From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 576E6C2B9F4 for ; Mon, 14 Jun 2021 13:37:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4260B61153 for ; Mon, 14 Jun 2021 13:37:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234159AbhFNNjb (ORCPT ); Mon, 14 Jun 2021 09:39:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:40941 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233421AbhFNNjV (ORCPT ); Mon, 14 Jun 2021 09:39:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623677838; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9zJYlNCno/HjzceWxClcR824bm7Ts8a212RDRVjhT0c=; b=gBXQVYqB9oYtIaiZeQ6O6l4egXJg/7rfRIF5+AGMtlCgkOOJVQggbpdFX1lal71O3cVQT/ 1wlEnE2k976Q+JcPnKEB8HxBAN7Ib5D/2nDjgvWREUlXSWmB7DHf8cu8oA4bA101LGJ9P+ wzyMnUjQcDK0xnjhQ0QAML7AenwFNEw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-334-jQ-WAJl7P3umr7wuJSXvNg-1; Mon, 14 Jun 2021 09:37:16 -0400 X-MC-Unique: jQ-WAJl7P3umr7wuJSXvNg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4D6F91084F49; Mon, 14 Jun 2021 13:37:14 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-118-65.rdu2.redhat.com [10.10.118.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id DD3D55D6B1; Mon, 14 Jun 2021 13:37:12 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <162367681795.460125.11729955608839747375.stgit@warthog.procyon.org.uk> <162367682522.460125.5652091227576721609.stgit@warthog.procyon.org.uk> To: Matthew Wilcox , Al Viro Cc: dhowells@redhat.com, jlayton@kernel.org, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] afs: Fix afs_write_end() to handle short writes MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <466589.1623677832.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Mon, 14 Jun 2021 14:37:12 +0100 Message-ID: <466590.1623677832@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Matthew Wilcox wrote: > > (1) If the page is not up to date, then we should just return 0 > > (ie. indicating a zero-length copy). The loop in > > generic_perform_write() will go around again, possibly breaking u= p the > > iterator into discrete chunks. > = > Does this actually work? What about the situation where you're reading > the last page of a file and thus (almost) always reading fewer bytes > than a PAGE_SIZE? Al Viro made such a change for Ceph - and we're writing, not reading. I was thinking that it would break if reading from a pipe, but Jeff pointe= d out that the iov_iter_advance() in generic_perform_write() uses the return value of ->write_end() to advance the iterator. So it might loop endlessl= y, but it doesn't appear it will corrupt your data. David