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#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)
{
struct strbuf revindex_name = STRBUF_INIT;
int ret;
if (m->revindex_data)
return 0;
if (m->chunk_revindex) {
/*
* 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(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;
}