linux-kernel - Re: [PATCH] net: af_packet: Don't initialize vnet

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Message-Id: <20110512.175959.1343349350164758016.davem@davemloft.net>
Date:	Thu, 12 May 2011 17:59:59 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	joe@...ches.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: af_packet: Don't initialize vnet_hdr

From: Joe Perches <joe@...ches.com>
Date: Thu, 12 May 2011 14:55:48 -0700

> Save an initialization because when this structure
> is used it's completely filled by memcpy_fromiovec.
> 
> Add a new variable used for the 0 sized allocation
> when this structure is not used.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> 
> ---
> 
> On Thu, 2011-05-12 at 17:36 -0400, David Miller wrote:
>> I would rather see the code rearranged such that this sort of
>> hackish scheme isn't necessary.

You misunderstood me.

It's this:

	struct virtio_net_hdr vnet_hdr;


	if (po->has_vnet_hdr) {
		initialize &vnet_hdr
	}

	...

	if (po->has_vnet_hdr) {
		use vnet_hdr
	}

which I'm talking about when I say "hackish scheme".

The compiler cannot conclusively see that the control flow always
goes to the code that initialized vnet_hdr every time it reaches
the code that uses it.

I want _that_ part rearranged, not what you decided to tackle
here.

For the third time, I'm not applying your patch.
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