linux-ext4 - Re: Splice & iomap dio problems

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Date:   Tue, 19 Nov 2019 08:48:45 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Bobrowski <mbobrowski@...browski.org>,
        linux-ext4@...r.kernel.org, Ted Tso <tytso@....edu>
Subject: Re: Splice & iomap dio problems

On Tue, Nov 19, 2019 at 08:34:54AM -0800, Darrick J. Wong wrote:
> > The slight concern I have with this is that that would change e.g. the
> > behavior of IOMAP_REPORT. We could specialcase IOMAP_REPORT but then it
> > gets kind of ugly. And it seems kind of fuzzy when do we truncate the
> > extent with i_size and when not... Generally i_size is kind of a side-band
> > thing for block mapping operations so if we could leave it out of
> > ->iomap_begin I'd find that nicer.
> 
> <nod>

Yes.  I'd prefer if the caller deals with any i_size limiting and
not the iomap methods themselves.  For now I'm tempted to just go
with the iov_iter_revert scheme.  Note that I particularly like it,
but it matches the most common direct I/O implementation at least.