trace: add syslog tracing backend

This patch adds a tracing backend which sends output using syslog().
The syslog backend is limited to POSIX compliant systems.

openlog() is called with facility set to LOG_DAEMON, with the LOG_PID
option. Trace events are logged at level LOG_INFO.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Message-id: 1470318254-29989-1-git-send-email-paul.durrant@citrix.com
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/backend/syslog.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Syslog built-in backend.
+"""
+
+__author__     = "Paul Durrant <paul.durrant@citrix.com>"
+__copyright__  = "Copyright 2016, Citrix Systems Inc."
+__license__    = "GPL version 2 or (at your option) any later version"
+
+__maintainer__ = "Stefan Hajnoczi"
+__email__      = "stefanha@redhat.com"
+
+
+from tracetool import out
+
+
+PUBLIC = True
+
+
+def generate_h_begin(events):
+    out('#include <syslog.h>',
+        '#include "trace/control.h"',
+        '')
+
+
+def generate_h(event):
+    argnames = ", ".join(event.args.names())
+    if len(event.args) > 0:
+        argnames = ", " + argnames
+
+    if "vcpu" in event.properties:
+        # already checked on the generic format code
+        cond = "true"
+    else:
+        cond = "trace_event_get_state(%s)" % ("TRACE_" + event.name.upper())
+
+    out('        if (%(cond)s) {',
+        '            syslog(LOG_INFO, "%(name)s " %(fmt)s %(argnames)s);',
+        '        }',
+        cond=cond,
+        name=event.name,
+        fmt=event.fmt.rstrip("\n"),
+        argnames=argnames)