Implement reading for multi-pack reverse indexes, as described in the
previous patch.
Note that these functions don't yet have any callers, and won't until
multi-pack reachability bitmaps are introduced in a later patch series.
In the meantime, this patch implements some of the infrastructure
necessary to support multi-pack bitmaps.
There are three new functions exposed by the revindex API:
- load_midx_revindex(): loads the reverse index corresponding to the
given multi-pack index.
- midx_to_pack_pos() and pack_pos_to_midx(): these convert between the
multi-pack index and pseudo-pack order.
load_midx_revindex() and pack_pos_to_midx() are both relatively
straightforward.
load_midx_revindex() needs a few functions to be exposed from the midx
API. One to get the checksum of a midx, and another to get the .rev's
filename. Similar to recent changes in the packed_git struct, three new
fields are added to the multi_pack_index struct: one to keep track of
the size, one to keep track of the mmap'd pointer, and another to point
past the header and at the reverse index's data.
pack_pos_to_midx() simply reads the corresponding entry out of the
table.
midx_to_pack_pos() is the trickiest, since it needs to find an object's
position in the psuedo-pack order, but that order can only be recovered
in the .rev file itself. This mapping can be implemented with a binary
search, but note that the thing we're binary searching over isn't an
array, but rather a _permutation_.
So, when comparing two items, it's helpful to keep in mind the
difference. Instead of a traditional binary search, where you are
comparing two things directly, here we're comparing a (pack, offset)
tuple with an index into the multi-pack index. That index describes
another (pack, offset) tuple, and it is _those_ two tuples that are
compared.
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
midx.c | 11 +++++
midx.h | 6 +++
pack-revindex.c | 112 ++++++++++++++++++++++++++++++++++++++++++++++++
pack-revindex.h | 46 ++++++++++++++++++++
packfile.c | 3 ++
5 files changed, 178 insertions(+)
diff --git a/midx.c b/midx.c
index bf258c4fde..12bfce8bb1 100644
--- a/midx.c
+++ b/midx.c
@@ -48,11 +48,22 @@ static uint8_t oid_version(void)
}
}
+static const unsigned char *get_midx_checksum(struct multi_pack_index *m)
+{
+ return m->data + m->data_len - the_hash_algo->rawsz;
+}
+
static char *get_midx_filename(const char *object_dir)
{
return xstrfmt("%s/pack/multi-pack-index", object_dir);
}
+char *get_midx_rev_filename(struct multi_pack_index *m)
+{
+ return xstrfmt("%s/pack/multi-pack-index-%s.rev",
+ m->object_dir, hash_to_hex(get_midx_checksum(m)));
+}
+
struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local)
{
struct multi_pack_index *m = NULL;
diff --git a/midx.h b/midx.h
index 93bd68189e..0a8294d2ee 100644
--- a/midx.h
+++ b/midx.h
@@ -15,6 +15,10 @@ struct multi_pack_index {
const unsigned char *data;
size_t data_len;
+ const uint32_t *revindex_data;
+ const uint32_t *revindex_map;
+ size_t revindex_len;
+
uint32_t signature;
unsigned char version;
unsigned char hash_len;
@@ -37,6 +41,8 @@ struct multi_pack_index {
#define MIDX_PROGRESS (1 << 0)
+char *get_midx_rev_filename(struct multi_pack_index *m);
+
struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
diff --git a/pack-revindex.c b/pack-revindex.c
index 83fe4de773..da4101f4b2 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -3,6 +3,7 @@
#include "object-store.h"
#include "packfile.h"
#include "config.h"
+#include "midx.h"
struct revindex_entry {
off_t offset;
@@ -292,6 +293,29 @@ int load_pack_revindex(struct packed_git *p)
return -1;
}
+int load_midx_revindex(struct multi_pack_index *m)
+{
+ char *revindex_name;
+ int ret;
+ if (m->revindex_data)
+ return 0;
+
+ revindex_name = get_midx_rev_filename(m);
+
+ ret = load_revindex_from_disk(revindex_name,
+ 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:
+ free(revindex_name);
+ return ret;
+}
+
int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)
{
unsigned lo, hi;
@@ -346,3 +370,91 @@ off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos)
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((const char *)m->revindex_data + (pos * sizeof(uint32_t)));
+}
+
+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(uint32_t), midx_pack_order_cmp);
+
+ if (!found)
+ return error("bad offset for revindex");
+
+ *pos = found - m->revindex_data;
+ return 0;
+}
diff --git a/pack-revindex.h b/pack-revindex.h
index ba7c82c125..49d604aa9a 100644
--- a/pack-revindex.h
+++ b/pack-revindex.h
@@ -14,6 +14,20 @@
*
* - offset: the byte offset within the .pack file at which the object contents
* can be found
+ *
+ * The revindex can also be used with a multi-pack index (MIDX). In this
+ * setting:
+ *
+ * - index position refers to an object's numeric position within the MIDX
+ *
+ * - pack position refers to an object's position within a non-existent pack
+ * described by the MIDX. The pack structure is described in
+ * Documentation/technical/pack-format.txt.
+ *
+ * It is effectively a concatanation of all packs in the MIDX (ordered by
+ * their numeric ID within the MIDX) in their original order within each
+ * pack), removing duplicates, and placing the preferred pack (if any)
+ * first.
*/
@@ -24,6 +38,7 @@
#define GIT_TEST_REV_INDEX_DIE_IN_MEMORY "GIT_TEST_REV_INDEX_DIE_IN_MEMORY"
struct packed_git;
+struct multi_pack_index;
/*
* load_pack_revindex populates the revindex's internal data-structures for the
@@ -34,6 +49,15 @@ struct packed_git;
*/
int load_pack_revindex(struct packed_git *p);
+/*
+ * load_midx_revindex loads the '.rev' file corresponding to the given
+ * multi-pack index by mmap-ing it and assigning pointers in the
+ * multi_pack_index to point at it.
+ *
+ * A negative number is returned on error.
+ */
+int load_midx_revindex(struct multi_pack_index *m);
+
/*
* offset_to_pack_pos converts an object offset to a pack position. This
* function returns zero on success, and a negative number otherwise. The
@@ -71,4 +95,26 @@ uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos);
*/
off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos);
+/*
+ * pack_pos_to_midx converts the object at position "pos" within the MIDX
+ * pseudo-pack into a MIDX position.
+ *
+ * If the reverse index has not yet been loaded, or the position is out of
+ * bounds, this function aborts.
+ *
+ * This function runs in time O(log N) with the number of objects in the MIDX.
+ */
+uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos);
+
+/*
+ * midx_to_pack_pos converts from the MIDX-relative position at "at" to the
+ * corresponding pack position.
+ *
+ * If the reverse index has not yet been loaded, or the position is out of
+ * bounds, this function aborts.
+ *
+ * This function runs in constant time.
+ */
+int midx_to_pack_pos(struct multi_pack_index *midx, uint32_t at, uint32_t *pos);
+
#endif
diff --git a/packfile.c b/packfile.c
index 1fec12ac5f..82623e0cb4 100644
--- a/packfile.c
+++ b/packfile.c
@@ -862,6 +862,9 @@ static void prepare_pack(const char *full_name, size_t full_name_len,
if (!strcmp(file_name, "multi-pack-index"))
return;
+ if (starts_with(file_name, "multi-pack-index") &&
+ ends_with(file_name, ".rev"))
+ return;
if (ends_with(file_name, ".idx") ||
ends_with(file_name, ".rev") ||
ends_with(file_name, ".pack") ||
--
2.30.0.667.g81c0cbc6fd
