From owner-svn-src-all@freebsd.org Tue Jul 9 07:19:37 2019 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 7F7CC15D20AD; Tue, 9 Jul 2019 07:19:37 +0000 (UTC) (envelope-from kib@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 2684583641; Tue, 9 Jul 2019 07:19:37 +0000 (UTC) (envelope-from kib@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 16146245D5; Tue, 9 Jul 2019 07:19:37 +0000 (UTC) (envelope-from kib@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id x697Jab8040603; Tue, 9 Jul 2019 07:19:36 GMT (envelope-from kib@FreeBSD.org) Received: (from kib@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id x697JaVG040602; Tue, 9 Jul 2019 07:19:36 GMT (envelope-from kib@FreeBSD.org) Message-Id: <201907090719.x697JaVG040602@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: kib set sender to kib@FreeBSD.org using -f From: Konstantin Belousov Date: Tue, 9 Jul 2019 07:19:36 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r349854 - stable/12/lib/libc/sys X-SVN-Group: stable-12 X-SVN-Commit-Author: kib X-SVN-Commit-Paths: stable/12/lib/libc/sys X-SVN-Commit-Revision: 349854 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2684583641 X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-2.95 / 15.00]; local_wl_from(0.00)[FreeBSD.org]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; NEURAL_HAM_SHORT(-0.95)[-0.949,0]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; ASN(0.00)[asn:11403, ipnet:2610:1c1:1::/48, country:US] X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Jul 2019 07:19:37 -0000 Author: kib Date: Tue Jul 9 07:19:36 2019 New Revision: 349854 URL: https://svnweb.freebsd.org/changeset/base/349854 Log: MFC r349794: Document atomicity for read(2) and write(2). Modified: stable/12/lib/libc/sys/read.2 Directory Properties: stable/12/ (props changed) Modified: stable/12/lib/libc/sys/read.2 ============================================================================== --- stable/12/lib/libc/sys/read.2 Mon Jul 8 22:20:25 2019 (r349853) +++ stable/12/lib/libc/sys/read.2 Tue Jul 9 07:19:36 2019 (r349854) @@ -28,7 +28,7 @@ .\" @(#)read.2 8.4 (Berkeley) 2/26/94 .\" $FreeBSD$ .\" -.Dd December 1, 2017 +.Dd July 6, 2019 .Dt READ 2 .Os .Sh NAME @@ -128,6 +128,25 @@ return the number of bytes actually read and placed in The system guarantees to read the number of bytes requested if the descriptor references a normal file that has that many bytes left before the end-of-file, but in no other case. +.Pp +In accordance with +.St -p1003.1-2004 , +both +.Xr read 2 +and +.Xr write 2 +syscalls are atomic with respect to each other in the effects on file +content, when they operate on regular files. +If two threads each call one of the +.Xr read 2 +or +.Xr write 2 , +syscalls, each call will see either all of the changes of the other call, +or none of them. +The +.Fx +kernel implements this guarantee by locking the file ranges affected by +the calls. .Sh RETURN VALUES If successful, the number of bytes actually read is returned.