vlog: deprecate --syslog-target argument

Commit fe089c0d1e18 ("vlog: abstract out interface to syslog daemon")
introduced --syslog-method flag that supersedes --syslog-target flag by:
1. making logging format configurable
2. letting daemon to also talk over UNIX domain socket (this is handy
   when local rsyslog daemon is running in different network namespace
   on the same host)

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

NEWS

@@ -21,6 +21,8 @@ Post-v2.4.0
      targets to run a new system testsuite.  These tests can be run inside
      a Vagrant box.  See INSTALL.md for details
    - Dropped support for GRE64 tunnel.
+   - Mark --syslog-target argument as deprecated.  It will be removed in
+     the next OVS release.
 
 
 v2.4.0 - 20 Aug 2015

lib/vlog.c

@@ -706,6 +706,7 @@ vlog_init(void)
     if (ovsthread_once_start(&once)) {
         long long int now;
         int facility;
+        bool print_syslog_target_deprecation;
 
         /* Do initialization work that needs to be done before any logging
          * occurs.  We want to keep this really minimal because any attempt to
@@ -740,6 +741,15 @@ vlog_init(void)
                                  0, INT_MAX, vlog_disable_rate_limit, NULL);
         unixctl_command_register("vlog/reopen", "", 0, 0,
                                  vlog_unixctl_reopen, NULL);
+
+        ovs_rwlock_rdlock(&pattern_rwlock);
+        print_syslog_target_deprecation = syslog_fd >= 0;
+        ovs_rwlock_unlock(&pattern_rwlock);
+
+        if (print_syslog_target_deprecation) {
+            VLOG_WARN("--syslog-target flag is deprecated, use "
+                      "--syslog-method instead");
+        }
     }
 }