* [Qemu-devel] Re: user space virtio-net exits with "truncating packet" error
[not found] <Pine.LNX.4.64.0905141258570.31748@zuben.voltaire.com>
@ 2009-05-14 11:22 ` Mark McLoughlin
2009-05-14 12:25 ` Or Gerlitz
0 siblings, 1 reply; 2+ messages in thread
From: Mark McLoughlin @ 2009-05-14 11:22 UTC (permalink / raw)
To: Or Gerlitz; +Cc: netdev, Rusty Russell, Gregory Haskins, Avi Kivity, qemu-devel
On Thu, 2009-05-14 at 13:07 +0300, Or Gerlitz wrote:
> Hi,
>
> When running with jumbo frames (i.e set tap0 and guest nic mtu to 9k)
> and using 8k sized packets with iperf, the qemu process exits with
> "virtio-net truncating packet" which I see in the code of qemu/hw/virtio-net.c
> :: virtio_net_receive(). This happens only when the VM is receiving, if I
> send 8K packets from the VM things go fine.
>
> I use virtio based NIC in the VM and Linux 2.6.29.1 in both the VM and the host.
> Qemu is the one provided by kvm release 84
That sounds like a bug in qemu's mergeable receive buffers
implementation - the host is running out of buffers for the packet, even
though it supposedly has already checked that there is enough buffers
available on the ring.
Hmm, I think I see the bug - does the patch below work? Please try
several mtu values around the 9k mark to be sure
Cheers,
Mark.
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index f125edc..3ffd2c0 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -438,16 +438,16 @@ static void virtio_net_receive(void *opaque, const uint8_t *buf, int size)
struct virtio_net_hdr_mrg_rxbuf *mhdr = NULL;
size_t hdr_len, offset, i;
- if (!do_virtio_net_can_receive(n, size))
+ /* hdr_len refers to the header we supply to the guest */
+ hdr_len = n->mergeable_rx_bufs ?
+ sizeof(struct virtio_net_hdr_mrg_rxbuf) : sizeof(struct virtio_net_hdr);
+
+ if (!do_virtio_net_can_receive(n, size + hdr_len))
return;
if (!receive_filter(n, buf, size))
return;
- /* hdr_len refers to the header we supply to the guest */
- hdr_len = n->mergeable_rx_bufs ?
- sizeof(struct virtio_net_hdr_mrg_rxbuf) : sizeof(struct virtio_net_hdr);
-
offset = i = 0;
while (offset < size) {
^ permalink raw reply related [flat|nested] 2+ messages in thread