From: Jeff Layton <jlayton@redhat.com>
Subject: Re: [PATCH v7 16/22] block: convert to errseq_t based writeback
 error tracking
Date: Sat, 24 Jun 2017 09:16:06 -0400
Message-ID: <1498310166.4796.4.camel@redhat.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>, Al Viro
 <viro@ZenIV.linux.org.uk>,  Jan Kara <jack@suse.cz>, tytso@mit.edu,
 axboe@kernel.dk, mawilcox@microsoft.com,  ross.zwisler@linux.intel.com,
 corbet@lwn.net, Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>,
 David Sterba <dsterba@suse.com>, "Darrick J . Wong"
 <darrick.wong@oracle.com>, Carlos Maiolino <cmaiolino@redhat.com>, Eryu
 Guan <eguan@redhat.com>, David Howells <dhowells@redhat.com>,
 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
 linux-ext4@vger.kernel.org,  linux-xfs@vger.kernel.org,
 linux-btrfs@vger.kernel.org,  linux-block@vger.kernel.org
To: Christoph Hellwig <hch@infradead.org>
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On Sat, 2017-06-24 at 04:59 -0700, Christoph Hellwig wrote:
> On Tue, Jun 20, 2017 at 01:44:44PM -0400, Jeff Layton wrote:
> > In order to query for errors with errseq_t, you need a previously-
> > sampled point from which to check. When you call
> > filemap_write_and_wait_range though you don't have a struct file and so
> > no previously-sampled value.
> 
> So can we simply introduce variants of them that take a struct file?
> That would be:
> 
>  a) less churn
>  b) less code
>  c) less chance to get data integrity wrong

Yeah, I had that thought after I sent the reply to you earlier.

The main reason I didn't do that before was that I had myself convinced
that we needed to do the check_and_advance as late as possible in the
fsync process, after the metadata had been written.

Now that I think about it more, I think you're probably correct. As long
as we do the check and advance at some point after doing the
write_and_wait, we're fine here and shouldn't violate exactly once
semantics on the fsync return.
-- 
Jeff Layton <jlayton@redhat.com>

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