mirror of
https://github.com/git/git.git
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24deea5273
Signed-off-by: Pierre Habouzit <madcoder@debian.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
157 lines
4.0 KiB
C
157 lines
4.0 KiB
C
#include "cache.h"
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#include "pack-revindex.h"
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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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* We build a hashtable of existing packs (pack_revindex), and keep reverse
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* index here -- pack index file is sorted by object name mapping to offset;
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* this pack_revindex[].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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struct pack_revindex {
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struct packed_git *p;
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struct revindex_entry *revindex;
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};
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static struct pack_revindex *pack_revindex;
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static int pack_revindex_hashsz;
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static int pack_revindex_ix(struct packed_git *p)
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{
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unsigned long ui = (unsigned long)p;
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int i;
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ui = ui ^ (ui >> 16); /* defeat structure alignment */
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i = (int)(ui % pack_revindex_hashsz);
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while (pack_revindex[i].p) {
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if (pack_revindex[i].p == p)
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return i;
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if (++i == pack_revindex_hashsz)
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i = 0;
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}
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return -1 - i;
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}
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static void init_pack_revindex(void)
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{
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int num;
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struct packed_git *p;
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for (num = 0, p = packed_git; p; p = p->next)
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num++;
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if (!num)
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return;
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pack_revindex_hashsz = num * 11;
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pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
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for (p = packed_git; p; p = p->next) {
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num = pack_revindex_ix(p);
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num = - 1 - num;
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pack_revindex[num].p = p;
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}
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/* revindex elements are lazily initialized */
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}
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static int cmp_offset(const void *a_, const void *b_)
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{
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const struct revindex_entry *a = a_;
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const struct revindex_entry *b = b_;
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return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0;
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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 pack_revindex *rix)
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{
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struct packed_git *p = rix->p;
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int num_ent = p->num_objects;
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int i;
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const char *index = p->index_data;
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rix->revindex = xmalloc(sizeof(*rix->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 + p->num_objects * (20 + 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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uint32_t off = ntohl(*off_32++);
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if (!(off & 0x80000000)) {
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rix->revindex[i].offset = off;
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} else {
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rix->revindex[i].offset =
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((uint64_t)ntohl(*off_64++)) << 32;
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rix->revindex[i].offset |=
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ntohl(*off_64++);
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}
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rix->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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uint32_t hl = *((uint32_t *)(index + 24 * i));
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rix->revindex[i].offset = ntohl(hl);
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rix->revindex[i].nr = i;
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}
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}
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/* This knows the pack format -- the 20-byte trailer
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* follows immediately after the last object data.
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*/
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rix->revindex[num_ent].offset = p->pack_size - 20;
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rix->revindex[num_ent].nr = -1;
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qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset);
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}
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struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
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{
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int num;
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int lo, hi;
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struct pack_revindex *rix;
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struct revindex_entry *revindex;
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if (!pack_revindex_hashsz)
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init_pack_revindex();
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num = pack_revindex_ix(p);
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if (num < 0)
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die("internal error: pack revindex fubar");
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rix = &pack_revindex[num];
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if (!rix->revindex)
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create_pack_revindex(rix);
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revindex = rix->revindex;
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lo = 0;
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hi = p->num_objects + 1;
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do {
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int mi = (lo + hi) / 2;
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if (revindex[mi].offset == ofs) {
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return revindex + mi;
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} else if (ofs < revindex[mi].offset)
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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 NULL;
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}
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void discard_revindex(void)
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{
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if (pack_revindex_hashsz) {
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int i;
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for (i = 0; i < pack_revindex_hashsz; i++)
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free(pack_revindex[i].revindex);
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free(pack_revindex);
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pack_revindex_hashsz = 0;
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}
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}
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