bgpctl(8) has this in show mrt:
             file name  Read the MRT dump from file name instead of using
                        stdin.

So if no file argument is passed to bgpctl then stdin should be used.
I broke this when fixing a coverity report that something like
	bgpctl show mrt file a file b
would leak a filedescriptor.

Adjust the code to use STDIN_FILENO instead of -1 as initial value of
res.mrtfd.

-- 
:wq Claudio

Index: parser.c
===================================================================
RCS file: /cvs/src/usr.sbin/bgpctl/parser.c,v
diff -u -p -r1.139 parser.c
--- parser.c	4 Nov 2025 15:30:50 -0000	1.139
+++ parser.c	6 May 2026 18:37:29 -0000
@@ -489,7 +489,7 @@ parse(int argc, char *argv[])
 
 	memset(&res, 0, sizeof(res));
 	res.rtableid = getrtable();
-	res.mrtfd = -1;
+	res.mrtfd = STDIN_FILENO;
 	TAILQ_INIT(&res.set);
 
 	while (argc >= 0) {
@@ -802,7 +802,7 @@ match_token(int argc, char *argv[], cons
 			break;
 		case FILENAME:
 			if (word != NULL && wordlen > 0) {
-				if (res.mrtfd != -1)
+				if (res.mrtfd != STDIN_FILENO)
 					errx(1, "mrt file already set");
 				if ((res.mrtfd = open(word, O_RDONLY)) == -1) {
 					/*