linux-ext4 - Re: RFC: iomap write invalidation

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Message-ID: <20200721153136.GJ15516@casper.infradead.org>
Date:   Tue, 21 Jul 2020 16:31:36 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@....de>
Cc:     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 05:16:16PM +0200, Christoph Hellwig wrote:
> On Tue, Jul 21, 2020 at 04:14:37PM +0100, Matthew Wilcox wrote:
> > On Tue, Jul 21, 2020 at 05:06:15PM +0200, Christoph Hellwig wrote:
> > > On Tue, Jul 21, 2020 at 04:04:32PM +0100, Matthew Wilcox wrote:
> > > > I thought you were going to respin this with EREMCHG changed to ENOTBLK?
> > > 
> > > Oh, true.  I'll do that ASAP.
> > 
> > Michael, could we add this to manpages?
> 
> 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?