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[Qemu-devel] [Tracing] [PATCH 3/4] Add a header to the trace file format
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [Tracing] [PATCH 3/4] Add a header to the trace file format |
Date: |
Thu, 22 Jul 2010 16:58:45 +0100 |
The trace file format needs a header so that future extension is
possible. There is a version number that can be bumped when file format
changes are made.
There is still the issue of endianness and sizeof(long). This patch
does not address those.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
simpletrace.c | 17 ++++++++++++++++-
simpletrace.py | 33 ++++++++++++++++++++++++++-------
2 files changed, 42 insertions(+), 8 deletions(-)
diff --git a/simpletrace.c b/simpletrace.c
index 71110b3..df21609 100644
--- a/simpletrace.c
+++ b/simpletrace.c
@@ -28,6 +28,17 @@ void st_print_trace_file_status(FILE *stream, int
(*stream_printf)(FILE *stream,
getpid(), trace_file_enabled ? "on" : "off");
}
+static bool write_header(FILE *fp)
+{
+ TraceRecord header = {
+ .event = -1UL, /* max avoids conflicting with TraceEventIDs */
+ .timestamp_ns = 0xf2b177cb0aa429b4, /* magic number */
+ .x1 = 0, /* bump this version number if file format changes */
+ };
+
+ return fwrite(&header, sizeof header, 1, fp) == 1;
+}
+
static bool open_trace_file(void)
{
char *filename;
@@ -38,7 +49,11 @@ static bool open_trace_file(void)
trace_fp = fopen(filename, "w");
free(filename);
- return trace_fp != NULL;
+ if (!trace_fp) {
+ return false;
+ }
+
+ return write_header(trace_fp);
}
static void flush_trace_file(void)
diff --git a/simpletrace.py b/simpletrace.py
index c951023..16ab2e7 100755
--- a/simpletrace.py
+++ b/simpletrace.py
@@ -13,10 +13,18 @@ import sys
import struct
import re
+header_event_id = 0xffffffffffffffff
+header_magic = 0xf2b177cb0aa429b4
+header_version = 0
+
trace_fmt = 'LLLLLLL'
trace_len = struct.calcsize(trace_fmt)
event_re = re.compile(r'(disable\s+)?([a-zA-Z0-9_]+)\(([^)]*)\)\s+"([^"]*)"')
+def err(msg):
+ sys.stderr.write(msg + '\n')
+ sys.exit(1)
+
def parse_events(fobj):
"""Parse a trace-events file."""
@@ -46,6 +54,22 @@ def read_record(fobj):
return None
return struct.unpack(trace_fmt, s)
+def read_trace_file(fobj):
+ """Deserialize trace records from a file."""
+ header = read_record(fobj)
+ if header is None or \
+ header[0] != header_event_id or \
+ header[1] != header_magic or \
+ header[2] != header_version:
+ err('not a trace file or incompatible version')
+
+ while True:
+ rec = read_record(fobj)
+ if rec is None:
+ break
+
+ yield rec
+
class Formatter(object):
"""Trace record pretty-printer"""
@@ -67,15 +91,10 @@ class Formatter(object):
return ' '.join(fields)
if len(sys.argv) != 3:
- sys.stderr.write('usage: %s <trace-events> <trace-file>\n' % sys.argv[0])
- sys.exit(1)
+ err('usage: %s <trace-events> <trace-file>' % sys.argv[0])
events = parse_events(open(sys.argv[1], 'r'))
f = open(sys.argv[2], 'rb')
formatter = Formatter(events)
-while True:
- rec = read_record(f)
- if rec is None:
- break
-
+for rec in read_trace_file(f):
print formatter.format_record(rec)
--
1.7.1