From c323ac7d9c573c5ee8b45b9b9def92a4d4d8204d Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 25 Jun 2005 14:42:43 -0700 Subject: [PATCH] git-pack-objects: create a packed object representation. This is kind of like a tar-ball for a set of objects, ready to be shipped off to another end. Alternatively, you could use is as a packed representation of the object database directly, if you changed "read_sha1_file()" to read these kinds of packs. The latter is partiularly useful to generate a "packed history", ie you could pack up your old history efficiently, but still have it available (at a performance hit, of course). I haven't actually written an unpacker yet, so the end result has not been verified in any way yet. I obviously always write bug-free code, so it just has to work, no? --- Makefile | 4 +- pack-objects.c | 403 +++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 406 insertions(+), 1 deletion(-) create mode 100644 pack-objects.c diff --git a/Makefile b/Makefile index fd5c80f75..37fdbb04e 100644 --- a/Makefile +++ b/Makefile @@ -35,7 +35,8 @@ PROG= git-update-cache git-diff-files git-init-db git-write-tree \ git-http-pull git-ssh-push git-ssh-pull git-rev-list git-mktag \ git-diff-helper git-tar-tree git-local-pull git-write-blob \ git-get-tar-commit-id git-mkdelta git-apply git-stripspace \ - git-cvs2git git-diff-stages git-rev-parse git-patch-id + git-cvs2git git-diff-stages git-rev-parse git-patch-id \ + git-pack-objects all: $(PROG) @@ -122,6 +123,7 @@ git-cvs2git: cvs2git.c git-diff-stages: diff-stages.c git-rev-parse: rev-parse.c git-patch-id: patch-id.c +git-pack-objects: pack-objects.c git-http-pull: LIBS += -lcurl git-rev-list: LIBS += -lssl diff --git a/pack-objects.c b/pack-objects.c new file mode 100644 index 000000000..322c4bc3e --- /dev/null +++ b/pack-objects.c @@ -0,0 +1,403 @@ +#include "cache.h" +#include "object.h" +#include "delta.h" + +static const char pack_usage[] = "git-pack-objects [--window=N] base-name < object-list"; + +enum object_type { + OBJ_NONE, + OBJ_COMMIT, + OBJ_TREE, + OBJ_BLOB, + OBJ_DELTA // NOTE! This is _not_ the same as a "delta" object in the filesystem +}; + +struct object_entry { + unsigned char sha1[20]; + unsigned long size; + unsigned long offset; + unsigned int depth; + unsigned int flags; + enum object_type type; + unsigned long delta_size; + struct object_entry *delta; +}; + +static struct object_entry **sorted_by_sha, **sorted_by_type; +static struct object_entry *objects = NULL; +static int nr_objects = 0, nr_alloc = 0; +static int delta_window = 10; +static const char *base_name; + +struct myfile { + int fd; + unsigned long chars; + unsigned char buffer[8192]; +}; + +static FILE *create_file(const char *suffix) +{ + static char filename[PATH_MAX]; + unsigned len; + + len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix); + if (len >= PATH_MAX) + die("you wascally wabbit, you"); + return fopen(filename, "w"); +} + +static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f) +{ + z_stream stream; + unsigned long maxsize; + void *out; + + memset(&stream, 0, sizeof(stream)); + deflateInit(&stream, Z_DEFAULT_COMPRESSION); + maxsize = deflateBound(&stream, size); + out = xmalloc(maxsize); + + /* Compress it */ + stream.next_in = in; + stream.avail_in = size; + + stream.next_out = out; + stream.avail_out = maxsize; + + while (deflate(&stream, Z_FINISH) == Z_OK) + /* nothing */; + deflateEnd(&stream); + + size = stream.total_out; + fwrite(out, size, 1, f); + free(out); + return size; +} + +static void *delta_against(void *buf, unsigned long size, struct object_entry *entry) +{ + unsigned long othersize, delta_size; + char type[10]; + void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize); + void *delta_buf; + + if (!otherbuf) + die("unable to read %s", sha1_to_hex(entry->delta->sha1)); + delta_buf = diff_delta(buf, size, otherbuf, othersize, &delta_size); + if (delta_size != entry->delta_size) + die("delta size changed"); + free(buf); + free(otherbuf); + return delta_buf; +} + +static unsigned long write_object(FILE *f, struct object_entry *entry) +{ + unsigned long size; + char type[10]; + void *buf = read_sha1_file(entry->sha1, type, &size); + char header[21]; + unsigned hdrlen, datalen; + + if (!buf) + die("unable to read %s", sha1_to_hex(entry->sha1)); + if (size != entry->size) + die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size); + + /* + * The object header is a byte of 'type' followed by four bytes of + * length, except for deltas that has the 20 bytes of delta sha + * instead. + */ + header[0] = ".CTB"[entry->type]; + datalen = htonl(size); + memcpy(header+1, &datalen, 4); + hdrlen = 5; + if (entry->delta) { + memcpy(header+1, entry->delta, 20); + buf = delta_against(buf, size, entry); + size = entry->delta_size; + hdrlen = 21; + } + fwrite(header, hdrlen, 1, f); + datalen = fwrite_compressed(buf, size, f); + free(buf); + return hdrlen + datalen; +} + +static void write_pack_file(void) +{ + int i; + FILE *f = create_file("pack"); + unsigned long offset = 0; + unsigned long mb; + + for (i = 0; i < nr_objects; i++) { + struct object_entry *entry = objects + i; + entry->offset = offset; + offset += write_object(f, entry); + } + fclose(f); + mb = offset >> 20; + offset &= 0xfffff; +} + +static void write_index_file(void) +{ + int i; + FILE *f = create_file("idx"); + struct object_entry **list = sorted_by_sha; + struct object_entry **last = list + nr_objects; + unsigned int array[256]; + + /* + * 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++) { + struct object_entry **next = list; + while (next < last) { + struct object_entry *entry = *next; + if (entry->sha1[0] != i) + break; + next++; + } + array[i] = htonl(next - sorted_by_sha); + list = next; + } + fwrite(array, 256, sizeof(int), f); + + /* + * Write the actual SHA1 entries.. + */ + list = sorted_by_sha; + for (i < 0; i < nr_objects; i++) { + struct object_entry *entry = *list++; + unsigned int offset = htonl(entry->offset); + fwrite(&offset, 4, 1, f); + fwrite(entry->sha1, 20, 1, f); + } + fclose(f); +} + +static void add_object_entry(unsigned char *sha1) +{ + unsigned int idx = nr_objects; + struct object_entry *entry; + + if (idx >= nr_alloc) { + unsigned int needed = (idx + 1024) * 3 / 2; + objects = xrealloc(objects, needed * sizeof(*entry)); + nr_alloc = needed; + } + entry = objects + idx; + memset(entry, 0, sizeof(*entry)); + memcpy(entry->sha1, sha1, 20); + nr_objects = idx+1; +} + +static void check_object(struct object_entry *entry) +{ + char buffer[128]; + char type[10]; + unsigned long mapsize; + z_stream stream; + void *map; + + map = map_sha1_file(entry->sha1, &mapsize); + if (!map) + die("unable to map %s", sha1_to_hex(entry->sha1)); + if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0) + die("unable to unpack %s header", sha1_to_hex(entry->sha1)); + munmap(map, mapsize); + if (parse_sha1_header(buffer, type, &entry->size) < 0) + die("unable to parse %s header", sha1_to_hex(entry->sha1)); + if (!strcmp(type, "commit")) { + entry->type = OBJ_COMMIT; + } else if (!strcmp(type, "tree")) { + entry->type = OBJ_TREE; + } else if (!strcmp(type, "blob")) { + entry->type = OBJ_BLOB; + } else + die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type); +} + +static void get_object_details(void) +{ + int i; + struct object_entry *entry = objects; + + for (i = 0; i < nr_objects; i++) + check_object(entry++); +} + +typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *); + +static entry_sort_t current_sort; + +static int sort_comparator(const void *_a, const void *_b) +{ + struct object_entry *a = *(struct object_entry **)_a; + struct object_entry *b = *(struct object_entry **)_b; + return current_sort(a,b); +} + +static struct object_entry **create_sorted_list(entry_sort_t sort) +{ + struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *)); + int i; + + for (i = 0; i < nr_objects; i++) + list[i] = objects + i; + current_sort = sort; + qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator); + return list; +} + +static int sha1_sort(const struct object_entry *a, const struct object_entry *b) +{ + return memcmp(a->sha1, b->sha1, 20); +} + +static int type_size_sort(const struct object_entry *a, const struct object_entry *b) +{ + if (a->type < b->type) + return -1; + if (a->type > b->type) + return 1; + if (a->size < b->size) + return -1; + if (a->size > b->size) + return 1; + return a < b ? -1 : (a > b); +} + +struct unpacked { + struct object_entry *entry; + void *data; +}; + +/* + * We search for deltas in a list sorted by type and by size, and + * walk the "old" chain backwards in the list, so if the type + * has changed or the size difference is too big, there's no point + * in even continuing the walk, since the other old objects are + * going to be even smaller or of a different type. So return -1 + * once we determine that there's no point even trying. + */ +static int try_delta(struct unpacked *cur, struct unpacked *old) +{ + struct object_entry *cur_entry = cur->entry; + struct object_entry *old_entry = old->entry; + unsigned long size, oldsize, delta_size; + void *delta_buf; + + /* Don't bother doing diffs between different types */ + if (cur_entry->type != old_entry->type) + return -1; + + /* Size is guaranteed to be larger than or equal to oldsize */ + size = cur_entry->size; + oldsize = old_entry->size; + if (size - oldsize > oldsize / 4) + return -1; + + /* + * NOTE! + * + * We always delta from the bigger to the smaller, since that's + * more space-efficient (deletes don't have to say _what_ they + * delete). + */ + delta_buf = diff_delta(cur->data, size, old->data, oldsize, &delta_size); + if (!delta_buf) + die("unable to create delta"); + if (delta_size + 20 < size / 2) { + if (!cur_entry->delta || cur_entry->delta_size > delta_size) { + cur_entry->delta = old_entry; + cur_entry->delta_size = delta_size; + } + } + free(delta_buf); +} + +static void find_deltas(struct object_entry **list, int window) +{ + unsigned int i; + unsigned int array_size = window * sizeof(struct unpacked); + struct unpacked *array = xmalloc(array_size); + + memset(array, 0, array_size); + for (i = 0; i < nr_objects; i++) { + unsigned int idx = i % window; + struct object_entry *entry = list[i]; + struct unpacked *n = array + idx; + unsigned long size; + char type[10]; + int j; + + free(n->data); + n->entry = entry; + n->data = read_sha1_file(entry->sha1, type, &size); + if (size != entry->size) + die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size); + for (j = 0; j < window; j++) { + unsigned int other_idx = idx - 1 - j; + struct unpacked *m; + if (other_idx < 0) + other_idx += window; + m = array + other_idx; + if (!m->entry) + break; + if (try_delta(n, m) < 0) + break; + } + } +} + +int main(int argc, char **argv) +{ + char line[128]; + int i; + + for (i = 1; i < argc; i++) { + const char *arg = argv[i]; + + if (*arg == '-') { + if (!strncmp("--window=", arg, 9)) { + char *end; + delta_window = strtoul(arg+9, &end, 0); + if (!arg[9] || *end) + usage(pack_usage); + continue; + } + usage(pack_usage); + } + if (base_name) + usage(pack_usage); + base_name = arg; + } + + if (!base_name) + usage(pack_usage); + + while (fgets(line, sizeof(line), stdin) != NULL) { + unsigned char sha1[20]; + if (get_sha1_hex(line, sha1)) + die("expected sha1, got garbage"); + add_object_entry(sha1); + } + get_object_details(); + + printf("Packing %d objects\n", nr_objects); + + sorted_by_sha = create_sorted_list(sha1_sort); + sorted_by_type = create_sorted_list(type_size_sort); + if (delta_window) + find_deltas(sorted_by_type, delta_window); + + write_pack_file(); + write_index_file(); + return 0; +} -- 2.30.2