implement the LOG_CONS option in syslog

this was previously a no-op, somewhat intentionally, because I failed
to understand that it only has an effect when sending to the logging
facility fails and thus is not the nuisance that it would be if always
sent output to the console.

src/misc/syslog.c

@@ -8,6 +8,7 @@
 #include <string.h>
 #include <pthread.h>
 #include <errno.h>
+#include <fcntl.h>
 #include "libc.h"
 #include "atomic.h"
 
@@ -81,6 +82,7 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 	int pid;
 	int l, l2;
 	int hlen;
+	int fd;
 
 	if (log_fd < 0) __openlog();
 
@@ -99,7 +101,13 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 		if (l2 >= sizeof buf - l) l = sizeof buf - 1;
 		else l += l2;
 		if (buf[l-1] != '\n') buf[l++] = '\n';
-		send(log_fd, buf, l, 0);
+		if (send(log_fd, buf, l, 0) < 0 && (log_opt & LOG_CONS)) {
+			fd = open("/dev/console", O_WRONLY|O_NOCTTY|O_CLOEXEC);
+			if (fd >= 0) {
+				dprintf(fd, "%.*s", l-hlen, buf+hlen);
+				close(fd);
+			}
+		}
 		if (log_opt & LOG_PERROR) dprintf(2, "%.*s", l-hlen, buf+hlen);
 	}
 }