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Mon, 15 Jan 2024 01:31:50 -0800 (PST) Received: from x1n ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id db11-20020a17090ad64b00b00286da7407f2sm11671189pjb.7.2024.01.15.01.31.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jan 2024 01:31:49 -0800 (PST) Date: Mon, 15 Jan 2024 17:31:41 +0800 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Fabiano Rosas , qemu-devel@nongnu.org, armbru@redhat.com, Juan Quintela , Leonardo Bras , Claudio Fontana Subject: Re: [RFC PATCH v3 04/30] io: fsync before closing a file channel Message-ID: References: <20231127202612.23012-1-farosas@suse.de> <20231127202612.23012-5-farosas@suse.de> <87wmsfn1xx.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.758, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SORBS_WEB=1.5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Jan 15, 2024 at 09:03:20AM +0000, Daniel P. Berrangé wrote: > On Mon, Jan 15, 2024 at 04:57:42PM +0800, Peter Xu wrote: > > On Thu, Jan 11, 2024 at 03:46:02PM -0300, Fabiano Rosas wrote: > > > > (2) Why metadata doesn't matter (v.s. fsync(), when CONFIG_FDATASYNC=y)? > > > > > > Syncing the inode information is not critical, it's mostly timestamp > > > information (man inode). And fdatasync makes sure to sync any metadata > > > that would be relevant for the retrieval of the data. > > > > I forgot to reply to this one in the previous reply.. > > > > Timestamps look all fine to be old. What about file size? That's also in > > "man inode" as metadata, but I'm not sure whether data will be fully valid > > if e.g. size enlarged but not flushed along with the page caches. > > If the size wasn't updated, then syncing of the data would be pointless. > The man page confirms that size is synced: > > [quote] > fdatasync() is similar to fsync(), but does not flush modified metadata > unless that metadata is needed in order to allow a subsequent data re‐ > trieval to be correctly handled. For example, changes to st_atime or > st_mtime (respectively, time of last access and time of last modifica‐ > tion; see inode(7)) do not require flushing because they are not neces‐ > sary for a subsequent data read to be handled correctly. On the other > hand, a change to the file size (st_size, as made by say ftruncate(2)), > would require a metadata flush. > [/quote] I should have read more carefully, sorry for the noise. -- Peter Xu