sendsyslog failure logging

[Alexander Bluhm]

Hi,

My goal is to make logging via syslog reliable.  At least I want
to see when a message gets lost.

So my idea is to write a kernel log message if sendsyslog(2) cannot
deliver a message.  Then you see the problem on the console and in
the dmesg buffer.  If syslogd comes back later, you will also get
the error into the log files via /dev/klog.

comments? ok?

bluhm

Index: kern/subr_log.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/kern/subr_log.c,v
retrieving revision 1.25
diff -u -p -u -p -r1.25 subr_log.c
--- kern/subr_log.c     13 Dec 2014 21:05:33 -0000      1.25
+++ kern/subr_log.c     3 Jan 2015 13:48:32 -0000
@@ -347,14 +347,21 @@ sys_sendsyslog(struct proc *p, void *v, 
        struct iovec *ktriov = NULL;
        int iovlen;
 #endif
+#ifndef SMALL_KERNEL
+       const struct timeval mininterval = { 30, 0 };
+       static struct timeval lasttime;
+       static unsigned int failed;
+#endif
        struct iovec aiov;
        struct uio auio;
        struct file *f;
        size_t len;
        int error;
 
-       if (syslogf == NULL)
-               return (ENOTCONN);
+       if (syslogf == NULL) {
+               error = ENOTCONN;
+               goto out;
+       }
        f = syslogf;
        FREF(f);
 
@@ -390,5 +397,19 @@ sys_sendsyslog(struct proc *p, void *v, 
        }
 #endif
        FRELE(f, p);
-       return error;
+
+ out:
+#ifndef SMALL_KERNEL
+       if (error)
+               failed++;
+       if (failed && ratecheck(&lasttime, &mininterval)) {
+               if (failed == 1)
+                       log(LOG_ERR, "send message to syslog failed\n");
+               else
+                       log(LOG_ERR, "send message to syslog failed %u times\n",
+                           failed);
+               failed = 0;
+       }
+#endif
+       return (error);
 }