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Sat, 24 Jul 2021 14:38:31 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx1Kv/M6qskCAa2iYidDcO94F9rO3w70hsI/xsveCv4ij53/4AEZQooofItTEg7clN8/LfjbNCETI0gEwwmduY= X-Received: by 2002:adf:f6ca:: with SMTP id y10mr11408629wrp.211.1627162711767; Sat, 24 Jul 2021 14:38:31 -0700 (PDT) MIME-Version: 1.0 References: <20210724193449.361667-1-agruenba@redhat.com> <20210724193449.361667-2-agruenba@redhat.com> In-Reply-To: From: Andreas Gruenbacher Date: Sat, 24 Jul 2021 23:38:20 +0200 Message-ID: To: Al Viro Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=agruenba@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-SPF-VenPass: Allowed X-Source-IP: 216.205.24.124 X-ServerName: us-smtp-delivery-124.mimecast.com X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10055 signatures=668682 X-Proofpoint-Spam-Reason: safe X-Spam: OrgSafeList X-SpamRule: orgsafelist X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10055 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 malwarescore=0 adultscore=0 bulkscore=0 phishscore=0 suspectscore=0 mlxscore=0 mlxlogscore=991 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2107240130 Cc: cluster-devel , Jan Kara , Linux Kernel Mailing List , Christoph Hellwig , linux-fsdevel , Linus Torvalds , ocfs2-devel@oss.oracle.com Subject: Re: [Ocfs2-devel] [PATCH v4 1/8] iov_iter: Introduce iov_iter_fault_in_writeable helper X-BeenThere: ocfs2-devel@oss.oracle.com X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: ocfs2-devel-bounces@oss.oracle.com Errors-To: ocfs2-devel-bounces@oss.oracle.com X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10055 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 bulkscore=0 phishscore=0 malwarescore=0 spamscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2107240131 X-Proofpoint-GUID: b4XM8nZw6-xe3eiFtcsU95_Zree2qOqn X-Proofpoint-ORIG-GUID: b4XM8nZw6-xe3eiFtcsU95_Zree2qOqn On Sat, Jul 24, 2021 at 10:24 PM Al Viro wrote: > On Sat, Jul 24, 2021 at 12:52:34PM -0700, Linus Torvalds wrote: > > ... > > > + if (fault_in_user_pages(start, len, true) != len) > > > + return -EFAULT; > > > > Looking at this once more, I think this is likely wrong. > > > > Why? > > > > Because any user can/should only care about at least *part* of the > > area being writable. > > > > Imagine that you're doing a large read. If the *first* page is > > writable, you should still return the partial read, not -EFAULT. > > Agreed. > > > So I think the code needs to return 0 if _any_ fault was successful. > > s/any/the first/... > > The same goes for fault-in for read, of course; I've a half-baked conversion > to such semantics (-EFAULT vs. 0; precise length is unreliable anyway, > especially if you have sub-page failure areas), need to finish and post > it... Hmm, how could we have sub-page failure areas when this is about if and how pages are mapped? If we return the number of bytes that are accessible, then users will know if they got nothing, something, or everything, and they can act accordingly. Thanks, Andreas _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel