netdev - Re: [PATCHv2 net-next 1/8] skb: report completion status for zero copy skbs

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Date:	Thu, 1 Nov 2012 18:16:11 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	vyasevic@...hat.com, edumazet@...gle.com,
	akpm@...ux-foundation.org, alexander.h.duyck@...el.com,
	Ian.Campbell@...rix.com, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 net-next 1/8] skb: report completion status for zero
 copy skbs

On Thu, Nov 01, 2012 at 11:50:24AM -0400, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Wed, 31 Oct 2012 12:31:06 +0200
> 
> > -void vhost_zerocopy_callback(struct ubuf_info *ubuf)
> > +void vhost_zerocopy_callback(struct ubuf_info *ubuf, int zerocopy_status)
> 
> If you're only reporting true/false values, even just for now,
> please use 'bool' for this.

In fact next patch reports -ENOMEM when tun hits OOM so callback can
distinguish between copy (>0 value) and error (<0 value)
and reduce zerocopy more aggressively in case of errors.

The *callback* in vhost-net currently handles all non-zero
values identically, but I am not sure it's the optimal behaviour
so I thought it's worth it to give callbacks the info.

Do you think it's over-engineering, or a good idea?

-- 
MST
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