp(type, "tree")) {
 666                 entry->type = OBJ_TREE;
 667         } else if (!strcmp(type, "blob")) {
 668                 entry->type = OBJ_BLOB;
 669         } else if (!strcmp(type, "tag")) {
 670                 entry->type = OBJ_TAG;
 671         } else
 672                 die("unable to pack object %s of type %s",
 673                     sha1_to_hex(entry->sha1), type);
 674 }
 675
 676 static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
 677 {
 678         struct object_entry *child = me->delta_child;
 679         unsigned int m = n;
 680         while (child) {
 681                 unsigned int c = check_delta_limit(child, n + 1);
 682                 if (m < c)
 683                         m = c;
 684                 child = child->delta_sibling;
 685         }
 686         return m;
 687 }
 688
 689 static void get_object_details(void)
 690 {
 691         int i;
 692         struct object_entry *entry;
 693
 694         prepare_pack_ix();
 695         for (i = 0, entry = objects; i < nr_objects; i++, entry++)
 696                 check_object(entry);
 697
 698         if (nr_objects == nr_result) {
 699                 /*
 700                  * Depth of objects that depend on the entry -- this
 701                  * is subtracted from depth-max to break too deep
 702                  * delta chain because of delta data reusing.
 703                  * However, we loosen this restriction when we know we
 704                  * are creating a thin pack -- it will have to be
 705                  * expanded on the other end anyway, so do not
 706                  * artificially cut the delta chain and let it go as
 707                  * deep as it wants.
 708                  */
 709                 for (i = 0, entry = objects; i < nr_objects; i++, entry++)
 710                         if (!entry->delta && entry->delta_child)
 711                                 entry->delta_limit =
 712                                         check_delta_limit(entry, 1);
 713         }
 714 }
 715
 716 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 717
 718 static entry_sort_t current_sort;
 719
 720 static int sort_comparator(const void *_a, const void *_b)
 721 {
 722         struct object_entry *a = *(struct object_entry **)_a;
 723         struct object_entry *b = *(struct object_entry **)_b;
 724         return current_sort(a,b);
 725 }
 726
 727 static struct object_entry **create_sorted_list(entry_sort_t sort)
 728 {
 729         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 730         int i;
 731
 732         for (i = 0; i < nr_objects; i++)
 733                 list[i] = objects + i;
 734         current_sort = sort;
 735         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 736         return list;
 737 }
 738
 739 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 740 {
 741         return memcmp(a->sha1, b->sha1, 20);
 742 }
 743
 744 static struct object_entry **create_final_object_list()
 745 {
 746         struct object_entry **list;
 747         int i, j;
 748
 749         for (i = nr_result = 0; i < nr_objects; i++)
 750                 if (!objects[i].preferred_base)
 751                         nr_result++;
 752         list = xmalloc(nr_result * sizeof(struct object_entry *));
 753         for (i = j = 0; i < nr_objects; i++) {
 754                 if (!objects[i].preferred_base)
 755                         list[j++] = objects + i;
 756         }
 757         current_sort = sha1_sort;
 758         qsort(list, nr_result, sizeof(struct object_entry *), sort_comparator);
 759         return list;
 760 }
 761
 762 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 763 {
 764         if (a->type < b->type)
 765                 return -1;
 766         if (a->type > b->type)
 767                 return 1;
 768         if (a->hash < b->hash)
 769                 return -1;
 770         if (a->hash > b->hash)
 771                 return 1;
 772         if (a->preferred_base < b->preferred_base)
 773                 return -1;
 774         if (a->preferred_base > b->preferred_base)
 775                 return 1;
 776         if (a->size < b->size)
 777                 return -1;
 778         if (a->size > b->size)
 779                 return 1;
 780         return a < b ? -1 : (a > b);
 781 }
 782
 783 struct unpacked {
 784         struct object_entry *entry;
 785         void *data;
 786 };
 787
 788 /*
 789  * We search for deltas _backwards_ in a list sorted by type and
 790  * by size, so that we see progressively smaller and smaller files.
 791  * That's because we prefer deltas to be from the bigger file
 792  * to the smaller - deletes are potentially cheaper, but perhaps
 793  * more importantly, the bigger file is likely the more recent
 794  * one.
 795  */
 796 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 797 {
 798         struct object_entry *cur_entry = cur->entry;
 799         struct object_entry *old_entry = old->entry;
 800         int old_preferred = (old_entry->preferred_base ||
 801                              old_entry->based_on_preferred);
 802         unsigned long size, oldsize, delta_size, sizediff;
 803         long max_size;
 804         void *delta_buf;
 805
 806         /* Don't bother doing diffs between different types */
 807         if (cur_entry->type != old_entry->type)
 808                 return -1;
 809
 810         /* We do not compute delta to *create* objects we are not
 811          * going to pack.
 812          */
 813         if (cur_entry->preferred_base)
 814                 return -1;
 815
 816         /* If the current object is at pack edge, take the depth the
 817          * objects that depend on the current object into account --
 818          * otherwise they would become too deep.
 819          */
 820         if (cur_entry->delta_child) {
 821                 if (max_depth <= cur_entry->delta_limit)
 822                         return 0;
 823                 max_depth -= cur_entry->delta_limit;
 824         }
 825
 826         size = cur_entry->size;
 827         if (size < 50)
 828                 return -1;
 829         oldsize = old_entry->size;
 830         sizediff = oldsize > size ? oldsize - size : size - oldsize;
 831         if (sizediff > size / 8)
 832                 return -1;
 833         if (old_entry->depth >= max_depth)
 834                 return 0;
 835
 836         /*
 837          * NOTE!
 838          *
 839          * We always delta from the bigger to the smaller, since that's
 840          * more space-efficient (deletes don't have to say _what_ they
 841          * delete).
 842          */
 843         max_size = size / 2 - 20;
 844         if (cur_entry->delta) {
 845                 if (cur_entry->based_on_preferred) {
 846                         if (old_preferred)
 847                                 max_size = cur_entry->delta_size-1;
 848                         else
 849                                 /* trying with non-preferred one when we
 850                                  * already have a delta based on preferred
 851                                  * one is pointless.
 852                                  */
 853                                 return -1;
 854                 }
 855                 else if (!old_preferred)
 856                         max_size = cur_entry->delta_size-1;
 857                 else
 858                         /* otherwise...  even if delta with a
 859                          * preferred one produces a bigger result than
 860                          * what we currently have, which is based on a
 861                          * non-preferred one, it is OK.
 862                          */
 863                         ;
 864         }
 865         if (sizediff >= max_size)
 866                 return -1;
 867         delta_buf = diff_delta(old->data, oldsize,
 868                                cur->data, size, &delta_size, max_size);
 869         if (!delta_buf)
 870                 return 0;
 871         cur_entry->delta = old_entry;
 872         cur_entry->delta_size = delta_size;
 873         cur_entry->depth = old_entry->depth + 1;
 874         cur_entry->based_on_preferred = old_preferred;
 875         free(delta_buf);
 876         return 0;
 877 }
 878
 879 static void find_deltas(struct object_entry **list, int window, int depth)
 880 {
 881         int i, idx;
 882         unsigned int array_size = window * sizeof(struct unpacked);
 883         struct unpacked *array = xmalloc(array_size);
 884         int eye_candy;
 885
 886         memset(array, 0, array_size);
 887         i = nr_objects;
 888         idx = 0;
 889         eye_candy = i - (nr_objects / 20);
 890
 891         while (--i >= 0) {
 892                 struct object_entry *entry = list[i];
 893                 struct unpacked *n = array + idx;
 894                 unsigned long size;
 895                 char type[10];
 896                 int j;
 897
 898                 if (progress && i <= eye_candy) {
 899                         eye_candy -= nr_objects / 20;
 900                         fputc('.', stderr);
 901                 }
 902
 903                 if (entry->delta)
 904                         /* This happens if we decided to reuse existing
 905                          * delta from a pack.  "!no_reuse_delta &&" is implied.
 906                          */
 907                         continue;
 908
 909                 free(n->data);
 910                 n->entry = entry;
 911                 n->data = read_sha1_file(entry->sha1, type, &size);
 912                 if (size != entry->size)
 913                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 914
 915                 j = window;
 916                 while (--j > 0) {
 917                         unsigned int other_idx = idx + j;
 918                         struct unpacked *m;
 919                         if (other_idx >= window)
 920                                 other_idx -= window;
 921                         m = array + other_idx;
 922                         if (!m->entry)
 923                                 break;
 924                         if (try_delta(n, m, depth) < 0)
 925                                 break;
 926                 }
 927                 idx++;
 928                 if (idx >= window)
 929                         idx = 0;
 930         }
 931
 932         for (i = 0; i < window; ++i)
 933                 free(array[i].data);
 934         free(array);
 935 }
 936
 937 static void prepare_pack(int window, int depth)
 938 {
 939         if (progress)
 940                 fprintf(stderr, "Packing %d objects", nr_result);
 941         get_object_details();
 942         if (progress)
 943                 fputc('.', stderr);
 944
 945         sorted_by_type = create_sorted_list(type_size_sort);
 946         if (window && depth)
 947                 find_deltas(sorted_by_type, window+1, depth);
 948         if (progress)
 949                 fputc('\n', stderr);
 950         write_pack_file();
 951 }
 952
 953 static int reuse_cached_pack(unsigned char *sha1, int pack_to_stdout)
 954 {
 955         static const char cache[] = "pack-cache/pack-%s.%s";
 956         char *cached_pack, *cached_idx;
 957         int ifd, ofd, ifd_ix = -1;
 958
 959         cached_pack = git_path(cache, sha1_to_hex(sha1), "pack");
 960         ifd = open(cached_pack, O_RDONLY);
 961         if (ifd < 0)
 962                 return 0;
 963
 964         if (!pack_to_stdout) {
 965                 cached_idx = git_path(cache, sha1_to_hex(sha1), "idx");
 966                 ifd_ix = open(cached_idx, O_RDONLY);
 967                 if (ifd_ix < 0) {
 968                         close(ifd);
 969                         return 0;
 970                 }
 971         }
 972
 973         if (progress)
 974                 fprintf(stderr, "Reusing %d objects pack %s\n", nr_objects,
 975                         sha1_to_hex(sha1));
 976
 977         if (pack_to_stdout) {
 978                 if (copy_fd(ifd, 1))
 979                         exit(1);
 980                 close(ifd);
 981         }
 982         else {
 983                 char name[PATH_MAX];
 984                 snprintf(name, sizeof(name),
 985                          "%s-%s.%s", base_name, sha1_to_hex(sha1), "pack");
 986                 ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
 987                 if (ofd < 0)
 988                         die("unable to open %s (%s)", name, strerror(errno));
 989                 if (copy_fd(ifd, ofd))
 990                         exit(1);
 991                 close(ifd);
 992
 993                 snprintf(name, sizeof(name),
 994                          "%s-%s.%s", base_name, sha1_to_hex(sha1), "idx");
 995                 ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
 996                 if (ofd < 0)
 997                         die("unable to open %s (%s)", name, strerror(errno));
 998                 if (copy_fd(ifd_ix, ofd))
 999                         exit(1);
1000                 close(ifd_ix);
1001                 puts(sha1_to_hex(sha1));
1002         }
1003
1004         return 1;
1005 }
1006
1007 int main(int argc, char **argv)
1008 {
1009         SHA_CTX ctx;
1010         char line[PATH_MAX + 20];
1011         int window = 10, depth = 10, pack_to_stdout = 0;
1012         struct object_entry **list;
1013         int i;
1014         struct timeval prev_tv;
1015         int eye_candy = 0;
1016         int eye_candy_incr = 500;
1017
1018
1019         setup_git_directory();
1020
1021         for (i = 1; i < argc; i++) {
1022                 const char *arg = argv[i];
1023
1024                 if (*arg == '-') {
1025                         if (!strcmp("--non-empty", arg)) {
1026                                 non_empty = 1;
1027                                 continue;
1028                         }
1029                         if (!strcmp("--local", arg)) {
1030                                 local = 1;
1031                                 continue;
1032                         }
1033                         if (!strcmp("--incremental", arg)) {
1034                                 incremental = 1;
1035                                 continue;
1036                         }
1037                         if (!strncmp("--window=", arg, 9)) {
1038                                 char *end;
1039                                 window = strtoul(arg+9, &end, 0);
1040                                 if (!arg[9] || *end)
1041                                         usage(pack_usage);
1042                                 continue;
1043                         }
1044                         if (!strncmp("--depth=", arg, 8)) {
1045                                 char *end;
1046                                 depth = strtoul(arg+8, &end, 0);
1047                                 if (!arg[8] || *end)
1048                                         usage(pack_usage);
1049                                 continue;
1050                         }
1051                         if (!strcmp("-q", arg)) {
1052                                 progress = 0;
1053                                 continue;
1054                         }
1055                         if (!strcmp("--no-reuse-delta", arg)) {
1056                                 no_reuse_delta = 1;
1057                                 continue;
1058                         }
1059                         if (!strcmp("--stdout", arg)) {
1060                                 pack_to_stdout = 1;
1061                                 continue;
1062                         }
1063                         usage(pack_usage);
1064                 }
1065                 if (base_name)
1066                         usage(pack_usage);
1067                 base_name = arg;
1068         }
1069
1070         if (pack_to_stdout != !base_name)
1071                 usage(pack_usage);
1072
1073         prepare_packed_git();
1074         if (progress) {
1075                 fprintf(stderr, "Generating pack...\n");
1076                 gettimeofday(&prev_tv, NULL);
1077         }
1078         while (fgets(line, sizeof(line), stdin) != NULL) {
1079                 unsigned char sha1[20];
1080
1081                 if (progress && (eye_candy <= nr_objects)) {
1082                         fprintf(stderr, "Counting objects...%d\r", nr_objects);
1083                         if (eye_candy && (50 <= eye_candy_incr)) {
1084                                 struct timeval tv;
1085                                 int time_diff;
1086                                 gettimeofday(&tv, NULL);
1087                                 time_diff = (tv.tv_sec - prev_tv.tv_sec);
1088                                 time_diff <<= 10;
1089                                 time_diff += (tv.tv_usec - prev_tv.tv_usec);
1090                                 if ((1 << 9) < time_diff)
1091                                         eye_candy_incr += 50;
1092                                 else if (50 < eye_candy_incr)
1093                                         eye_candy_incr -= 50;
1094                         }
1095                         eye_candy += eye_candy_incr;
1096                 }
1097                 if (line[0] == '-') {
1098                         if (get_sha1_hex(line+1, sha1))
1099                                 die("expected edge sha1, got garbage:\n %s",
1100                                     line+1);
1101                         add_preferred_base(sha1);
1102                         continue;
1103                 }
1104                 if (get_sha1_hex(line, sha1))
1105                         die("expected sha1, got garbage:\n %s", line);
1106                 add_object_entry(sha1, name_hash(NULL, line+41), 0);
1107         }
1108         if (progress)
1109                 fprintf(stderr, "Done counting %d objects.\n", nr_objects);
1110         if (non_empty && !nr_objects)
1111                 return 0;
1112
1113         sorted_by_sha = create_final_object_list();
1114         SHA1_Init(&ctx);
1115         list = sorted_by_sha;
1116         for (i = 0; i < nr_result; i++) {
1117                 struct object_entry *entry = *list++;
1118                 SHA1_Update(&ctx, entry->sha1, 20);
1119         }
1120         SHA1_Final(object_list_sha1, &ctx);
1121         if (progress && (nr_objects != nr_result))
1122                 fprintf(stderr, "Result has %d objects.\n", nr_result);
1123
1124         if (reuse_cached_pack(object_list_sha1, pack_to_stdout))
1125                 ;
1126         else {
1127                 prepare_pack(window, depth);
1128                 if (!pack_to_stdout) {
1129                         write_index_file();
1130                         puts(sha1_to_hex(object_list_sha1));
1131                 }
1132         }
1133         if (progress)
1134                 fprintf(stderr, "Total %d, written %d (delta %d), reused %d (delta %d)\n",
1135                         nr_result, written, written_delta, reused, reused_delta);
1136         return 0;
1137 }