selftests/livepatch: push and pop dynamic debug config

The livepatching self-tests tweak the dynamic debug config to verify
the kernel log during the tests.  Enhance set_dynamic_debug() so that
the config changes are restored when the script exits.

Note this functionality needs to keep in sync with:
  - dynamic_debug input/output formatting
  - functions affected by set_dynamic_debug()

  For example, push_dynamic_debug() transforms:
    kernel/livepatch/transition.c:530 [livepatch]klp_init_transition =_ "'%s': initializing %s transition\012"
  to the following:
    file kernel/livepatch/transition.c line 530 =_
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/livepatch/functions.sh

@@ -29,13 +29,27 @@ function die() {
 	exit 1
 }
 
-# set_dynamic_debug() - setup kernel dynamic debug
-#	TODO - push and pop this config?
+function push_dynamic_debug() {
+        DYNAMIC_DEBUG=$(grep '^kernel/livepatch' /sys/kernel/debug/dynamic_debug/control | \
+                awk -F'[: ]' '{print "file " $1 " line " $2 " " $4}')
+}
+
+function pop_dynamic_debug() {
+	if [[ -n "$DYNAMIC_DEBUG" ]]; then
+		echo -n "$DYNAMIC_DEBUG" > /sys/kernel/debug/dynamic_debug/control
+	fi
+}
+
+# set_dynamic_debug() - save the current dynamic debug config and tweak
+# 			it for the self-tests.  Set a script exit trap
+#			that restores the original config.
 function set_dynamic_debug() {
-	cat << EOF > /sys/kernel/debug/dynamic_debug/control
-file kernel/livepatch/* +p
-func klp_try_switch_task -p
-EOF
+        push_dynamic_debug
+        trap pop_dynamic_debug EXIT INT TERM HUP
+        cat <<-EOF > /sys/kernel/debug/dynamic_debug/control
+		file kernel/livepatch/* +p
+		func klp_try_switch_task -p
+		EOF
 }
 
 # loop_until(cmd) - loop a command until it is successful or $MAX_RETRIES,