tools: add mtrace-reader.py

Tool to stream data from Linux SOF driver "mtrace" debugfs
interface to standard output. Plain "cat" is not sufficient
as each read() syscall returns log data with a 32bit binary
header, containing the payload length.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

tools/mtrace/mtrace-reader.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: BSD-3-Clause
+#
+# Copyright (c) 2022, Intel Corporation. All rights reserved.
+
+#pylint:disable=mixed-indentation
+
+# Tool to stream data from Linux SOF driver "mtrace" debugfs
+# interface to standard output. Plain "cat" is not sufficient
+# as each read() syscall returns log data with a 32bit binary
+# header, containing the payload length.
+
+import struct
+import os
+import sys
+
+READ_BUFFER = 16384
+MTRACE_FILE = "/sys/kernel/debug/sof/mtrace/core0"
+
+fd = os.open(MTRACE_FILE, os.O_RDONLY)
+while fd >= 0:
+    # direct unbuffered os.read() must be used to comply with
+    # debugfs protocol used. each non-zero read will return
+    # a buffer containing a 32bit header and a payload
+    read_bytes = os.read(fd, READ_BUFFER)
+
+    # handle end-of-file
+    if len(read_bytes) == 0:
+        continue
+
+    if len(read_bytes) <= 4:
+        continue
+
+    header = struct.unpack('I', read_bytes[0:4])
+    data_len = header[0]
+    data = read_bytes[4:4+data_len]
+
+    os.write(sys.stdout.fileno(), data)