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

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Message-ID: <1305236000.6124.67.camel@Joe-Laptop>
Date:	Thu, 12 May 2011 14:33:20 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: af_packet: Don't initialize vnet_hdr

On Thu, 2011-05-12 at 17:26 -0400, David Miller wrote:
> From: Joe Perches <joe@...ches.com>
> Date: Thu, 12 May 2011 13:36:10 -0700
> 
> > Save a memset, initialize only the portion necessary.
> > 
> > packet_snd either gets this structure completely from
> > memcpy_fromiovec or uses only the hdr_len set to 0,
> > so don't always initialize the structure to 0.
> > 
> > Signed-off-by: Joe Perches <joe@...ches.com>
> 
> On ARM this won't be tightly packed, therefore you'll leave
> uninitialized pieces of padding in this structure and this
> thing is an "on-the-wire" network header.
> 
> I'm not applying this.

I believe that it's only sent when po->has_vnet_hdr
is set.  In that case, it's completely filled from
memcpy_fromiovec.  In the not set po->has_vnet_hdr case,
only vnet_hdr.hdr_len is accessed by packet_alloc_skb.

cheers, Joe


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