netdev - Re: [PATCH net-2.6 3/3] bonding/vlan: Fix mangled NAs on slaves without VLAN tag insertion

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Date:	Mon, 13 Dec 2010 14:20:57 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>,
	Jay Vosburgh <fubar@...ibm.com>, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com
Subject: Re: [PATCH net-2.6 3/3] bonding/vlan: Fix mangled NAs on slaves
 without VLAN tag insertion

On Mon, Dec 13, 2010 at 10:20 AM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
> bond_na_send() attempts to insert a VLAN tag in between building and
> sending packets of the respective formats.  If the slave does not
> implement hardware VLAN tag insertion then vlan_put_tag() will mangle
> the network-layer header because the Ethernet header is not present at
> this point (unlike in bond_arp_send()).
>
> Fix this by adding the tag out-of-line and relying on
> dev_hard_start_xmit() to insert it inline if necessary.
>
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
> ---
>  drivers/net/bonding/bond_ipv6.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/bonding/bond_ipv6.c b/drivers/net/bonding/bond_ipv6.c
> index 121b073..84fbd4e 100644
> --- a/drivers/net/bonding/bond_ipv6.c
> +++ b/drivers/net/bonding/bond_ipv6.c
> @@ -88,7 +88,12 @@ static void bond_na_send(struct net_device *slave_dev,
>        }
>
>        if (vlan_id) {
> -               skb = vlan_put_tag(skb, vlan_id);
> +               /* The Ethernet header is not present yet, so it is
> +                * too early to insert a VLAN tag.  Force use of an
> +                * out-of-line tag here and let dev_hard_start_xmit()
> +                * insert it if the slave hardware can't.
> +                */
> +               skb = __vlan_hwaccel_put_tag(skb, vlan_id);
>                if (!skb) {
>                        pr_err("failed to insert VLAN tag\n");
>                        return;

You could drop the check for !skb, since __vlan_hwaccel_put_tag() can
never fail.

Actually, my plan is to remove all current users of vlan_put_tag() and
replace them with __vlan_hwaccel_put_tag (and then rename that to
vlan_put_tag()).  There's really no reason why the upper layers should
have to care what the underlying device is capable of, now that
dev_hard_start_xmit() can handle it.

Reviewed-by: Jesse Gross <jesse@...ira.com>
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