selftests: rds: Fix gcov collection

debugfs is not mounted automatically in a virtme-ng 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, which causes
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>
Link: https://patch.msgid.link/20260504054143.4027538-10-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/rds/run.sh

@@ -215,6 +215,12 @@ fi
 
 if [[ -n "$LOG_DIR" ]] && [ "$GENERATE_GCOV_REPORT" -eq 1 ]; then
        echo saving coverage data...
+
+       # Ensure debugfs is mounted before reading gcov data.
+       if ! mountpoint -q /sys/kernel/debug 2>/dev/null; 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
@@ -223,7 +229,7 @@ if [[ -n "$LOG_DIR" ]] && [ "$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