pack-objects.c

   1 #include <ctype.h>
   2 #include "cache.h"
   3 #include "object.h"
   4 #include "delta.h"
   5 #include "csum-file.h"
   6
   7 static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] base-name < object-list";
   8
   9 enum object_type {
  10         OBJ_NONE,
  11         OBJ_COMMIT,
  12         OBJ_TREE,
  13         OBJ_BLOB,
  14         OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
  15 };
  16
  17 struct object_entry {
  18         unsigned char sha1[20];
  19         unsigned long size;
  20         unsigned long offset;
  21         unsigned int depth;
  22         unsigned int hash;
  23         enum object_type type;
  24         unsigned long delta_size;
  25         struct object_entry *delta;
  26 };
  27
  28 static struct object_entry **sorted_by_sha, **sorted_by_type;
  29 static struct object_entry *objects = NULL;
  30 static int nr_objects = 0, nr_alloc = 0;
  31 static const char *base_name;
  32
  33 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
  34 {
  35         unsigned long othersize, delta_size;
  36         char type[10];
  37         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
  38         void *delta_buf;
  39
  40         if (!otherbuf)
  41                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
  42         delta_buf = diff_delta(otherbuf, othersize,
  43                                buf, size, &delta_size, ~0UL);
  44         if (!delta_buf || delta_size != entry->delta_size)
  45                 die("delta size changed");
  46         free(buf);
  47         free(otherbuf);
  48         return delta_buf;
  49 }
  50
  51 static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
  52 {
  53         unsigned long size;
  54         char type[10];
  55         void *buf = read_sha1_file(entry->sha1, type, &size);
  56         char header[25];
  57         unsigned hdrlen, datalen;
  58
  59         if (!buf)
  60                 die("unable to read %s", sha1_to_hex(entry->sha1));
  61         if (size != entry->size)
  62                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
  63
  64         /*
  65          * The object header is a byte of 'type' followed by four bytes of
  66          * length, except for deltas that has the 20 bytes of delta sha
  67          * instead.
  68          */
  69         header[0] = ".CTB"[entry->type];
  70         hdrlen = 5;
  71         if (entry->delta) {
  72                 header[0] = 'D';
  73                 memcpy(header+5, entry->delta, 20);
  74                 buf = delta_against(buf, size, entry);
  75                 size = entry->delta_size;
  76                 hdrlen = 25;
  77         }
  78         datalen = htonl(size);
  79         memcpy(header+1, &datalen, 4);
  80         sha1write(f, header, hdrlen);
  81         datalen = sha1write_compressed(f, buf, size);
  82         free(buf);
  83         return hdrlen + datalen;
  84 }
  85
  86 static void write_pack_file(void)
  87 {
  88         int i;
  89         struct sha1file *f = sha1create("%s.%s", base_name, "pack");
  90         unsigned long offset = 0;
  91         unsigned long mb;
  92
  93         for (i = 0; i < nr_objects; i++) {
  94                 struct object_entry *entry = objects + i;
  95                 entry->offset = offset;
  96                 offset += write_object(f, entry);
  97         }
  98         sha1close(f);
  99         mb = offset >> 20;
 100         offset &= 0xfffff;
 101 }
 102
 103 static void write_index_file(void)
 104 {
 105         int i;
 106         struct sha1file *f = sha1create("%s.%s", base_name, "idx");
 107         struct object_entry **list = sorted_by_sha;
 108         struct object_entry **last = list + nr_objects;
 109         unsigned int array[256];
 110
 111         /*
 112          * Write the first-level table (the list is sorted,
 113          * but we use a 256-entry lookup to be able to avoid
 114          * having to do eight extra binary search iterations)
 115          */
 116         for (i = 0; i < 256; i++) {
 117                 struct object_entry **next = list;
 118                 while (next < last) {
 119                         struct object_entry *entry = *next;
 120                         if (entry->sha1[0] != i)
 121                                 break;
 122                         next++;
 123                 }
 124                 array[i] = htonl(next - sorted_by_sha);
 125                 list = next;
 126         }
 127         sha1write(f, array, 256 * sizeof(int));
 128
 129         /*
 130          * Write the actual SHA1 entries..
 131          */
 132         list = sorted_by_sha;
 133         for (i = 0; i < nr_objects; i++) {
 134                 struct object_entry *entry = *list++;
 135                 unsigned int offset = htonl(entry->offset);
 136                 sha1write(f, &offset, 4);
 137                 sha1write(f, entry->sha1, 20);
 138         }
 139         sha1close(f);
 140 }
 141
 142 static void add_object_entry(unsigned char *sha1, unsigned int hash)
 143 {
 144         unsigned int idx = nr_objects;
 145         struct object_entry *entry;
 146
 147         if (idx >= nr_alloc) {
 148                 unsigned int needed = (idx + 1024) * 3 / 2;
 149                 objects = xrealloc(objects, needed * sizeof(*entry));
 150                 nr_alloc = needed;
 151         }
 152         entry = objects + idx;
 153         memset(entry, 0, sizeof(*entry));
 154         memcpy(entry->sha1, sha1, 20);
 155         entry->hash = hash;
 156         nr_objects = idx+1;
 157 }
 158
 159 static void check_object(struct object_entry *entry)
 160 {
 161         char buffer[128];
 162         char type[10];
 163         unsigned long mapsize;
 164         z_stream stream;
 165         void *map;
 166
 167         map = map_sha1_file(entry->sha1, &mapsize);
 168         if (!map)
 169                 die("unable to map %s", sha1_to_hex(entry->sha1));
 170         if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
 171                 die("unable to unpack %s header", sha1_to_hex(entry->sha1));
 172         munmap(map, mapsize);
 173         if (parse_sha1_header(buffer, type, &entry->size) < 0)
 174                 die("unable to parse %s header", sha1_to_hex(entry->sha1));
 175         if (!strcmp(type, "commit")) {
 176                 entry->type = OBJ_COMMIT;
 177         } else if (!strcmp(type, "tree")) {
 178                 entry->type = OBJ_TREE;
 179         } else if (!strcmp(type, "blob")) {
 180                 entry->type = OBJ_BLOB;
 181         } else
 182                 die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
 183 }
 184
 185 static void get_object_details(void)
 186 {
 187         int i;
 188         struct object_entry *entry = objects;
 189
 190         for (i = 0; i < nr_objects; i++)
 191                 check_object(entry++);
 192 }
 193
 194 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 195
 196 static entry_sort_t current_sort;
 197
 198 static int sort_comparator(const void *_a, const void *_b)
 199 {
 200         struct object_entry *a = *(struct object_entry **)_a;
 201         struct object_entry *b = *(struct object_entry **)_b;
 202         return current_sort(a,b);
 203 }
 204
 205 static struct object_entry **create_sorted_list(entry_sort_t sort)
 206 {
 207         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 208         int i;
 209
 210         for (i = 0; i < nr_objects; i++)
 211                 list[i] = objects + i;
 212         current_sort = sort;
 213         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 214         return list;
 215 }
 216
 217 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 218 {
 219         return memcmp(a->sha1, b->sha1, 20);
 220 }
 221
 222 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 223 {
 224         if (a->type < b->type)
 225                 return -1;
 226         if (a->type > b->type)
 227                 return 1;
 228         if (a->hash < b->hash)
 229                 return -1;
 230         if (a->hash > b->hash)
 231                 return 1;
 232         if (a->size < b->size)
 233                 return -1;
 234         if (a->size > b->size)
 235                 return 1;
 236         return a < b ? -1 : (a > b);
 237 }
 238
 239 struct unpacked {
 240         struct object_entry *entry;
 241         void *data;
 242 };
 243
 244 /*
 245  * We search for deltas _backwards_ in a list sorted by type and
 246  * by size, so that we see progressively smaller and smaller files.
 247  * That's because we prefer deltas to be from the bigger file
 248  * to the smaller - deletes are potentially cheaper, but perhaps
 249  * more importantly, the bigger file is likely the more recent
 250  * one.
 251  */
 252 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 253 {
 254         struct object_entry *cur_entry = cur->entry;
 255         struct object_entry *old_entry = old->entry;
 256         unsigned long size, oldsize, delta_size, sizediff;
 257         long max_size;
 258         void *delta_buf;
 259
 260         /* Don't bother doing diffs between different types */
 261         if (cur_entry->type != old_entry->type)
 262                 return -1;
 263
 264         size = cur_entry->size;
 265         if (size < 50)
 266                 return -1;
 267         oldsize = old_entry->size;
 268         sizediff = oldsize > size ? oldsize - size : size - oldsize;
 269         if (sizediff > size / 8)
 270                 return -1;
 271         if (old_entry->depth >= max_depth)
 272                 return 0;
 273
 274         /*
 275          * NOTE!
 276          *
 277          * We always delta from the bigger to the smaller, since that's
 278          * more space-efficient (deletes don't have to say _what_ they
 279          * delete).
 280          */
 281         max_size = size / 2 - 20;
 282         if (cur_entry->delta)
 283                 max_size = cur_entry->delta_size-1;
 284         if (sizediff >= max_size)
 285                 return -1;
 286         delta_buf = diff_delta(old->data, oldsize,
 287                                cur->data, size, &delta_size, max_size);
 288         if (!delta_buf)
 289                 return 0;
 290         cur_entry->delta = old_entry;
 291         cur_entry->delta_size = delta_size;
 292         cur_entry->depth = old_entry->depth + 1;
 293         free(delta_buf);
 294         return 0;
 295 }
 296
 297 static void find_deltas(struct object_entry **list, int window, int depth)
 298 {
 299         int i, idx;
 300         unsigned int array_size = window * sizeof(struct unpacked);
 301         struct unpacked *array = xmalloc(array_size);
 302
 303         memset(array, 0, array_size);
 304         i = nr_objects;
 305         idx = 0;
 306         while (--i >= 0) {
 307                 struct object_entry *entry = list[i];
 308                 struct unpacked *n = array + idx;
 309                 unsigned long size;
 310                 char type[10];
 311                 int j;
 312
 313                 free(n->data);
 314                 n->entry = entry;
 315                 n->data = read_sha1_file(entry->sha1, type, &size);
 316                 if (size != entry->size)
 317                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 318                 j = window;
 319                 while (--j > 0) {
 320                         unsigned int other_idx = idx + j;
 321                         struct unpacked *m;
 322                         if (other_idx >= window)
 323                                 other_idx -= window;
 324                         m = array + other_idx;
 325                         if (!m->entry)
 326                                 break;
 327                         if (try_delta(n, m, depth) < 0)
 328                                 break;
 329                 }
 330                 idx++;
 331                 if (idx >= window)
 332                         idx = 0;
 333         }
 334 }
 335
 336 int main(int argc, char **argv)
 337 {
 338         char line[PATH_MAX + 20];
 339         int window = 10, depth = 10;
 340         int i;
 341
 342         for (i = 1; i < argc; i++) {
 343                 const char *arg = argv[i];
 344
 345                 if (*arg == '-') {
 346                         if (!strncmp("--window=", arg, 9)) {
 347                                 char *end;
 348                                 window = strtoul(arg+9, &end, 0);
 349                                 if (!arg[9] || *end)
 350                                         usage(pack_usage);
 351                                 continue;
 352                         }
 353                         if (!strncmp("--depth=", arg, 8)) {
 354                                 char *end;
 355                                 depth = strtoul(arg+8, &end, 0);
 356                                 if (!arg[8] || *end)
 357                                         usage(pack_usage);
 358                                 continue;
 359                         }
 360                         usage(pack_usage);
 361                 }
 362                 if (base_name)
 363                         usage(pack_usage);
 364                 base_name = arg;
 365         }
 366
 367         if (!base_name)
 368                 usage(pack_usage);
 369
 370         while (fgets(line, sizeof(line), stdin) != NULL) {
 371                 unsigned int hash;
 372                 char *p;
 373                 unsigned char sha1[20];
 374
 375                 if (get_sha1_hex(line, sha1))
 376                         die("expected sha1, got garbage");
 377                 hash = 0;
 378                 p = line+40;
 379                 while (*p) {
 380                         unsigned char c = *p++;
 381                         if (isspace(c))
 382                                 continue;
 383                         hash = hash * 11 + c;
 384                 }
 385                 add_object_entry(sha1, hash);
 386         }
 387         get_object_details();
 388
 389         printf("Packing %d objects\n", nr_objects);
 390
 391         sorted_by_sha = create_sorted_list(sha1_sort);
 392         sorted_by_type = create_sorted_list(type_size_sort);
 393         if (window && depth)
 394                 find_deltas(sorted_by_type, window+1, depth);
 395
 396         write_pack_file();
 397         write_index_file();
 398         return 0;
 399 }