Add an option (-j) to set the Jack client name. Moreover, add equivalent directives for both the -j and -o options, so that they can also be set from the midizaprc file.

example.midizaprc

@@ -6,11 +6,38 @@
 
 # This program works pretty much like Eric Messick's shuttlepro program,
 # but it translates MIDI input rather than input events from the Contour
-# Design Shuttle devices.  The program creates a Jack MIDI client named
-# "midizap" with a single input port, which you'll have to connect to
-# the MIDI controller that you want to use (e.g., using a patchbay
-# program like qjackctl; non-Jack ALSA MIDI inputs can be accommodated
-# using a2jmidid).
+# Design Shuttle devices.  By default, the program creates a Jack MIDI
+# client named "midizap" with a single input port, which you'll have to
+# connect to the MIDI controller that you want to use (e.g., using a
+# patchbay program like qjackctl; non-Jack ALSA MIDI inputs can be
+# accommodated using a2jmidid).
+
+# Both the Jack client name and the number of (input and output) ports
+# can be adjusted, either from the command line, using the -j and -o
+# options (these always take priority), or by employing the following
+# midizaprc directives.  NOTE: These options only take effect
+# immediately after program start, when the Jack client is initialized.
+# If you edit them later, you need to restart the program, so that a new
+# Jack client is created.
+
+# The JACK_NAME directive is used to change the client name.
+# (Uncomment the line and edit the name as needed.)  This is useful,
+# e.g., if you're running multiple instances of midizap using different
+# configurations for different controllers, and you want to have them
+# named appropriately so that they can be wired up more easily using the
+# qjackctl patchbay.
+
+#JACK_NAME "hello midizap"
+
+# The number of ports given with the JACK_PORTS directive must be
+# 1 or 2.  It causes the given number of both input and output ports to
+# be created.  This option is useful if you want to translate MIDI
+# messages, see the [MIDI] section below for details.  Two input and
+# output ports can be employed, e.g., if you also need to provide
+# backward translations for controller feedback, see the [MIDI2] section
+# below for an example.
+
+#JACK_PORTS 2
 
 # Other than the input being MIDI instead of the Shuttle's key and wheel
 # events, the program works exactly the same. Each section in the file

jackdriver.c

@@ -376,10 +376,11 @@ int
 init_jack(JACK_SEQ* seq, uint8_t verbose)
 {
     int err, k;
-    char portname[100];
+    char portname[100],
+      *client_name = seq->client_name?seq->client_name:"midizap";
 
     if(verbose)printf("opening client...\n");
-    seq->jack_client = jack_client_open("midizap", JackNullOption, NULL);
+    seq->jack_client = jack_client_open(client_name, JackNullOption, NULL);
 
     if (seq->jack_client == NULL)
     {

jackdriver.h

@@ -5,6 +5,7 @@
 
 typedef struct _jseq
 {
+  char *client_name;
   jack_ringbuffer_t **ringbuffer_out;
   jack_ringbuffer_t **ringbuffer_in;
   jack_client_t	*jack_client;

midizap.c

@@ -23,7 +23,7 @@ typedef struct input_event EV;
 Display *display;
 
 JACK_SEQ seq;
-int enable_jack_output = 0, debug_jack = 0;
+int jack_num_outputs = 0, debug_jack = 0;
 
 void
 initdisplay(void)
@@ -70,7 +70,7 @@ static int16_t pbvalue[16] =
 void
 send_midi(uint8_t portno, int status, int data, int step, int incr, int index, int dir)
 {
-  if (!enable_jack_output) return; // MIDI output not enabled
+  if (!jack_num_outputs) return; // MIDI output not enabled
   uint8_t msg[3];
   int chan = status & 0x0f;
   msg[0] = status;
@@ -273,7 +273,7 @@ send_strokes(translation *tr, uint8_t portno, int status, int chan, int data,
   int nkeys = 0;
   stroke *s = fetch_stroke(tr, portno, status, chan, data, index, dir);
 
-  if (!s && enable_jack_output) {
+  if (!s && jack_num_outputs) {
     // fall back to default MIDI translation
     tr = default_midi_translation[portno];
     s = fetch_stroke(tr, portno, status, chan, data, index, dir);
@@ -603,11 +603,12 @@ handle_event(uint8_t *msg, uint8_t portno)
 
 void help(char *progname)
 {
-  fprintf(stderr, "Usage: %s [-h] [-o[2]] [-r rcfile] [-d[rskj]]\n", progname);
+  fprintf(stderr, "Usage: %s [-h] [-o[2]] [-j name] [-r rcfile] [-d[rskmj]]\n", progname);
   fprintf(stderr, "-h print this message\n");
   fprintf(stderr, "-o enable MIDI output (add 2 for a second pair of ports)\n");
+  fprintf(stderr, "-j jack client name (default: midizap)\n");
   fprintf(stderr, "-r config file name (default: MIDIZAP_CONFIG_FILE variable or ~/.midizaprc)\n");
-  fprintf(stderr, "-d debug (r = regex, s = strokes, k = keys, j = jack; default: all)\n");
+  fprintf(stderr, "-d debug (r = regex, s = strokes, k = keys, m = midi, j = jack; default: all)\n");
 }
 
 uint8_t quit = 0;
@@ -623,25 +624,23 @@ void quitter()
 #define CONF_FREQ 1
 #define MAX_COUNT (1000000/CONF_FREQ/POLL_INTERVAL)
 
-int n_ports = 1;
-
 int
 main(int argc, char **argv)
 {
   uint8_t msg[3];
   int opt, count = 0;
 
-  while ((opt = getopt(argc, argv, "ho::d::r:")) != -1) {
+  while ((opt = getopt(argc, argv, "ho::d::j:r:")) != -1) {
     switch (opt) {
     case 'h':
       help(argv[0]);
       exit(0);
     case 'o':
-      enable_jack_output = 1;
+      jack_num_outputs = 1;
       if (optarg && *optarg) {
 	const char *a = optarg;
 	if (*a == '2') {
-	  n_ports = 2;
+	  jack_num_outputs = 2;
 	} else if (*a && *a != '1') {
 	  fprintf(stderr, "%s: wrong port number (-o), must be 1 or 2\n", argv[0]);
 	  fprintf(stderr, "Try -h for help.\n");
@@ -682,6 +681,9 @@ main(int argc, char **argv)
 	debug_jack = 1;
       }
       break;
+    case 'j':
+      jack_client_name = optarg;
+      break;
     case 'r':
       config_file_name = optarg;
       break;
@@ -698,14 +700,20 @@ main(int argc, char **argv)
 
   initdisplay();
 
-  seq.n_in = n_ports; seq.n_out = enable_jack_output?n_ports:0;
+  // Force the config file to be loaded initially, so that we pick up the Jack
+  // client name to be used (if not set from the command line). This cannot be
+  // changed later, so if you want to make changes to the client name in the
+  // config file take effect, you need to restart the program.
+  read_config_file();
+
+  seq.client_name = jack_client_name;
+  seq.n_in = jack_num_outputs>1?jack_num_outputs:1;
+  seq.n_out = jack_num_outputs;
   if (!init_jack(&seq, debug_jack)) {
     exit(1);
   }
 
   signal(SIGINT, quitter);
-  // force the config file to be loaded initially
-  count = MAX_COUNT;
   while (!quit) {
     uint8_t portno;
     while (pop_midi(&seq, msg, &portno)) {

midizap.h

@@ -93,5 +93,6 @@ extern int debug_regex, debug_strokes, debug_keys, debug_midi;
 extern int default_debug_regex, default_debug_strokes, default_debug_keys,
   default_debug_midi;
 extern char *config_file_name;
-extern int enable_jack_output;
+extern int jack_num_outputs;
 extern int midi_octave;
+extern char *jack_client_name;

readconfig.c

@@ -199,6 +199,8 @@ int debug_midi = 0;
 
 int midi_octave = 0;
 
+char *jack_client_name = NULL;
+
 char *
 allocate(size_t len)
 {
@@ -1211,6 +1213,27 @@ read_config_file(void)
 	debug_midi = 1;
 	continue;
       }
+      if (!strcmp(tok, "JACK_NAME")) {
+	char *a = token(NULL, &delim);
+	if (!jack_client_name) {
+	  static char buf[100];
+	  strncpy(buf, a, 100); buf[99] = 0; // just in case...
+	  jack_client_name = buf;
+	}
+	continue;
+      }
+      if (!strcmp(tok, "JACK_PORTS")) {
+	char *a = token(NULL, &delim);
+	int k, n;
+	if (!jack_num_outputs) {
+	  if (sscanf(a, "%d%n", &k, &n) == 1 && !a[n] && k>=1 && k<=2) {
+	    jack_num_outputs = k;
+	  } else {
+	    fprintf(stderr, "invalid port number: %s, must be 1 or 2\n", a);
+	  }
+	}
+	continue;
+      }
       if (!strncmp(tok, "MIDI_OCTAVE", 11)) {
 	char *a = tok+11;
 	int k, n;