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git/pack-revindex.c
Patrick Steinhardt e7da938570 global: introduce USE_THE_REPOSITORY_VARIABLE macro
Use of the `the_repository` variable is deprecated nowadays, and we
slowly but steadily convert the codebase to not use it anymore. Instead,
callers should be passing down the repository to work on via parameters.

It is hard though to prove that a given code unit does not use this
variable anymore. The most trivial case, merely demonstrating that there
is no direct use of `the_repository`, is already a bit of a pain during
code reviews as the reviewer needs to manually verify claims made by the
patch author. The bigger problem though is that we have many interfaces
that implicitly rely on `the_repository`.

Introduce a new `USE_THE_REPOSITORY_VARIABLE` macro that allows code
units to opt into usage of `the_repository`. The intent of this macro is
to demonstrate that a certain code unit does not use this variable
anymore, and to keep it from new dependencies on it in future changes,
be it explicit or implicit

For now, the macro only guards `the_repository` itself as well as
`the_hash_algo`. There are many more known interfaces where we have an
implicit dependency on `the_repository`, but those are not guarded at
the current point in time. Over time though, we should start to add
guards as required (or even better, just remove them).

Define the macro as required in our code units. As expected, most of our
code still relies on the global variable. Nearly all of our builtins
rely on the variable as there is no way yet to pass `the_repository` to
their entry point. For now, declare the macro in "biultin.h" to keep the
required changes at least a little bit more contained.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2024-06-14 10:26:33 -07:00

581 lines
15 KiB
C

#define USE_THE_REPOSITORY_VARIABLE
#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_filename_ext(&revindex_name, m->object_dir,
get_midx_checksum(m), MIDX_EXT_REV);
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;
}
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);
}