say: allow to set a logger file descriptor

It is necessary to decouple stderr from a logger file descriptor in the
popen implementation.

Part of #4031

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>

src/lib/core/say.c

@@ -174,6 +174,12 @@ log_get_fd(void)
 	return log_default->fd;
 }
 
+void
+log_set_fd(int new_fd)
+{
+	log_default->fd = new_fd;
+}
+
 void
 log_set_level(struct log *log, enum say_level level)
 {

src/lib/core/say.h

@@ -204,10 +204,18 @@ enum say_logger_type
 log_type();
 
 /**
- * Default logger file descriptor.
+ * Accessors for default logger file descriptor.
+ *
+ * It is needed for decoupling of a logger file descriptor from
+ * stderr in the popen implementation.
+ *
+ * Those functions break logger incapsulation, so use them with
+ * caution.
  */
 int
 log_get_fd(void);
+void
+log_set_fd(int new_fd);
 
 /**
  * Set log level. Can be used dynamically.