commit-graph: implement write_commit_graph()
authorDerrick Stolee <dstolee@microsoft.com>
Mon, 2 Apr 2018 20:34:19 +0000 (16:34 -0400)
committerJunio C Hamano <gitster@pobox.com>
Mon, 2 Apr 2018 21:27:38 +0000 (14:27 -0700)
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>
Makefile
commit-graph.c [new file with mode: 0644]
commit-graph.h [new file with mode: 0644]

index 2e4956f..bf91b2d 100644 (file)
--- 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 (file)
index 0000000..f3f7c4f
--- /dev/null
@@ -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;
+}
diff --git a/commit-graph.h b/commit-graph.h
new file mode 100644 (file)
index 0000000..16fea99
--- /dev/null
@@ -0,0 +1,6 @@
+#ifndef COMMIT_GRAPH_H
+#define COMMIT_GRAPH_H
+
+void write_commit_graph(const char *obj_dir);
+
+#endif