Formed in 2009, the Archive Team (not to be confused with the archive.org Archive-It Team) is a rogue archivist collective dedicated to saving copies of rapidly dying or deleted websites for the sake of history and digital heritage. The group is 100% composed of volunteers and interested parties, and has expanded into a large amount of related projects for saving online and digital history.
Permalink
Cannot retrieve contributors at this time
475 lines (403 sloc)
12.3 KB
| #include "cache.h" | |
| #include "pack-revindex.h" | |
| #include "object-store.h" | |
| #include "packfile.h" | |
| #include "config.h" | |
| #include "midx.h" | |
| struct revindex_entry { | |
| off_t offset; | |
| unsigned int nr; | |
| }; | |
| /* | |
| * Pack index for existing packs give us easy access to the offsets into | |
| * corresponding pack file where each object's data starts, but the entries | |
| * do not store the size of the compressed representation (uncompressed | |
| * size is easily available by examining the pack entry header). It is | |
| * also rather expensive to find the sha1 for an object given its offset. | |
| * | |
| * The pack index file is sorted by object name mapping to offset; | |
| * this revindex array is a list of offset/index_nr pairs | |
| * ordered by offset, so if you know the offset of an object, next offset | |
| * is where its packed representation ends and the index_nr can be used to | |
| * get the object sha1 from the main index. | |
| */ | |
| /* | |
| * This is a least-significant-digit radix sort. | |
| * | |
| * It sorts each of the "n" items in "entries" by its offset field. The "max" | |
| * parameter must be at least as large as the largest offset in the array, | |
| * and lets us quit the sort early. | |
| */ | |
| static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max) | |
| { | |
| /* | |
| * We use a "digit" size of 16 bits. That keeps our memory | |
| * usage reasonable, and we can generally (for a 4G or smaller | |
| * packfile) quit after two rounds of radix-sorting. | |
| */ | |
| #define DIGIT_SIZE (16) | |
| #define BUCKETS (1 << DIGIT_SIZE) | |
| /* | |
| * We want to know the bucket that a[i] will go into when we are using | |
| * the digit that is N bits from the (least significant) end. | |
| */ | |
| #define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1)) | |
| /* | |
| * We need O(n) temporary storage. Rather than do an extra copy of the | |
| * partial results into "entries", we sort back and forth between the | |
| * real array and temporary storage. In each iteration of the loop, we | |
| * keep track of them with alias pointers, always sorting from "from" | |
| * to "to". | |
| */ | |
| struct revindex_entry *tmp, *from, *to; | |
| int bits; | |
| unsigned *pos; | |
| ALLOC_ARRAY(pos, BUCKETS); | |
| ALLOC_ARRAY(tmp, n); | |
| from = entries; | |
| to = tmp; | |
| /* | |
| * If (max >> bits) is zero, then we know that the radix digit we are | |
| * on (and any higher) will be zero for all entries, and our loop will | |
| * be a no-op, as everybody lands in the same zero-th bucket. | |
| */ | |
| for (bits = 0; max >> bits; bits += DIGIT_SIZE) { | |
| unsigned i; | |
| memset(pos, 0, BUCKETS * sizeof(*pos)); | |
| /* | |
| * We want pos[i] to store the index of the last element that | |
| * will go in bucket "i" (actually one past the last element). | |
| * To do this, we first count the items that will go in each | |
| * bucket, which gives us a relative offset from the last | |
| * bucket. We can then cumulatively add the index from the | |
| * previous bucket to get the true index. | |
| */ | |
| for (i = 0; i < n; i++) | |
| pos[BUCKET_FOR(from, i, bits)]++; | |
| for (i = 1; i < BUCKETS; i++) | |
| pos[i] += pos[i-1]; | |
| /* | |
| * Now we can drop the elements into their correct buckets (in | |
| * our temporary array). We iterate the pos counter backwards | |
| * to avoid using an extra index to count up. And since we are | |
| * going backwards there, we must also go backwards through the | |
| * array itself, to keep the sort stable. | |
| * | |
| * Note that we use an unsigned iterator to make sure we can | |
| * handle 2^32-1 objects, even on a 32-bit system. But this | |
| * means we cannot use the more obvious "i >= 0" loop condition | |
| * for counting backwards, and must instead check for | |
| * wrap-around with UINT_MAX. | |
| */ | |
| for (i = n - 1; i != UINT_MAX; i--) | |
| to[--pos[BUCKET_FOR(from, i, bits)]] = from[i]; | |
| /* | |
| * Now "to" contains the most sorted list, so we swap "from" and | |
| * "to" for the next iteration. | |
| */ | |
| SWAP(from, to); | |
| } | |
| /* | |
| * If we ended with our data in the original array, great. If not, | |
| * we have to move it back from the temporary storage. | |
| */ | |
| if (from != entries) | |
| COPY_ARRAY(entries, tmp, n); | |
| free(tmp); | |
| free(pos); | |
| #undef BUCKET_FOR | |
| #undef BUCKETS | |
| #undef DIGIT_SIZE | |
| } | |
| /* | |
| * Ordered list of offsets of objects in the pack. | |
| */ | |
| static void create_pack_revindex(struct packed_git *p) | |
| { | |
| const unsigned num_ent = p->num_objects; | |
| unsigned i; | |
| const char *index = p->index_data; | |
| const unsigned hashsz = the_hash_algo->rawsz; | |
| ALLOC_ARRAY(p->revindex, num_ent + 1); | |
| index += 4 * 256; | |
| if (p->index_version > 1) { | |
| const uint32_t *off_32 = | |
| (uint32_t *)(index + 8 + (size_t)p->num_objects * (hashsz + 4)); | |
| const uint32_t *off_64 = off_32 + p->num_objects; | |
| for (i = 0; i < num_ent; i++) { | |
| const uint32_t off = ntohl(*off_32++); | |
| if (!(off & 0x80000000)) { | |
| p->revindex[i].offset = off; | |
| } else { | |
| p->revindex[i].offset = get_be64(off_64); | |
| off_64 += 2; | |
| } | |
| p->revindex[i].nr = i; | |
| } | |
| } else { | |
| for (i = 0; i < num_ent; i++) { | |
| const uint32_t hl = *((uint32_t *)(index + (hashsz + 4) * i)); | |
| p->revindex[i].offset = ntohl(hl); | |
| p->revindex[i].nr = i; | |
| } | |
| } | |
| /* | |
| * This knows the pack format -- the hash trailer | |
| * follows immediately after the last object data. | |
| */ | |
| p->revindex[num_ent].offset = p->pack_size - hashsz; | |
| p->revindex[num_ent].nr = -1; | |
| sort_revindex(p->revindex, num_ent, p->pack_size); | |
| } | |
| static int create_pack_revindex_in_memory(struct packed_git *p) | |
| { | |
| if (git_env_bool(GIT_TEST_REV_INDEX_DIE_IN_MEMORY, 0)) | |
| die("dying as requested by '%s'", | |
| GIT_TEST_REV_INDEX_DIE_IN_MEMORY); | |
| if (open_pack_index(p)) | |
| return -1; | |
| create_pack_revindex(p); | |
| return 0; | |
| } | |
| static char *pack_revindex_filename(struct packed_git *p) | |
| { | |
| size_t len; | |
| if (!strip_suffix(p->pack_name, ".pack", &len)) | |
| BUG("pack_name does not end in .pack"); | |
| return xstrfmt("%.*s.rev", (int)len, p->pack_name); | |
| } | |
| #define RIDX_HEADER_SIZE (12) | |
| #define RIDX_MIN_SIZE (RIDX_HEADER_SIZE + (2 * the_hash_algo->rawsz)) | |
| struct revindex_header { | |
| uint32_t signature; | |
| uint32_t version; | |
| uint32_t hash_id; | |
| }; | |
| static int load_revindex_from_disk(char *revindex_name, | |
| uint32_t num_objects, | |
| const uint32_t **data_p, size_t *len_p) | |
| { | |
| int fd, ret = 0; | |
| struct stat st; | |
| void *data = NULL; | |
| size_t revindex_size; | |
| struct revindex_header *hdr; | |
| fd = git_open(revindex_name); | |
| if (fd < 0) { | |
| ret = -1; | |
| goto cleanup; | |
| } | |
| if (fstat(fd, &st)) { | |
| ret = error_errno(_("failed to read %s"), revindex_name); | |
| goto cleanup; | |
| } | |
| revindex_size = xsize_t(st.st_size); | |
| if (revindex_size < RIDX_MIN_SIZE) { | |
| ret = error(_("reverse-index file %s is too small"), revindex_name); | |
| goto cleanup; | |
| } | |
| if (revindex_size - RIDX_MIN_SIZE != st_mult(sizeof(uint32_t), num_objects)) { | |
| ret = error(_("reverse-index file %s is corrupt"), revindex_name); | |
| goto cleanup; | |
| } | |
| data = xmmap(NULL, revindex_size, PROT_READ, MAP_PRIVATE, fd, 0); | |
| hdr = data; | |
| if (ntohl(hdr->signature) != RIDX_SIGNATURE) { | |
| ret = error(_("reverse-index file %s has unknown signature"), revindex_name); | |
| goto cleanup; | |
| } | |
| if (ntohl(hdr->version) != 1) { | |
| ret = error(_("reverse-index file %s has unsupported version %"PRIu32), | |
| revindex_name, ntohl(hdr->version)); | |
| goto cleanup; | |
| } | |
| if (!(ntohl(hdr->hash_id) == 1 || ntohl(hdr->hash_id) == 2)) { | |
| ret = error(_("reverse-index file %s has unsupported hash id %"PRIu32), | |
| revindex_name, ntohl(hdr->hash_id)); | |
| goto cleanup; | |
| } | |
| cleanup: | |
| if (ret) { | |
| if (data) | |
| munmap(data, revindex_size); | |
| } else { | |
| *len_p = revindex_size; | |
| *data_p = (const uint32_t *)data; | |
| } | |
| if (fd >= 0) | |
| close(fd); | |
| return ret; | |
| } | |
| static int load_pack_revindex_from_disk(struct packed_git *p) | |
| { | |
| char *revindex_name; | |
| int ret; | |
| if (open_pack_index(p)) | |
| return -1; | |
| revindex_name = pack_revindex_filename(p); | |
| ret = load_revindex_from_disk(revindex_name, | |
| p->num_objects, | |
| &p->revindex_map, | |
| &p->revindex_size); | |
| if (ret) | |
| goto cleanup; | |
| p->revindex_data = (const uint32_t *)((const char *)p->revindex_map + RIDX_HEADER_SIZE); | |
| cleanup: | |
| free(revindex_name); | |
| return ret; | |
| } | |
| int load_pack_revindex(struct packed_git *p) | |
| { | |
| if (p->revindex || p->revindex_data) | |
| return 0; | |
| if (!load_pack_revindex_from_disk(p)) | |
| return 0; | |
| else if (!create_pack_revindex_in_memory(p)) | |
| return 0; | |
| return -1; | |
| } | |
| int load_midx_revindex(struct multi_pack_index *m) | |
| { | |
| char *revindex_name; | |
| int ret; | |
| if (m->revindex_data) | |
| return 0; | |
| revindex_name = get_midx_rev_filename(m); | |
| ret = load_revindex_from_disk(revindex_name, | |
| m->num_objects, | |
| &m->revindex_map, | |
| &m->revindex_len); | |
| if (ret) | |
| goto cleanup; | |
| m->revindex_data = (const uint32_t *)((const char *)m->revindex_map + RIDX_HEADER_SIZE); | |
| cleanup: | |
| free(revindex_name); | |
| return ret; | |
| } | |
| int close_midx_revindex(struct multi_pack_index *m) | |
| { | |
| if (!m || !m->revindex_map) | |
| return 0; | |
| munmap((void*)m->revindex_map, m->revindex_len); | |
| m->revindex_map = NULL; | |
| m->revindex_data = NULL; | |
| m->revindex_len = 0; | |
| return 0; | |
| } | |
| int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos) | |
| { | |
| unsigned lo, hi; | |
| if (load_pack_revindex(p) < 0) | |
| return -1; | |
| lo = 0; | |
| hi = p->num_objects + 1; | |
| do { | |
| const unsigned mi = lo + (hi - lo) / 2; | |
| off_t got = pack_pos_to_offset(p, mi); | |
| if (got == ofs) { | |
| *pos = mi; | |
| return 0; | |
| } else if (ofs < got) | |
| hi = mi; | |
| else | |
| lo = mi + 1; | |
| } while (lo < hi); | |
| error("bad offset for revindex"); | |
| return -1; | |
| } | |
| uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos) | |
| { | |
| if (!(p->revindex || p->revindex_data)) | |
| BUG("pack_pos_to_index: reverse index not yet loaded"); | |
| if (p->num_objects <= pos) | |
| BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos); | |
| if (p->revindex) | |
| return p->revindex[pos].nr; | |
| else | |
| return get_be32(p->revindex_data + pos); | |
| } | |
| off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos) | |
| { | |
| if (!(p->revindex || p->revindex_data)) | |
| BUG("pack_pos_to_index: reverse index not yet loaded"); | |
| if (p->num_objects < pos) | |
| BUG("pack_pos_to_offset: out-of-bounds object at %"PRIu32, pos); | |
| if (p->revindex) | |
| return p->revindex[pos].offset; | |
| else if (pos == p->num_objects) | |
| return p->pack_size - the_hash_algo->rawsz; | |
| else | |
| return nth_packed_object_offset(p, pack_pos_to_index(p, pos)); | |
| } | |
| uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos) | |
| { | |
| if (!m->revindex_data) | |
| BUG("pack_pos_to_midx: reverse index not yet loaded"); | |
| if (m->num_objects <= pos) | |
| BUG("pack_pos_to_midx: out-of-bounds object at %"PRIu32, pos); | |
| return get_be32(m->revindex_data + pos); | |
| } | |
| struct midx_pack_key { | |
| uint32_t pack; | |
| off_t offset; | |
| uint32_t preferred_pack; | |
| struct multi_pack_index *midx; | |
| }; | |
| static int midx_pack_order_cmp(const void *va, const void *vb) | |
| { | |
| const struct midx_pack_key *key = va; | |
| struct multi_pack_index *midx = key->midx; | |
| uint32_t versus = pack_pos_to_midx(midx, (uint32_t*)vb - (const uint32_t *)midx->revindex_data); | |
| uint32_t versus_pack = nth_midxed_pack_int_id(midx, versus); | |
| off_t versus_offset; | |
| uint32_t key_preferred = key->pack == key->preferred_pack; | |
| uint32_t versus_preferred = versus_pack == key->preferred_pack; | |
| /* | |
| * First, compare the preferred-ness, noting that the preferred pack | |
| * comes first. | |
| */ | |
| if (key_preferred && !versus_preferred) | |
| return -1; | |
| else if (!key_preferred && versus_preferred) | |
| return 1; | |
| /* Then, break ties first by comparing the pack IDs. */ | |
| if (key->pack < versus_pack) | |
| return -1; | |
| else if (key->pack > versus_pack) | |
| return 1; | |
| /* Finally, break ties by comparing offsets within a pack. */ | |
| versus_offset = nth_midxed_offset(midx, versus); | |
| if (key->offset < versus_offset) | |
| return -1; | |
| else if (key->offset > versus_offset) | |
| return 1; | |
| return 0; | |
| } | |
| int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos) | |
| { | |
| struct midx_pack_key key; | |
| uint32_t *found; | |
| if (!m->revindex_data) | |
| BUG("midx_to_pack_pos: reverse index not yet loaded"); | |
| if (m->num_objects <= at) | |
| BUG("midx_to_pack_pos: out-of-bounds object at %"PRIu32, at); | |
| key.pack = nth_midxed_pack_int_id(m, at); | |
| key.offset = nth_midxed_offset(m, at); | |
| key.midx = m; | |
| /* | |
| * The preferred pack sorts first, so determine its identifier by | |
| * looking at the first object in pseudo-pack order. | |
| * | |
| * Note that if no --preferred-pack is explicitly given when writing a | |
| * multi-pack index, then whichever pack has the lowest identifier | |
| * implicitly is preferred (and includes all its objects, since ties are | |
| * broken first by pack identifier). | |
| */ | |
| key.preferred_pack = nth_midxed_pack_int_id(m, pack_pos_to_midx(m, 0)); | |
| found = bsearch(&key, m->revindex_data, m->num_objects, | |
| sizeof(*m->revindex_data), midx_pack_order_cmp); | |
| if (!found) | |
| return error("bad offset for revindex"); | |
| *pos = found - m->revindex_data; | |
| return 0; | |
| } |