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.
Signed-off-by: Derrick Stolee <dsto...@microsoft.com>
---
Makefile | 1 +
commit-graph.c | 360 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
commit-graph.h | 7 ++
3 files changed, 368 insertions(+)
create mode 100644 commit-graph.c
create mode 100644 commit-graph.h
diff --git a/Makefile b/Makefile
index 2e4956f..bf91b2d 100644
--- a/Makefile
+++ b/Makefile
@@ -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
diff --git a/commit-graph.c b/commit-graph.c
new file mode 100644
index 0000000..2251397
--- /dev/null
+++ b/commit-graph.c
@@ -0,0 +1,360 @@
+#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;
+ unsigned long size;
+ void *inner_data;
+ off_t offset = nth_packed_object_offset(pack, pos);
+ inner_data = unpack_entry(pack, offset, &type, &size);
+ FREE_AND_NULL(inner_data);
+
+ 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;
+ unsigned char final_hash[GIT_MAX_RAWSZ];
+ 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);
+
+ hashclose(f, final_hash, CSUM_CLOSE | CSUM_FSYNC | CSUM_KEEP_OPEN);
+ commit_lock_file(&lk);
+
+ free(oids.list);
+ oids.alloc = 0;
+ oids.nr = 0;
+}
+
diff --git a/commit-graph.h b/commit-graph.h
new file mode 100644
index 0000000..4cb3f12
--- /dev/null
+++ b/commit-graph.h
@@ -0,0 +1,7 @@
+#ifndef COMMIT_GRAPH_H
+#define COMMIT_GRAPH_H
+
+void write_commit_graph(const char *obj_dir);
+
+#endif
+
--
2.7.4
