Returns the file descriptor of the connection to the kernel sound audio interface. Function returns an error code if an error was encountered.
The file descriptor should be used for the poll or select functions (see man 2 poll or man 2 select for more details) for determining, if something can be read or write. Application should call snd_rawmidi_read or snd_rawmidi_write functions if data is waiting to be read or a write can be done. Calling these functions is highly recommended.