selftests: drv-net: so_txtime: only send test traffic to sch_etf

The ETF qdiscs drops traffic without a socket or txtime. Even with
parameter skip_sock_check regular traffic is affected by ETF.

This test ran fine when run manually in a pure software environment.
But with drv-net across two hosts tests fail as early as when calling
cfg.remote.deploy due to effectively losing connectivity.

Isolate the intended test traffic:
- mark that with SO_MARK 100
- install a regular permissive root prio qdisc for background traffic
- install the ETF qdisc as leaf
- install a filter that only directs SO_MARK 100 traffic to this leaf

Technically other high prio traffic will map onto this leaf based on
ToS band mapping too. But that is immaterial in practice.

Fixes: 5c6baef388 ("selftests: drv-net: convert so_txtime to drv-net")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260808160129.890119-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/config

@@ -8,6 +8,7 @@ CONFIG_NET_ACT_SKBEDIT=m
 CONFIG_NET_CLS_ACT=y
 CONFIG_NET_CLS_BPF=y
 CONFIG_NET_CLS_FLOWER=m
+CONFIG_NET_CLS_FW=m
 CONFIG_NET_CLS_MATCHALL=m
 CONFIG_NETCONSOLE=m
 CONFIG_NETCONSOLE_DYNAMIC=y
@@ -17,6 +18,7 @@ CONFIG_NETKIT=y
 CONFIG_NET_SCH_ETF=m
 CONFIG_NET_SCH_FQ=m
 CONFIG_NET_SCH_INGRESS=y
+CONFIG_NET_SCH_PRIO=m
 CONFIG_PPP=y
 CONFIG_PPPOE=y
 CONFIG_VLAN_8021Q=m

tools/testing/selftests/drivers/net/so_txtime.py

@@ -27,7 +27,7 @@ def test_so_txtime(cfg, clockid, ipver, args_tx, args_rx, expect_success):
     cmd_addr = f"-S {cfg.addr_v[ipver]} -D {cfg.remote_addr_v[ipver]}"
     cmd_args = f"-{ipver} -c {clockid} -t {tstart} {cmd_addr}"
     cmd_rx = f"{cfg.bin_remote} {cmd_args} {args_rx} -r"
-    cmd_tx = f"{cfg.bin_local} {cmd_args} {args_tx}"
+    cmd_tx = f"{cfg.bin_local} -m 100 {cmd_args} {args_tx}"
 
     expect_fail = not expect_success
     if slow_machine:
@@ -45,7 +45,7 @@ def _qdisc_setup(ifname, qdisc, optargs=""):
     """
     orig = tc(f"qdisc show dev {ifname} root", json=True)[0].get("kind", None)
     defer(tc, f"qdisc replace dev {ifname} root {orig}")
-    tc(f"qdisc replace dev {ifname} root {qdisc} {optargs}")
+    tc(f"qdisc replace dev {ifname} root handle 1: {qdisc} {optargs}")
 
 
 def _test_variants_fq():
@@ -96,11 +96,21 @@ def _test_variants_etf():
 def test_so_txtime_etf(cfg, ipver, args_tx, args_rx, expect_fail):
     """Run all variants of etf tests."""
     cfg.require_ipver(ipver)
+
+    # root qdisc for background traffic (e.g., bkg())
+    _qdisc_setup(cfg.ifname, "prio")
+
+    # leaf ETF qdisc only for intended packets
     try:
-        _qdisc_setup(cfg.ifname, "etf", "clockid CLOCK_TAI delta 400000")
+        etf_args = "clockid CLOCK_TAI delta 400000"
+        tc(f"qdisc add dev {cfg.ifname} parent 1:1 handle 10: etf {etf_args}")
     except Exception as e:
         raise KsftSkipEx("tc does not support qdisc etf. skipping") from e
 
+    # redirect mark 100 to leaf
+    filter_args = "protocol all handle 100 fw flowid 1:1"
+    tc(f"filter add dev {cfg.ifname} parent 1: {filter_args}")
+
     test_so_txtime(cfg, "tai", ipver, args_tx, args_rx, expect_fail)