[PATCH net-next-2.6] macvtap: Return error when macvlan drops the packet

[PATCH net-next-2.6] macvtap: Return error when macvlan drops the packet

[Shirley Ma]

Return err when macvlan dropps the packet.

Signed-off-by: Shirley Ma <xma@us.ibm.com>
---
 drivers/net/macvtap.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 2b4d59b..36d52b5 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -492,9 +492,11 @@ static ssize_t macvtap_get_user(struct
macvtap_queue *q,
 
 	rcu_read_lock_bh();
 	vlan = rcu_dereference(q->vlan);
-	if (vlan)
-		macvlan_start_xmit(skb, vlan->dev);
-	else
+	if (vlan) {
+		err = macvlan_start_xmit(skb, vlan->dev);
+		if (err)
+			count = err;
+	} else
 		kfree_skb(skb);
 	rcu_read_unlock_bh();
 

Re: [PATCH net-next-2.6] macvtap: Return error when macvlan drops the packet

[Arnd Bergmann]

On Monday 12 July 2010, Shirley Ma wrote:
> 
> Return err when macvlan dropps the packet.

Can you be more specific why you think this is the right idea?

As far as I can tell, this will return '1' to user space for a dropped
packet (NET_XMIT_DROP) or another positive return value.
While this might be nice for a user application to know, neither does
qemu check for this nor does it match the read(2) documentation.

I fear if we want congestion control to improve, we need to do it
differently.

	Arnd

Re: [PATCH net-next-2.6] macvtap: Return error when macvlan drops the packet

[Shirley Ma]

Hello Arnd,

I am working on macvtap zero-copy patch. I found that the packet was
silently dropped and packet out of order when using zero-copy. That was
a reason I submitted this patch to switch to copy mode when that
happens. I think I might need more time to debug why first.

Thanks
Shirley