diff options
Diffstat (limited to 'pack-revindex.c')
| -rw-r--r-- | pack-revindex.c | 555 |
1 files changed, 555 insertions, 0 deletions
diff --git a/pack-revindex.c b/pack-revindex.c new file mode 100644 index 0000000..acf1dd9 --- /dev/null +++ b/pack-revindex.c @@ -0,0 +1,555 @@ +#include "git-compat-util.h" +#include "gettext.h" +#include "pack-revindex.h" +#include "object-file.h" +#include "object-store-ll.h" +#include "packfile.h" +#include "strbuf.h" +#include "trace2.h" +#include "parse.h" +#include "midx.h" +#include "csum-file.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; + + if (git_env_bool(GIT_TEST_REV_INDEX_DIE_ON_DISK, 0)) + die("dying as requested by '%s'", GIT_TEST_REV_INDEX_DIE_ON_DISK); + + fd = git_open(revindex_name); + + if (fd < 0) { + /* "No file" means return 1. */ + 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; +} + +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 repository *r, struct packed_git *p) +{ + if (p->revindex || p->revindex_data) + return 0; + + prepare_repo_settings(r); + + if (r->settings.pack_read_reverse_index && + !load_pack_revindex_from_disk(p)) + return 0; + else if (!create_pack_revindex_in_memory(p)) + return 0; + return -1; +} + +/* + * verify_pack_revindex verifies that the on-disk rev-index for the given + * pack-file is the same that would be created if written from scratch. + * + * A negative number is returned on error. + */ +int verify_pack_revindex(struct packed_git *p) +{ + int res = 0; + + /* Do not bother checking if not initialized. */ + if (!p->revindex_map || !p->revindex_data) + return res; + + if (!hashfile_checksum_valid((const unsigned char *)p->revindex_map, p->revindex_size)) { + error(_("invalid checksum")); + res = -1; + } + + /* This may fail due to a broken .idx. */ + if (create_pack_revindex_in_memory(p)) + return res; + + for (size_t i = 0; i < p->num_objects; i++) { + uint32_t nr = p->revindex[i].nr; + uint32_t rev_val = get_be32(p->revindex_data + i); + + if (nr != rev_val) { + error(_("invalid rev-index position at %"PRIu64": %"PRIu32" != %"PRIu32""), + (uint64_t)i, nr, rev_val); + res = -1; + } + } + + return res; +} + +static int can_use_midx_ridx_chunk(struct multi_pack_index *m) +{ + if (!m->chunk_revindex) + return 0; + if (m->chunk_revindex_len != st_mult(sizeof(uint32_t), m->num_objects)) { + error(_("multi-pack-index reverse-index chunk is the wrong size")); + return 0; + } + return 1; +} + +int load_midx_revindex(struct multi_pack_index *m) +{ + struct strbuf revindex_name = STRBUF_INIT; + int ret; + + if (m->revindex_data) + return 0; + + if (can_use_midx_ridx_chunk(m)) { + /* + * If the MIDX `m` has a `RIDX` chunk, then use its contents for + * the reverse index instead of trying to load a separate `.rev` + * file. + * + * Note that we do *not* set `m->revindex_map` here, since we do + * not want to accidentally call munmap() in the middle of the + * MIDX. + */ + trace2_data_string("load_midx_revindex", the_repository, + "source", "midx"); + m->revindex_data = (const uint32_t *)m->chunk_revindex; + return 0; + } + + trace2_data_string("load_midx_revindex", the_repository, + "source", "rev"); + + get_midx_rev_filename(&revindex_name, m); + + ret = load_revindex_from_disk(revindex_name.buf, + 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: + strbuf_release(&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(the_repository, 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; +} |