Well, here's the output from the `ip link` cmd:
3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq
state UP mode DEFAULT group default qlen 1000
link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
prog/xdp id 1 tag 1cd982ef22273bda jited
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq
state UP mode DEFAULT group default qlen 1000
link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
prog/xdp id 1 tag 1cd982ef22273bda jited
As you can see, there's the XDP program ID 1 executing on them.
However, there's definitely something interesting happening when
bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
program just returns XDP_PASS while the following line gets printed in
kern.log:
eth3: bad gso: type: 164, size: 256
No idea what's wrong here.
Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
which my XDP program executes bpf_redirect_map(&dev_map,
fib_params.ifindex, 0), the following gets printed in
/sys/kernel/debug/tracing/trace_pipe:
xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
to_ifindex=0 err=-14 map_id=0 map_index=4
I feel this last one to be somewhat related to the comment here
https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
Is it correct? If so, what does this precisely mean? Is there any way
to get around with this? Because what I'm doing is simply using the
BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
packets between "XDP ports".
Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
<dsahern@xxxxxxxxx> ha scritto:
>
> On 11/20/18 7:18 AM, Pavel Popa wrote:
> > Hi all,
> >
> > I've implemented a XDP forwarding program using the bpf_fib_lookup()
> > helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> > at the virtio_net driver level). The only problem is that the
> > receiving virtio network interface seems to drop the XDP packet after
> > successfully executing my XDP program.
> > Kernel: 4.18.10
> >
> > my_xdp_fwd_kern.c:
> > /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> > rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> > BPF_FIB_LOOKUP_DIRECT);
> > /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> > rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> > return rc;
> >
> > I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> > is the correct dev index from FIB lookup.
> > dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> > for (i = 1; i < 64; i++)
> > bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> >
> > I'm passing the following to the qemu cmd line for the 2 devices I
> > want to run XDP on (as stated here
> > https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > \
> > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > \
> >
> > In the guest enabling also the MultiQueue feature, as stated here
> > https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> > What I'm left with is debugging the virtio_net kernel module by adding
> > a bunch of printk() and see what happens, especially here
> > https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> >
> > Am I doing something wrong here? What I'm missing?
> >
>
> I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> virtio for development and these days start my VMs with only:
>
> ...,mq=on,guest_csum=off,...
>
> After that are you installing the xdp program on all interfaces that can
> be used for forwarding? ie., if it transmits a packet in XDP mode it
> needs the xdp program loaded. For example I use:
>
> xdp_fwd eth1 eth2 eth3 eth4
>
>
> From there:
>
> echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> cat /sys/kernel/debug/tracing/trace_pipe
>
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