netdev - Re: [PATCH RFC 0/6] copy aside frags with destructors (was [PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)

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Date:	Tue, 8 May 2012 12:41:14 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: Re: [PATCH RFC 0/6] copy aside frags with destructors (was [PATCH
 7/9] net: add skb_orphan_frags to copy aside frags with destructors)

On Mon, May 07, 2012 at 04:53:46PM +0300, Michael S. Tsirkin wrote:
> > > > But I fear we're about to toss Ian into yet another rabbit hole. :-)
> > > > 
> > > > Let's try to converge on something quickly as I think integration of
> > > > his work has been delayed enough as-is.

...

> Here's a first stub at a fix. Basically to be able to modify frags on
> the fly we must make sure the skb isn't cloned, so the moment someone
> clones the skb we need to trigger the frag copy logic.  And this is
> exactly what happens with SKBTX_DEV_ZEROCOPY so it seems to make sense
> to reuse that logic.
> 
> The below patchset replaces patch 7
> ([PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)
> in Ian's patchset and needs to be applied there.
> 
> 
> Compiled only but I'd like to hear what people think all the same
> because it does add a couple of branches on fast path.  On the other
> hand this makes it generic so the same logic will be reusable for packet
> sockets (which IIRC are currently buggy in the same way as sunrpc) and
> for adding zero copy support to tun.
> 
> Please comment,
> Thanks!

Ian, just to stress, need your ack that this does what you wanted.

-- 
MST
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