[PATCH net-next] selftests/net: convert so_txtime to drv-net

[PATCH net-next] selftests/net: convert so_txtime to drv-net

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

In preparation for extending to pacing hardware offload, convert the
so_txtime.sh test to a drv-net test that can be run against netdevsim
and real hardware.

Also move so_txtime.c to lib so that it is easily accessible for the
new drv-net test, similar to gro.c in commit 8888bf4fb980 ("selftests:
net: move gro to lib for HW vs SW reuse").

Also update so_txtime.c to not exit on first failure, but run to
completion and report exit code there. This helps with debugging
unexpected results, especially when processing multiple packets,
as in the "reverse_order" testcase.

Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 tools/testing/selftests/drivers/net/Makefile  |   1 +
 tools/testing/selftests/drivers/net/config    |   2 +
 .../selftests/drivers/net/so_txtime.py        |  87 ++++++++++++++
 tools/testing/selftests/net/.gitignore        |   1 -
 tools/testing/selftests/net/Makefile          |   2 -
 tools/testing/selftests/net/lib/.gitignore    |   1 +
 tools/testing/selftests/net/lib/Makefile      |   1 +
 .../selftests/net/{ => lib}/so_txtime.c       |  25 +++-
 tools/testing/selftests/net/so_txtime.sh      | 110 ------------------
 9 files changed, 111 insertions(+), 119 deletions(-)
 create mode 100755 tools/testing/selftests/drivers/net/so_txtime.py
 rename tools/testing/selftests/net/{ => lib}/so_txtime.c (97%)
 delete mode 100755 tools/testing/selftests/net/so_txtime.sh

diff --git a/tools/testing/selftests/drivers/net/Makefile b/tools/testing/selftests/drivers/net/Makefile
index 7c7fa75b80c2..bfa72e07ca89 100644
--- a/tools/testing/selftests/drivers/net/Makefile
+++ b/tools/testing/selftests/drivers/net/Makefile
@@ -20,6 +20,7 @@ TEST_PROGS := \
 	queues.py \
 	ring_reconfig.py \
 	shaper.py \
+	so_txtime.py \
 	stats.py \
 	xdp.py \
 # end of TEST_PROGS
diff --git a/tools/testing/selftests/drivers/net/config b/tools/testing/selftests/drivers/net/config
index 77ccf83d87e0..a3301d4da540 100644
--- a/tools/testing/selftests/drivers/net/config
+++ b/tools/testing/selftests/drivers/net/config
@@ -3,6 +3,8 @@ CONFIG_DEBUG_INFO_BTF=y
 CONFIG_DEBUG_INFO_BTF_MODULES=n
 CONFIG_INET_PSP=y
 CONFIG_IPV6=y
+CONFIG_NET_SCH_ETF=m
+CONFIG_NET_SCH_FQ=m
 CONFIG_NETCONSOLE=m
 CONFIG_NETCONSOLE_DYNAMIC=y
 CONFIG_NETCONSOLE_EXTENDED_LOG=y
diff --git a/tools/testing/selftests/drivers/net/so_txtime.py b/tools/testing/selftests/drivers/net/so_txtime.py
new file mode 100755
index 000000000000..565cecf307dd
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/so_txtime.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+"""Regression tests for the SO_TXTIME interface.
+
+Test delivery time in FQ and ETF qdiscs.
+"""
+
+import time
+
+from lib.py import ksft_exit, ksft_run
+from lib.py import KsftNamedVariant, KsftSkipEx, ksft_variants
+from lib.py import NetDrvEpEnv, bkg, cmd
+
+
+def test_so_txtime(cfg, clockid, ipver, args_tx, args_rx, expect_fail):
+  bin_path = cfg.net_lib_dir / "so_txtime"
+
+  tstart = time.time_ns() + 100_000_000
+
+  cmd_addr = f"-S {cfg.addr_v[ipver]} -D {cfg.remote_addr_v[ipver]}"
+  cmd_base = f"{bin_path} -{ipver} -c {clockid} -t {tstart} {cmd_addr}"
+  cmd_rx = f"{cmd_base} {args_rx} -r"
+  cmd_tx = f"{cmd_base} {args_tx}"
+
+  try:
+    with bkg(cmd_rx, host=cfg.remote, exit_wait=True):
+      cmd(cmd_tx)
+  except:
+    if not expect_fail:
+      raise
+
+
+def _test_variants_mono():
+  for ipver in ["4", "6"]:
+    for testcase in [
+        ["no_delay", "a,-1", "a,-1"],
+        ["zero_delay", "a,0", "a,0"],
+        ["one_pkt", "a,10", "a,10"],
+        ["in_order", "a,10,b,20", "a,10,b,20"],
+        ["reverse_order", "a,20,b,10", "b,20,a,20"],
+    ]:
+      name = f"_v{ipver}_{testcase[0]}"
+      yield KsftNamedVariant(name, ipver, testcase[1], testcase[2])
+
+
+@ksft_variants(_test_variants_mono())
+def test_so_txtime_mono(cfg, ipver, args_tx, args_rx):
+  cmd(f"tc qdisc replace dev {cfg.ifname} root fq")
+  test_so_txtime(cfg, "mono", ipver, args_tx, args_rx, False)
+
+
+def _test_variants_etf():
+  for ipver in ["4", "6"]:
+    for testcase in [
+        ["no_delay", "a,-1", "a,-1", True],
+        ["zero_delay", "a,0", "a,0", True],
+        ["one_pkt", "a,10", "a,10", False],
+        ["in_order", "a,10,b,20", "a,10,b,20", False],
+        ["reverse_order", "a,20,b,10", "b,10,a,20", False],
+    ]:
+      name = f"_v{ipver}_{testcase[0]}"
+      yield KsftNamedVariant(name, ipver, testcase[1], testcase[2], testcase[3])
+
+
+@ksft_variants(_test_variants_etf())
+def test_so_txtime_etf(cfg, ipver, args_tx, args_rx, expect_fail):
+  try:
+    # ETF does not support change, so remove and re-add it instead.
+    cmd(f"tc qdisc replace dev {cfg.ifname} root pfifo_fast")
+    etf_args = "clockid CLOCK_TAI delta 400000"
+    cmd(f"tc qdisc replace dev {cfg.ifname} root etf {etf_args}")
+  except Exception as e:
+    raise KsftSkipEx("tc does not support qdisc etf. skipping") from e
+
+  test_so_txtime(cfg, "tai", ipver, args_tx, args_rx, expect_fail)
+
+
+def main() -> None:
+  with NetDrvEpEnv(__file__) as cfg:
+    ksft_run([test_so_txtime_mono], args=(cfg,))
+    ksft_run([test_so_txtime_etf], args=(cfg,))
+  ksft_exit()
+
+
+if __name__ == "__main__":
+  main()
diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index 97ad4d551d44..02ad4c99a2b4 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -40,7 +40,6 @@ skf_net_off
 socket
 so_incoming_cpu
 so_netns_cookie
-so_txtime
 so_rcv_listener
 stress_reuseport_listen
 tap
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 6bced3ed798b..b7f51e8f190f 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -81,7 +81,6 @@ TEST_PROGS := \
 	rxtimestamp.sh \
 	sctp_vrf.sh \
 	skf_net_off.sh \
-	so_txtime.sh \
 	srv6_end_dt46_l3vpn_test.sh \
 	srv6_end_dt4_l3vpn_test.sh \
 	srv6_end_dt6_l3vpn_test.sh \
@@ -154,7 +153,6 @@ TEST_GEN_FILES := \
 	skf_net_off \
 	so_netns_cookie \
 	so_rcv_listener \
-	so_txtime \
 	socket \
 	stress_reuseport_listen \
 	tcp_fastopen_backup_key \
diff --git a/tools/testing/selftests/net/lib/.gitignore b/tools/testing/selftests/net/lib/.gitignore
index 6cd2b762af5d..c57d22e72c75 100644
--- a/tools/testing/selftests/net/lib/.gitignore
+++ b/tools/testing/selftests/net/lib/.gitignore
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-only
 csum
 gro
+so_txtime
 xdp_helper
diff --git a/tools/testing/selftests/net/lib/Makefile b/tools/testing/selftests/net/lib/Makefile
index ff83603397d0..8c50b6631524 100644
--- a/tools/testing/selftests/net/lib/Makefile
+++ b/tools/testing/selftests/net/lib/Makefile
@@ -15,6 +15,7 @@ TEST_GEN_FILES := \
 	$(patsubst %.c,%.o,$(wildcard *.bpf.c)) \
 	csum \
 	gro \
+	so_txtime \
 	xdp_helper \
 # end of TEST_GEN_FILES
 
diff --git a/tools/testing/selftests/net/so_txtime.c b/tools/testing/selftests/net/lib/so_txtime.c
similarity index 97%
rename from tools/testing/selftests/net/so_txtime.c
rename to tools/testing/selftests/net/lib/so_txtime.c
index b76df1efc2ef..6583e1a83758 100644
--- a/tools/testing/selftests/net/so_txtime.c
+++ b/tools/testing/selftests/net/lib/so_txtime.c
@@ -33,6 +33,8 @@
 #include <unistd.h>
 #include <poll.h>
 
+#include "kselftest.h"
+
 static int	cfg_clockid	= CLOCK_TAI;
 static uint16_t	cfg_port	= 8000;
 static int	cfg_variance_us	= 4000;
@@ -43,6 +45,8 @@ static bool	cfg_rx;
 static uint64_t glob_tstart;
 static uint64_t tdeliver_max;
 
+static int errors;
+
 /* encode one timed transmission (of a 1B payload) */
 struct timed_send {
 	char	data;
@@ -131,13 +135,15 @@ static void do_recv_one(int fdr, struct timed_send *ts)
 	fprintf(stderr, "payload:%c delay:%lld expected:%lld (us)\n",
 			rbuf[0], (long long)tstop, (long long)texpect);
 
-	if (rbuf[0] != ts->data)
-		error(1, 0, "payload mismatch. expected %c", ts->data);
+	if (rbuf[0] != ts->data) {
+		fprintf(stderr, "payload mismatch. expected %c", ts->data);
+		errors++;
+	}
 
 	if (llabs(tstop - texpect) > cfg_variance_us) {
 		fprintf(stderr, "exceeds variance (%d us)\n", cfg_variance_us);
 		if (!getenv("KSFT_MACHINE_SLOW"))
-			exit(1);
+			errors++;
 	}
 }
 
@@ -255,8 +261,10 @@ static void start_time_wait(void)
 		return;
 
 	now = gettime_ns(CLOCK_REALTIME);
-	if (cfg_start_time_ns < now)
-		return;
+	if (cfg_start_time_ns < now) {
+		fprintf(stderr, "FAIL: start time already passed\n");
+		errors++;
+	}
 
 	err = usleep((cfg_start_time_ns - now) / 1000);
 	if (err)
@@ -513,5 +521,10 @@ int main(int argc, char **argv)
 	else
 		do_test_tx((void *)&cfg_src_addr, cfg_alen);
 
-	return 0;
+	if (errors) {
+		fprintf(stderr, "FAIL: %d errors\n", errors);
+		return KSFT_FAIL;
+	}
+
+	return KSFT_PASS;
 }
diff --git a/tools/testing/selftests/net/so_txtime.sh b/tools/testing/selftests/net/so_txtime.sh
deleted file mode 100755
index 5e861ad32a42..000000000000
--- a/tools/testing/selftests/net/so_txtime.sh
+++ /dev/null
@@ -1,110 +0,0 @@
-#!/bin/bash
-# SPDX-License-Identifier: GPL-2.0
-#
-# Regression tests for the SO_TXTIME interface
-
-set -e
-
-readonly ksft_skip=4
-readonly DEV="veth0"
-readonly BIN="./so_txtime"
-
-readonly RAND="$(mktemp -u XXXXXX)"
-readonly NSPREFIX="ns-${RAND}"
-readonly NS1="${NSPREFIX}1"
-readonly NS2="${NSPREFIX}2"
-
-readonly SADDR4='192.168.1.1'
-readonly DADDR4='192.168.1.2'
-readonly SADDR6='fd::1'
-readonly DADDR6='fd::2'
-
-cleanup() {
-	ip netns del "${NS2}"
-	ip netns del "${NS1}"
-}
-
-trap cleanup EXIT
-
-# Create virtual ethernet pair between network namespaces
-ip netns add "${NS1}"
-ip netns add "${NS2}"
-
-ip link add "${DEV}" netns "${NS1}" type veth \
-  peer name "${DEV}" netns "${NS2}"
-
-# Bring the devices up
-ip -netns "${NS1}" link set "${DEV}" up
-ip -netns "${NS2}" link set "${DEV}" up
-
-# Set fixed MAC addresses on the devices
-ip -netns "${NS1}" link set dev "${DEV}" address 02:02:02:02:02:02
-ip -netns "${NS2}" link set dev "${DEV}" address 06:06:06:06:06:06
-
-# Add fixed IP addresses to the devices
-ip -netns "${NS1}" addr add 192.168.1.1/24 dev "${DEV}"
-ip -netns "${NS2}" addr add 192.168.1.2/24 dev "${DEV}"
-ip -netns "${NS1}" addr add       fd::1/64 dev "${DEV}" nodad
-ip -netns "${NS2}" addr add       fd::2/64 dev "${DEV}" nodad
-
-run_test() {
-	local readonly IP="$1"
-	local readonly CLOCK="$2"
-	local readonly TXARGS="$3"
-	local readonly RXARGS="$4"
-
-	if [[ "${IP}" == "4" ]]; then
-		local readonly SADDR="${SADDR4}"
-		local readonly DADDR="${DADDR4}"
-	elif [[ "${IP}" == "6" ]]; then
-		local readonly SADDR="${SADDR6}"
-		local readonly DADDR="${DADDR6}"
-	else
-		echo "Invalid IP version ${IP}"
-		exit 1
-	fi
-
-	local readonly START="$(date +%s%N --date="+ 0.1 seconds")"
-
-	ip netns exec "${NS2}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${RXARGS}" -r &
-	ip netns exec "${NS1}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${TXARGS}"
-	wait "$!"
-}
-
-do_test() {
-	run_test $@
-	[ $? -ne 0 ] && ret=1
-}
-
-do_fail_test() {
-	run_test $@
-	[ $? -eq 0 ] && ret=1
-}
-
-ip netns exec "${NS1}" tc qdisc add dev "${DEV}" root fq
-set +e
-ret=0
-do_test 4 mono a,-1 a,-1
-do_test 6 mono a,0 a,0
-do_test 6 mono a,10 a,10
-do_test 4 mono a,10,b,20 a,10,b,20
-do_test 6 mono a,20,b,10 b,20,a,20
-
-if ip netns exec "${NS1}" tc qdisc replace dev "${DEV}" root etf clockid CLOCK_TAI delta 400000; then
-	do_fail_test 4 tai a,-1 a,-1
-	do_fail_test 6 tai a,0 a,0
-	do_test 6 tai a,10 a,10
-	do_test 4 tai a,10,b,20 a,10,b,20
-	do_test 6 tai a,20,b,10 b,10,a,20
-else
-	echo "tc ($(tc -V)) does not support qdisc etf. skipping"
-	[ $ret -eq 0 ] && ret=$ksft_skip
-fi
-
-if [ $ret -eq 0 ]; then
-	echo OK. All tests passed
-elif [[ $ret -ne $ksft_skip && -n "$KSFT_MACHINE_SLOW" ]]; then
-	echo "Ignoring errors due to slow environment" 1>&2
-	ret=0
-fi
-exit $ret
-- 
2.53.0.1213.gd9a14994de-goog

Re: [PATCH net-next] selftests/net: convert so_txtime to drv-net

[Willem de Bruijn]

Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> In preparation for extending to pacing hardware offload, convert the
> so_txtime.sh test to a drv-net test that can be run against netdevsim
> and real hardware.
> 
> Also move so_txtime.c to lib so that it is easily accessible for the
> new drv-net test, similar to gro.c in commit 8888bf4fb980 ("selftests:
> net: move gro to lib for HW vs SW reuse").
> 
> Also update so_txtime.c to not exit on first failure, but run to
> completion and report exit code there. This helps with debugging
> unexpected results, especially when processing multiple packets,
> as in the "reverse_order" testcase.
> 
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Sashiko already has a few correct comments (below). Will fix in v2.

Also, indentation incorrectly uses 2 instead of 4 spaces.

> +def test_so_txtime(cfg, clockid, ipver, args_tx, args_rx, expect_fail):
> +  bin_path = cfg.net_lib_dir / "so_txtime"
> +
> +  tstart = time.time_ns() + 100_000_000
> +
> +  cmd_addr = f"-S {cfg.addr_v[ipver]} -D {cfg.remote_addr_v[ipver]}"
> +  cmd_base = f"{bin_path} -{ipver} -c {clockid} -t {tstart} {cmd_addr}"
> +  cmd_rx = f"{cmd_base} {args_rx} -r"
> +  cmd_tx = f"{cmd_base} {args_tx}"
> +
> +  try:
> +    with bkg(cmd_rx, host=cfg.remote, exit_wait=True):
> +      cmd(cmd_tx)
> +  except:
> +    if not expect_fail:
> +      raise

Also test against a test succeeding when failure is expected. Will add
an else: clause.


> @@ -131,13 +135,15 @@ static void do_recv_one(int fdr, struct timed_send *ts)
>  	fprintf(stderr, "payload:%c delay:%lld expected:%lld (us)\n",
>  			rbuf[0], (long long)tstop, (long long)texpect);
>  
> -	if (rbuf[0] != ts->data)
> -		error(1, 0, "payload mismatch. expected %c", ts->data);
> +	if (rbuf[0] != ts->data) {
> +		fprintf(stderr, "payload mismatch. expected %c", ts->data);

Add \n when converting from error to fprintf

> @@ -255,8 +261,10 @@ static void start_time_wait(void)
>  		return;
>  
>  	now = gettime_ns(CLOCK_REALTIME);
> -	if (cfg_start_time_ns < now)
> -		return;
> +	if (cfg_start_time_ns < now) {
> +		fprintf(stderr, "FAIL: start time already passed\n");
> +		errors++;
> +	}
>  
>  	err = usleep((cfg_start_time_ns - now) / 1000);

Do not call usleep when already late: uint64_t will have negative
overflow. Also, waiting makes no sense when late. Add return to the
error branch.

Re: [PATCH net-next] selftests/net: convert so_txtime to drv-net

[Jakub Kicinski]

On Fri,  3 Apr 2026 13:50:12 -0400 Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> In preparation for extending to pacing hardware offload, convert the
> so_txtime.sh test to a drv-net test that can be run against netdevsim
> and real hardware.
> 
> Also move so_txtime.c to lib so that it is easily accessible for the
> new drv-net test, similar to gro.c in commit 8888bf4fb980 ("selftests:
> net: move gro to lib for HW vs SW reuse").
> 
> Also update so_txtime.c to not exit on first failure, but run to
> completion and report exit code there. This helps with debugging
> unexpected results, especially when processing multiple packets,
> as in the "reverse_order" testcase.

> diff --git a/tools/testing/selftests/drivers/net/config b/tools/testing/selftests/drivers/net/config
> index 77ccf83d87e0..a3301d4da540 100644
> --- a/tools/testing/selftests/drivers/net/config
> +++ b/tools/testing/selftests/drivers/net/config
> @@ -3,6 +3,8 @@ CONFIG_DEBUG_INFO_BTF=y
>  CONFIG_DEBUG_INFO_BTF_MODULES=n
>  CONFIG_INET_PSP=y
>  CONFIG_IPV6=y
> +CONFIG_NET_SCH_ETF=m
> +CONFIG_NET_SCH_FQ=m

I think our sort order puts _ after characters

>  CONFIG_NETCONSOLE=m
>  CONFIG_NETCONSOLE_DYNAMIC=y
>  CONFIG_NETCONSOLE_EXTENDED_LOG=y
> diff --git a/tools/testing/selftests/drivers/net/so_txtime.py b/tools/testing/selftests/drivers/net/so_txtime.py
> new file mode 100755
> index 000000000000..565cecf307dd
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/net/so_txtime.py
> @@ -0,0 +1,87 @@
> +#!/usr/bin/env python3
> +# SPDX-License-Identifier: GPL-2.0
> +
> +"""Regression tests for the SO_TXTIME interface.
> +
> +Test delivery time in FQ and ETF qdiscs.
> +"""

> +import time
> +
> +from lib.py import ksft_exit, ksft_run
> +from lib.py import KsftNamedVariant, KsftSkipEx, ksft_variants
> +from lib.py import NetDrvEpEnv, bkg, cmd
> +
> +
> +def test_so_txtime(cfg, clockid, ipver, args_tx, args_rx, expect_fail):
> +  bin_path = cfg.net_lib_dir / "so_txtime"
> +
> +  tstart = time.time_ns() + 100_000_000
> +
> +  cmd_addr = f"-S {cfg.addr_v[ipver]} -D {cfg.remote_addr_v[ipver]}"
> +  cmd_base = f"{bin_path} -{ipver} -c {clockid} -t {tstart} {cmd_addr}"
> +  cmd_rx = f"{cmd_base} {args_rx} -r"
> +  cmd_tx = f"{cmd_base} {args_tx}"
> +
> +  try:
> +    with bkg(cmd_rx, host=cfg.remote, exit_wait=True):
> +      cmd(cmd_tx)
> +  except:
> +    if not expect_fail:
> +      raise

ruff check says:
tools/testing/selftests/drivers/net/so_txtime.py:29: [E722] Do not use bare `except`

Why not pass fail=(not expect_fail) to bkg ?

> +def main() -> None:

pylint --disable=R should be clean, please
I usually add something like:

	"""Boilerplate ksft main"""

> +  with NetDrvEpEnv(__file__) as cfg:
> +    ksft_run([test_so_txtime_mono], args=(cfg,))
> +    ksft_run([test_so_txtime_etf], args=(cfg,))

ksft_run() is not supposed to be called multiple times, it will break
KTAP format

> diff --git a/tools/testing/selftests/net/lib/Makefile b/tools/testing/selftests/net/lib/Makefile
> index ff83603397d0..8c50b6631524 100644
> --- a/tools/testing/selftests/net/lib/Makefile
> +++ b/tools/testing/selftests/net/lib/Makefile
> @@ -15,6 +15,7 @@ TEST_GEN_FILES := \
>  	$(patsubst %.c,%.o,$(wildcard *.bpf.c)) \
>  	csum \
>  	gro \
> +	so_txtime \

is there a reason for the binary to be in lib?
gro is used by drivers/net and drivers/net/hw
if the C helper / binary is only used by a single target it should live
in the same dir as the python code

Re: [PATCH net-next] selftests/net: convert so_txtime to drv-net

[Willem de Bruijn]

Jakub Kicinski wrote:
> On Fri,  3 Apr 2026 13:50:12 -0400 Willem de Bruijn wrote:
> > From: Willem de Bruijn <willemb@google.com>
> > 
> > In preparation for extending to pacing hardware offload, convert the
> > so_txtime.sh test to a drv-net test that can be run against netdevsim
> > and real hardware.
> > 
> > Also move so_txtime.c to lib so that it is easily accessible for the
> > new drv-net test, similar to gro.c in commit 8888bf4fb980 ("selftests:
> > net: move gro to lib for HW vs SW reuse").
> > 
> > Also update so_txtime.c to not exit on first failure, but run to
> > completion and report exit code there. This helps with debugging
> > unexpected results, especially when processing multiple packets,
> > as in the "reverse_order" testcase.
> 
> > diff --git a/tools/testing/selftests/drivers/net/config b/tools/testing/selftests/drivers/net/config
> > index 77ccf83d87e0..a3301d4da540 100644
> > --- a/tools/testing/selftests/drivers/net/config
> > +++ b/tools/testing/selftests/drivers/net/config
> > @@ -3,6 +3,8 @@ CONFIG_DEBUG_INFO_BTF=y
> >  CONFIG_DEBUG_INFO_BTF_MODULES=n
> >  CONFIG_INET_PSP=y
> >  CONFIG_IPV6=y
> > +CONFIG_NET_SCH_ETF=m
> > +CONFIG_NET_SCH_FQ=m
> 
> I think our sort order puts _ after characters
> 
> >  CONFIG_NETCONSOLE=m
> >  CONFIG_NETCONSOLE_DYNAMIC=y
> >  CONFIG_NETCONSOLE_EXTENDED_LOG=y
> > diff --git a/tools/testing/selftests/drivers/net/so_txtime.py b/tools/testing/selftests/drivers/net/so_txtime.py
> > new file mode 100755
> > index 000000000000..565cecf307dd
> > --- /dev/null
> > +++ b/tools/testing/selftests/drivers/net/so_txtime.py
> > @@ -0,0 +1,87 @@
> > +#!/usr/bin/env python3
> > +# SPDX-License-Identifier: GPL-2.0
> > +
> > +"""Regression tests for the SO_TXTIME interface.
> > +
> > +Test delivery time in FQ and ETF qdiscs.
> > +"""
> 
> > +import time
> > +
> > +from lib.py import ksft_exit, ksft_run
> > +from lib.py import KsftNamedVariant, KsftSkipEx, ksft_variants
> > +from lib.py import NetDrvEpEnv, bkg, cmd
> > +
> > +
> > +def test_so_txtime(cfg, clockid, ipver, args_tx, args_rx, expect_fail):
> > +  bin_path = cfg.net_lib_dir / "so_txtime"
> > +
> > +  tstart = time.time_ns() + 100_000_000
> > +
> > +  cmd_addr = f"-S {cfg.addr_v[ipver]} -D {cfg.remote_addr_v[ipver]}"
> > +  cmd_base = f"{bin_path} -{ipver} -c {clockid} -t {tstart} {cmd_addr}"
> > +  cmd_rx = f"{cmd_base} {args_rx} -r"
> > +  cmd_tx = f"{cmd_base} {args_tx}"
> > +
> > +  try:
> > +    with bkg(cmd_rx, host=cfg.remote, exit_wait=True):
> > +      cmd(cmd_tx)
> > +  except:
> > +    if not expect_fail:
> > +      raise
> 
> ruff check says:
> tools/testing/selftests/drivers/net/so_txtime.py:29: [E722] Do not use bare `except`
> 
> Why not pass fail=(not expect_fail) to bkg ?

That's indeed a lot simpler.

Thanks for the feedback! Will include all these changes in v2.