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Date:   Tue, 04 Apr 2017 12:25:46 -0400
From:   Jeff Layton <>
To:     Matthew Wilcox <>
Cc:     NeilBrown <>,,,,,,
Subject: Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking
 infrastructure and convert ext4 to use it

On Tue, 2017-04-04 at 09:12 -0700, Matthew Wilcox wrote:
> On Tue, Apr 04, 2017 at 08:17:48AM -0400, Jeff Layton wrote:
> > Agreed that we should focus on POSIX compliance. I'll also note that
> > POSIX states:
> > 
> > "If more than one error occurs in processing a function call, any one
> > of the possible errors may be returned, as the order of
> > detection is undefined."
> > 
> >
> > 
> > So, I'd like to push back on this idea that we need to prefer reporting
> > -EIO over other errors. POSIX certainly doesn't mandate that. 
> I honestly wonder if we need to support ENOSPC from writeback at all.
> Looking at our history, the AS_EIO / AS_ENOSPC came from this patch
> in 2003:
> That seems to come from here:
> which is marked as a resend, but I can't find the original.
> It's a little misleading because the immediately preceding patch
> introduced mapping->error, so there's no precedent here to speak of.
> It looks like we used to just silently lose writeback errors (*cough*).
> I'd like to suggest that maybe we don't need to support multiple errors
> at all.  That all errors, including ENOSPC, get collapsed into EIO.
> POSIX already tells us to do that for close() and permits us to do that
> for fsync().

That is certainly allowed under POSIX as I interpret the spec. At a
minimum we just need a single flag and can collapse all errors under

That said, I think giving more specific errors where we can is useful.
When your program is erroring out and writing 'I/O error' to the logs,
then how much time will your admins burn before they figure out that it
really failed because the filesystem was full?
Jeff Layton <>

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