Re: [PATCH v7 16/22] block: convert to errseq_t based writeback error tracking

[Jeff Layton <jlayton@redhat.com>]

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>