selftests: drv-net: add checksum tests

Run tools/testing/selftest/net/csum.c as part of drv-net.
This binary covers multiple scenarios, based on arguments given,
for both IPv4 and IPv6:

- Accept UDP correct checksum
- Detect UDP invalid checksum
- Accept TCP correct checksum
- Detect TCP invalid checksum

- Transmit UDP: basic checksum offload
- Transmit UDP: zero checksum conversion

The test direction is reversed between receive and transmit tests, so
that the NIC under test is always the local machine.

In total this adds up to 12 testcases, with more to follow. For
conciseness, I replaced individual functions with a function factory.

Also detect hardware offload feature availability using Ethtool
netlink and skip tests when either feature is off. This need may be
common for offload feature tests and eventually deserving of a thin
wrapper in lib.py.

Missing are the PF_PACKET based send tests ('-P'). These use
virtio_net_hdr to program hardware checksum offload. Which requires
looking up the local MAC address and (harder) the MAC of the next hop.
I'll have to give it some though how to do that robustly and where
that code would belong.

Tested:

        make -C tools/testing/selftests/ \
                TARGETS="drivers/net drivers/net/hw" \
                install INSTALL_PATH=/tmp/ksft
        cd /tmp/ksft

	sudo NETIF=ens4 REMOTE_TYPE=ssh \
		REMOTE_ARGS="root@10.40.0.2" \
		LOCAL_V4="10.40.0.1" \
		REMOTE_V4="10.40.0.2" \
		./run_kselftest.sh -t drivers/net/hw:csum.py

Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20240507154216.501111-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

5 files changed, 9 insertions, 2 deletions

diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index d996a0ab0765..74ae1068229c 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -2,7 +2,6 @@
 bind_bhash
 bind_timewait
 bind_wildcard
-csum
 cmsg_sender
 diag_uid
 fin_ack_lat
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 5befca249452..052c21438dc4 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -81,7 +81,6 @@ TEST_PROGS += test_ingress_egress_chaining.sh
 TEST_GEN_PROGS += so_incoming_cpu
 TEST_PROGS += sctp_vrf.sh
 TEST_GEN_FILES += sctp_hello
-TEST_GEN_FILES += csum
 TEST_GEN_FILES += ip_local_port_range
 TEST_GEN_FILES += bind_wildcard
 TEST_PROGS += test_vxlan_mdb.sh
diff --git a/tools/testing/selftests/net/lib/.gitignore b/tools/testing/selftests/net/lib/.gitignore
new file mode 100644
index 000000000000..1ebc6187f421
--- /dev/null
+++ b/tools/testing/selftests/net/lib/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+csum
diff --git a/tools/testing/selftests/net/lib/Makefile b/tools/testing/selftests/net/lib/Makefile
index 48557e6250dd..82c3264b115e 100644
--- a/tools/testing/selftests/net/lib/Makefile
+++ b/tools/testing/selftests/net/lib/Makefile
@@ -1,8 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0
 
+CFLAGS =  -Wall -Wl,--no-as-needed -O2 -g
+CFLAGS += -I../../../../../usr/include/ $(KHDR_INCLUDES)
+# Additional include paths needed by kselftest.h
+CFLAGS += -I../../
+
 TEST_FILES := ../../../../../Documentation/netlink/specs
 TEST_FILES += ../../../../net/ynl
 
+TEST_GEN_FILES += csum
+
 TEST_INCLUDES := $(wildcard py/*.py)
 
 include ../../lib.mk
diff --git a/tools/testing/selftests/net/csum.c b/tools/testing/selftests/net/lib/csum.c
index b9f3fc3c3426..b9f3fc3c3426 100644
--- a/tools/testing/selftests/net/csum.c
+++ b/tools/testing/selftests/net/lib/csum.c