From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.8 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 33A912035F for ; Fri, 28 Oct 2016 13:32:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756637AbcJ1Ncd (ORCPT ); Fri, 28 Oct 2016 09:32:33 -0400 Received: from pb-smtp2.pobox.com ([64.147.108.71]:51403 "EHLO sasl.smtp.pobox.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754599AbcJ1Ncc (ORCPT ); Fri, 28 Oct 2016 09:32:32 -0400 Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id CA91F48910; Fri, 28 Oct 2016 09:32:30 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=from:to:cc :subject:references:date:in-reply-to:message-id:mime-version :content-type; s=sasl; bh=f+wWAEuGaV6041NDpJYBhiFC7cE=; b=UGKORd iS0q6VIIvHzOrmaua7DFdRDZ1tmIASD+U2Fv7iYOSbgfcRDu8Xs63I82kR56r+Kn L22JBpP+eldNml9k5m4zA9+W6NZNjriMj/27g/t390fDHOYuMn2L9FRVWztZO45E UJdAI30aJI1wthFFzKcG79sr6MZBZODqTUFeA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=pobox.com; h=from:to:cc :subject:references:date:in-reply-to:message-id:mime-version :content-type; q=dns; s=sasl; b=M4K6E5YvajUnxm1ifuOzzgwsoMx2gEhm SmLLrTCkwg9WNP78pI2WfcT5ncojvl0IviR3/C0D94geaturl0KzBPNjuP9M3Vue 9+GtzgT+k7+usyo58xSOlBaPTguN1x16xf9janR2U5IoZIdvCbCgQxaeZGcI947t T4x3ZdNYeQ0= Received: from pb-smtp2.nyi.icgroup.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id C1BE74890F; Fri, 28 Oct 2016 09:32:30 -0400 (EDT) Received: from pobox.com (unknown [104.132.0.95]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by pb-smtp2.pobox.com (Postfix) with ESMTPSA id 234A54890E; Fri, 28 Oct 2016 09:32:30 -0400 (EDT) From: Junio C Hamano To: Linus Torvalds Cc: Jeff King , Git Mailing List , Lars Schneider , Eric Wong , Johannes Schindelin Subject: Re: [PATCH v3 2/3] sha1_file: open window into packfiles with O_CLOEXEC References: <20161025181621.4201-1-gitster@pobox.com> <20161025181621.4201-3-gitster@pobox.com> <20161026042555.neaxvnmggtcku5cc@sigill.intra.peff.net> <20161026164746.2fu57f4pji5qdtnh@sigill.intra.peff.net> <20161026201721.2pw4slsuyhxhcwxj@sigill.intra.peff.net> <20161027102419.dbzigj7wtr355ofh@sigill.intra.peff.net> Date: Fri, 28 Oct 2016 06:32:28 -0700 In-Reply-To: (Junio C. Hamano's message of "Thu, 27 Oct 2016 19:37:35 -0700") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Pobox-Relay-ID: F98001CE-9D12-11E6-AEEB-3AB77A1B28F4-77302942!pb-smtp2.pobox.com Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Junio C Hamano writes: > Hmph. This may not fly well in practice, though. We can flip the order around, and then it becomes simpler to later drop atime support. The first step goes like this. -- >8 -- From: Junio C Hamano Date: Fri, 28 Oct 2016 06:23:07 -0700 Subject: [PATCH] git_open(): untangle possible NOATIME and CLOEXEC interactions The way we structured the fallback/retry mechanism for opening with O_NOATIME and O_CLOEXEC meant that if we failed due to lack of support to open the file with O_NOATIME option (i.e. EINVAL), we would still try to drop O_CLOEXEC first and retry, and then drop O_NOATIME. A platform on which O_NOATIME is defined in the header without support from the kernel wouldn't have a chance to open with O_CLOEXEC option due to this code structure. Arguably, O_CLOEXEC is more important than O_NOATIME, as the latter is mostly about performance, while the former can affect correctness. Instead use O_CLOEXEC to open the file, and then use fcntl(2) to set O_NOATIME on the resulting file descriptor. open(2) itself does not cause atime to be updated according to Linus [*1*]. The helper to do the former can be usable in the codepath in ce_compare_data() that was recently added to open a file descriptor with O_CLOEXEC; use it while we are at it. *1* Signed-off-by: Junio C Hamano --- cache.h | 1 + read-cache.c | 9 +-------- sha1_file.c | 39 +++++++++++++++++++-------------------- 3 files changed, 21 insertions(+), 28 deletions(-) diff --git a/cache.h b/cache.h index a902ca1f8e..6f1c21a352 100644 --- a/cache.h +++ b/cache.h @@ -1122,6 +1122,7 @@ extern int write_sha1_file(const void *buf, unsigned long len, const char *type, extern int hash_sha1_file_literally(const void *buf, unsigned long len, const char *type, unsigned char *sha1, unsigned flags); extern int pretend_sha1_file(void *, unsigned long, enum object_type, unsigned char *); extern int force_object_loose(const unsigned char *sha1, time_t mtime); +extern int git_open_cloexec(const char *name, int flags); extern int git_open(const char *name); extern void *map_sha1_file(const unsigned char *sha1, unsigned long *size); extern int unpack_sha1_header(git_zstream *stream, unsigned char *map, unsigned long mapsize, void *buffer, unsigned long bufsiz); diff --git a/read-cache.c b/read-cache.c index db5d910642..c27d3e240b 100644 --- a/read-cache.c +++ b/read-cache.c @@ -156,14 +156,7 @@ void fill_stat_cache_info(struct cache_entry *ce, struct stat *st) static int ce_compare_data(const struct cache_entry *ce, struct stat *st) { int match = -1; - static int cloexec = O_CLOEXEC; - int fd = open(ce->name, O_RDONLY | cloexec); - - if ((cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) { - /* Try again w/o O_CLOEXEC: the kernel might not support it */ - cloexec &= ~O_CLOEXEC; - fd = open(ce->name, O_RDONLY | cloexec); - } + int fd = git_open_cloexec(ce->name, O_RDONLY); if (fd >= 0) { unsigned char sha1[20]; diff --git a/sha1_file.c b/sha1_file.c index 09045df1dc..dfbf398183 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -1559,31 +1559,30 @@ int check_sha1_signature(const unsigned char *sha1, void *map, return hashcmp(sha1, real_sha1) ? -1 : 0; } -int git_open(const char *name) +int git_open_cloexec(const char *name, int flags) { - static int sha1_file_open_flag = O_NOATIME | O_CLOEXEC; - - for (;;) { - int fd; - - errno = 0; - fd = open(name, O_RDONLY | sha1_file_open_flag); - if (fd >= 0) - return fd; + static int cloexec = O_CLOEXEC; + int fd = open(name, flags | cloexec); + if ((cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) { /* Try again w/o O_CLOEXEC: the kernel might not support it */ - if ((sha1_file_open_flag & O_CLOEXEC) && errno == EINVAL) { - sha1_file_open_flag &= ~O_CLOEXEC; - continue; - } + cloexec &= ~O_CLOEXEC; + fd = open(name, flags | cloexec); + } + return fd; +} - /* Might the failure be due to O_NOATIME? */ - if (errno != ENOENT && (sha1_file_open_flag & O_NOATIME)) { - sha1_file_open_flag &= ~O_NOATIME; - continue; - } - return -1; +int git_open(const char *name) +{ + static int noatime = O_NOATIME; + int fd = git_open_cloexec(name, O_RDONLY); + + if (0 <= fd && (noatime & O_NOATIME)) { + int flags = fcntl(fd, F_GETFL); + if (fcntl(fd, F_SETFL, flags | noatime)) + noatime = 0; } + return fd; } static int stat_sha1_file(const unsigned char *sha1, struct stat *st) -- 2.10.1-791-g404733b9cf