linux-ext4 - Re: RFC: iomap write invalidation

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Date:   Tue, 21 Jul 2020 17:42:40 +0200
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@....de>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Dave Chinner <david@...morbit.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Naohiro Aota <naohiro.aota@....com>,
        Johannes Thumshirn <jth@...nel.org>,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        cluster-devel@...hat.com, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org,
        Michael Kerrisk <mtk.manpages@...il.com>,
        linux-man@...r.kernel.org
Subject: Re: RFC: iomap write invalidation

On Tue, Jul 21, 2020 at 04:31:36PM +0100, Matthew Wilcox wrote:
> > Umm, no.  -ENOTBLK is internal - the file systems will retry using
> > buffered I/O and the error shall never escape to userspace (or even the
> > VFS for that matter).
> 
> Ah, I made the mistake of believing the comments that I could see in
> your patch instead of reading the code.
> 
> Can I suggest deleting this comment:
> 
>         /*
>          * No fallback to buffered IO on errors for XFS, direct IO will either
>          * complete fully or fail.
>          */
> 
> and rewording this one:
> 
>                 /*
>                  * Allow a directio write to fall back to a buffered
>                  * write *only* in the case that we're doing a reflink
>                  * CoW.  In all other directio scenarios we do not
>                  * allow an operation to fall back to buffered mode.
>                  */
> 
> as part of your revised patchset?

That isn't actually true.  In current mainline we only fallback on
reflink RMW cases, but with this series we also fall back for
invalidation failures.