netdev - Re: [PATCH 2/2 v2] bonding: COW before overwriting the destination MAC address

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Date:	Thu, 03 Mar 2011 09:35:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Jay Vosburgh <fubar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2 v2] bonding: COW before overwriting the destination
 MAC address

Le jeudi 03 mars 2011 à 16:21 +0800, Changli Gao a écrit :
> On Thu, Mar 3, 2011 at 3:55 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> >
> >
> > Thats minor, but using :
> >
> > u16 *dest = eth_hdr(skb)->h_dest;
> >
> > memcpy(dest, ptr, ETH_ALEN);
> >
> > Is better because compiler knows both destination and source are at
> > least aligned on shorts.
> >
> > On some arches, it helps to not using 6 bytes copy, but 3 shorts.
> >
> >
> 
> Is it still true if ptr isn't aligned on shorts? And
> net_device.dev_addr is an unsigned char *pointer. Thanks.
> 

dev_addr[] was aligned to word boundaries (because of natural structure
alignment), but the recent changes made it a char *pointer, so gcc is
not able to make this true anymore.

This could change if dev_addr was a pointer to struct netdev_hw_addr



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