[logging] rework locking around logging

make sure to check/fill data after locking and complete write
before release the lock.

also use trylock vs lock since most log are called while already
locked and it's cleaner.

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

libknet/logging.c

@@ -175,37 +175,33 @@ void log_msg(knet_handle_t knet_h, uint8_t subsystem, uint8_t msglevel,
 	int len, err;
 
 	if ((!knet_h) ||
-	    (knet_h->logfd <= 0) ||
 	    (subsystem > KNET_SUB_LAST) ||
 	    (msglevel > knet_h->log_levels[subsystem]))
 			return;
 
-	memset(&msg, 0, sizeof(struct knet_log_msg));
-	msg.subsystem = subsystem;
-	msg.msglevel = msglevel;
-
 	/*
 	 * most logging calls will take place with locking in place.
 	 * if we get an EINVAL and locking is initialized, then
 	 * we are getting a real error and we need to stop
 	 */
-	err = pthread_rwlock_rdlock(&knet_h->global_rwlock);
-	if ((err == EINVAL) && (knet_h->lock_init_done))
+	err = pthread_rwlock_tryrdlock(&knet_h->global_rwlock);
+	if ((err == EAGAIN) && (knet_h->lock_init_done))
 		return;
 
+	if (knet_h->logfd <= 0)
+		goto out_unlock;
+
+	memset(&msg, 0, sizeof(struct knet_log_msg));
+	msg.subsystem = subsystem;
+	msg.msglevel = msglevel;
+
 	va_start(ap, fmt);
 	vsnprintf(msg.msg, sizeof(msg.msg) - 2, fmt, ap);
 	va_end(ap);
 
 	len = strlen(msg.msg);
 	msg.msg[len+1] = '\n';
 
-	/*
-	 * unlock only if we are holding the lock
-	 */
-	if (!err)
-		pthread_rwlock_unlock(&knet_h->global_rwlock);
-
 	while (byte_cnt < sizeof(struct knet_log_msg)) {
 		len = write(knet_h->logfd, &msg, sizeof(struct knet_log_msg) - byte_cnt);
 		if (len <= 0)
@@ -214,5 +210,12 @@ void log_msg(knet_handle_t knet_h, uint8_t subsystem, uint8_t msglevel,
 		byte_cnt += len;
 	}
 
+out_unlock:
+	/*
+	 * unlock only if we are holding the lock
+	 */
+	if (!err)
+		pthread_rwlock_unlock(&knet_h->global_rwlock);
+
 	return;
 }