git/pack-objects.c

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#include <ctype.h>
#include "cache.h"
#include "object.h"
#include "delta.h"
#include "pack.h"
#include "csum-file.h"
static const char pack_usage[] = "git-pack-objects [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
struct object_entry {
unsigned char sha1[20];
unsigned long size;
unsigned long offset;
unsigned int depth;
unsigned int hash;
enum object_type type;
unsigned long delta_size;
struct object_entry *delta;
};
static unsigned char object_list_sha1[20];
static int non_empty = 0;
static int incremental = 0;
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 const char *base_name;
static unsigned char pack_file_sha1[20];
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(otherbuf, othersize,
buf, size, &delta_size, 0);
if (!delta_buf || delta_size != entry->delta_size)
die("delta size changed");
free(buf);
free(otherbuf);
return delta_buf;
}
/*
* The per-object header is a pretty dense thing, which is
* - first byte: low four bits are "size", then three bits of "type",
* and the high bit is "size continues".
* - each byte afterwards: low seven bits are size continuation,
* with the high bit being "size continues"
*/
static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
{
int n = 1;
unsigned char c;
if (type < OBJ_COMMIT || type > OBJ_DELTA)
die("bad type %d", type);
c = (type << 4) | (size & 15);
size >>= 4;
while (size) {
*hdr++ = c | 0x80;
c = size & 0x7f;
size >>= 7;
n++;
}
*hdr = c;
return n;
}
static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
{
unsigned long size;
char type[10];
void *buf = read_sha1_file(entry->sha1, type, &size);
unsigned char header[10];
unsigned hdrlen, datalen;
enum object_type obj_type;
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 zero or
* more bytes of length. For deltas, the 20 bytes of delta sha1
* follows that.
*/
obj_type = entry->type;
if (entry->delta) {
buf = delta_against(buf, size, entry);
size = entry->delta_size;
obj_type = OBJ_DELTA;
}
hdrlen = encode_header(obj_type, size, header);
sha1write(f, header, hdrlen);
if (entry->delta) {
sha1write(f, entry->delta, 20);
hdrlen += 20;
}
datalen = sha1write_compressed(f, buf, size);
free(buf);
return hdrlen + datalen;
}
static unsigned long write_one(struct sha1file *f,
struct object_entry *e,
unsigned long offset)
{
if (e->offset)
/* offset starts from header size and cannot be zero
* if it is written already.
*/
return offset;
e->offset = offset;
offset += write_object(f, e);
/* if we are delitified, write out its base object. */
if (e->delta)
offset = write_one(f, e->delta, offset);
return offset;
}
static void write_pack_file(void)
{
int i;
struct sha1file *f;
unsigned long offset;
unsigned long mb;
struct pack_header hdr;
if (!base_name)
f = sha1fd(1, "<stdout>");
else
f = sha1create("%s-%s.%s", base_name, sha1_to_hex(object_list_sha1), "pack");
hdr.hdr_signature = htonl(PACK_SIGNATURE);
hdr.hdr_version = htonl(PACK_VERSION);
hdr.hdr_entries = htonl(nr_objects);
sha1write(f, &hdr, sizeof(hdr));
offset = sizeof(hdr);
for (i = 0; i < nr_objects; i++)
offset = write_one(f, objects + i, offset);
sha1close(f, pack_file_sha1, 1);
mb = offset >> 20;
offset &= 0xfffff;
}
static void write_index_file(void)
{
int i;
struct sha1file *f = sha1create("%s-%s.%s", base_name, sha1_to_hex(object_list_sha1), "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;
}
sha1write(f, array, 256 * sizeof(int));
/*
* 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);
sha1write(f, &offset, 4);
sha1write(f, entry->sha1, 20);
}
sha1write(f, pack_file_sha1, 20);
sha1close(f, NULL, 1);
}
static int add_object_entry(unsigned char *sha1, unsigned int hash)
{
unsigned int idx = nr_objects;
struct object_entry *entry;
if (incremental && has_sha1_pack(sha1))
return 0;
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);
entry->hash = hash;
nr_objects = idx+1;
return 1;
}
static void check_object(struct object_entry *entry)
{
char type[20];
if (!sha1_object_info(entry->sha1, type, &entry->size)) {
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 if (!strcmp(type, "tag")) {
entry->type = OBJ_TAG;
} else
die("unable to pack object %s of type %s",
sha1_to_hex(entry->sha1), type);
}
else
die("unable to get type of object %s",
sha1_to_hex(entry->sha1));
}
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->hash < b->hash)
return -1;
if (a->hash > b->hash)
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 _backwards_ in a list sorted by type and
* by size, so that we see progressively smaller and smaller files.
* That's because we prefer deltas to be from the bigger file
* to the smaller - deletes are potentially cheaper, but perhaps
* more importantly, the bigger file is likely the more recent
* one.
*/
static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
{
struct object_entry *cur_entry = cur->entry;
struct object_entry *old_entry = old->entry;
unsigned long size, oldsize, delta_size, sizediff;
long max_size;
void *delta_buf;
/* Don't bother doing diffs between different types */
if (cur_entry->type != old_entry->type)
return -1;
size = cur_entry->size;
if (size < 50)
return -1;
oldsize = old_entry->size;
sizediff = oldsize > size ? oldsize - size : size - oldsize;
if (sizediff > size / 8)
return -1;
if (old_entry->depth >= max_depth)
return 0;
/*
* 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).
*/
max_size = size / 2 - 20;
if (cur_entry->delta)
max_size = cur_entry->delta_size-1;
if (sizediff >= max_size)
return -1;
delta_buf = diff_delta(old->data, oldsize,
cur->data, size, &delta_size, max_size);
if (!delta_buf)
return 0;
cur_entry->delta = old_entry;
cur_entry->delta_size = delta_size;
cur_entry->depth = old_entry->depth + 1;
free(delta_buf);
return 0;
}
static void find_deltas(struct object_entry **list, int window, int depth)
{
int i, idx;
unsigned int array_size = window * sizeof(struct unpacked);
struct unpacked *array = xmalloc(array_size);
memset(array, 0, array_size);
i = nr_objects;
idx = 0;
while (--i >= 0) {
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);
j = window;
while (--j > 0) {
unsigned int other_idx = idx + j;
struct unpacked *m;
if (other_idx >= window)
other_idx -= window;
m = array + other_idx;
if (!m->entry)
break;
if (try_delta(n, m, depth) < 0)
break;
}
idx++;
if (idx >= window)
idx = 0;
}
for (i = 0; i < window; ++i)
free(array[i].data);
free(array);
}
int main(int argc, char **argv)
{
SHA_CTX ctx;
char line[PATH_MAX + 20];
int window = 10, depth = 10, pack_to_stdout = 0;
int i;
for (i = 1; i < argc; i++) {
const char *arg = argv[i];
if (*arg == '-') {
if (!strcmp("--non-empty", arg)) {
non_empty = 1;
continue;
}
if (!strcmp("--incremental", arg)) {
incremental = 1;
continue;
}
if (!strncmp("--window=", arg, 9)) {
char *end;
window = strtoul(arg+9, &end, 0);
if (!arg[9] || *end)
usage(pack_usage);
continue;
}
if (!strncmp("--depth=", arg, 8)) {
char *end;
depth = strtoul(arg+8, &end, 0);
if (!arg[8] || *end)
usage(pack_usage);
continue;
}
if (!strcmp("--stdout", arg)) {
pack_to_stdout = 1;
continue;
}
usage(pack_usage);
}
if (base_name)
usage(pack_usage);
base_name = arg;
}
if (pack_to_stdout != !base_name)
usage(pack_usage);
SHA1_Init(&ctx);
while (fgets(line, sizeof(line), stdin) != NULL) {
unsigned int hash;
char *p;
unsigned char sha1[20];
if (get_sha1_hex(line, sha1))
die("expected sha1, got garbage");
hash = 0;
p = line+40;
while (*p) {
unsigned char c = *p++;
if (isspace(c))
continue;
hash = hash * 11 + c;
}
if (add_object_entry(sha1, hash))
SHA1_Update(&ctx, sha1, 20);
}
SHA1_Final(object_list_sha1, &ctx);
if (non_empty && !nr_objects)
return 0;
get_object_details();
fprintf(stderr, "Packing %d objects\n", nr_objects);
sorted_by_sha = create_sorted_list(sha1_sort);
sorted_by_type = create_sorted_list(type_size_sort);
if (window && depth)
find_deltas(sorted_by_type, window+1, depth);
write_pack_file();
if (!pack_to_stdout) {
write_index_file();
puts(sha1_to_hex(object_list_sha1));
}
return 0;
}