trace: add tracetool simpletrace_stap format

This new tracetool "format" generates a SystemTap .stp file that outputs
simpletrace binary trace data.

In contrast to simpletrace or ftrace, SystemTap does not define its own
trace format.  All output from SystemTap is generated by .stp files.
This patch lets us generate a .stp file that outputs in the simpletrace
binary format.

This makes it possible to reuse simpletrace.py to analyze traces
recorded using SystemTap.  The simpletrace binary format is especially
useful for long-running traces like flight-recorder mode where string
formatting can be expensive.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/format/simpletrace_stap.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Generate .stp file that outputs simpletrace binary traces (DTrace with SystemTAP only).
+"""
+
+__author__     = "Stefan Hajnoczi <redhat.com>"
+__copyright__  = "Copyright (C) 2014, Red Hat, Inc."
+__license__    = "GPL version 2 or (at your option) any later version"
+
+__maintainer__ = "Stefan Hajnoczi"
+__email__      = "stefanha@redhat.com"
+
+
+from tracetool import out
+from tracetool.backend.dtrace import binary, probeprefix
+from tracetool.backend.simple import is_string
+from tracetool.format.stap import stap_escape
+
+
+def generate(events, backend):
+    out('/* This file is autogenerated by tracetool, do not edit. */',
+        '')
+
+    for event_id, e in enumerate(events):
+        if 'disable' in e.properties:
+            continue
+
+        out('probe %(probeprefix)s.simpletrace.%(name)s = %(probeprefix)s.%(name)s ?',
+            '{',
+            probeprefix=probeprefix(),
+            name=e.name)
+
+        # Calculate record size
+        sizes = ['24'] # sizeof(TraceRecord)
+        for type_, name in e.args:
+            name = stap_escape(name)
+            if is_string(type_):
+                out('    try {',
+                    '        arg%(name)s_str = %(name)s ? user_string_n(%(name)s, 512) : "<null>"',
+                    '    } catch {}',
+                    '    arg%(name)s_len = strlen(arg%(name)s_str)',
+                    name=name)
+                sizes.append('4 + arg%s_len' % name)
+            else:
+                sizes.append('8')
+        sizestr = ' + '.join(sizes)
+
+        # Generate format string and value pairs for record header and arguments
+        fields = [('8b', str(event_id)),
+                  ('8b', 'gettimeofday_ns()'),
+                  ('4b', sizestr),
+                  ('4b', 'pid()')]
+        for type_, name in e.args:
+            name = stap_escape(name)
+            if is_string(type_):
+                fields.extend([('4b', 'arg%s_len' % name),
+                               ('.*s', 'arg%s_len, arg%s_str' % (name, name))])
+            else:
+                fields.append(('8b', name))
+
+        # Emit the entire record in a single SystemTap printf()
+        fmt_str = '%'.join(fmt for fmt, _ in fields)
+        arg_str = ', '.join(arg for _, arg in fields)
+        out('    printf("%%%(fmt_str)s", %(arg_str)s)',
+            fmt_str=fmt_str, arg_str=arg_str)
+
+        out('}')
+
+    out()