linux-ext4 - Re: RFC: iomap write invalidation

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Message-ID: <20200721160542.GD3151642@magnolia>
Date:   Tue, 21 Jul 2020 09:05:42 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Matthew Wilcox <willy@...radead.org>,
        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 06:01:43PM +0200, Christoph Hellwig wrote:
> On Tue, Jul 21, 2020 at 08:59:25AM -0700, Darrick J. Wong wrote:
> > In the comment that precedes iomap_dio_rw() for the iomap version,
> 
> maybe let's just do that..
> 
> > ``direct_IO``
> > 	called by the generic read/write routines to perform direct_IO -
> > 	that is IO requests which bypass the page cache and transfer
> > 	data directly between the storage and the application's address
> > 	space.  This function can return -ENOTBLK to signal that it is
> > 	necessary to fallback to buffered IO.  Note that
> > 	blockdev_direct_IO and variants can also return -ENOTBLK.
> 
> ->direct_IO is not used for iomap and various other implementations.
> In fact it is a horrible hack that I've been trying to get rid of
> for a while.

Agreed, but for now there are still a number of fses who are still on
the old directio code; let's try to keep the drainbamage/confusion
potential to a minimum so it doesn't spread to our iomap shinyness. :)

--D