linux-kernel - Re: [PATCH 00/10] iov_iter: Add new iters and use with AFS

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Message-ID: <20180913164351.GC11574@bombadil.infradead.org>
Date:   Thu, 13 Sep 2018 09:43:51 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/10] iov_iter: Add new iters and use with AFS

On Thu, Sep 13, 2018 at 05:18:23PM +0100, David Howells wrote:
> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > >  (5) Add an ITER_DISCARD iterator type.  This provides an iterator that
> > >      simply discards anything written to it.  It cannot be used as a data
> > >      source.
> > 
> > May I suggest an ITER_ZERO iterator type instead?  It acts like /dev/zero;
> > writes are discarded (as you have here) and reads return zeroes.
> > I've wanted such a thing in the past, but got distracted away from
> > that project.
> 
> I thought about that, but the zero-filling is not as easy to implement as the
> discard side - plus I don't have any use case to test it with.
> 
> Do you have a use case in mind?

At the time I did it, it was useful in dax, but I don't know if it is
any more.  It might serve to replace iov_iter_zero().