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

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Message-ID: <20150203142728.GC29656@ZenIV.linux.org.uk>
Date:	Tue, 3 Feb 2015 14:27:28 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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 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.
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