[PATCH v2] fstests: add basic ftrace support

[Qu Wenruo <wqu@suse.com>]

Sometimes developers want trace dump for certain test cases.

Normally I just add "trace-cmd" calls in "check", but it would be much
better to let fstests to support ftrace dumping.

This patchset will add basic ftrace dumping support by:

- Clear all buffers before running each test
- Start tracing before running each test
- End tracing after test finished
- Copy the trace to "$seqres.trace" if needed
  The condition is either:
  * $KEEP_TRACE environment is set to "yes"
  * The test case failed

Currently we only support the main ftrace buffer, but all supporting
functions have support for ftrace instances, for later expansion.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Add explanation in "common/config" for how to use it
- Make variables local
- Don't create the instance when clearing buffers
---
 check         | 12 +++++++-
 common/config |  8 +++++
 common/ftrace | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++
 common/rc     |  1 +
 4 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 common/ftrace

diff --git a/check b/check
index ba192042..0a09dcf9 100755
--- a/check
+++ b/check
@@ -801,7 +801,7 @@ function run_section()
 		fi
 
 		# really going to try and run this one
-		rm -f $seqres.out.bad
+		rm -f $seqres.out.bad $seqres.trace
 
 		# check if we really should run it
 		_expunge_test $seqnum
@@ -839,6 +839,10 @@ function run_section()
 		# to be reported for each test
 		(echo 1 > $DEBUGFS_MNT/clear_warn_once) > /dev/null 2>&1
 
+		# Clear previous trace and start new trace
+		_clear_trace_buffers
+		_start_trace
+
 		if [ "$DUMP_OUTPUT" = true ]; then
 			_run_seq 2>&1 | tee $tmp.out
 			# Because $? would get tee's return code
@@ -848,6 +852,11 @@ function run_section()
 			sts=$?
 		fi
 
+		_end_trace
+		if [ "$KEEP_TRACE" == "yes" ]; then
+			_copy_trace "$seqres.trace"
+		fi
+
 		if [ -f core ]; then
 			_dump_err_cont "[dumped core]"
 			mv core $RESULT_BASE/$seqnum.core
@@ -932,6 +941,7 @@ function run_section()
 
 	# make sure we record the status of the last test we ran.
 	if $err ; then
+		_copy_trace "$seqres.trace"
 		bad="$bad $seqnum"
 		n_bad=`expr $n_bad + 1`
 		tc_status="fail"
diff --git a/common/config b/common/config
index ad1c9eb0..4dec2bfa 100644
--- a/common/config
+++ b/common/config
@@ -25,6 +25,14 @@
 # KEEP_DMESG -      whether to keep all dmesg for each test case.
 #                   yes: keep all dmesg
 #                   no: only keep dmesg with error/warning (default)
+# KEEP_TRACE -	    whether to keep all non-empty ftrace buffer for each test case.
+#                   yes: keep all non-empty ftrace buffer
+#                   no: only keep non-empty ftrace buffer when the test fails (default)
+#
+#                   NOTE: to dump ftrace buffer one needs to enable ftrace
+#                   events or add custom trace_printk() into the fs code.
+#                   And since fstest will clear buffer before running one
+#                   test case, existing trace-cmd can be interrupted.
 #
 # - These can be added to $HOST_CONFIG_DIR (witch default to ./config)
 #   below or a separate local configuration file can be used (using
diff --git a/common/ftrace b/common/ftrace
new file mode 100644
index 00000000..9eec0f53
--- /dev/null
+++ b/common/ftrace
@@ -0,0 +1,83 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Common ftrace related helpers
+#
+
+TRACE_DIR="/sys/kernel/debug/tracing"
+
+_clear_trace_buffers()
+{
+	if [ ! -d "${TRACE_DIR}" ]; then
+		return
+	fi
+
+	# Clear the main buffer
+	echo 0 > "${TRACE_DIR}/trace"
+
+	# Clear each instance buffer
+	for i in $(ls "${TRACE_DIR}/instances"); do
+		echo 0 > "${i}/trace"
+	done
+}
+
+_start_trace()
+{
+	local instance=$1
+
+	if [ ! -d "${TRACE_DIR}" ]; then
+		return
+	fi
+
+	if [ -z "${instance}" ]; then
+		echo 1 > "${TRACE_DIR}/tracing_on"
+	else
+		mkdir -p "${TRACE_DIR}/instances/${instance}"
+		echo 1 > "${TRACE_DIR}/instances/${instance}/tracing_on"
+	fi
+}
+
+_end_trace()
+{
+	local instance=$1
+
+	if [ ! -d "${TRACE_DIR}" ]; then
+		return
+	fi
+
+	if [ -z "${instance}" ]; then
+		echo 0 > "${TRACE_DIR}/tracing_on"
+	elif [ -d "${TRACE_DIR}/instances/${instance}" ]; then
+		echo 0 > "${TRACE_DIR}/instances/${instance}/tracing_on"
+	fi
+}
+
+_remove_empty_trace()
+{
+	local file="$1"
+
+	if [ ! -f "$file" ]; then
+		return
+	fi
+
+	if [ -z "$(head -n 15 $file | sed '/^#/d')" ]; then
+		rm $file
+	fi
+}
+
+_copy_trace()
+{
+	local dest="$1"
+	local instance="$2"
+
+	if [ ! -d "${TRACE_DIR}" ]; then
+		return
+	fi
+
+	if [ -z "${instance}" ]; then
+		cp "${TRACE_DIR}/trace" "$dest"
+	elif [ -d "${TRACE_DIR}/instances/${instance}" ]; then
+		cp "${TRACE_DIR}/instances/${instance}/trace" "$dest"
+	fi
+
+	_remove_empty_trace "$dest"
+}
diff --git a/common/rc b/common/rc
index a0aa7300..d828dca8 100644
--- a/common/rc
+++ b/common/rc
@@ -3,6 +3,7 @@
 # Copyright (c) 2000-2006 Silicon Graphics, Inc.  All Rights Reserved.
 
 . common/config
+. common/ftrace
 
 BC=$(which bc 2> /dev/null) || BC=
 
-- 
2.31.1