[PATCH 5/6] Allow to use crc32 as a lighter checksum on index
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
Documentation/git-update-index.txt | 12 +++++++-
builtin/update-index.c | 11 +++++++
cache.h | 2 +
read-cache.c | 54 ++++++++++++++++++++++++++++--------
4 files changed, 66 insertions(+), 13 deletions(-)
diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index a3081f4..2574a4e 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -13,7 +13,7 @@ SYNOPSIS
[--add] [--remove | --force-remove] [--replace]
[--refresh] [-q] [--unmerged] [--ignore-missing]
[(--cacheinfo <mode> <object> <file>)...]
- [--chmod=(+|-)x]
+ [--chmod=(+|-)x] [--[no-]crc32]
[--assume-unchanged | --no-assume-unchanged]
[--skip-worktree | --no-skip-worktree]
[--ignore-submodules]
@@ -109,6 +109,16 @@ you will need to handle the situation manually.
set and unset the "skip-worktree" bit for the paths. See
section "Skip-worktree bit" below for more information.
+--crc32::
+--no-crc32::
+ Normally SHA-1 is used to check for index integrity. When the
+ index is large, SHA-1 computation cost can be significant.
+ --crc32 will convert current index to use (cheaper) crc32
+ instead. Note that later writes to index by other commands can
+ convert the index back to SHA-1. Older git versions may not
+ understand crc32 index, --no-crc32 can be used to convert it
+ back to SHA-1.
+
-g::
--again::
Runs 'git update-index' itself on the paths whose index
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a6a23fa..6913226 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -707,6 +707,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
{
int newfd, entries, has_errors = 0, line_termination = '\n';
int read_from_stdin = 0;
+ int do_crc = -1;
int prefix_length = prefix ? strlen(prefix) : 0;
char set_executable_bit = 0;
struct refresh_params refresh_args = {0, &has_errors};
@@ -791,6 +792,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
"(for porcelains) forget saved unresolved conflicts",
PARSE_OPT_NOARG | PARSE_OPT_NONEG,
resolve_undo_clear_callback},
+ OPT_BOOL(0, "crc32", &do_crc,
+ "use crc32 as checksum instead of sha1"),
OPT_END()
};
@@ -852,6 +855,14 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
}
argc = parse_options_end(&ctx);
+ if (do_crc != -1) {
+ if (do_crc)
+ the_index.hdr_flags |= CACHE_F_CRC;
+ else
+ the_index.hdr_flags &= ~CACHE_F_CRC;
+ active_cache_changed = 1;
+ }
+
if (read_from_stdin) {
struct strbuf buf = STRBUF_INIT, nbuf = STRBUF_INIT;
diff --git a/cache.h b/cache.h
index c2e884a..7352402 100644
--- a/cache.h
+++ b/cache.h
@@ -105,6 +105,8 @@ struct cache_header {
unsigned int hdr_entries;
};
+#define CACHE_F_CRC 1 /* use crc32 instead of sha1 for index checksum */
+
struct ext_cache_header {
struct cache_header h;
unsigned int hdr_flags;
diff --git a/read-cache.c b/read-cache.c
index fd21af6..a34878e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1185,20 +1185,33 @@ static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int reall
static int verify_hdr(struct cache_header *hdr, unsigned long size)
{
+ int do_crc;
git_SHA_CTX c;
unsigned char sha1[20];
if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
return error("bad signature");
- if (hdr->hdr_version != htonl(2) &&
- hdr->hdr_version != htonl(3) &&
- hdr->hdr_version != htonl(4))
+ if (hdr->hdr_version == htonl(2) ||
+ hdr->hdr_version == htonl(3))
+ do_crc = 0;
+ else if (hdr->hdr_version == htonl(4)) {
+ struct ext_cache_header *ehdr = (struct ext_cache_header *)hdr;
+ do_crc = ntohl(ehdr->hdr_flags) & CACHE_F_CRC;
+ }
+ else
return error("bad index version");
- git_SHA1_Init(&c);
- git_SHA1_Update(&c, hdr, size - 20);
- git_SHA1_Final(sha1, &c);
- if (hashcmp(sha1, (unsigned char *)hdr + size - 20))
- return error("bad index file sha1 signature");
+ if (do_crc) {
+ uint32_t crc = crc32(0, NULL, 0);
+ crc = crc32(crc,(void *) hdr, size - sizeof(uint32_t));
+ if (crc != *(uint32_t*)((unsigned char *)hdr + size - sizeof(uint32_t)))
+ return error("bad index file crc32 signature");
+ } else {
+ git_SHA1_Init(&c);
+ git_SHA1_Update(&c, hdr, size - 20);
+ git_SHA1_Final(sha1, &c);
+ if (hashcmp(sha1, (unsigned char *)hdr + size - 20))
+ return error("bad index file sha1 signature");
+ }
return 0;
}
@@ -1421,11 +1434,24 @@ static int write_index_ext_header(struct sha1file *f,
static int ce_flush(struct sha1file *f)
{
unsigned char sha1[20];
- int fd = sha1close(f, sha1, 0);
+ int fd;
- if (fd < 0)
- return -1;
- return (write_in_full(fd, sha1, 20) != 20) ? -1 : 0;
+ if (f->do_crc) {
+ uint32_t crc;
+
+ assert(f->do_sha1 == 0);
+ sha1flush(f);
+ crc = crc32_end(f);
+ fd = sha1close(f, sha1, 0);
+ if (fd < 0)
+ return -1;
+ return (write_in_full(fd, &crc, sizeof(crc)) != sizeof(crc)) ? -1 : 0;
+ } else {
+ fd = sha1close(f, sha1, 0);
+ if (fd < 0)
+ return -1;
+ return (write_in_full(fd, sha1, 20) != 20) ? -1 : 0;
+ }
}
static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
@@ -1568,6 +1594,10 @@ int write_index(struct index_state *istate, int newfd)
hdr.h.hdr_entries = htonl(entries - removed);
f = sha1fd(newfd, NULL);
+ if (istate->hdr_flags & CACHE_F_CRC) {
+ crc32_begin(f);
+ f->do_sha1 = 0;
+ }
if (ce_write(f, &hdr, hdr_size) < 0)
return -1;
--
1.7.8.36.g69ee2
Nguyễn Thái Ngọc Duy <pclouds@gmail.com>