[PATCH net 2/2] selftests: net: veth: test XDP_TX to a peer with GRO enabled

[Tianyi Gao <tianyi@cloudflare.com>]

Test that XDP_TX frames reach a peer that has GRO enabled and no XDP
program. GRO enables NAPI on the peer, so the frames are queued on the
peer's ring, and the peer's NAPI must be scheduled to process them.

Attach a program that returns XDP_TX for every frame, send 5 echo
requests and check that all of them were sent back and that the peer's
NAPI received them, as counted in its xdp_packets statistic. IPv6 is
disabled on both devices, so that only the echo requests are counted.

Add the program to xdp_dummy.bpf.c in a section of its own, so that the
tests that load "section xdp" still get XDP_PASS.

Signed-off-by: Tianyi Gao <tianyi@cloudflare.com>
---
The XDP_TX program goes into xdp_dummy.bpf.c as a new section instead of
a new file, since it is a single line; 75cc19c8ff89 ("selftests:
drv-net: add xdp cases for ping.py") added the xdp.frags variant there
the same way. libbpf does not know the section name "xdp_tx", but
iproute2 loads it, as tc loads the custom sections in nat6to4.bpf.c.

 .../testing/selftests/net/lib/xdp_dummy.bpf.c |  6 +++++
 tools/testing/selftests/net/veth.sh           | 25 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/tools/testing/selftests/net/lib/xdp_dummy.bpf.c b/tools/testing/selftests/net/lib/xdp_dummy.bpf.c
index e73fab3edd9f..95abd67cc184 100644
--- a/tools/testing/selftests/net/lib/xdp_dummy.bpf.c
+++ b/tools/testing/selftests/net/lib/xdp_dummy.bpf.c
@@ -16,4 +16,10 @@ int xdp_dummy_prog_frags(struct xdp_md *ctx)
 	return XDP_PASS;
 }
 
+SEC("xdp_tx")
+int xdp_dummy_tx(struct xdp_md *ctx)
+{
+	return XDP_TX;
+}
+
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/net/veth.sh b/tools/testing/selftests/net/veth.sh
index 8b867e0675a7..0167f78604ef 100755
--- a/tools/testing/selftests/net/veth.sh
+++ b/tools/testing/selftests/net/veth.sh
@@ -334,6 +334,31 @@ ip netns exec $NS_DST ethtool -K veth$DST rx-udp-gro-forwarding on
 chk_gro "        - aggregation with TSO off" 1
 cleanup
 
+create_ns
+ip netns exec $NS_SRC sysctl -qw net.ipv6.conf.veth$SRC.disable_ipv6=1
+ip netns exec $NS_DST sysctl -qw net.ipv6.conf.veth$DST.disable_ipv6=1
+ip netns exec $NS_SRC ethtool -K veth$SRC gro on
+ip -n $NS_DST link set dev veth$DST xdp object ${BPF_FILE} section xdp_tx
+# veth$DST sends every frame back, so neither ARP nor ping gets an answer
+mac=`ip netns exec $NS_DST cat /sys/class/net/veth$DST/address`
+ip -n $NS_SRC neigh replace $BM_NET_V4$DST lladdr $mac dev veth$SRC
+ip netns exec $NS_SRC ping -qc 5 -i 0.01 -W 1 $BM_NET_V4$DST >/dev/null
+tx=`ip netns exec $NS_DST ethtool -S veth$DST | \
+    awk '/rx_queue_[0-9]+_xdp_tx:/ {s += $2} END {print s + 0}'`
+rx=`ip netns exec $NS_SRC ethtool -S veth$SRC | \
+    awk '/rx_queue_[0-9]+_xdp_packets:/ {s += $2} END {print s + 0}'`
+printf "%-60s" "xdp_tx to peer with gro on"
+if [ $tx -ne 5 ]; then
+	echo " fail - $tx frames sent back, expected 5"
+	ret=1
+elif [ $rx -ne 5 ]; then
+	echo " fail - $rx frames received by the peer NAPI, expected 5"
+	ret=1
+else
+	echo " ok "
+fi
+cleanup
+
 create_ns
 
 CUR_TX=1
-- 
2.55.0