Notify application to refresh MIDI ports in user-mode MIDI driver

NTDEV
1

I'm writing a user-mode MIDI driver which creates multiple virtual MIDI ports.
The driver can change number of ports on configuration change. But now the user application can only see new ports after restart. How can a user-mode driver notify application to refresh MIDI ports?
The driver is an Installable Drivers, and use Audio Device Messages for MIDI to create MIDI ports.

[Installable Drivers](https://learn.microsoft.com/en-us/windows/win32/multimedia/installable-drivers)
[Audio Device Messages for MIDI](https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/audio-device-messages-for-midi)

2

Unfortunately, the mmsystem user-mode installable driver model has not been supported for many years. It still works, but you aren't going to find any official Microsoft support for it.

There aren't any APIs for sending unsolicited messages like that. I suppose if the application changes the number of ports it wants, it should call MODM_GETNUMDEVS until that changes.

Installable drivers are just user-mode apps. You could create a custom named event for this, I suppose.