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![Nicolas Pitre](/assets/img/avatar_default.png)
This adds a new object, namely OBJ_OFS_DELTA, renames OBJ_DELTA to OBJ_REF_DELTA to better make the distinction between those two delta objects, and adds support for the handling of those new delta objects in sha1_file.c only. The OBJ_OFS_DELTA contains a relative offset from the delta object's position in a pack instead of the 20-byte SHA1 reference to identify the base object. Since the base is likely to be not so far away, the relative offset is more likely to have a smaller encoding on average than an absolute offset. And for those delta objects the base must always be stored first because there is no way to know the distance of later objects when streaming a pack. Hence this relative offset is always meant to be negative. The offset encoding is slightly denser than the one used for object size -- credits to <linux@horizon.com> (whoever this is) for bringing it to my attention. This allows for pack size reduction between 3.2% (Linux-2.6) to over 5% (linux-historic). Runtime pack access should be faster too since delta replay does skip a search in the pack index for each delta in a chain. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
328 lines
6.8 KiB
C
328 lines
6.8 KiB
C
#include "builtin.h"
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#include "cache.h"
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#include "object.h"
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#include "delta.h"
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#include "pack.h"
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#include "blob.h"
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#include "commit.h"
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#include "tag.h"
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#include "tree.h"
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#include <sys/time.h>
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static int dry_run, quiet, recover, has_errors;
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static const char unpack_usage[] = "git-unpack-objects [-n] [-q] [-r] < pack-file";
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/* We always read in 4kB chunks. */
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static unsigned char buffer[4096];
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static unsigned long offset, len;
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static SHA_CTX ctx;
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/*
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* Make sure at least "min" bytes are available in the buffer, and
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* return the pointer to the buffer.
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*/
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static void * fill(int min)
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{
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if (min <= len)
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return buffer + offset;
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if (min > sizeof(buffer))
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die("cannot fill %d bytes", min);
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if (offset) {
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SHA1_Update(&ctx, buffer, offset);
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memcpy(buffer, buffer + offset, len);
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offset = 0;
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}
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do {
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int ret = xread(0, buffer + len, sizeof(buffer) - len);
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if (ret <= 0) {
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if (!ret)
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die("early EOF");
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die("read error on input: %s", strerror(errno));
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}
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len += ret;
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} while (len < min);
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return buffer;
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}
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static void use(int bytes)
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{
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if (bytes > len)
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die("used more bytes than were available");
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len -= bytes;
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offset += bytes;
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}
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static void *get_data(unsigned long size)
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{
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z_stream stream;
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void *buf = xmalloc(size);
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memset(&stream, 0, sizeof(stream));
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stream.next_out = buf;
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stream.avail_out = size;
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stream.next_in = fill(1);
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stream.avail_in = len;
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inflateInit(&stream);
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for (;;) {
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int ret = inflate(&stream, 0);
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use(len - stream.avail_in);
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if (stream.total_out == size && ret == Z_STREAM_END)
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break;
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if (ret != Z_OK) {
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error("inflate returned %d\n", ret);
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free(buf);
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buf = NULL;
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if (!recover)
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exit(1);
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has_errors = 1;
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break;
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}
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stream.next_in = fill(1);
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stream.avail_in = len;
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}
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inflateEnd(&stream);
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return buf;
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}
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struct delta_info {
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unsigned char base_sha1[20];
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unsigned long size;
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void *delta;
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struct delta_info *next;
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};
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static struct delta_info *delta_list;
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static void add_delta_to_list(unsigned char *base_sha1, void *delta, unsigned long size)
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{
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struct delta_info *info = xmalloc(sizeof(*info));
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hashcpy(info->base_sha1, base_sha1);
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info->size = size;
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info->delta = delta;
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info->next = delta_list;
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delta_list = info;
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}
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static void added_object(unsigned char *sha1, const char *type, void *data, unsigned long size);
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static void write_object(void *buf, unsigned long size, const char *type)
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{
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unsigned char sha1[20];
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if (write_sha1_file(buf, size, type, sha1) < 0)
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die("failed to write object");
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added_object(sha1, type, buf, size);
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}
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static void resolve_delta(const char *type,
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void *base, unsigned long base_size,
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void *delta, unsigned long delta_size)
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{
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void *result;
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unsigned long result_size;
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result = patch_delta(base, base_size,
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delta, delta_size,
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&result_size);
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if (!result)
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die("failed to apply delta");
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free(delta);
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write_object(result, result_size, type);
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free(result);
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}
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static void added_object(unsigned char *sha1, const char *type, void *data, unsigned long size)
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{
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struct delta_info **p = &delta_list;
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struct delta_info *info;
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while ((info = *p) != NULL) {
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if (!hashcmp(info->base_sha1, sha1)) {
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*p = info->next;
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p = &delta_list;
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resolve_delta(type, data, size, info->delta, info->size);
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free(info);
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continue;
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}
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p = &info->next;
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}
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}
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static void unpack_non_delta_entry(enum object_type kind, unsigned long size)
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{
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void *buf = get_data(size);
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const char *type;
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switch (kind) {
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case OBJ_COMMIT: type = commit_type; break;
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case OBJ_TREE: type = tree_type; break;
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case OBJ_BLOB: type = blob_type; break;
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case OBJ_TAG: type = tag_type; break;
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default: die("bad type %d", kind);
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}
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if (!dry_run && buf)
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write_object(buf, size, type);
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free(buf);
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}
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static void unpack_delta_entry(unsigned long delta_size)
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{
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void *delta_data, *base;
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unsigned long base_size;
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char type[20];
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unsigned char base_sha1[20];
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hashcpy(base_sha1, fill(20));
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use(20);
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delta_data = get_data(delta_size);
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if (dry_run || !delta_data) {
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free(delta_data);
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return;
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}
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if (!has_sha1_file(base_sha1)) {
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add_delta_to_list(base_sha1, delta_data, delta_size);
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return;
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}
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base = read_sha1_file(base_sha1, type, &base_size);
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if (!base) {
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error("failed to read delta-pack base object %s",
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sha1_to_hex(base_sha1));
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if (!recover)
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exit(1);
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has_errors = 1;
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return;
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}
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resolve_delta(type, base, base_size, delta_data, delta_size);
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free(base);
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}
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static void unpack_one(unsigned nr, unsigned total)
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{
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unsigned shift;
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unsigned char *pack, c;
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unsigned long size;
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enum object_type type;
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pack = fill(1);
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c = *pack;
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use(1);
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type = (c >> 4) & 7;
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size = (c & 15);
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shift = 4;
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while (c & 0x80) {
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pack = fill(1);
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c = *pack++;
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use(1);
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size += (c & 0x7f) << shift;
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shift += 7;
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}
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if (!quiet) {
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static unsigned long last_sec;
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static unsigned last_percent;
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struct timeval now;
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unsigned percentage = (nr * 100) / total;
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gettimeofday(&now, NULL);
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if (percentage != last_percent || now.tv_sec != last_sec) {
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last_sec = now.tv_sec;
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last_percent = percentage;
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fprintf(stderr, "%4u%% (%u/%u) done\r", percentage, nr, total);
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}
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}
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switch (type) {
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case OBJ_COMMIT:
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case OBJ_TREE:
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case OBJ_BLOB:
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case OBJ_TAG:
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unpack_non_delta_entry(type, size);
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return;
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case OBJ_REF_DELTA:
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unpack_delta_entry(size);
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return;
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default:
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error("bad object type %d", type);
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has_errors = 1;
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if (recover)
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return;
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exit(1);
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}
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}
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static void unpack_all(void)
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{
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int i;
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struct pack_header *hdr = fill(sizeof(struct pack_header));
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unsigned nr_objects = ntohl(hdr->hdr_entries);
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if (ntohl(hdr->hdr_signature) != PACK_SIGNATURE)
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die("bad pack file");
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if (!pack_version_ok(hdr->hdr_version))
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die("unknown pack file version %d", ntohl(hdr->hdr_version));
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fprintf(stderr, "Unpacking %d objects\n", nr_objects);
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use(sizeof(struct pack_header));
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for (i = 0; i < nr_objects; i++)
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unpack_one(i+1, nr_objects);
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if (delta_list)
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die("unresolved deltas left after unpacking");
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}
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int cmd_unpack_objects(int argc, const char **argv, const char *prefix)
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{
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int i;
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unsigned char sha1[20];
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git_config(git_default_config);
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quiet = !isatty(2);
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for (i = 1 ; i < argc; i++) {
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const char *arg = argv[i];
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if (*arg == '-') {
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if (!strcmp(arg, "-n")) {
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dry_run = 1;
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continue;
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}
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if (!strcmp(arg, "-q")) {
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quiet = 1;
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continue;
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}
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if (!strcmp(arg, "-r")) {
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recover = 1;
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continue;
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}
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usage(unpack_usage);
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}
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/* We don't take any non-flag arguments now.. Maybe some day */
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usage(unpack_usage);
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}
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SHA1_Init(&ctx);
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unpack_all();
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SHA1_Update(&ctx, buffer, offset);
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SHA1_Final(sha1, &ctx);
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if (hashcmp(fill(20), sha1))
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die("final sha1 did not match");
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use(20);
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/* Write the last part of the buffer to stdout */
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while (len) {
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int ret = xwrite(1, buffer + offset, len);
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if (ret <= 0)
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break;
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len -= ret;
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offset += ret;
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}
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/* All done */
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if (!quiet)
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fprintf(stderr, "\n");
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return has_errors;
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}
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