linux-kernel - Re: iov_iter

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Message-ID: <20170911125141.GJ5426@ZenIV.linux.org.uk>
Date:   Mon, 11 Sep 2017 13:51:42 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dave Chinner <david@...morbit.com>,
        Dave Jones <davej@...emonkey.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org
Subject: Re: iov_iter_pipe warning.

On Mon, Sep 11, 2017 at 05:07:57AM -0700, Christoph Hellwig wrote:
> On Mon, Sep 11, 2017 at 12:07:23AM +0100, Al Viro wrote:
> > BTW, another problem I see there is that iomap_dio_actor() should *NOT*
> > assume that do-while loop in there will always manage to shove 'length'
> > bytes out in case of success.  That is simply not true for pipe-backed
> > destination.  And I'm not sure if outright failures halfway through
> > are handled correctly.  What does it need a copy of dio->submit.iter for,
> > anyway?  Why not work with dio->submit.iter directly?
> > --
> 
> So that we only walk the pagetables and pin down the pages that
> we can actually use in this iteration.

Er...  So why not simply do iov_iter_reexpand() in the end of segment with the
right argument?  IDGI...