BUG/MINOR: logs: properly initialize and count log sockets

Commit 81ae195 ("[MEDIUM] add support for logging via a UNIX socket")
merged in 1.3.14 introduced a few minor issues with log sockets. All
of them happen only when a failure is encountered when trying to set
up the logging socket (eg: socket family is not available or is
temporarily short in resources).

The first socket which experiences an error causes the socket setup
loop to abort, possibly preventing any log from being sent if it was
the first logger. The second issue is that if this socket finally
succeeds after a second attempt, errors are reported for the wrong
logger (eg: logger #1 failed instead of #2).  The last point is that
we now have multiple loggers, and it's a waste of time to walk over
their list for every log while they're almost always properly set up.

So in order to fix all this, let's merge the two lists. If a logger
experiences an error, it simply sends an alert and skips to the next
one. That way they don't prevent messages from being sent and are
all properly accounted for.

src/log.c

@@ -813,37 +813,6 @@ void __send_log(struct proxy *p, int level, char *message, size_t size)
 
 	message[size - 1] = '\n';
 
-	/* Lazily set up syslog sockets for protocol families of configured
-	 * syslog servers. */
-	nblogger = 0;
-	list_for_each_entry(tmp, logsrvs, list) {
-		const struct logsrv *logsrv = tmp;
-		int proto, *plogfd;
-
-		if (logsrv->addr.ss_family == AF_UNIX) {
-			proto = 0;
-			plogfd = &logfdunix;
-		} else {
-			proto = IPPROTO_UDP;
-			plogfd = &logfdinet;
-		}
-		if (*plogfd >= 0) {
-			/* socket already created. */
-			continue;
-		}
-		if ((*plogfd = socket(logsrv->addr.ss_family, SOCK_DGRAM,
-				proto)) < 0) {
-			Alert("socket for logger #%d failed: %s (errno=%d)\n",
-				nblogger + 1, strerror(errno), errno);
-			return;
-		}
-		/* we don't want to receive anything on this socket */
-		setsockopt(*plogfd, SOL_SOCKET, SO_RCVBUF, &zero, sizeof(zero));
-		/* does nothing under Linux, maybe needed for others */
-		shutdown(*plogfd, SHUT_RD);
-		nblogger++;
-	}
-
 	/* Send log messages to syslog server. */
 	nblogger = 0;
 	list_for_each_entry(tmp, logsrvs, list) {
@@ -852,10 +821,27 @@ void __send_log(struct proxy *p, int level, char *message, size_t size)
 			&logfdunix : &logfdinet;
 		int sent;
 
+		nblogger++;
+
 		/* we can filter the level of the messages that are sent to each logger */
 		if (level > logsrv->level)
 			continue;
 
+		if (unlikely(*plogfd < 0)) {
+			/* socket not successfully initialized yet */
+			int proto = logsrv->addr.ss_family == AF_UNIX ? 0 : IPPROTO_UDP;
+
+			if ((*plogfd = socket(logsrv->addr.ss_family, SOCK_DGRAM, proto)) < 0) {
+				Alert("socket for logger #%d failed: %s (errno=%d)\n",
+				      nblogger, strerror(errno), errno);
+				continue;
+			}
+			/* we don't want to receive anything on this socket */
+			setsockopt(*plogfd, SOL_SOCKET, SO_RCVBUF, &zero, sizeof(zero));
+			/* does nothing under Linux, maybe needed for others */
+			shutdown(*plogfd, SHUT_RD);
+		}
+
 		/* For each target, we may have a different facility.
 		 * We can also have a different log level for each message.
 		 * This induces variations in the message header length.
@@ -879,7 +865,6 @@ void __send_log(struct proxy *p, int level, char *message, size_t size)
 			Alert("sendto logger #%d failed: %s (errno=%d)\n",
 				nblogger, strerror(errno), errno);
 		}
-		nblogger++;
 	}
 }