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update-server-info: avoid needless overwrites

Do not change the existing info/refs and objects/info/packs
files if they match the existing content on the filesystem.
This is intended to preserve mtime and make it easier for dumb
HTTP pollers to rely on the If-Modified-Since header.

Combined with stdio and kernel buffering; the kernel should be
able to avoid block layer writes and reduce wear for small files.

As a result, the --force option is no longer needed.  So stop
documenting it, but let it remain for compatibility (and
debugging, if necessary).

v3: perform incremental comparison while generating to avoid
    OOM with giant files.  Remove documentation for --force.

Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Eric Wong 2019-05-13 23:17:08 +00:00 committed by Junio C Hamano
parent ab15ad1a3b
commit f4f476b6a1
3 changed files with 158 additions and 34 deletions

View File

@ -9,7 +9,7 @@ git-update-server-info - Update auxiliary info file to help dumb servers
SYNOPSIS
--------
[verse]
'git update-server-info' [--force]
'git update-server-info'
DESCRIPTION
-----------
@ -19,15 +19,6 @@ $GIT_OBJECT_DIRECTORY/info directories to help clients discover
what references and packs the server has. This command
generates such auxiliary files.
OPTIONS
-------
-f::
--force::
Update the info files from scratch.
OUTPUT
------

View File

@ -6,82 +6,174 @@
#include "tag.h"
#include "packfile.h"
#include "object-store.h"
#include "strbuf.h"
struct update_info_ctx {
FILE *cur_fp;
FILE *old_fp; /* becomes NULL if it differs from cur_fp */
struct strbuf cur_sb;
struct strbuf old_sb;
};
static void uic_mark_stale(struct update_info_ctx *uic)
{
fclose(uic->old_fp);
uic->old_fp = NULL;
}
static int uic_is_stale(const struct update_info_ctx *uic)
{
return uic->old_fp == NULL;
}
static int uic_printf(struct update_info_ctx *uic, const char *fmt, ...)
{
va_list ap;
int ret = -1;
va_start(ap, fmt);
if (uic_is_stale(uic)) {
ret = vfprintf(uic->cur_fp, fmt, ap);
} else {
ssize_t r;
struct strbuf *cur = &uic->cur_sb;
struct strbuf *old = &uic->old_sb;
strbuf_reset(cur);
strbuf_vinsertf(cur, 0, fmt, ap);
strbuf_reset(old);
strbuf_grow(old, cur->len);
r = fread(old->buf, 1, cur->len, uic->old_fp);
if (r != cur->len || memcmp(old->buf, cur->buf, r))
uic_mark_stale(uic);
if (fwrite(cur->buf, 1, cur->len, uic->cur_fp) == cur->len)
ret = 0;
}
va_end(ap);
return ret;
}
/*
* Create the file "path" by writing to a temporary file and renaming
* it into place. The contents of the file come from "generate", which
* should return non-zero if it encounters an error.
*/
static int update_info_file(char *path, int (*generate)(FILE *))
static int update_info_file(char *path,
int (*generate)(struct update_info_ctx *),
int force)
{
char *tmp = mkpathdup("%s_XXXXXX", path);
int ret = -1;
int fd = -1;
FILE *fp = NULL, *to_close;
FILE *to_close;
struct update_info_ctx uic = {
.cur_fp = NULL,
.old_fp = NULL,
.cur_sb = STRBUF_INIT,
.old_sb = STRBUF_INIT
};
safe_create_leading_directories(path);
fd = git_mkstemp_mode(tmp, 0666);
if (fd < 0)
goto out;
to_close = fp = fdopen(fd, "w");
if (!fp)
to_close = uic.cur_fp = fdopen(fd, "w");
if (!uic.cur_fp)
goto out;
fd = -1;
ret = generate(fp);
/* no problem on ENOENT and old_fp == NULL, it's stale, now */
if (!force)
uic.old_fp = fopen_or_warn(path, "r");
/*
* uic_printf will compare incremental comparison aginst old_fp
* and mark uic as stale if needed
*/
ret = generate(&uic);
if (ret)
goto out;
fp = NULL;
/* new file may be shorter than the old one, check here */
if (!uic_is_stale(&uic)) {
struct stat st;
long new_len = ftell(uic.cur_fp);
int old_fd = fileno(uic.old_fp);
if (new_len < 0) {
ret = -1;
goto out;
}
if (fstat(old_fd, &st) || (st.st_size != (size_t)new_len))
uic_mark_stale(&uic);
}
uic.cur_fp = NULL;
if (fclose(to_close))
goto out;
if (adjust_shared_perm(tmp) < 0)
goto out;
if (rename(tmp, path) < 0)
goto out;
if (uic_is_stale(&uic)) {
if (adjust_shared_perm(tmp) < 0)
goto out;
if (rename(tmp, path) < 0)
goto out;
} else {
unlink(tmp);
}
ret = 0;
out:
if (ret) {
error_errno("unable to update %s", path);
if (fp)
fclose(fp);
if (uic.cur_fp)
fclose(uic.cur_fp);
else if (fd >= 0)
close(fd);
unlink(tmp);
}
free(tmp);
if (uic.old_fp)
fclose(uic.old_fp);
strbuf_release(&uic.old_sb);
strbuf_release(&uic.cur_sb);
return ret;
}
static int add_info_ref(const char *path, const struct object_id *oid,
int flag, void *cb_data)
{
FILE *fp = cb_data;
struct update_info_ctx *uic = cb_data;
struct object *o = parse_object(the_repository, oid);
if (!o)
return -1;
if (fprintf(fp, "%s %s\n", oid_to_hex(oid), path) < 0)
if (uic_printf(uic, "%s %s\n", oid_to_hex(oid), path) < 0)
return -1;
if (o->type == OBJ_TAG) {
o = deref_tag(the_repository, o, path, 0);
if (o)
if (fprintf(fp, "%s %s^{}\n",
if (uic_printf(uic, "%s %s^{}\n",
oid_to_hex(&o->oid), path) < 0)
return -1;
}
return 0;
}
static int generate_info_refs(FILE *fp)
static int generate_info_refs(struct update_info_ctx *uic)
{
return for_each_ref(add_info_ref, fp);
return for_each_ref(add_info_ref, uic);
}
static int update_info_refs(void)
static int update_info_refs(int force)
{
char *path = git_pathdup("info/refs");
int ret = update_info_file(path, generate_info_refs);
int ret = update_info_file(path, generate_info_refs, force);
free(path);
return ret;
}
@ -236,14 +328,14 @@ static void free_pack_info(void)
free(info);
}
static int write_pack_info_file(FILE *fp)
static int write_pack_info_file(struct update_info_ctx *uic)
{
int i;
for (i = 0; i < num_pack; i++) {
if (fprintf(fp, "P %s\n", pack_basename(info[i]->p)) < 0)
if (uic_printf(uic, "P %s\n", pack_basename(info[i]->p)) < 0)
return -1;
}
if (fputc('\n', fp) == EOF)
if (uic_printf(uic, "\n") < 0)
return -1;
return 0;
}
@ -254,7 +346,7 @@ static int update_info_packs(int force)
int ret;
init_pack_info(infofile, force);
ret = update_info_file(infofile, write_pack_info_file);
ret = update_info_file(infofile, write_pack_info_file, force);
free_pack_info();
free(infofile);
return ret;
@ -269,7 +361,7 @@ int update_server_info(int force)
*/
int errs = 0;
errs = errs | update_info_refs();
errs = errs | update_info_refs(force);
errs = errs | update_info_packs(force);
/* remove leftover rev-cache file if there is any */

41
t/t5200-update-server-info.sh Executable file
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@ -0,0 +1,41 @@
#!/bin/sh
test_description='Test git update-server-info'
. ./test-lib.sh
test_expect_success 'setup' 'test_commit file'
test_expect_success 'create info/refs' '
git update-server-info &&
test_path_is_file .git/info/refs
'
test_expect_success 'modify and store mtime' '
test-tool chmtime =0 .git/info/refs &&
test-tool chmtime --get .git/info/refs >a
'
test_expect_success 'info/refs is not needlessly overwritten' '
git update-server-info &&
test-tool chmtime --get .git/info/refs >b &&
test_cmp a b
'
test_expect_success 'info/refs can be forced to update' '
git update-server-info -f &&
test-tool chmtime --get .git/info/refs >b &&
! test_cmp a b
'
test_expect_success 'info/refs updates when changes are made' '
test-tool chmtime =0 .git/info/refs &&
test-tool chmtime --get .git/info/refs >b &&
test_cmp a b &&
git update-ref refs/heads/foo HEAD &&
git update-server-info &&
test-tool chmtime --get .git/info/refs >b &&
! test_cmp a b
'
test_done