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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: <20210121190937.GE20964@fieldses.org> References: <20210121190937.GE20964@fieldses.org> <20210121174306.GB20964@fieldses.org> <20210121164645.GA20964@fieldses.org> <161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk> <1794286.1611248577@warthog.procyon.org.uk> <1851804.1611255313@warthog.procyon.org.uk> To: "J. Bruce Fields" Cc: dhowells@redhat.com, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Takashi Iwai , Matthew Wilcox , linux-afs@lists.infradead.org, Jeff Layton , David Wysochanski , Alexander Viro , linux-cachefs@redhat.com, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1856290.1611259704.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Thu, 21 Jan 2021 20:08:24 +0000 Message-ID: <1856291.1611259704@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org J. Bruce Fields wrote: > > J. Bruce Fields wrote: > > = > > > > Fixing this requires a much bigger overhaul of cachefiles than thi= s patchset > > > > performs. > > > = > > > That sounds like "sometimes you may get file corruption and there's > > > nothing you can do about it". But I know people actually use fscach= e, > > > so it must be reliable at least for some use cases. > > = > > Yes. That's true for the upstream code because that uses bmap. > = > Sorry, when you say "that's true", what part are you referring to? Sometimes, theoretically, you may get file corruption due to this. > > I'm switching > > to use SEEK_HOLE/SEEK_DATA to get rid of the bmap usage, but it doesn'= t change > > the issue. > > = > > > Is it that those "bridging" blocks only show up in certain corner ca= ses > > > that users can arrange to avoid? Or that it's OK as long as you use > > > certain specific file systems whose behavior goes beyond what's > > > technically required by the bamp or seek interfaces? > > = > > That's a question for the xfs, ext4 and btrfs maintainers, and may var= y > > between kernel versions and fsck or filesystem packing utility version= s. > = > So, I'm still confused: there must be some case where we know fscache > actually works reliably and doesn't corrupt your data, right? Using ext2/3, for example. I don't know under what circumstances xfs, ext= 4 and btrfs might insert/remove blocks of zeros, but I'm told it can happen. David