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mkdelta.c
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mkdelta.c
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/*
* Deltafication of a GIT database.
*
* (C) 2005 Nicolas Pitre <[email protected]>
*
* This code is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include "cache.h"
#include "delta.h"
static int replace_object(char *buf, unsigned long size, unsigned char *sha1)
{
char tmpfile[PATH_MAX];
int fd;
snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX", get_object_directory());
fd = mkstemp(tmpfile);
if (fd < 0)
return error("%s: %s\n", tmpfile, strerror(errno));
if (write(fd, buf, size) != size) {
perror("unable to write file");
close(fd);
unlink(tmpfile);
return -1;
}
fchmod(fd, 0444);
close(fd);
if (rename(tmpfile, sha1_file_name(sha1))) {
perror("unable to replace original object");
unlink(tmpfile);
return -1;
}
return 0;
}
static void *create_object(unsigned char *buf, unsigned long len,
char *hdr, int hdrlen, unsigned long *retsize)
{
unsigned char *compressed;
unsigned long size;
z_stream stream;
/* Set it up */
memset(&stream, 0, sizeof(stream));
deflateInit(&stream, Z_BEST_COMPRESSION);
size = deflateBound(&stream, len+hdrlen);
compressed = xmalloc(size);
/* Compress it */
stream.next_out = compressed;
stream.avail_out = size;
/* First header.. */
stream.next_in = (unsigned char *)hdr;
stream.avail_in = hdrlen;
while (deflate(&stream, 0) == Z_OK)
/* nothing */;
/* Then the data itself.. */
stream.next_in = buf;
stream.avail_in = len;
while (deflate(&stream, Z_FINISH) == Z_OK)
/* nothing */;
deflateEnd(&stream);
*retsize = stream.total_out;
return compressed;
}
static int restore_original_object(unsigned char *buf, unsigned long len,
char *type, unsigned char *sha1)
{
char hdr[50];
int hdrlen, ret;
void *compressed;
unsigned long size;
hdrlen = sprintf(hdr, "%s %lu", type, len)+1;
compressed = create_object(buf, len, hdr, hdrlen, &size);
ret = replace_object(compressed, size, sha1);
free(compressed);
return ret;
}
static void *create_delta_object(unsigned char *buf, unsigned long len,
unsigned char *sha1_ref, unsigned long *size)
{
char hdr[50];
int hdrlen;
/* Generate the header + sha1 of reference for delta */
hdrlen = sprintf(hdr, "delta %lu", len+20)+1;
memcpy(hdr + hdrlen, sha1_ref, 20);
hdrlen += 20;
return create_object(buf, len, hdr, hdrlen, size);
}
static void *get_buffer(unsigned char *sha1, char *type,
unsigned long *size, unsigned long *compsize)
{
unsigned long mapsize;
void *map = map_sha1_file(sha1, &mapsize);
if (map) {
void *buffer = unpack_sha1_file(map, mapsize, type, size);
munmap(map, mapsize);
if (compsize)
*compsize = mapsize;
if (buffer)
return buffer;
}
error("unable to get object %s", sha1_to_hex(sha1));
return NULL;
}
static void *expand_delta(void *delta, unsigned long *size, char *type,
unsigned int *depth, unsigned char **links)
{
void *buf = NULL;
unsigned int level = (*depth)++;
if (*size < 20) {
error("delta object is bad");
free(delta);
} else {
unsigned long ref_size;
void *ref = get_buffer(delta, type, &ref_size, NULL);
if (ref && !strcmp(type, "delta"))
ref = expand_delta(ref, &ref_size, type, depth, links);
else if (ref)
{
*links = xmalloc(*depth * 20);
}
if (ref) {
buf = patch_delta(ref, ref_size, delta+20, *size-20, size);
free(ref);
if (buf)
memcpy(*links + level*20, delta, 20);
else
free(*links);
}
free(delta);
}
return buf;
}
static char *mkdelta_usage =
"mkdelta [--max-depth=N] [--max-behind=N] <reference_sha1> <target_sha1> [<next_sha1> ...]";
struct delta {
unsigned char sha1[20]; /* object sha1 */
unsigned long size; /* object size */
void *buf; /* object content */
unsigned char *links; /* delta reference links */
unsigned int depth; /* delta depth */
};
int main(int argc, char **argv)
{
struct delta *ref, trg;
char ref_type[20], trg_type[20], *skip_reason;
void *best_buf;
unsigned long best_size, orig_size, orig_compsize;
unsigned int r, orig_ref, best_ref, nb_refs, next_ref, max_refs = 0;
unsigned int i, duplicate, skip_lvl, verbose = 0, quiet = 0;
unsigned int max_depth = -1;
for (i = 1; i < argc; i++) {
if (!strcmp(argv[i], "-v")) {
verbose = 1;
quiet = 0;
} else if (!strcmp(argv[i], "-q")) {
quiet = 1;
verbose = 0;
} else if (!strcmp(argv[i], "-d") && i+1 < argc) {
max_depth = atoi(argv[++i]);
} else if (!strncmp(argv[i], "--max-depth=", 12)) {
max_depth = atoi(argv[i]+12);
} else if (!strcmp(argv[i], "-b") && i+1 < argc) {
max_refs = atoi(argv[++i]);
} else if (!strncmp(argv[i], "--max-behind=", 13)) {
max_refs = atoi(argv[i]+13);
} else
break;
}
if (i + (max_depth != 0) >= argc)
usage(mkdelta_usage);
if (!max_refs || max_refs > argc - i)
max_refs = argc - i;
ref = xmalloc(max_refs * sizeof(*ref));
for (r = 0; r < max_refs; r++)
ref[r].buf = ref[r].links = NULL;
next_ref = nb_refs = 0;
do {
if (get_sha1(argv[i], trg.sha1))
die("bad sha1 %s", argv[i]);
trg.buf = get_buffer(trg.sha1, trg_type, &trg.size, &orig_compsize);
if (trg.buf && !trg.size) {
if (verbose)
printf("skip %s (object is empty)\n", argv[i]);
continue;
}
orig_size = trg.size;
orig_ref = -1;
trg.depth = 0;
trg.links = NULL;
if (trg.buf && !strcmp(trg_type, "delta")) {
for (r = 0; r < nb_refs; r++)
if (!memcmp(trg.buf, ref[r].sha1, 20))
break;
if (r < nb_refs) {
/* no need to reload the reference object */
trg.depth = ref[r].depth + 1;
trg.links = xmalloc(trg.depth*20);
memcpy(trg.links, trg.buf, 20);
memcpy(trg.links+20, ref[r].links, ref[r].depth*20);
trg.buf = patch_delta(ref[r].buf, ref[r].size,
trg.buf+20, trg.size-20,
&trg.size);
strcpy(trg_type, ref_type);
orig_ref = r;
} else {
trg.buf = expand_delta(trg.buf, &trg.size, trg_type,
&trg.depth, &trg.links);
}
}
if (!trg.buf)
die("unable to read target object %s", argv[i]);
if (!nb_refs) {
strcpy(ref_type, trg_type);
} else if (max_depth && strcmp(ref_type, trg_type)) {
die("type mismatch for object %s", argv[i]);
}
duplicate = 0;
best_buf = NULL;
best_size = -1;
best_ref = -1;
skip_lvl = 0;
skip_reason = NULL;
for (r = 0; max_depth && r < nb_refs; r++) {
void *delta_buf, *comp_buf;
unsigned long delta_size, comp_size;
unsigned int l;
duplicate = !memcmp(trg.sha1, ref[r].sha1, 20);
if (duplicate) {
skip_reason = "already seen";
break;
}
if (ref[r].depth >= max_depth) {
if (skip_lvl < 1) {
skip_reason = "exceeding max link depth";
skip_lvl = 1;
}
continue;
}
for (l = 0; l < ref[r].depth; l++)
if (!memcmp(trg.sha1, ref[r].links + l*20, 20))
break;
if (l != ref[r].depth) {
if (skip_lvl < 2) {
skip_reason = "would create a loop";
skip_lvl = 2;
}
continue;
}
if (trg.depth < max_depth && r == orig_ref) {
if (skip_lvl < 3) {
skip_reason = "delta already in place";
skip_lvl = 3;
}
continue;
}
delta_buf = diff_delta(ref[r].buf, ref[r].size,
trg.buf, trg.size,
&delta_size, ~0UL);
if (!delta_buf)
die("out of memory");
if (trg.depth < max_depth &&
delta_size+20 >= orig_size) {
/* no need to even try to compress if original
object is smaller than this delta */
free(delta_buf);
if (skip_lvl < 4) {
skip_reason = "no size reduction";
skip_lvl = 4;
}
continue;
}
comp_buf = create_delta_object(delta_buf, delta_size,
ref[r].sha1, &comp_size);
if (!comp_buf)
die("out of memory");
free(delta_buf);
if (trg.depth < max_depth &&
comp_size >= orig_compsize) {
free(comp_buf);
if (skip_lvl < 5) {
skip_reason = "no size reduction";
skip_lvl = 5;
}
continue;
}
if ((comp_size < best_size) ||
(comp_size == best_size &&
ref[r].depth < ref[best_ref].depth)) {
free(best_buf);
best_buf = comp_buf;
best_size = comp_size;
best_ref = r;
}
}
if (best_buf) {
if (replace_object(best_buf, best_size, trg.sha1))
die("unable to write delta for %s", argv[i]);
free(best_buf);
free(trg.links);
trg.depth = ref[best_ref].depth + 1;
trg.links = xmalloc(trg.depth*20);
memcpy(trg.links, ref[best_ref].sha1, 20);
memcpy(trg.links+20, ref[best_ref].links, ref[best_ref].depth*20);
if (!quiet)
printf("delta %s (size=%ld.%02ld%% depth=%d dist=%d)\n",
argv[i], best_size*100 / orig_compsize,
(best_size*10000 / orig_compsize)%100,
trg.depth,
(next_ref - best_ref + max_refs)
% (max_refs + 1) + 1);
} else if (trg.depth > max_depth) {
if (restore_original_object(trg.buf, trg.size, trg_type, trg.sha1))
die("unable to restore %s", argv[i]);
if (!quiet)
printf("undelta %s (depth was %d)\n",
argv[i], trg.depth);
trg.depth = 0;
free(trg.links);
trg.links = NULL;
} else if (skip_reason && verbose) {
printf("skip %s (%s)\n", argv[i], skip_reason);
}
if (!duplicate) {
free(ref[next_ref].buf);
free(ref[next_ref].links);
ref[next_ref] = trg;
if (++next_ref > nb_refs)
nb_refs = next_ref;
if (next_ref == max_refs)
next_ref = 0;
} else {
free(trg.buf);
free(trg.links);
}
} while (++i < argc);
return 0;
}