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: NPaul 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: NStefan Hajnoczi <stefanha@redhat.com>

configure

@@ -4191,6 +4191,18 @@ if compile_prog "" "" ; then
     posix_madvise=yes
 fi
 
+##########################################
+# check if we have posix_syslog
+
+posix_syslog=no
+cat > $TMPC << EOF
+#include <syslog.h>
+int main(void) { openlog("qemu", LOG_PID, LOG_DAEMON); syslog(LOG_INFO, "configure"); return 0; }
+EOF
+if compile_prog "" "" ; then
+    posix_syslog=yes
+fi
+
 ##########################################
 # check if trace backend exists
 
@@ -5468,6 +5480,13 @@ if have_backend "ftrace"; then
     feature_not_found "ftrace(trace backend)" "ftrace requires Linux"
   fi
 fi
+if have_backend "syslog"; then
+  if test "$posix_syslog" = "yes" ; then
+    echo "CONFIG_TRACE_SYSLOG=y" >> $config_host_mak
+  else
+    feature_not_found "syslog(trace backend)" "syslog not available"
+  fi
+fi
 echo "CONFIG_TRACE_FILE=$trace_file" >> $config_host_mak
 
 if test "$rdma" = "yes" ; then

docs/tracing.txt

@@ -192,6 +192,18 @@ After running qemu by root user, you can get the trace:
 
 Restriction: "ftrace" backend is restricted to Linux only.
 
+=== Syslog ===
+
+The "syslog" backend sends trace events using the POSIX syslog API. The log
+is opened specifying the LOG_DAEMON facility and LOG_PID option (so events
+are tagged with the pid of the particular QEMU process that generated
+them). All events are logged at LOG_INFO level.
+
+NOTE: syslog may squash duplicate consecutive trace events and apply rate
+      limiting.
+
+Restriction: "syslog" backend is restricted to POSIX compliant OS.
+
 ==== Monitor commands ====
 
 * trace-file on|off|flush|set <path>

scripts/tracetool/backend/syslog.py

+#!/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)

trace/control.c

@@ -19,6 +19,9 @@
 #ifdef CONFIG_TRACE_LOG
 #include "qemu/log.h"
 #endif
+#ifdef CONFIG_TRACE_SYSLOG
+#include <syslog.h>
+#endif
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/config-file.h"
@@ -250,6 +253,10 @@ bool trace_init_backends(void)
     }
 #endif
 
+#ifdef CONFIG_TRACE_SYSLOG
+    openlog(NULL, LOG_PID, LOG_DAEMON);
+#endif
+
     return true;
 }