[PATCH net-next v1 4/6] selftests: rds: Fix gcov and pcap collection

Allison Henderson
2026-04-27T23:29:31Z

The vng guest shares the host filesystem via 9p and runs a minimal
systemd inherited from the host's /lib/systemd/system/. As a result,
which filesystems get auto-mounted in the guest depends on the host OS
and its systemd version.

The tcpdump pcaps are initially saved to /tmp because 9p does not support
chown which tcpdump requires. But whether /tmp is already a tmpfs depends
on the host's systemd configuration and may still sometimes fail if /tmp
is not mounted by default. Fix this by mounting tmpfs on /tmp in run.sh
when it is not already a separately mounted filesystem.

A similar dependency exists for gcov. debugfs is not mounted automatically
in vng guest, so the gcov data copy from /sys/kernel/debug/gcov/
silently finds nothing depending on whether debugfs is mounted by default
on the host OS. Fix this by mounting debugfs in run.sh before copying the
gcda files.

Finally, when invoked through the kselftest runner, the working directory
is the test directory rather than the kernel source root. gcovr defaults
--root to the current working directory, causing it to filter out all
coverage data for files under net/rds/ since they are not under the test
directory. Fix this by passing --root to gcovr explicitly.

Signed-off-by: Allison Henderson <achender@kernel.org>
---
tools/testing/selftests/net/rds/run.sh | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/rds/run.sh b/tools/testing/selftests/net/rds/run.sh
index bc2e53126aab..3fc116d23410 100755
--- a/tools/testing/selftests/net/rds/run.sh
+++ b/tools/testing/selftests/net/rds/run.sh
@@ -197,6 +197,13 @@ COVR_DIR="${LOG_DIR}/coverage/"
mkdir -p "$LOG_DIR"
mkdir -p "$COVR_DIR"

+# tcpdump saves pcaps to /tmp because it requires chown to save the
+# pcap but chown is not supported by 9p. Mount tmpfs on /tmp if it is
+# not already a separate filesystem
+if ! mountpoint -q /tmp 2>/dev/null; then
+ mount -t tmpfs tmpfs /tmp
+fi
+
set +e
echo running RDS tests...
echo Traces will be logged to "$TRACE_FILE"
@@ -210,6 +217,12 @@ dmesg > "${LOG_DIR}/dmesg.out"

if [ "$GENERATE_GCOV_REPORT" -eq 1 ]; then
echo saving coverage data...
+
+ # Ensure debugfs is mounted
+ if ! test -d /sys/kernel/debug/gcov; then
+ mount -t debugfs debugfs /sys/kernel/debug 2>/dev/null || true
+ fi
+
(set +x; cd /sys/kernel/debug/gcov; find ./* -name '*.gcda' | \
while read -r f
do
@@ -218,7 +231,7 @@ if [ "$GENERATE_GCOV_REPORT" -eq 1 ]; then

echo running gcovr...
gcovr -s --html-details --gcov-executable "$GCOV_CMD" --gcov-ignore-parse-errors \
- -o "${COVR_DIR}/gcovr" "${ksrc_dir}/net/rds/"
+ --root "${ksrc_dir}" -o "${COVR_DIR}/gcovr" "${ksrc_dir}/net/rds/"
else
echo "Coverage report will be skipped"
fi
--
2.25.1