Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 13 Sep 2018 09:43:51 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
        linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] iov_iter: Add new iters and use with AFS
Message-ID: <20180913164351.GC11574@bombadil.infradead.org>
References: <20180913161054.GB11574@bombadil.infradead.org>
 <153685389564.14766.11306559824641824935.stgit@warthog.procyon.org.uk>
 <17352.1536855503@warthog.procyon.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <17352.1536855503@warthog.procyon.org.uk>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Sep 13, 2018 at 05:18:23PM +0100, David Howells wrote:
> Matthew Wilcox <willy@infradead.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().