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![Taylor Blau](/assets/img/avatar_default.png)
Now that we have extracted the `midx_key_to_pack_pos()` function, we can implement the `midx_pair_to_pack_pos()` function which accepts (pack_id, offset) tuples and returns an index into the psuedo-pack order. This will be used in a following commit in order to figure out whether or not the MIDX chose a given delta's base object from the same pack as the delta resides in. It will do so by locating the base object's offset in the pack, and then performing a binary search using the same pack ID with the base object's offset. If (and only if) it finds a match (at any position) we can guarantee that the MIDX selected both halves of the delta/base pair from the same pack. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
578 lines
15 KiB
C
578 lines
15 KiB
C
#include "git-compat-util.h"
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#include "gettext.h"
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#include "pack-revindex.h"
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#include "object-file.h"
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#include "object-store-ll.h"
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#include "packfile.h"
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#include "strbuf.h"
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#include "trace2.h"
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#include "parse.h"
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#include "midx.h"
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#include "csum-file.h"
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struct revindex_entry {
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off_t offset;
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unsigned int nr;
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};
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/*
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* Pack index for existing packs give us easy access to the offsets into
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* corresponding pack file where each object's data starts, but the entries
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* do not store the size of the compressed representation (uncompressed
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* size is easily available by examining the pack entry header). It is
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* also rather expensive to find the sha1 for an object given its offset.
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*
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* The pack index file is sorted by object name mapping to offset;
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* this revindex array is a list of offset/index_nr pairs
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* ordered by offset, so if you know the offset of an object, next offset
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* is where its packed representation ends and the index_nr can be used to
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* get the object sha1 from the main index.
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*/
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/*
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* This is a least-significant-digit radix sort.
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*
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* It sorts each of the "n" items in "entries" by its offset field. The "max"
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* parameter must be at least as large as the largest offset in the array,
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* and lets us quit the sort early.
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*/
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static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max)
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{
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/*
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* We use a "digit" size of 16 bits. That keeps our memory
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* usage reasonable, and we can generally (for a 4G or smaller
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* packfile) quit after two rounds of radix-sorting.
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*/
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#define DIGIT_SIZE (16)
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#define BUCKETS (1 << DIGIT_SIZE)
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/*
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* We want to know the bucket that a[i] will go into when we are using
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* the digit that is N bits from the (least significant) end.
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*/
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#define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1))
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/*
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* We need O(n) temporary storage. Rather than do an extra copy of the
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* partial results into "entries", we sort back and forth between the
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* real array and temporary storage. In each iteration of the loop, we
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* keep track of them with alias pointers, always sorting from "from"
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* to "to".
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*/
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struct revindex_entry *tmp, *from, *to;
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int bits;
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unsigned *pos;
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ALLOC_ARRAY(pos, BUCKETS);
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ALLOC_ARRAY(tmp, n);
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from = entries;
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to = tmp;
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/*
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* If (max >> bits) is zero, then we know that the radix digit we are
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* on (and any higher) will be zero for all entries, and our loop will
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* be a no-op, as everybody lands in the same zero-th bucket.
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*/
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for (bits = 0; max >> bits; bits += DIGIT_SIZE) {
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unsigned i;
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memset(pos, 0, BUCKETS * sizeof(*pos));
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/*
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* We want pos[i] to store the index of the last element that
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* will go in bucket "i" (actually one past the last element).
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* To do this, we first count the items that will go in each
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* bucket, which gives us a relative offset from the last
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* bucket. We can then cumulatively add the index from the
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* previous bucket to get the true index.
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*/
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for (i = 0; i < n; i++)
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pos[BUCKET_FOR(from, i, bits)]++;
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for (i = 1; i < BUCKETS; i++)
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pos[i] += pos[i-1];
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/*
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* Now we can drop the elements into their correct buckets (in
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* our temporary array). We iterate the pos counter backwards
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* to avoid using an extra index to count up. And since we are
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* going backwards there, we must also go backwards through the
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* array itself, to keep the sort stable.
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*
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* Note that we use an unsigned iterator to make sure we can
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* handle 2^32-1 objects, even on a 32-bit system. But this
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* means we cannot use the more obvious "i >= 0" loop condition
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* for counting backwards, and must instead check for
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* wrap-around with UINT_MAX.
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*/
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for (i = n - 1; i != UINT_MAX; i--)
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to[--pos[BUCKET_FOR(from, i, bits)]] = from[i];
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/*
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* Now "to" contains the most sorted list, so we swap "from" and
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* "to" for the next iteration.
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*/
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SWAP(from, to);
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}
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/*
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* If we ended with our data in the original array, great. If not,
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* we have to move it back from the temporary storage.
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*/
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if (from != entries)
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COPY_ARRAY(entries, tmp, n);
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free(tmp);
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free(pos);
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#undef BUCKET_FOR
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#undef BUCKETS
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#undef DIGIT_SIZE
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}
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/*
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* Ordered list of offsets of objects in the pack.
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*/
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static void create_pack_revindex(struct packed_git *p)
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{
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const unsigned num_ent = p->num_objects;
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unsigned i;
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const char *index = p->index_data;
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const unsigned hashsz = the_hash_algo->rawsz;
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ALLOC_ARRAY(p->revindex, num_ent + 1);
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index += 4 * 256;
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if (p->index_version > 1) {
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const uint32_t *off_32 =
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(uint32_t *)(index + 8 + (size_t)p->num_objects * (hashsz + 4));
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const uint32_t *off_64 = off_32 + p->num_objects;
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for (i = 0; i < num_ent; i++) {
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const uint32_t off = ntohl(*off_32++);
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if (!(off & 0x80000000)) {
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p->revindex[i].offset = off;
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} else {
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p->revindex[i].offset = get_be64(off_64);
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off_64 += 2;
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}
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p->revindex[i].nr = i;
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}
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} else {
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for (i = 0; i < num_ent; i++) {
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const uint32_t hl = *((uint32_t *)(index + (hashsz + 4) * i));
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p->revindex[i].offset = ntohl(hl);
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p->revindex[i].nr = i;
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}
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}
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/*
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* This knows the pack format -- the hash trailer
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* follows immediately after the last object data.
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*/
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p->revindex[num_ent].offset = p->pack_size - hashsz;
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p->revindex[num_ent].nr = -1;
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sort_revindex(p->revindex, num_ent, p->pack_size);
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}
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static int create_pack_revindex_in_memory(struct packed_git *p)
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{
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if (git_env_bool(GIT_TEST_REV_INDEX_DIE_IN_MEMORY, 0))
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die("dying as requested by '%s'",
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GIT_TEST_REV_INDEX_DIE_IN_MEMORY);
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if (open_pack_index(p))
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return -1;
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create_pack_revindex(p);
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return 0;
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}
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static char *pack_revindex_filename(struct packed_git *p)
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{
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size_t len;
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if (!strip_suffix(p->pack_name, ".pack", &len))
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BUG("pack_name does not end in .pack");
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return xstrfmt("%.*s.rev", (int)len, p->pack_name);
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}
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#define RIDX_HEADER_SIZE (12)
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#define RIDX_MIN_SIZE (RIDX_HEADER_SIZE + (2 * the_hash_algo->rawsz))
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struct revindex_header {
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uint32_t signature;
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uint32_t version;
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uint32_t hash_id;
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};
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static int load_revindex_from_disk(char *revindex_name,
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uint32_t num_objects,
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const uint32_t **data_p, size_t *len_p)
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{
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int fd, ret = 0;
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struct stat st;
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void *data = NULL;
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size_t revindex_size;
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struct revindex_header *hdr;
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if (git_env_bool(GIT_TEST_REV_INDEX_DIE_ON_DISK, 0))
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die("dying as requested by '%s'", GIT_TEST_REV_INDEX_DIE_ON_DISK);
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fd = git_open(revindex_name);
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if (fd < 0) {
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/* "No file" means return 1. */
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ret = 1;
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goto cleanup;
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}
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if (fstat(fd, &st)) {
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ret = error_errno(_("failed to read %s"), revindex_name);
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goto cleanup;
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}
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revindex_size = xsize_t(st.st_size);
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if (revindex_size < RIDX_MIN_SIZE) {
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ret = error(_("reverse-index file %s is too small"), revindex_name);
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goto cleanup;
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}
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if (revindex_size - RIDX_MIN_SIZE != st_mult(sizeof(uint32_t), num_objects)) {
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ret = error(_("reverse-index file %s is corrupt"), revindex_name);
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goto cleanup;
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}
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data = xmmap(NULL, revindex_size, PROT_READ, MAP_PRIVATE, fd, 0);
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hdr = data;
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if (ntohl(hdr->signature) != RIDX_SIGNATURE) {
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ret = error(_("reverse-index file %s has unknown signature"), revindex_name);
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goto cleanup;
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}
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if (ntohl(hdr->version) != 1) {
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ret = error(_("reverse-index file %s has unsupported version %"PRIu32),
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revindex_name, ntohl(hdr->version));
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goto cleanup;
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}
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if (!(ntohl(hdr->hash_id) == 1 || ntohl(hdr->hash_id) == 2)) {
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ret = error(_("reverse-index file %s has unsupported hash id %"PRIu32),
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revindex_name, ntohl(hdr->hash_id));
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goto cleanup;
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}
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cleanup:
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if (ret) {
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if (data)
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munmap(data, revindex_size);
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} else {
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*len_p = revindex_size;
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*data_p = (const uint32_t *)data;
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}
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if (fd >= 0)
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close(fd);
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return ret;
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}
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int load_pack_revindex_from_disk(struct packed_git *p)
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{
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char *revindex_name;
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int ret;
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if (open_pack_index(p))
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return -1;
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revindex_name = pack_revindex_filename(p);
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ret = load_revindex_from_disk(revindex_name,
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p->num_objects,
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&p->revindex_map,
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&p->revindex_size);
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if (ret)
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goto cleanup;
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p->revindex_data = (const uint32_t *)((const char *)p->revindex_map + RIDX_HEADER_SIZE);
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cleanup:
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free(revindex_name);
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return ret;
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}
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int load_pack_revindex(struct repository *r, struct packed_git *p)
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{
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if (p->revindex || p->revindex_data)
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return 0;
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prepare_repo_settings(r);
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if (r->settings.pack_read_reverse_index &&
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!load_pack_revindex_from_disk(p))
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return 0;
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else if (!create_pack_revindex_in_memory(p))
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return 0;
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return -1;
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}
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/*
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* verify_pack_revindex verifies that the on-disk rev-index for the given
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* pack-file is the same that would be created if written from scratch.
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*
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* A negative number is returned on error.
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*/
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int verify_pack_revindex(struct packed_git *p)
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{
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int res = 0;
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/* Do not bother checking if not initialized. */
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if (!p->revindex_map || !p->revindex_data)
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return res;
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if (!hashfile_checksum_valid((const unsigned char *)p->revindex_map, p->revindex_size)) {
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error(_("invalid checksum"));
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res = -1;
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}
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/* This may fail due to a broken .idx. */
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if (create_pack_revindex_in_memory(p))
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return res;
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for (size_t i = 0; i < p->num_objects; i++) {
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uint32_t nr = p->revindex[i].nr;
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uint32_t rev_val = get_be32(p->revindex_data + i);
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if (nr != rev_val) {
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error(_("invalid rev-index position at %"PRIu64": %"PRIu32" != %"PRIu32""),
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(uint64_t)i, nr, rev_val);
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res = -1;
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}
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}
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return res;
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}
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static int can_use_midx_ridx_chunk(struct multi_pack_index *m)
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{
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if (!m->chunk_revindex)
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return 0;
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if (m->chunk_revindex_len != st_mult(sizeof(uint32_t), m->num_objects)) {
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error(_("multi-pack-index reverse-index chunk is the wrong size"));
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return 0;
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}
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return 1;
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}
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int load_midx_revindex(struct multi_pack_index *m)
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{
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struct strbuf revindex_name = STRBUF_INIT;
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int ret;
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if (m->revindex_data)
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return 0;
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if (can_use_midx_ridx_chunk(m)) {
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/*
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* If the MIDX `m` has a `RIDX` chunk, then use its contents for
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* the reverse index instead of trying to load a separate `.rev`
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* file.
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*
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* Note that we do *not* set `m->revindex_map` here, since we do
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* not want to accidentally call munmap() in the middle of the
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* MIDX.
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*/
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trace2_data_string("load_midx_revindex", the_repository,
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"source", "midx");
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m->revindex_data = (const uint32_t *)m->chunk_revindex;
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return 0;
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}
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trace2_data_string("load_midx_revindex", the_repository,
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"source", "rev");
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get_midx_rev_filename(&revindex_name, m);
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ret = load_revindex_from_disk(revindex_name.buf,
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m->num_objects,
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&m->revindex_map,
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&m->revindex_len);
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if (ret)
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goto cleanup;
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m->revindex_data = (const uint32_t *)((const char *)m->revindex_map + RIDX_HEADER_SIZE);
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cleanup:
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strbuf_release(&revindex_name);
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return ret;
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}
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int close_midx_revindex(struct multi_pack_index *m)
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{
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if (!m || !m->revindex_map)
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return 0;
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munmap((void*)m->revindex_map, m->revindex_len);
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m->revindex_map = NULL;
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m->revindex_data = NULL;
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m->revindex_len = 0;
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return 0;
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}
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int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)
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{
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unsigned lo, hi;
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if (load_pack_revindex(the_repository, p) < 0)
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return -1;
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lo = 0;
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hi = p->num_objects + 1;
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do {
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const unsigned mi = lo + (hi - lo) / 2;
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off_t got = pack_pos_to_offset(p, mi);
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if (got == ofs) {
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*pos = mi;
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return 0;
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} else if (ofs < got)
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hi = mi;
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else
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lo = mi + 1;
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} while (lo < hi);
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error("bad offset for revindex");
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return -1;
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}
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uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos)
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{
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if (!(p->revindex || p->revindex_data))
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BUG("pack_pos_to_index: reverse index not yet loaded");
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if (p->num_objects <= pos)
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BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos);
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if (p->revindex)
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return p->revindex[pos].nr;
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else
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return get_be32(p->revindex_data + pos);
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}
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off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos)
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{
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if (!(p->revindex || p->revindex_data))
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BUG("pack_pos_to_index: reverse index not yet loaded");
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if (p->num_objects < pos)
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BUG("pack_pos_to_offset: out-of-bounds object at %"PRIu32, pos);
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if (p->revindex)
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return p->revindex[pos].offset;
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else if (pos == p->num_objects)
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return p->pack_size - the_hash_algo->rawsz;
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else
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return nth_packed_object_offset(p, pack_pos_to_index(p, pos));
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}
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uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos)
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{
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if (!m->revindex_data)
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BUG("pack_pos_to_midx: reverse index not yet loaded");
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if (m->num_objects <= pos)
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BUG("pack_pos_to_midx: out-of-bounds object at %"PRIu32, pos);
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return get_be32(m->revindex_data + pos);
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}
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struct midx_pack_key {
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uint32_t pack;
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off_t offset;
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uint32_t preferred_pack;
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struct multi_pack_index *midx;
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};
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static int midx_pack_order_cmp(const void *va, const void *vb)
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{
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const struct midx_pack_key *key = va;
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struct multi_pack_index *midx = key->midx;
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uint32_t versus = pack_pos_to_midx(midx, (uint32_t*)vb - (const uint32_t *)midx->revindex_data);
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uint32_t versus_pack = nth_midxed_pack_int_id(midx, versus);
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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;
|
|
}
|
|
|
|
static int midx_key_to_pack_pos(struct multi_pack_index *m,
|
|
struct midx_pack_key *key,
|
|
uint32_t *pos)
|
|
{
|
|
uint32_t *found;
|
|
|
|
/*
|
|
* 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).
|
|
*/
|
|
if (midx_preferred_pack(key->midx, &key->preferred_pack) < 0)
|
|
return error(_("could not determine preferred pack"));
|
|
|
|
found = bsearch(key, m->revindex_data, m->num_objects,
|
|
sizeof(*m->revindex_data),
|
|
midx_pack_order_cmp);
|
|
|
|
if (!found)
|
|
return -1;
|
|
|
|
*pos = found - m->revindex_data;
|
|
return 0;
|
|
}
|
|
|
|
int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)
|
|
{
|
|
struct midx_pack_key key;
|
|
|
|
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;
|
|
|
|
return midx_key_to_pack_pos(m, &key, pos);
|
|
}
|
|
|
|
int midx_pair_to_pack_pos(struct multi_pack_index *m, uint32_t pack_int_id,
|
|
off_t ofs, uint32_t *pos)
|
|
{
|
|
struct midx_pack_key key = {
|
|
.pack = pack_int_id,
|
|
.offset = ofs,
|
|
.midx = m,
|
|
};
|
|
return midx_key_to_pack_pos(m, &key, pos);
|
|
}
|