On 03/24/2016 05:06 PM, Ben Greear wrote:
On 03/24/2016 04:56 PM, Cong Wang wrote:
On Thu, Mar 24, 2016 at 3:01 PM, Ben Greear <gree...@candelatech.com> wrote:
I have an application that creates two pairs of veth devices.
a <-> b c <-> d
b and c have a raw packet socket opened on them and I 'bridge' frames
between b and c to provide network emulation (ie, configurable delay).
IIUC, you create two raw sockets in order to bridge these two veth pairs?
That is, to receive packets on one socket and deliver packets on the other?
Yes.
I put IP 1.1.1.1/24 on a, 1.1.1.2/24 on d, and then create a UDP connection
(using policy based routing to ensure frames are sent on the appropriate
interfaces).
This is user-space only app, and kernel in this case is completely
unmodified.
The commit below breaks this feature: UDP frames are sniffed on both a and
d ports
(in both directions), but the UDP socket does not receive frames.
Using normal ethernet ports, this network emulation feature works fine, so
it is
specific to VETH.
A similar test with just sending UDP between a single veth pair: e <-> f
works fine. Maybe it has something to do with raw packets?
Yeah, I have the same feeling. Could you trace kfree_skb() to see
where these packets are dropped? At UDP layer?
Since reverting the patch fixes this, it almost certainly has to be due to some
checksum checking logic. Since UDP sockets (between single veth pair)
works, it would appear to be related to my packet bridge, so maybe
it is specific to raw packets and/or sendmmsg api.
I'll investigate it better tomorrow.
So, I found time to poke at it this evening:
Sending between two veth pairs, no packet bridge involved.
UDP: ip_summed is 3 (CHECKSUM_PARTIAL) # Works fine.
raw packet frames, custom ether protocol (0x1111 type): ip_summed is 0 (NONE)
# Works fine.
When I try to send UDP through the veth pairs & pkt bridge, I see this:
(pkt-bridge connects to the 'b' side of the veth pairs)
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR0 rcv: rddVR0b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR1b rcv: rddVR1 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR1 rcv: rddVR1b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR0b rcv: rddVR0 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR0 rcv: rddVR0b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:34 ben-ota-1 kernel: dev: rddVR1b rcv: rddVR1 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR1 rcv: rddVR1b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0b rcv: rddVR0 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0 rcv: rddVR0b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR1b rcv: rddVR1 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR1 rcv: rddVR1b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0b rcv: rddVR0 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0 rcv: rddVR0b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR1b rcv: rddVR1 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR1 rcv: rddVR1b ip_summed: 3
rcv-features: 0x184074011e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0b rcv: rddVR0 ip_summed: 0
rcv-features: 0x184075b59e9
Mar 24 17:59:35 ben-ota-1 kernel: dev: rddVR0 rcv: rddVR0b ip_summed: 3
rcv-features: 0x184074011e9
I am guessing the issue is that when my pkt bridge sends a raw frame that is
actually a UDP packet,
the fact that it has ip_summed == 0 in the kernel causes the frame to be
dropped.
I modified veth.c like this for this test:
static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct veth_priv *priv = netdev_priv(dev);
struct net_device *rcv;
int length = skb->len;
rcu_read_lock();
rcv = rcu_dereference(priv->peer);
if (unlikely(!rcv)) {
kfree_skb(skb);
goto drop;
}
pr_err("dev: %s rcv: %s ip_summed: %d rcv-features: 0x%llx\n",
dev->name, rcv->name, skb->ip_summed, (unsigned long
long)rcv->features);
#if 0
/* don't change ip_summed == CHECKSUM_PARTIAL, as that
* will cause bad checksum on forwarded packets
*/
if (skb->ip_summed == CHECKSUM_NONE &&
rcv->features & NETIF_F_RXCSUM)
skb->ip_summed = CHECKSUM_UNNECESSARY;
#endif
Thanks,
Ben
--
Ben Greear <gree...@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
