On Tue, 12.05.09 13:40, Jaroslav Kysela (perex@xxxxxxxx) wrote: > > On Tue, 12 May 2009, Jaroslav Kysela wrote: > > > On Tue, 12 May 2009, Lennart Poettering wrote: > > > >> Heya! > >> > >> Traditionally low-level ALSA devices are opened with device strings like > >> 'hw:CARD' where CARD is either a numeric index or a card name. This > >> patch introduces a third syntax that allows you to specify the file name > >> of the control device node. The purpose for this is to make ALSA a bit > >> more like other Linux devices and allow implementaiton of udev device > >> symlinks similar to how disks are currently handled, with > >> /dev/disk/by-path/xxxx /dev/disk/by-id/xxxx and so on. > >> > >> With this patch this line: > >> > >> aplay -f CD -D hw:/dev/snd/controlC0 < /dev/urandom > >> > >> becomes equivalent to this line: > >> > >> aplay -f CD -D hw:0 < /dev/urandom > >> > >> A more useful example is this: > >> > >> aplay -f CD -D hw:/dev/snd/by-path/pci-0000:00:1a.7-usb-0:2:1.2 > >> > >> (this line requires a a few additional udev rules) > >> > >> This only works for control devices nodes, not for PCM or any other > >> device nodes. Since the control device node is used as 'entry point' > >> when opening PCM devices this is no limitation. > > > > NAK. Passing control device to open() functions is not a good idea. The > > snd_card_get_index() function might be extended to allow /dev style argument. > > Returned card index can be used as argument for hw: devices without this > > massive change. > > > > http://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=33ab0b5381c87e151e87e5000964edd868484886 > > I just noticed that snd_card_get_index() is used to parse "card" > configuration item when it's string, so control device name can be passed > instead card identification to all open() functions in alsa-lib with my > above patch, too. But it's preferred to use direct card index to reduce > control device open/close sequences. With my original patch there are no superfluous opens. Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net http://0pointer.net/lennart/ GnuPG 0x1A015CC4 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
