netdev - Re: [PATCH 1/4] xen-netfront: remove unused variable `extra'

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Message-ID: <1363608860.30193.39.camel@zakaz.uk.xensource.com>
Date:	Mon, 18 Mar 2013 12:14:20 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"annie.li@...cle.com" <annie.li@...cle.com>
Subject: Re: [PATCH 1/4] xen-netfront: remove unused variable `extra'

On Mon, 2013-03-18 at 12:04 +0000, Wei Liu wrote:
> On Mon, 2013-03-18 at 11:42 +0000, Ian Campbell wrote:
> > On Mon, 2013-03-18 at 10:35 +0000, Wei Liu wrote:
> > 
> > I think a few more words are needed here since from the code you are
> > removing it seems very much like gso is used for something. If you have
> > a proof that the "extra = gso" case is never hit then please explain it.
> > Perhaps a reference to the removal of the last user?
> > 
> > Or maybe it is the case that it should be used and the bug is that it
> > isn't?
> > 
> 
> Looks like the latter one. 'extra' field should  be used to get hold of
> the last extra info in the ring. ;-)
> 
> But, the only extra info in upstream kernel is XEN_NETIF_EXTRA_TYPE_GSO,
> so there's really no other extra info in the ring at that point. Could
> it be possible that it is something from classic Xen kernel?

The classic kernel netfront has exactly the same code it seems and
netif_extra_type_gso is the only one I've ever heard of.

Maybe this extra thing is just redundant unless/until a second extra
comes along.

Ian.


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