netdev - Re: [PATCH v3 net-next 1/1] net_sched: Introduce skbmod action

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Message-ID: <1473171919.10725.3.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 06 Sep 2016 07:25:19 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, daniel@...earbox.net,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH v3 net-next 1/1] net_sched: Introduce skbmod action

On Tue, 2016-09-06 at 08:08 -0400, Jamal Hadi Salim wrote:
> ng
> On 16-08-30 08:44 AM, Eric Dumazet wrote:
> > On Tue, 2016-08-30 at 07:57 -0400, Jamal Hadi Salim wrote:
> >>         if (flags & SKBMOD_F_SWAPMAC) {
> >>                 u8 tmpaddr[ETH_ALEN];
> >>                 /*XXX: I am sure we can come up with something more efficient */
> >>                 ether_addr_copy(tmpaddr, eth_hdr(skb)->h_dest);
> >>                 ether_addr_copy(eth_hdr(skb)->h_dest, eth_hdr(skb)->h_source);
> >>                 ether_addr_copy(eth_hdr(skb)->h_source, tmpaddr);
> >>         }
> >
> > While ether_addr_copy() is accepting u8 pointers, data must be aligned to u16 at least.
> >
> > (See comments in include/linux/etherdevice.h)
> >
> > Some arches/compilers might do things here that would generate a trap
> > if tmpaddr is not aligned.
> >
> 
> Hrm. How do you suggest dealing with this?

Just use u16 in the array ?

u16 tmpaddr[ETH_ALEN / 2]; /* ether_addr_copy() requirement */

ether_addr_copy((u8 *)tmpaddr, eth_hdr(skb)->h_dest);
...