From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 42B961F45F for ; Sat, 11 May 2019 01:34:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728320AbfEKBe5 (ORCPT ); Fri, 10 May 2019 21:34:57 -0400 Received: from dcvr.yhbt.net ([64.71.152.64]:49650 "EHLO dcvr.yhbt.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728165AbfEKBe5 (ORCPT ); Fri, 10 May 2019 21:34:57 -0400 Received: from localhost (dcvr.yhbt.net [127.0.0.1]) by dcvr.yhbt.net (Postfix) with ESMTP id 173B51F45F for ; Sat, 11 May 2019 01:34:56 +0000 (UTC) From: Eric Wong To: git@vger.kernel.org Subject: [PATCH] update-server-info: avoid needless overwrites Date: Sat, 11 May 2019 01:34:55 +0000 Message-Id: <20190511013455.5886-1-e@80x24.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org 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. Signed-off-by: Eric Wong --- server-info.c | 61 +++++++++++++++++++++++++++++------ t/t5200-update-server-info.sh | 41 +++++++++++++++++++++++ 2 files changed, 92 insertions(+), 10 deletions(-) create mode 100755 t/t5200-update-server-info.sh diff --git a/server-info.c b/server-info.c index 41274d098b..34599e4817 100644 --- a/server-info.c +++ b/server-info.c @@ -6,37 +6,78 @@ #include "tag.h" #include "packfile.h" #include "object-store.h" +#include "strbuf.h" + +static int files_differ(FILE *fp, const char *path) +{ + struct stat st; + git_hash_ctx c; + struct object_id oid_old, oid_new; + struct strbuf tmp = STRBUF_INIT; + long new_len = ftell(fp); + + if (new_len < 0 || stat(path, &st) < 0) + return 1; + if (!S_ISREG(st.st_mode)) + return 1; + if ((off_t)new_len != st.st_size) + return 1; + + rewind(fp); + if (strbuf_fread(&tmp, (size_t)new_len, fp) != (size_t)new_len) + return 1; + the_hash_algo->init_fn(&c); + the_hash_algo->update_fn(&c, tmp.buf, tmp.len); + the_hash_algo->final_fn(oid_new.hash, &c); + strbuf_release(&tmp); + + if (strbuf_read_file(&tmp, path, (size_t)st.st_size) < 0) + return 1; + the_hash_algo->init_fn(&c); + the_hash_algo->update_fn(&c, tmp.buf, tmp.len); + the_hash_algo->final_fn(oid_old.hash, &c); + strbuf_release(&tmp); + + return hashcmp(oid_old.hash, oid_new.hash); +} /* * 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)(FILE *), int force) { char *tmp = mkpathdup("%s_XXXXXX", path); int ret = -1; int fd = -1; FILE *fp = NULL, *to_close; + int do_update; safe_create_leading_directories(path); fd = git_mkstemp_mode(tmp, 0666); if (fd < 0) goto out; - to_close = fp = fdopen(fd, "w"); + to_close = fp = fdopen(fd, "w+"); if (!fp) goto out; fd = -1; ret = generate(fp); if (ret) goto out; + + do_update = force || files_differ(fp, path); fp = NULL; if (fclose(to_close)) goto out; - if (adjust_shared_perm(tmp) < 0) - goto out; - if (rename(tmp, path) < 0) - goto out; + if (do_update) { + if (adjust_shared_perm(tmp) < 0) + goto out; + if (rename(tmp, path) < 0) + goto out; + } else { + unlink(tmp); + } ret = 0; out: @@ -78,10 +119,10 @@ static int generate_info_refs(FILE *fp) return for_each_ref(add_info_ref, fp); } -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; } @@ -254,7 +295,7 @@ 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 +310,7 @@ 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 */ diff --git a/t/t5200-update-server-info.sh b/t/t5200-update-server-info.sh new file mode 100755 index 0000000000..f1cec46914 --- /dev/null +++ b/t/t5200-update-server-info.sh @@ -0,0 +1,41 @@ +#!/bin/sh + +test_description='Test git stash show configuration.' + +. ./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 -- EW