For MIDI ports, use the same open/close logic as for audio devices:

drop clients using it when the port is closed (eg. umidi disconnected)
and try to reopen it whenever a new client connects.

sndiod/midi.c

@@ -443,7 +443,8 @@ port_exit(void *arg)
 
 	if (log_level >= 3) {
 		port_log(p);
-		log_puts(": exit\n");
+		log_puts(": port exit\n");
+		panic();
 	}
 #endif
 }
@@ -489,6 +490,37 @@ port_del(struct port *c)
 	xfree(c);
 }
 
+int
+port_ref(struct port *c)
+{
+#ifdef DEBUG
+	if (log_level >= 3) {
+		port_log(c);
+		log_puts(": port requested\n");
+	}
+#endif
+	if (c->state == PORT_CFG && !port_open(c))
+		return 0;
+	return 1;
+}
+
+void
+port_unref(struct port *c)
+{
+	int i, rxmask;
+
+#ifdef DEBUG
+	if (log_level >= 3) {
+		port_log(c);
+		log_puts(": port released\n");
+	}
+#endif
+	for (rxmask = 0, i = 0; i < MIDI_NEP; i++)
+		rxmask |= midi_ep[i].txmask;
+	if ((rxmask & c->midi->self) == 0 && c->state == PORT_INIT)
+		port_close(c);
+}
+
 struct port *
 port_bynum(int num)
 {
@@ -518,14 +550,24 @@ port_open(struct port *c)
 int
 port_close(struct port *c)
 {
+	int i;
+	struct midi *ep;
 #ifdef DEBUG
 	if (c->state == PORT_CFG) {
 		port_log(c);
 		log_puts(": can't close port (not opened)\n");
+		panic();
 	}
 #endif
-	port_mio_close(c);
 	c->state = PORT_CFG;	
+	port_mio_close(c);
+	
+	for (i = 0; i < MIDI_NEP; i++) {
+		ep = midi_ep + i;
+		if ((ep->txmask & c->midi->self) ||
+		    (c->midi->txmask & ep->self))
+			ep->ops->exit(ep->arg);
+	}
 	return 1;
 }
 

sndiod/midi.h

@@ -89,7 +89,6 @@ struct port {
 	unsigned int state;
 	char *path;
 	struct midi *midi;
-	unsigned int refs;
 };
 
 /*
@@ -113,6 +112,8 @@ void midi_link(struct midi *, struct midi *);
 struct port *port_new(char *, unsigned int);
 struct port *port_bynum(int);
 void port_del(struct port *);
+int  port_ref(struct port *);
+void port_unref(struct port *);
 int  port_init(struct port *);
 void port_done(struct port *);
 int  port_close(struct port *);

sndiod/sock.c

@@ -151,6 +151,10 @@ sock_close(struct sock *f)
 		midi_del(f->midi);
 		f->midi = NULL;
 	}
+	if (f->port) {
+		port_unref(f->port);
+		f->port = NULL;
+	}
 	file_del(f->file);
 	close(f->fd);
 	xfree(f);
@@ -850,6 +854,7 @@ sock_hello(struct sock *f)
 	}
 	f->pstate = SOCK_INIT;
 	if (mode & MODE_MIDIMASK) {
+		f->port = NULL;
 		f->slot = NULL;
 		f->midi = midi_new(&sock_midiops, f, mode);
 		if (f->midi == NULL)
@@ -864,8 +869,9 @@ sock_hello(struct sock *f)
 			midi_tag(f->midi, p->devnum);
 		} else if (p->devnum < 48) {
 			c = port_bynum(p->devnum - 32);
-			if (c == NULL)
+			if (c == NULL || !port_ref(c))
 				return 0;
+			f->port = c;
 			midi_link(f->midi, c->midi);
 		} else
 			return 0;

sndiod/sock.h

@@ -58,7 +58,8 @@ struct sock {
 	int lastvol;			/* last volume */
 	struct opt *opt;		/* "subdevice" definition */
 	struct slot *slot;		/* audio device slot number */
-	struct midi *midi;		/* midi endpoint number */
+	struct midi *midi;		/* midi endpoint */
+	struct port *port;		/* midi port */
 	char who[12];			/* label, mostly for debugging */
 };