netdev - Re: [PATCH v2 08/17] {macvtap,tun}_get_user(): switch to iov

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Message-ID: <20150203151925.GA9031@redhat.com>
Date:	Tue, 3 Feb 2015 16:19:25 +0100
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/17] {macvtap,tun}_get_user(): switch to iov_iter

On Tue, Feb 03, 2015 at 02:27:28PM +0000, Al Viro wrote:
> On Tue, Feb 03, 2015 at 12:10:44PM +0200, Michael S. Tsirkin wrote:
> 
> > Hmm does copy_from_iter actually modify the iovec?
> > If so, won't this break aio on tun/macvtap, by
> > reversing the effect of
> > commit 6f26c9a7555e5bcca3560919db9b852015077dae
> >     tun: fix tun_chr_aio_write so that aio works
> > ?
> > 
> > 
> > Maybe we should change iovec_iter to avoid modifying the
> > underlying iovec?
> 
> iov_iter never changes the underlying iovec (or kvec, or bvec).
> iter->iov_offset changes as you go and once you have consumed an
> entire iovec element ->iov is incremented to point to the next one
> (and ->iov_offset is reset to 0 at that point).  *Contents* of
> iter->iov is never modified.

I see, I think I misread the code.
Thanks for the clarification.

-- 
MST
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