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-rw-r--r--pack-revindex.c555
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;
+}