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commit-graph: implement write_commit_graph()

Teach Git to write a commit graph file by checking all packed objects
to see if they are commits, then store the file in the given object
directory.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
tags/v2.18.0-rc0
Derrick Stolee Junio C Hamano 1 year ago
parent
commit
08fd81c9b6
3 changed files with 366 additions and 0 deletions
  1. +1
    -0
      Makefile
  2. +359
    -0
      commit-graph.c
  3. +6
    -0
      commit-graph.h

+ 1
- 0
Makefile View File

@@ -771,6 +771,7 @@ LIB_OBJS += color.o
LIB_OBJS += column.o
LIB_OBJS += combine-diff.o
LIB_OBJS += commit.o
LIB_OBJS += commit-graph.o
LIB_OBJS += compat/obstack.o
LIB_OBJS += compat/terminal.o
LIB_OBJS += config.o


+ 359
- 0
commit-graph.c View File

@@ -0,0 +1,359 @@
#include "cache.h"
#include "config.h"
#include "git-compat-util.h"
#include "lockfile.h"
#include "pack.h"
#include "packfile.h"
#include "commit.h"
#include "object.h"
#include "revision.h"
#include "sha1-lookup.h"
#include "commit-graph.h"

#define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
#define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
#define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
#define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
#define GRAPH_CHUNKID_LARGEEDGES 0x45444745 /* "EDGE" */

#define GRAPH_DATA_WIDTH 36

#define GRAPH_VERSION_1 0x1
#define GRAPH_VERSION GRAPH_VERSION_1

#define GRAPH_OID_VERSION_SHA1 1
#define GRAPH_OID_LEN_SHA1 GIT_SHA1_RAWSZ
#define GRAPH_OID_VERSION GRAPH_OID_VERSION_SHA1
#define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1

#define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
#define GRAPH_PARENT_MISSING 0x7fffffff
#define GRAPH_EDGE_LAST_MASK 0x7fffffff
#define GRAPH_PARENT_NONE 0x70000000

#define GRAPH_LAST_EDGE 0x80000000

#define GRAPH_FANOUT_SIZE (4 * 256)
#define GRAPH_CHUNKLOOKUP_WIDTH 12
#define GRAPH_MIN_SIZE (5 * GRAPH_CHUNKLOOKUP_WIDTH + GRAPH_FANOUT_SIZE + \
GRAPH_OID_LEN + 8)


static char *get_commit_graph_filename(const char *obj_dir)
{
return xstrfmt("%s/info/commit-graph", obj_dir);
}

static void write_graph_chunk_fanout(struct hashfile *f,
struct commit **commits,
int nr_commits)
{
int i, count = 0;
struct commit **list = commits;

/*
* Write the first-level table (the list is sorted,
* but we use a 256-entry lookup to be able to avoid
* having to do eight extra binary search iterations).
*/
for (i = 0; i < 256; i++) {
while (count < nr_commits) {
if ((*list)->object.oid.hash[0] != i)
break;
count++;
list++;
}

hashwrite_be32(f, count);
}
}

static void write_graph_chunk_oids(struct hashfile *f, int hash_len,
struct commit **commits, int nr_commits)
{
struct commit **list = commits;
int count;
for (count = 0; count < nr_commits; count++, list++)
hashwrite(f, (*list)->object.oid.hash, (int)hash_len);
}

static const unsigned char *commit_to_sha1(size_t index, void *table)
{
struct commit **commits = table;
return commits[index]->object.oid.hash;
}

static void write_graph_chunk_data(struct hashfile *f, int hash_len,
struct commit **commits, int nr_commits)
{
struct commit **list = commits;
struct commit **last = commits + nr_commits;
uint32_t num_extra_edges = 0;

while (list < last) {
struct commit_list *parent;
int edge_value;
uint32_t packedDate[2];

parse_commit(*list);
hashwrite(f, (*list)->tree->object.oid.hash, hash_len);

parent = (*list)->parents;

if (!parent)
edge_value = GRAPH_PARENT_NONE;
else {
edge_value = sha1_pos(parent->item->object.oid.hash,
commits,
nr_commits,
commit_to_sha1);

if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING;
}

hashwrite_be32(f, edge_value);

if (parent)
parent = parent->next;

if (!parent)
edge_value = GRAPH_PARENT_NONE;
else if (parent->next)
edge_value = GRAPH_OCTOPUS_EDGES_NEEDED | num_extra_edges;
else {
edge_value = sha1_pos(parent->item->object.oid.hash,
commits,
nr_commits,
commit_to_sha1);
if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING;
}

hashwrite_be32(f, edge_value);

if (edge_value & GRAPH_OCTOPUS_EDGES_NEEDED) {
do {
num_extra_edges++;
parent = parent->next;
} while (parent);
}

if (sizeof((*list)->date) > 4)
packedDate[0] = htonl(((*list)->date >> 32) & 0x3);
else
packedDate[0] = 0;

packedDate[1] = htonl((*list)->date);
hashwrite(f, packedDate, 8);

list++;
}
}

static void write_graph_chunk_large_edges(struct hashfile *f,
struct commit **commits,
int nr_commits)
{
struct commit **list = commits;
struct commit **last = commits + nr_commits;
struct commit_list *parent;

while (list < last) {
int num_parents = 0;
for (parent = (*list)->parents; num_parents < 3 && parent;
parent = parent->next)
num_parents++;

if (num_parents <= 2) {
list++;
continue;
}

/* Since num_parents > 2, this initializer is safe. */
for (parent = (*list)->parents->next; parent; parent = parent->next) {
int edge_value = sha1_pos(parent->item->object.oid.hash,
commits,
nr_commits,
commit_to_sha1);

if (edge_value < 0)
edge_value = GRAPH_PARENT_MISSING;
else if (!parent->next)
edge_value |= GRAPH_LAST_EDGE;

hashwrite_be32(f, edge_value);
}

list++;
}
}

static int commit_compare(const void *_a, const void *_b)
{
const struct object_id *a = (const struct object_id *)_a;
const struct object_id *b = (const struct object_id *)_b;
return oidcmp(a, b);
}

struct packed_commit_list {
struct commit **list;
int nr;
int alloc;
};

struct packed_oid_list {
struct object_id *list;
int nr;
int alloc;
};

static int add_packed_commits(const struct object_id *oid,
struct packed_git *pack,
uint32_t pos,
void *data)
{
struct packed_oid_list *list = (struct packed_oid_list*)data;
enum object_type type;
off_t offset = nth_packed_object_offset(pack, pos);
struct object_info oi = OBJECT_INFO_INIT;

oi.typep = &type;
if (packed_object_info(pack, offset, &oi) < 0)
die("unable to get type of object %s", oid_to_hex(oid));

if (type != OBJ_COMMIT)
return 0;

ALLOC_GROW(list->list, list->nr + 1, list->alloc);
oidcpy(&(list->list[list->nr]), oid);
list->nr++;

return 0;
}

void write_commit_graph(const char *obj_dir)
{
struct packed_oid_list oids;
struct packed_commit_list commits;
struct hashfile *f;
uint32_t i, count_distinct = 0;
char *graph_name;
int fd;
struct lock_file lk = LOCK_INIT;
uint32_t chunk_ids[5];
uint64_t chunk_offsets[5];
int num_chunks;
int num_extra_edges;
struct commit_list *parent;

oids.nr = 0;
oids.alloc = approximate_object_count() / 4;

if (oids.alloc < 1024)
oids.alloc = 1024;
ALLOC_ARRAY(oids.list, oids.alloc);

for_each_packed_object(add_packed_commits, &oids, 0);

QSORT(oids.list, oids.nr, commit_compare);

count_distinct = 1;
for (i = 1; i < oids.nr; i++) {
if (oidcmp(&oids.list[i-1], &oids.list[i]))
count_distinct++;
}

if (count_distinct >= GRAPH_PARENT_MISSING)
die(_("the commit graph format cannot write %d commits"), count_distinct);

commits.nr = 0;
commits.alloc = count_distinct;
ALLOC_ARRAY(commits.list, commits.alloc);

num_extra_edges = 0;
for (i = 0; i < oids.nr; i++) {
int num_parents = 0;
if (i > 0 && !oidcmp(&oids.list[i-1], &oids.list[i]))
continue;

commits.list[commits.nr] = lookup_commit(&oids.list[i]);
parse_commit(commits.list[commits.nr]);

for (parent = commits.list[commits.nr]->parents;
parent; parent = parent->next)
num_parents++;

if (num_parents > 2)
num_extra_edges += num_parents - 1;

commits.nr++;
}
num_chunks = num_extra_edges ? 4 : 3;

if (commits.nr >= GRAPH_PARENT_MISSING)
die(_("too many commits to write graph"));

graph_name = get_commit_graph_filename(obj_dir);
fd = hold_lock_file_for_update(&lk, graph_name, 0);

if (fd < 0) {
struct strbuf folder = STRBUF_INIT;
strbuf_addstr(&folder, graph_name);
strbuf_setlen(&folder, strrchr(folder.buf, '/') - folder.buf);

if (mkdir(folder.buf, 0777) < 0)
die_errno(_("cannot mkdir %s"), folder.buf);
strbuf_release(&folder);

fd = hold_lock_file_for_update(&lk, graph_name, LOCK_DIE_ON_ERROR);

if (fd < 0)
die_errno("unable to create '%s'", graph_name);
}

f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);

hashwrite_be32(f, GRAPH_SIGNATURE);

hashwrite_u8(f, GRAPH_VERSION);
hashwrite_u8(f, GRAPH_OID_VERSION);
hashwrite_u8(f, num_chunks);
hashwrite_u8(f, 0); /* unused padding byte */

chunk_ids[0] = GRAPH_CHUNKID_OIDFANOUT;
chunk_ids[1] = GRAPH_CHUNKID_OIDLOOKUP;
chunk_ids[2] = GRAPH_CHUNKID_DATA;
if (num_extra_edges)
chunk_ids[3] = GRAPH_CHUNKID_LARGEEDGES;
else
chunk_ids[3] = 0;
chunk_ids[4] = 0;

chunk_offsets[0] = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
chunk_offsets[1] = chunk_offsets[0] + GRAPH_FANOUT_SIZE;
chunk_offsets[2] = chunk_offsets[1] + GRAPH_OID_LEN * commits.nr;
chunk_offsets[3] = chunk_offsets[2] + (GRAPH_OID_LEN + 16) * commits.nr;
chunk_offsets[4] = chunk_offsets[3] + 4 * num_extra_edges;

for (i = 0; i <= num_chunks; i++) {
uint32_t chunk_write[3];

chunk_write[0] = htonl(chunk_ids[i]);
chunk_write[1] = htonl(chunk_offsets[i] >> 32);
chunk_write[2] = htonl(chunk_offsets[i] & 0xffffffff);
hashwrite(f, chunk_write, 12);
}

write_graph_chunk_fanout(f, commits.list, commits.nr);
write_graph_chunk_oids(f, GRAPH_OID_LEN, commits.list, commits.nr);
write_graph_chunk_data(f, GRAPH_OID_LEN, commits.list, commits.nr);
write_graph_chunk_large_edges(f, commits.list, commits.nr);

finalize_hashfile(f, NULL, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
commit_lock_file(&lk);

free(oids.list);
oids.alloc = 0;
oids.nr = 0;
}

+ 6
- 0
commit-graph.h View File

@@ -0,0 +1,6 @@
#ifndef COMMIT_GRAPH_H
#define COMMIT_GRAPH_H

void write_commit_graph(const char *obj_dir);

#endif

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