util: Don't stop on unrelated values when looking for --fd in close_open_files()

Seen with krun: we get a file descriptor via --fd, but we close it and
happily use the same number for TCP files.

The issue is that if we also get other options before --fd, with
arguments, getopt_long() stops parsing them because it sees them as
non-option values.

Use the - modifier at the beginning of optstring (before :, which is
needed to avoid printing errors) instead of +, which means we'll
continue parsing after finding unrelated option values, but
getopt_long() won't reorder them anyway: they'll be passed with option
value '1', which we can ignore.

By the way, we also need to add : after F in the optstring, so that
we're able to parse the option when given as short name as well.

Now that we change the parsing mode between close_open_files() and
conf(), we need to reset optind to 0, not to 1, whenever we call
getopt_long() again in conf(), so that the internal initialisation
of getopt_long() evaluating GNU extensions is re-triggered.

Link: https://github.com/slp/krun/issues/17#issuecomment-2294943828
Fixes: baccfb95ce ("conf: Stop parsing options at first non-option argument")
Fixes: 09603cab28 ("passt, util: Close any open file that the parent might have leaked")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

conf.c

@@ -1312,7 +1312,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	c->udp.fwd_in.mode = c->udp.fwd_out.mode = FWD_UNSET;
 	memcpy(c->our_tap_mac, MAC_OUR_LAA, ETH_ALEN);
 
-	optind = 1;
+	optind = 0;
 	do {
 		name = getopt_long(argc, argv, optstring, options, NULL);
 
@@ -1712,7 +1712,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	 * settings)
 	 */
 	udp_portmap_clear();
-	optind = 1;
+	optind = 0;
 	do {
 		name = getopt_long(argc, argv, optstring, options, NULL);
 
@@ -1782,7 +1782,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		nl_sock_init(c, true);
 
 	/* ...and outbound port options now that namespaces are set up. */
-	optind = 1;
+	optind = 0;
 	do {
 		name = getopt_long(argc, argv, optstring, options, NULL);
 

util.c

@@ -728,7 +728,7 @@ void close_open_files(int argc, char **argv)
 	int name, rc;
 
 	do {
-		name = getopt_long(argc, argv, "+:F", optfd, NULL);
+		name = getopt_long(argc, argv, "-:F:", optfd, NULL);
 
 		if (name == 'F') {
 			errno = 0;