log: expose ability query/set fd

This allows for the logging FD to be queried and set -- which is useful
for modules to be able to know the FD for being able to use fvwm_debug()

fvwm/modconf.c

@@ -49,6 +49,7 @@
 #include "module_interface.h"
 #include "colorset.h"
 #include "libs/FScreen.h"
+#include "libs/log.h"
 #include "expand.h"
 
 extern int nColorsets;  /* in libs/Colorset.c */
@@ -365,6 +366,15 @@ void send_ignore_modifiers(fmodule *module)
 	return;
 }
 
+void
+send_logging_fd(fmodule *module)
+{
+	char msg[64];
+
+	snprintf(msg, sizeof(msg), "LoggingFD %d\n", log_get_fd());
+	SendName(module, M_CONFIG_INFO, 0, 0, 0, msg);
+}
+
 void send_monitor_list(fmodule *module)
 {
 	BroadcastMonitorList(module);
@@ -387,6 +397,7 @@ void CMD_Send_ConfigInfo(F_CMD_ARGS)
 	send_click_time(mod);
 	send_move_threshold(mod);
 	send_desktop_geometry(mod);
+	send_logging_fd(mod);
 	match = PeekToken(action, &action);
 	if (match)
 	{

libs/log.c

@@ -36,6 +36,24 @@ static char	*log_file_name;
 static FILE	*log_file;
 int	lib_log_level = 0;
 
+int
+log_get_fd(void)
+{
+	if (log_file == NULL)
+		return -1;
+	return fileno(log_file);
+}
+
+void
+log_set_fd(int fd)
+{
+	if (fd == -1)
+		return;
+
+	/* This is enough to allow modules to be able to log. */
+	log_file = fdopen(fd, "a");
+}
+
 void
 set_log_file(char *name)
 {

libs/log.h

@@ -9,6 +9,8 @@ void	set_log_file(char *name);
 void	log_open(const char *);
 void	log_toggle(const char *);
 void	log_close(void);
+int	log_get_fd(void);
+void	log_set_fd(int);
 void printflike(2, 3) fvwm_debug(const char *, const char *, ...);
 
 #endif