The second batch
[git.git] / pack-revindex.c
blob0e4a31d9db9e71aa67ac6812241b064f01bb02a2
1 #include "cache.h"
2 #include "pack-revindex.h"
3 #include "object-store.h"
4 #include "packfile.h"
5 #include "config.h"
6 #include "midx.h"
8 struct revindex_entry {
9 off_t offset;
10 unsigned int nr;
14 * Pack index for existing packs give us easy access to the offsets into
15 * corresponding pack file where each object's data starts, but the entries
16 * do not store the size of the compressed representation (uncompressed
17 * size is easily available by examining the pack entry header). It is
18 * also rather expensive to find the sha1 for an object given its offset.
20 * The pack index file is sorted by object name mapping to offset;
21 * this revindex array is a list of offset/index_nr pairs
22 * ordered by offset, so if you know the offset of an object, next offset
23 * is where its packed representation ends and the index_nr can be used to
24 * get the object sha1 from the main index.
28 * This is a least-significant-digit radix sort.
30 * It sorts each of the "n" items in "entries" by its offset field. The "max"
31 * parameter must be at least as large as the largest offset in the array,
32 * and lets us quit the sort early.
34 static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max)
37 * We use a "digit" size of 16 bits. That keeps our memory
38 * usage reasonable, and we can generally (for a 4G or smaller
39 * packfile) quit after two rounds of radix-sorting.
41 #define DIGIT_SIZE (16)
42 #define BUCKETS (1 << DIGIT_SIZE)
44 * We want to know the bucket that a[i] will go into when we are using
45 * the digit that is N bits from the (least significant) end.
47 #define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1))
50 * We need O(n) temporary storage. Rather than do an extra copy of the
51 * partial results into "entries", we sort back and forth between the
52 * real array and temporary storage. In each iteration of the loop, we
53 * keep track of them with alias pointers, always sorting from "from"
54 * to "to".
56 struct revindex_entry *tmp, *from, *to;
57 int bits;
58 unsigned *pos;
60 ALLOC_ARRAY(pos, BUCKETS);
61 ALLOC_ARRAY(tmp, n);
62 from = entries;
63 to = tmp;
66 * If (max >> bits) is zero, then we know that the radix digit we are
67 * on (and any higher) will be zero for all entries, and our loop will
68 * be a no-op, as everybody lands in the same zero-th bucket.
70 for (bits = 0; max >> bits; bits += DIGIT_SIZE) {
71 unsigned i;
73 memset(pos, 0, BUCKETS * sizeof(*pos));
76 * We want pos[i] to store the index of the last element that
77 * will go in bucket "i" (actually one past the last element).
78 * To do this, we first count the items that will go in each
79 * bucket, which gives us a relative offset from the last
80 * bucket. We can then cumulatively add the index from the
81 * previous bucket to get the true index.
83 for (i = 0; i < n; i++)
84 pos[BUCKET_FOR(from, i, bits)]++;
85 for (i = 1; i < BUCKETS; i++)
86 pos[i] += pos[i-1];
89 * Now we can drop the elements into their correct buckets (in
90 * our temporary array). We iterate the pos counter backwards
91 * to avoid using an extra index to count up. And since we are
92 * going backwards there, we must also go backwards through the
93 * array itself, to keep the sort stable.
95 * Note that we use an unsigned iterator to make sure we can
96 * handle 2^32-1 objects, even on a 32-bit system. But this
97 * means we cannot use the more obvious "i >= 0" loop condition
98 * for counting backwards, and must instead check for
99 * wrap-around with UINT_MAX.
101 for (i = n - 1; i != UINT_MAX; i--)
102 to[--pos[BUCKET_FOR(from, i, bits)]] = from[i];
105 * Now "to" contains the most sorted list, so we swap "from" and
106 * "to" for the next iteration.
108 SWAP(from, to);
112 * If we ended with our data in the original array, great. If not,
113 * we have to move it back from the temporary storage.
115 if (from != entries)
116 COPY_ARRAY(entries, tmp, n);
117 free(tmp);
118 free(pos);
120 #undef BUCKET_FOR
121 #undef BUCKETS
122 #undef DIGIT_SIZE
126 * Ordered list of offsets of objects in the pack.
128 static void create_pack_revindex(struct packed_git *p)
130 const unsigned num_ent = p->num_objects;
131 unsigned i;
132 const char *index = p->index_data;
133 const unsigned hashsz = the_hash_algo->rawsz;
135 ALLOC_ARRAY(p->revindex, num_ent + 1);
136 index += 4 * 256;
138 if (p->index_version > 1) {
139 const uint32_t *off_32 =
140 (uint32_t *)(index + 8 + (size_t)p->num_objects * (hashsz + 4));
141 const uint32_t *off_64 = off_32 + p->num_objects;
142 for (i = 0; i < num_ent; i++) {
143 const uint32_t off = ntohl(*off_32++);
144 if (!(off & 0x80000000)) {
145 p->revindex[i].offset = off;
146 } else {
147 p->revindex[i].offset = get_be64(off_64);
148 off_64 += 2;
150 p->revindex[i].nr = i;
152 } else {
153 for (i = 0; i < num_ent; i++) {
154 const uint32_t hl = *((uint32_t *)(index + (hashsz + 4) * i));
155 p->revindex[i].offset = ntohl(hl);
156 p->revindex[i].nr = i;
161 * This knows the pack format -- the hash trailer
162 * follows immediately after the last object data.
164 p->revindex[num_ent].offset = p->pack_size - hashsz;
165 p->revindex[num_ent].nr = -1;
166 sort_revindex(p->revindex, num_ent, p->pack_size);
169 static int create_pack_revindex_in_memory(struct packed_git *p)
171 if (git_env_bool(GIT_TEST_REV_INDEX_DIE_IN_MEMORY, 0))
172 die("dying as requested by '%s'",
173 GIT_TEST_REV_INDEX_DIE_IN_MEMORY);
174 if (open_pack_index(p))
175 return -1;
176 create_pack_revindex(p);
177 return 0;
180 static char *pack_revindex_filename(struct packed_git *p)
182 size_t len;
183 if (!strip_suffix(p->pack_name, ".pack", &len))
184 BUG("pack_name does not end in .pack");
185 return xstrfmt("%.*s.rev", (int)len, p->pack_name);
188 #define RIDX_HEADER_SIZE (12)
189 #define RIDX_MIN_SIZE (RIDX_HEADER_SIZE + (2 * the_hash_algo->rawsz))
191 struct revindex_header {
192 uint32_t signature;
193 uint32_t version;
194 uint32_t hash_id;
197 static int load_revindex_from_disk(char *revindex_name,
198 uint32_t num_objects,
199 const uint32_t **data_p, size_t *len_p)
201 int fd, ret = 0;
202 struct stat st;
203 void *data = NULL;
204 size_t revindex_size;
205 struct revindex_header *hdr;
207 fd = git_open(revindex_name);
209 if (fd < 0) {
210 ret = -1;
211 goto cleanup;
213 if (fstat(fd, &st)) {
214 ret = error_errno(_("failed to read %s"), revindex_name);
215 goto cleanup;
218 revindex_size = xsize_t(st.st_size);
220 if (revindex_size < RIDX_MIN_SIZE) {
221 ret = error(_("reverse-index file %s is too small"), revindex_name);
222 goto cleanup;
225 if (revindex_size - RIDX_MIN_SIZE != st_mult(sizeof(uint32_t), num_objects)) {
226 ret = error(_("reverse-index file %s is corrupt"), revindex_name);
227 goto cleanup;
230 data = xmmap(NULL, revindex_size, PROT_READ, MAP_PRIVATE, fd, 0);
231 hdr = data;
233 if (ntohl(hdr->signature) != RIDX_SIGNATURE) {
234 ret = error(_("reverse-index file %s has unknown signature"), revindex_name);
235 goto cleanup;
237 if (ntohl(hdr->version) != 1) {
238 ret = error(_("reverse-index file %s has unsupported version %"PRIu32),
239 revindex_name, ntohl(hdr->version));
240 goto cleanup;
242 if (!(ntohl(hdr->hash_id) == 1 || ntohl(hdr->hash_id) == 2)) {
243 ret = error(_("reverse-index file %s has unsupported hash id %"PRIu32),
244 revindex_name, ntohl(hdr->hash_id));
245 goto cleanup;
248 cleanup:
249 if (ret) {
250 if (data)
251 munmap(data, revindex_size);
252 } else {
253 *len_p = revindex_size;
254 *data_p = (const uint32_t *)data;
257 if (fd >= 0)
258 close(fd);
259 return ret;
262 static int load_pack_revindex_from_disk(struct packed_git *p)
264 char *revindex_name;
265 int ret;
266 if (open_pack_index(p))
267 return -1;
269 revindex_name = pack_revindex_filename(p);
271 ret = load_revindex_from_disk(revindex_name,
272 p->num_objects,
273 &p->revindex_map,
274 &p->revindex_size);
275 if (ret)
276 goto cleanup;
278 p->revindex_data = (const uint32_t *)((const char *)p->revindex_map + RIDX_HEADER_SIZE);
280 cleanup:
281 free(revindex_name);
282 return ret;
285 int load_pack_revindex(struct packed_git *p)
287 if (p->revindex || p->revindex_data)
288 return 0;
290 if (!load_pack_revindex_from_disk(p))
291 return 0;
292 else if (!create_pack_revindex_in_memory(p))
293 return 0;
294 return -1;
297 int load_midx_revindex(struct multi_pack_index *m)
299 char *revindex_name;
300 int ret;
301 if (m->revindex_data)
302 return 0;
304 revindex_name = get_midx_rev_filename(m);
306 ret = load_revindex_from_disk(revindex_name,
307 m->num_objects,
308 &m->revindex_map,
309 &m->revindex_len);
310 if (ret)
311 goto cleanup;
313 m->revindex_data = (const uint32_t *)((const char *)m->revindex_map + RIDX_HEADER_SIZE);
315 cleanup:
316 free(revindex_name);
317 return ret;
320 int close_midx_revindex(struct multi_pack_index *m)
322 if (!m || !m->revindex_map)
323 return 0;
325 munmap((void*)m->revindex_map, m->revindex_len);
327 m->revindex_map = NULL;
328 m->revindex_data = NULL;
329 m->revindex_len = 0;
331 return 0;
334 int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)
336 unsigned lo, hi;
338 if (load_pack_revindex(p) < 0)
339 return -1;
341 lo = 0;
342 hi = p->num_objects + 1;
344 do {
345 const unsigned mi = lo + (hi - lo) / 2;
346 off_t got = pack_pos_to_offset(p, mi);
348 if (got == ofs) {
349 *pos = mi;
350 return 0;
351 } else if (ofs < got)
352 hi = mi;
353 else
354 lo = mi + 1;
355 } while (lo < hi);
357 error("bad offset for revindex");
358 return -1;
361 uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos)
363 if (!(p->revindex || p->revindex_data))
364 BUG("pack_pos_to_index: reverse index not yet loaded");
365 if (p->num_objects <= pos)
366 BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos);
368 if (p->revindex)
369 return p->revindex[pos].nr;
370 else
371 return get_be32(p->revindex_data + pos);
374 off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos)
376 if (!(p->revindex || p->revindex_data))
377 BUG("pack_pos_to_index: reverse index not yet loaded");
378 if (p->num_objects < pos)
379 BUG("pack_pos_to_offset: out-of-bounds object at %"PRIu32, pos);
381 if (p->revindex)
382 return p->revindex[pos].offset;
383 else if (pos == p->num_objects)
384 return p->pack_size - the_hash_algo->rawsz;
385 else
386 return nth_packed_object_offset(p, pack_pos_to_index(p, pos));
389 uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos)
391 if (!m->revindex_data)
392 BUG("pack_pos_to_midx: reverse index not yet loaded");
393 if (m->num_objects <= pos)
394 BUG("pack_pos_to_midx: out-of-bounds object at %"PRIu32, pos);
395 return get_be32(m->revindex_data + pos);
398 struct midx_pack_key {
399 uint32_t pack;
400 off_t offset;
402 uint32_t preferred_pack;
403 struct multi_pack_index *midx;
406 static int midx_pack_order_cmp(const void *va, const void *vb)
408 const struct midx_pack_key *key = va;
409 struct multi_pack_index *midx = key->midx;
411 uint32_t versus = pack_pos_to_midx(midx, (uint32_t*)vb - (const uint32_t *)midx->revindex_data);
412 uint32_t versus_pack = nth_midxed_pack_int_id(midx, versus);
413 off_t versus_offset;
415 uint32_t key_preferred = key->pack == key->preferred_pack;
416 uint32_t versus_preferred = versus_pack == key->preferred_pack;
419 * First, compare the preferred-ness, noting that the preferred pack
420 * comes first.
422 if (key_preferred && !versus_preferred)
423 return -1;
424 else if (!key_preferred && versus_preferred)
425 return 1;
427 /* Then, break ties first by comparing the pack IDs. */
428 if (key->pack < versus_pack)
429 return -1;
430 else if (key->pack > versus_pack)
431 return 1;
433 /* Finally, break ties by comparing offsets within a pack. */
434 versus_offset = nth_midxed_offset(midx, versus);
435 if (key->offset < versus_offset)
436 return -1;
437 else if (key->offset > versus_offset)
438 return 1;
440 return 0;
443 int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)
445 struct midx_pack_key key;
446 uint32_t *found;
448 if (!m->revindex_data)
449 BUG("midx_to_pack_pos: reverse index not yet loaded");
450 if (m->num_objects <= at)
451 BUG("midx_to_pack_pos: out-of-bounds object at %"PRIu32, at);
453 key.pack = nth_midxed_pack_int_id(m, at);
454 key.offset = nth_midxed_offset(m, at);
455 key.midx = m;
457 * The preferred pack sorts first, so determine its identifier by
458 * looking at the first object in pseudo-pack order.
460 * Note that if no --preferred-pack is explicitly given when writing a
461 * multi-pack index, then whichever pack has the lowest identifier
462 * implicitly is preferred (and includes all its objects, since ties are
463 * broken first by pack identifier).
465 key.preferred_pack = nth_midxed_pack_int_id(m, pack_pos_to_midx(m, 0));
467 found = bsearch(&key, m->revindex_data, m->num_objects,
468 sizeof(*m->revindex_data), midx_pack_order_cmp);
470 if (!found)
471 return error("bad offset for revindex");
473 *pos = found - m->revindex_data;
474 return 0;