tracing/selftests: Add tracefs mount options test

Add a selftest to check that the tracefs gid mount option is applied
correctly.

   ./ftracetest test.d/00basic/mount_options.tc

Use the new readme string "[gid=<gid>] as a requirement and also update
test_ownership.tc requirements to use this.

Cc: Eric Sandeen <sandeen@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Ali Zahraee <ahzahraee@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/20241030171928.4168869-4-kaleshsingh@google.com
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc

@@ -0,0 +1,101 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test tracefs GID mount option
+# requires: "[gid=<gid>]":README
+
+fail() {
+	local msg="$1"
+
+	echo "FAILED: $msg"
+	exit_fail
+}
+
+find_alternate_gid() {
+	local original_gid="$1"
+	tac /etc/group | grep -v ":$original_gid:" | head -1 | cut -d: -f3
+}
+
+mount_tracefs_with_options() {
+	local mount_point="$1"
+	local options="$2"
+
+	mount -t tracefs -o "$options" nodev "$mount_point"
+
+	setup
+}
+
+unmount_tracefs() {
+	local mount_point="$1"
+
+	# Need to make sure the mount isn't busy so that we can umount it
+	(cd $mount_point; finish_ftrace;)
+
+	cleanup
+}
+
+create_instance() {
+	local mount_point="$1"
+	local instance="$mount_point/instances/$(mktemp -u test-XXXXXX)"
+
+	mkdir "$instance"
+	echo "$instance"
+}
+
+remove_instance() {
+	local instance="$1"
+
+	rmdir "$instance"
+}
+
+check_gid() {
+	local mount_point="$1"
+	local expected_gid="$2"
+
+	echo "Checking permission group ..."
+
+	cd "$mount_point"
+
+	for file in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable"; do
+		local gid=`stat -c "%g" $file`
+		if [ "$gid" -ne "$expected_gid" ]; then
+			cd - # Return to the previous working directory (tracefs root)
+			fail "$(realpath $file): Expected group $expected_gid; Got group $gid"
+		fi
+	done
+
+	cd - # Return to the previous working directory (tracefs root)
+}
+
+test_gid_mount_option() {
+	local mount_point=$(get_mount_point)
+	local mount_options=$(get_mnt_options "$mount_point")
+	local original_group=$(stat -c "%g" .)
+	local other_group=$(find_alternate_gid "$original_group")
+
+	# Set up mount options with new GID for testing
+	local new_options=`echo "$mount_options" | sed -e "s/gid=[0-9]*/gid=$other_group/"`
+	if [ "$new_options" = "$mount_options" ]; then
+		new_options="$mount_options,gid=$other_group"
+		mount_options="$mount_options,gid=$original_group"
+	fi
+
+	# Unmount existing tracefs instance and mount with new GID
+	unmount_tracefs "$mount_point"
+	mount_tracefs_with_options "$mount_point" "$new_options"
+
+	check_gid "$mount_point" "$other_group"
+
+	# Check that files created after the mount inherit the GID
+	local instance=$(create_instance "$mount_point")
+	check_gid "$instance" "$other_group"
+	remove_instance "$instance"
+
+	# Unmount and remount with the original GID
+	unmount_tracefs "$mount_point"
+	mount_tracefs_with_options "$mount_point" "$mount_options"
+	check_gid "$mount_point" "$original_group"
+}
+
+test_gid_mount_option
+
+exit 0

tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc

@@ -1,24 +1,14 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 # description: Test file and directory ownership changes for eventfs
+# requires: "[gid=<gid>]":README
 
 original_group=`stat -c "%g" .`
 original_owner=`stat -c "%u" .`
 
-mount_point=`stat -c '%m' .`
+local mount_point=$(get_mount_point)
 
-# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the
-# current working directory (which should be a tracefs) as the mount point.
-if [ ! -d "$mount_point" ]; then
-	if mount | grep -qw $PWD ; then
-		mount_point=$PWD
-	else
-		# If PWD doesn't work, that is an environmental problem.
-		exit_unresolved
-	fi
-fi
-
-mount_options=`mount | grep "$mount_point" | sed -e 's/.*(\(.*\)).*/\1/'`
+mount_options=$(get_mnt_options "$mount_point")
 
 # find another owner and group that is not the original
 other_group=`tac /etc/group | grep -v ":$original_group:" | head -1 | cut -d: -f3`

tools/testing/selftests/ftrace/test.d/functions

@@ -193,3 +193,28 @@ ftrace_errlog_check() { # err-prefix command-with-error-pos-by-^ command-file
     # "  Command: " and "^\n" => 13
     test $(expr 13 + $pos) -eq $N
 }
+
+# Helper to get the tracefs mount point
+get_mount_point() {
+	local mount_point=`stat -c '%m' .`
+
+	# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the
+	# current working directory (which should be a tracefs) as the mount point.
+	if [ ! -d "$mount_point" ]; then
+		if mount | grep -qw "$PWD"; then
+			mount_point=$PWD
+		else
+			# If PWD doesn't work, that is an environmental problem.
+			exit_unresolved
+		fi
+	fi
+	echo "$mount_point"
+}
+
+# Helper function to retrieve mount options for a given mount point
+get_mnt_options() {
+	local mnt_point="$1"
+	local opts=$(mount | grep -m1 "$mnt_point" | sed -e 's/.*(\(.*\)).*/\1/')
+
+	echo "$opts"
+}