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SubjectRe: [PATCH net 1/2] macvlan: forbid L2 fowarding offload for macvtap
On 01/05/2014 07:21 PM, Jason Wang wrote:
> L2 fowarding offload will bypass the rx handler of real device. This will make
> the packet could not be forwarded to macvtap device. Another problem is the
> dev_hard_start_xmit() called for macvtap does not have any synchronization.
>
> Fix this by forbidding L2 forwarding for macvtap.
>
> Cc: John Fastabend <john.r.fastabend@intel.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> drivers/net/macvlan.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>

I must be missing something.

The lower layer device should set skb->dev to the correct macvtap
device on receive so that in netif_receive_skb_core() the macvtap
handler is hit. Skipping the macvlan receive handler should be OK
because the switching was done by the hardware. If I read macvtap.c
correctly macvlan_common_newlink() is called with 'dev' where 'dev'
is the macvtap device. Any idea what I'm missing? I guess I'll need
to setup a macvtap test case.

And what synchronization are you worried about on dev_hard_start_xmit()?
In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX
flag so HARD_TX_LOCK protects the driver txq. We might hit this warning
in dev_queue_xmit() though,

net_crit_ratelimited("Virtual device %s asks to queue packet!\n",

Perhaps we can remove it.

> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index 60406b0..5360f73 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -338,6 +338,8 @@ static const struct header_ops macvlan_hard_header_ops = {
> .cache_update = eth_header_cache_update,
> };
>
> +static struct rtnl_link_ops macvlan_link_ops;
> +
> static int macvlan_open(struct net_device *dev)
> {
> struct macvlan_dev *vlan = netdev_priv(dev);
> @@ -353,7 +355,8 @@ static int macvlan_open(struct net_device *dev)
> goto hash_add;
> }
>
> - if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD) {
> + if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD &&
> + dev->rtnl_link_ops == &macvlan_link_ops) {
> vlan->fwd_priv =
> lowerdev->netdev_ops->ndo_dfwd_add_station(lowerdev, dev);
>
>


--
John Fastabend Intel Corporation


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