pack-objects.c

   1 #include "cache.h"
   2 #include "object.h"
   3 #include "delta.h"
   4
   5 static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] base-name < object-list";
   6
   7 enum object_type {
   8         OBJ_NONE,
   9         OBJ_COMMIT,
  10         OBJ_TREE,
  11         OBJ_BLOB,
  12         OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
  13 };
  14
  15 struct object_entry {
  16         unsigned char sha1[20];
  17         unsigned long size;
  18         unsigned long offset;
  19         unsigned int depth;
  20         unsigned int flags;
  21         enum object_type type;
  22         unsigned long delta_size;
  23         struct object_entry *delta;
  24 };
  25
  26 static struct object_entry **sorted_by_sha, **sorted_by_type;
  27 static struct object_entry *objects = NULL;
  28 static int nr_objects = 0, nr_alloc = 0;
  29 static const char *base_name;
  30
  31 struct myfile {
  32         int fd;
  33         unsigned long chars;
  34         unsigned char buffer[8192];
  35 };
  36
  37 static FILE *create_file(const char *suffix)
  38 {
  39         static char filename[PATH_MAX];
  40         unsigned len;
  41
  42         len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
  43         if (len >= PATH_MAX)
  44                 die("you wascally wabbit, you");
  45         return fopen(filename, "w");
  46 }
  47
  48 static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
  49 {
  50         z_stream stream;
  51         unsigned long maxsize;
  52         void *out;
  53
  54         memset(&stream, 0, sizeof(stream));
  55         deflateInit(&stream, Z_DEFAULT_COMPRESSION);
  56         maxsize = deflateBound(&stream, size);
  57         out = xmalloc(maxsize);
  58
  59         /* Compress it */
  60         stream.next_in = in;
  61         stream.avail_in = size;
  62
  63         stream.next_out = out;
  64         stream.avail_out = maxsize;
  65
  66         while (deflate(&stream, Z_FINISH) == Z_OK)
  67                 /* nothing */;
  68         deflateEnd(&stream);
  69
  70         size = stream.total_out;
  71         fwrite(out, size, 1, f);
  72         free(out);
  73         return size;
  74 }
  75
  76 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
  77 {
  78         unsigned long othersize, delta_size;
  79         char type[10];
  80         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
  81         void *delta_buf;
  82
  83         if (!otherbuf)
  84                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
  85         delta_buf = diff_delta(otherbuf, othersize,
  86                                buf, size, &delta_size, ~0UL);
  87         if (!delta_buf || delta_size != entry->delta_size)
  88                 die("delta size changed");
  89         free(buf);
  90         free(otherbuf);
  91         return delta_buf;
  92 }
  93
  94 static unsigned long write_object(FILE *f, struct object_entry *entry)
  95 {
  96         unsigned long size;
  97         char type[10];
  98         void *buf = read_sha1_file(entry->sha1, type, &size);
  99         char header[25];
 100         unsigned hdrlen, datalen;
 101
 102         if (!buf)
 103                 die("unable to read %s", sha1_to_hex(entry->sha1));
 104         if (size != entry->size)
 105                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 106
 107         /*
 108          * The object header is a byte of 'type' followed by four bytes of
 109          * length, except for deltas that has the 20 bytes of delta sha
 110          * instead.
 111          */
 112         header[0] = ".CTB"[entry->type];
 113         hdrlen = 5;
 114         if (entry->delta) {
 115                 header[0] = 'D';
 116                 memcpy(header+5, entry->delta, 20);
 117                 buf = delta_against(buf, size, entry);
 118                 size = entry->delta_size;
 119                 hdrlen = 25;
 120         }
 121         datalen = htonl(size);
 122         memcpy(header+1, &datalen, 4);
 123         fwrite(header, hdrlen, 1, f);
 124         datalen = fwrite_compressed(buf, size, f);
 125         free(buf);
 126         return hdrlen + datalen;
 127 }
 128
 129 static void write_pack_file(void)
 130 {
 131         int i;
 132         FILE *f = create_file("pack");
 133         unsigned long offset = 0;
 134         unsigned long mb;
 135
 136         for (i = 0; i < nr_objects; i++) {
 137                 struct object_entry *entry = objects + i;
 138                 entry->offset = offset;
 139                 offset += write_object(f, entry);
 140         }
 141         fclose(f);
 142         mb = offset >> 20;
 143         offset &= 0xfffff;
 144 }
 145
 146 static void write_index_file(void)
 147 {
 148         int i;
 149         FILE *f = create_file("idx");
 150         struct object_entry **list = sorted_by_sha;
 151         struct object_entry **last = list + nr_objects;
 152         unsigned int array[256];
 153
 154         /*
 155          * Write the first-level table (the list is sorted,
 156          * but we use a 256-entry lookup to be able to avoid
 157          * having to do eight extra binary search iterations)
 158          */
 159         for (i = 0; i < 256; i++) {
 160                 struct object_entry **next = list;
 161                 while (next < last) {
 162                         struct object_entry *entry = *next;
 163                         if (entry->sha1[0] != i)
 164                                 break;
 165                         next++;
 166                 }
 167                 array[i] = htonl(next - sorted_by_sha);
 168                 list = next;
 169         }
 170         fwrite(array, 256, sizeof(int), f);
 171
 172         /*
 173          * Write the actual SHA1 entries..
 174          */
 175         list = sorted_by_sha;
 176         for (i = 0; i < nr_objects; i++) {
 177                 struct object_entry *entry = *list++;
 178                 unsigned int offset = htonl(entry->offset);
 179                 fwrite(&offset, 4, 1, f);
 180                 fwrite(entry->sha1, 20, 1, f);
 181         }
 182         fclose(f);
 183 }
 184
 185 static void add_object_entry(unsigned char *sha1)
 186 {
 187         unsigned int idx = nr_objects;
 188         struct object_entry *entry;
 189
 190         if (idx >= nr_alloc) {
 191                 unsigned int needed = (idx + 1024) * 3 / 2;
 192                 objects = xrealloc(objects, needed * sizeof(*entry));
 193                 nr_alloc = needed;
 194         }
 195         entry = objects + idx;
 196         memset(entry, 0, sizeof(*entry));
 197         memcpy(entry->sha1, sha1, 20);
 198         nr_objects = idx+1;
 199 }
 200
 201 static void check_object(struct object_entry *entry)
 202 {
 203         char buffer[128];
 204         char type[10];
 205         unsigned long mapsize;
 206         z_stream stream;
 207         void *map;
 208
 209         map = map_sha1_file(entry->sha1, &mapsize);
 210         if (!map)
 211                 die("unable to map %s", sha1_to_hex(entry->sha1));
 212         if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
 213                 die("unable to unpack %s header", sha1_to_hex(entry->sha1));
 214         munmap(map, mapsize);
 215         if (parse_sha1_header(buffer, type, &entry->size) < 0)
 216                 die("unable to parse %s header", sha1_to_hex(entry->sha1));
 217         if (!strcmp(type, "commit")) {
 218                 entry->type = OBJ_COMMIT;
 219         } else if (!strcmp(type, "tree")) {
 220                 entry->type = OBJ_TREE;
 221         } else if (!strcmp(type, "blob")) {
 222                 entry->type = OBJ_BLOB;
 223         } else
 224                 die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
 225 }
 226
 227 static void get_object_details(void)
 228 {
 229         int i;
 230         struct object_entry *entry = objects;
 231
 232         for (i = 0; i < nr_objects; i++)
 233                 check_object(entry++);
 234 }
 235
 236 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 237
 238 static entry_sort_t current_sort;
 239
 240 static int sort_comparator(const void *_a, const void *_b)
 241 {
 242         struct object_entry *a = *(struct object_entry **)_a;
 243         struct object_entry *b = *(struct object_entry **)_b;
 244         return current_sort(a,b);
 245 }
 246
 247 static struct object_entry **create_sorted_list(entry_sort_t sort)
 248 {
 249         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 250         int i;
 251
 252         for (i = 0; i < nr_objects; i++)
 253                 list[i] = objects + i;
 254         current_sort = sort;
 255         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 256         return list;
 257 }
 258
 259 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 260 {
 261         return memcmp(a->sha1, b->sha1, 20);
 262 }
 263
 264 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 265 {
 266         if (a->type < b->type)
 267                 return -1;
 268         if (a->type > b->type)
 269                 return 1;
 270         if (a->size < b->size)
 271                 return -1;
 272         if (a->size > b->size)
 273                 return 1;
 274         return a < b ? -1 : (a > b);
 275 }
 276
 277 struct unpacked {
 278         struct object_entry *entry;
 279         void *data;
 280 };
 281
 282 /*
 283  * We search for deltas _backwards_ in a list sorted by type and
 284  * by size, so that we see progressively smaller and smaller files.
 285  * That's because we prefer deltas to be from the bigger file
 286  * to the smaller - deletes are potentially cheaper, but perhaps
 287  * more importantly, the bigger file is likely the more recent
 288  * one.
 289  */
 290 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 291 {
 292         struct object_entry *cur_entry = cur->entry;
 293         struct object_entry *old_entry = old->entry;
 294         unsigned long size, oldsize, delta_size, sizediff;
 295         long max_size;
 296         void *delta_buf;
 297
 298         /* Don't bother doing diffs between different types */
 299         if (cur_entry->type != old_entry->type)
 300                 return -1;
 301
 302         size = cur_entry->size;
 303         if (size < 50)
 304                 return -1;
 305         oldsize = old_entry->size;
 306         sizediff = oldsize > size ? oldsize - size : size - oldsize;
 307         if (sizediff > size / 8)
 308                 return -1;
 309         if (old_entry->depth >= max_depth)
 310                 return 0;
 311
 312         /*
 313          * NOTE!
 314          *
 315          * We always delta from the bigger to the smaller, since that's
 316          * more space-efficient (deletes don't have to say _what_ they
 317          * delete).
 318          */
 319         max_size = size / 2 - 20;
 320         if (cur_entry->delta)
 321                 max_size = cur_entry->delta_size-1;
 322         delta_buf = diff_delta(old->data, oldsize,
 323                                cur->data, size, &delta_size, max_size);
 324         if (!delta_buf)
 325                 return 0;
 326         cur_entry->delta = old_entry;
 327         cur_entry->delta_size = delta_size;
 328         cur_entry->depth = old_entry->depth + 1;
 329         free(delta_buf);
 330         return 0;
 331 }
 332
 333 static void find_deltas(struct object_entry **list, int window, int depth)
 334 {
 335         int i, idx;
 336         unsigned int array_size = window * sizeof(struct unpacked);
 337         struct unpacked *array = xmalloc(array_size);
 338
 339         memset(array, 0, array_size);
 340         i = nr_objects;
 341         idx = 0;
 342         while (--i >= 0) {
 343                 struct object_entry *entry = list[i];
 344                 struct unpacked *n = array + idx;
 345                 unsigned long size;
 346                 char type[10];
 347                 int j;
 348
 349                 free(n->data);
 350                 n->entry = entry;
 351                 n->data = read_sha1_file(entry->sha1, type, &size);
 352                 if (size != entry->size)
 353                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 354                 j = window;
 355                 while (--j > 0) {
 356                         unsigned int other_idx = idx + j;
 357                         struct unpacked *m;
 358                         if (other_idx >= window)
 359                                 other_idx -= window;
 360                         m = array + other_idx;
 361                         if (!m->entry)
 362                                 break;
 363                         if (try_delta(n, m, depth) < 0)
 364                                 break;
 365                 }
 366                 idx++;
 367                 if (idx >= window)
 368                         idx = 0;
 369         }
 370 }
 371
 372 int main(int argc, char **argv)
 373 {
 374         char line[128];
 375         int window = 10, depth = 10;
 376         int i;
 377
 378         for (i = 1; i < argc; i++) {
 379                 const char *arg = argv[i];
 380
 381                 if (*arg == '-') {
 382                         if (!strncmp("--window=", arg, 9)) {
 383                                 char *end;
 384                                 window = strtoul(arg+9, &end, 0);
 385                                 if (!arg[9] || *end)
 386                                         usage(pack_usage);
 387                                 continue;
 388                         }
 389                         if (!strncmp("--depth=", arg, 8)) {
 390                                 char *end;
 391                                 depth = strtoul(arg+8, &end, 0);
 392                                 if (!arg[8] || *end)
 393                                         usage(pack_usage);
 394                                 continue;
 395                         }
 396                         usage(pack_usage);
 397                 }
 398                 if (base_name)
 399                         usage(pack_usage);
 400                 base_name = arg;
 401         }
 402
 403         if (!base_name)
 404                 usage(pack_usage);
 405
 406         while (fgets(line, sizeof(line), stdin) != NULL) {
 407                 unsigned char sha1[20];
 408                 if (get_sha1_hex(line, sha1))
 409                         die("expected sha1, got garbage");
 410                 add_object_entry(sha1);
 411         }
 412         get_object_details();
 413
 414         printf("Packing %d objects\n", nr_objects);
 415
 416         sorted_by_sha = create_sorted_list(sha1_sort);
 417         sorted_by_type = create_sorted_list(type_size_sort);
 418         if (window && depth)
 419                 find_deltas(sorted_by_type, window+1, depth);
 420
 421         write_pack_file();
 422         write_index_file();
 423         return 0;
 424 }