From owner-freebsd-questions@freebsd.org Tue Jun 15 22:30:07 2021 Return-Path: Delivered-To: freebsd-questions@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id A410D655610 for ; Tue, 15 Jun 2021 22:30:07 +0000 (UTC) (envelope-from 4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com) Received: from s1-b0c6.socketlabs.email-od.com (s1-b0c6.socketlabs.email-od.com [142.0.176.198]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4G4NL65Rhlz3j47 for ; Tue, 15 Jun 2021 22:30:06 +0000 (UTC) (envelope-from 4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com) DKIM-Signature: v=1; a=rsa-sha256; d=email-od.com;i=@email-od.com;s=dkim; c=relaxed/relaxed; q=dns/txt; t=1623796207; x=1626388207; h=content-transfer-encoding:content-type:mime-version:references:in-reply-to:message-id:subject:to:from:date:x-thread-info; bh=hjVuMcyHS+BPBRNiS6v67ZUBWb12G8fHcNmRmX9nzvw=; b=sr4GUljstmZnHN9FQr7AEt6IIRWqXrOTooGajcEQCA6msOf3ipB9A7kzS4U67VEkKkFOwfwmZwonZS4RSAI74/Z4P9/MCviXk5HKc8daTh3dZGQdPSxMRCJcu+mNz+8zYbgoYZQZpvT+BdzdFBQnkORDsWvr2OP9DYuoVVHfa+E= X-Thread-Info: NDI1MC4xMi4xZDRkMjAwMDRiYTI4NzcuZnJlZWJzZC1xdWVzdGlvbnM9ZnJlZWJzZC5vcmc= Received: from r2.h.in.socketlabs.com (r2.h.in.socketlabs.com [142.0.180.12]) by mxsg2.email-od.com with ESMTP(version=Tls12 cipher=Aes256 bits=256); Tue, 15 Jun 2021 18:29:54 -0400 Received: from smtp.lan.sohara.org (EMTPY [185.202.17.215]) by r2.h.in.socketlabs.com with ESMTP(version=Tls12 cipher=Aes256 bits=256); Tue, 15 Jun 2021 18:29:54 -0400 Received: from [192.168.63.1] (helo=steve.lan.sohara.org) by smtp.lan.sohara.org with smtp (Exim 4.94 (FreeBSD)) (envelope-from ) id 1ltHZA-000PLO-Er for freebsd-questions@freebsd.org; Tue, 15 Jun 2021 23:29:52 +0100 Date: Tue, 15 Jun 2021 23:29:52 +0100 From: Steve O'Hara-Smith To: freebsd-questions@freebsd.org Subject: Re: Is a successful call to write(2) atomic? Message-Id: <20210615232952.661a4fa1783c0c5bf1bb77d6@sohara.org> In-Reply-To: <22223.1623737465@segfault.tristatelogic.com> References: <22223.1623737465@segfault.tristatelogic.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; amd64-portbld-freebsd12.1) X-Clacks-Overhead: "GNU Terry Pratchett" Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4G4NL65Rhlz3j47 X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=pass header.d=email-od.com header.s=dkim header.b=sr4GUljs; dmarc=none; spf=pass (mx1.freebsd.org: domain of 4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com designates 142.0.176.198 as permitted sender) smtp.mailfrom=4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com X-Spamd-Result: default: False [-1.70 / 15.00]; RCVD_TLS_LAST(0.00)[]; ARC_NA(0.00)[]; R_DKIM_ALLOW(-0.20)[email-od.com:s=dkim]; MID_RHS_MATCH_FROM(0.00)[]; FROM_HAS_DN(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[142.0.176.198:from]; MV_CASE(0.50)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; TO_DN_NONE(0.00)[]; DMARC_NA(0.00)[sohara.org]; RCPT_COUNT_ONE(0.00)[1]; SPAMHAUS_ZRD(0.00)[142.0.176.198:from:127.0.2.255]; RCVD_COUNT_THREE(0.00)[4]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; R_SPF_ALLOW(-0.20)[+ip4:142.0.176.0/20]; DKIM_TRACE(0.00)[email-od.com:+]; NEURAL_HAM_SHORT(-1.00)[-1.000]; NEURAL_HAM_LONG(-1.00)[-1.000]; FORGED_SENDER(0.30)[steve@sohara.org,4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com]; MIME_TRACE(0.00)[0:+]; SUBJECT_ENDS_QUESTION(1.00)[]; ASN(0.00)[asn:7381, ipnet:142.0.176.0/22, country:US]; FROM_NEQ_ENVFROM(0.00)[steve@sohara.org,4250.82.1d4d20004ba2877.ccb876393aa6d69205f10de412cbe983@email-od.com]; MAILMAN_DEST(0.00)[freebsd-questions] X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 15 Jun 2021 22:30:07 -0000 On Mon, 14 Jun 2021 23:11:05 -0700 "Ronald F. Guilmette" wrote: > In other words: Is a block of data that is successfully written by a > single call to write() itself treated as being effectively atomic and > indivisible, i.e. with repsect to the physical output file? In a word ... no. There is no guarantee that a write(2) operation will result in contiguous data in the file. To ensure that you need locking or a single writer. -- Steve O'Hara-Smith