Re: ALSA USB MIDI port names are poorly constructed and truncate iJACK names

[Takashi Iwai <tiwai@suse.de>]

On Tue, 22 Apr 2025 19:31:59 +0200,
Paul Davis wrote:
> 
> This patch was developed using the Debian 6.12.12 kernel source, but I
> believe it works without changes for current git.
> 
> The approach taken is to always look for the iProduct name
> (umidi->card->shortname) in the iJACK name (jack_name). If not found,
> the code path is unchanged. If found, a different string format is
> used to create the port name, using only the jack name. Note that
> since finding the product name in the jack name implies the jack name
> is not default_jack_name, there is never any reason to use "number" in
> constructing the port name.
> 
> This generates the expected port names for several USB MIDI devices
> here, some of which have "product name in jack name" and some which do
> not:
> 
> % aplaymidi -l
>  Port    Client name                      Port name
>  14:0    Midi Through                     Midi Through Port-0
>  16:0    Scarlett 18i20 USB               Scarlett 18i20 USB MIDI 1
>  36:0    Keystation 88                    Keystation 88 MIDI 1
>  40:0    Launchkey MK4 49                 Launchkey MK4 49 MIDI In
>  40:1    Launchkey MK4 49                 Launchkey MK4 49 DAW In
>  44:0    MidiSport 2x2                    MidiSport 2x2 MIDI 1
>  44:1    MidiSport 2x2                    MidiSport 2x2 MIDI 2
> 
> 
> Signed-off-by: Paul Davis <paul@linuxaudiosystems.com>
> 
> --- midi.c.orig    2025-04-22 11:20:30.192338737 -0600
> +++ midi.c    2025-04-22 11:20:47.373155820 -0600
> @@ -1817,10 +1817,18 @@ static void snd_usbmidi_init_substream(s
>      }
> 
>      port_info = find_port_info(umidi, number);
> -    name_format = port_info ? port_info->name :
> -        (jack_name != default_jack_name  ? "%s %s" : "%s %s %d");
> -    snprintf(substream->name, sizeof(substream->name),
> -         name_format, umidi->card->shortname, jack_name, number + 1);
> +
> +    if (strncmp (umidi->card->shortname, jack_name, strlen
> (umidi->card->shortname)) != 0) {
> +        name_format = port_info ? port_info->name :
> +            (jack_name != default_jack_name  ? "%s %s" : "%s %s %d");
> +        snprintf(substream->name, sizeof(substream->name),
> +                 name_format, umidi->card->shortname, jack_name, number + 1);
> +    } else {
> +        /* The manufacturer included the iProduct name in the jack
> name, do not use both */
> +        name_format = port_info ? port_info->name : "%s";
> +        snprintf(substream->name, sizeof(substream->name),
> name_format, jack_name);
> +    }

Thanks for the patch.

However, dropping the number suffix will break the uniqueness.
For example, in your case above, MidiSport 2x2 will have two identical
port names, I suppose?

IMO, we should keep adding the suffix number unless the uniqueness is
guaranteed instead of blindly dropping.  Admittedly the current code
isn't in the best form and this also needs more modification, too.

Also, the pre-defined port names defined in snd_usb_midi_port_info[]
have the format like "%s Synth", too, and those should be adjusted, as
well.

Last but not least, after we get a final form, could you try to submit
a patch in the proper format as defined in
  Documentation/process/submitting-patches.rst?


thanks,

Takashi