[xdp-hints] Re: [RFC net-next v4 8/8] selftests/bpf: Add TX side to xdp_hw_metadata

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Stanislav Fomichev wrote:
> When we get packets on port 9091, we swap src/dst and send it out.
> At this point, we also request the timestamp and plumb it back
> to the userspace. The userspace simply prints the timestamp.
> 
> Also print current UDP checksum, rewrite it with the pseudo-header
> checksum and offload TX checksum calculation to devtx. Upon
> completion, report TX checksum back (mlx5 doesn't put it back, so
> I've used tcpdump to confirm that the checksum is correct).
> 
> Some other related changes:
> - switched to zerocopy mode by default; new flag can be used to force
>   old behavior
> - request fixed TX_METADATA_LEN headroom
> - some other small fixes (umem size, fill idx+i, etc)
> 
> mvbz3:~# ./xdp_hw_metadata eth3 -c mlx5e_devtx_complete_xdp -s mlx5e_devtx_submit_xd
> attach rx bpf program...
> ...
> 0x206d298: rx_desc[0]->addr=80100 addr=80100 comp_addr=80100
> rx_hash: 0x2BFB7FEC with RSS type:0x2A
> rx_timestamp:  1690238278345877848 (sec:1690238278.3459)
> XDP RX-time:   1690238278538397674 (sec:1690238278.5384) delta sec:0.1925 (192519.826 usec)
> AF_XDP time:   1690238278538515250 (sec:1690238278.5385) delta sec:0.0001 (117.576 usec)
> 0x206d298: ping-pong with csum=8e3b (want 57c9) csum_start=54 csum_offset=6
> 0x206d298: complete tx idx=0 addr=10
> 0x206d298: tx_timestamp:  1690238278577008140 (sec:1690238278.5770)
> 0x206d298: complete rx idx=128 addr=80100
> 
> mvbz4:~# nc  -Nu -q1 ${MVBZ3_LINK_LOCAL_IP}%eth3 9091
> 
> mvbz4:~# tcpdump -vvx -i eth3 udp
> tcpdump: listening on eth3, link-type EN10MB (Ethernet), snapshot length 262144 bytes
> 10:12:43.901436 IP6 (flowlabel 0x7a5d2, hlim 127, next-header UDP (17) payload length: 11) fe80::1270:fdff:fe48:1087.44339 > fe80::1270:fdff:fe48:1077.9091: [bad udp cksum 0x3b8e -> 0x0b4b!] UDP, length 3
>         0x0000:  6007 a5d2 000b 117f fe80 0000 0000 0000
>         0x0010:  1270 fdff fe48 1087 fe80 0000 0000 0000
>         0x0020:  1270 fdff fe48 1077 ad33 2383 000b 3b8e
>         0x0030:  7864 70
> 10:12:43.902125 IP6 (flowlabel 0x7a5d2, hlim 127, next-header UDP (17) payload length: 11) fe80::1270:fdff:fe48:1077.9091 > fe80::1270:fdff:fe48:1087.44339: [udp sum ok] UDP, length 3
>         0x0000:  6007 a5d2 000b 117f fe80 0000 0000 0000
>         0x0010:  1270 fdff fe48 1077 fe80 0000 0000 0000
>         0x0020:  1270 fdff fe48 1087 2383 ad33 000b 0b4b
>         0x0030:  7864 70
> 
> Signed-off-by: Stanislav Fomichev <sdf@google.com>
> ---
>  tools/testing/selftests/bpf/xdp_hw_metadata.c | 201 +++++++++++++++++-
>  1 file changed, 191 insertions(+), 10 deletions(-)
> 

> +static void usage(const char *prog)
> +{
> +	fprintf(stderr,
> +		"usage: %s [OPTS] <ifname>\n"
> +		"OPTS:\n"
> +		"    -T    don't generate AF_XDP reply (rx metadata only)\n"
> +		"    -Z    run in copy mode\n",

nit: makes more sense to call copy mode 'C', rather than 'Z'