[PATCH] tracing/selftests: Add test to test max subbuf size with trace_marker

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Now that the trace_marker can write up to the max size of the sub buffer.
Add a test to see if it actually can happen.

The README is updated to state that the trace_marker writes can be broken
up, and the test checks the README for that statement so that it does not
fail on older kernels that does not support this.

If the README does not have the specified update, the test will still test
if all the string is written (although it would be broken up), as that
should work with older kernels.

Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c                          |   1 +
 .../ftrace/test.d/00basic/trace_marker.tc     | 112 ++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100755 tools/testing/selftests/ftrace/test.d/00basic/trace_marker.tc

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2f8d59834c00..cbfcdd882590 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5595,6 +5595,7 @@ static const char readme_msg[] =
 	"       delta:   Delta difference against a buffer-wide timestamp\n"
 	"    absolute:   Absolute (standalone) timestamp\n"
 	"\n  trace_marker\t\t- Writes into this file writes into the kernel buffer\n"
+	"\n           May be broken into multiple events based on sub-buffer size.\n"
 	"\n  trace_marker_raw\t\t- Writes into this file writes binary data into the kernel buffer\n"
 	"  tracing_cpumask\t- Limit which CPUs to trace\n"
 	"  instances\t\t- Make sub-buffers with: mkdir instances/foo\n"
diff --git a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker.tc b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker.tc
new file mode 100755
index 000000000000..bcb2dc6b8a66
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker.tc
@@ -0,0 +1,112 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Change the ringbuffer sub-buffer size
+# requires: trace_marker
+# flags: instance
+
+get_buffer_data_size() {
+	sed -ne 's/^.*data.*size:\([0-9][0-9]*\).*/\1/p' events/header_page
+}
+
+get_buffer_data_offset() {
+	sed -ne 's/^.*data.*offset:\([0-9][0-9]*\).*/\1/p' events/header_page
+}
+
+get_event_header_size() {
+	type_len=`sed -ne 's/^.*type_len.*:[^0-9]*\([0-9][0-9]*\).*/\1/p' events/header_event`
+	time_len=`sed -ne 's/^.*time_delta.*:[^0-9]*\([0-9][0-9]*\).*/\1/p' events/header_event`
+	array_len=`sed -ne 's/^.*array.*:[^0-9]*\([0-9][0-9]*\).*/\1/p' events/header_event`
+	total_bits=$((type_len+time_len+array_len))
+	total_bits=$((total_bits+7))
+	echo $((total_bits/8))
+}
+
+get_print_event_buf_offset() {
+	sed -ne 's/^.*buf.*offset:\([0-9][0-9]*\).*/\1/p' events/ftrace/print/format
+}
+
+event_header_size=`get_event_header_size`
+print_header_size=`get_print_event_buf_offset`
+
+# Find the README
+README=""
+if [ -f README ]; then
+	README="README"
+# instance?
+elif [ -f ../../README ]; then
+	README="../../README"
+fi
+
+testone=0
+if [ ! -z "$README" ]; then
+	if grep -q  "May be broken into multiple events based on sub-buffer size" $README; then
+		testone=1
+	fi
+fi
+
+data_offset=`get_buffer_data_offset`
+
+marker_meta=$((event_header_size+print_header_size))
+
+make_str() {
+        cnt=$1
+	# subtract two for \n\0 as marker adds these
+	cnt=$((cnt-2))
+	printf -- 'X%.0s' $(seq $cnt)
+}
+
+write_buffer() {
+	size=$1
+
+	str=`make_str $size`
+
+	# clear the buffer
+	echo > trace
+
+	# write the string into the marker
+	echo -n $str > trace_marker
+
+	echo $str
+}
+
+test_buffer() {
+
+	size=`get_buffer_data_size`
+	oneline_size=$((size-marker_meta))
+	echo size = $size
+	echo meta size = $marker_meta
+
+	if [ $testone -eq 1 ]; then
+		echo oneline size = $oneline_size
+
+		str=`write_buffer $oneline_size`
+
+		# Should be in one single event
+		new_str=`awk ' /tracing_mark_write:/ { sub(/^.*tracing_mark_write: */,"");printf "%s", $0; exit}' trace`
+
+		if [ "$new_str" != "$str" ]; then
+			exit fail;
+		fi
+	fi
+
+	# Now add a little more the meta data overhead will overflow
+
+	str=`write_buffer $size`
+
+	# Make sure the line was broken
+	new_str=`awk ' /tracing_mark_write:/ { sub(/^.*tracing_mark_write: /,"");printf "%s", $0; exit}' trace`
+
+	if [ "$new_str" = "$str" ]; then
+		exit fail;
+	fi
+
+	# Make sure the entire line can be found
+	new_str=`awk ' /tracing_mark_write:/ { sub(/^.*tracing_mark_write: */,"");printf "%s", $0; }' trace`
+
+	if [ "$new_str" != "$str" ]; then
+		exit fail;
+	fi
+}
+
+test_buffer
+
-- 
2.42.0