Re: [PATCH] udev: Allow ALSA input jacks to be accessed by the current user

[Takashi Iwai <tiwai@suse.de>]

At Thu, 16 Jun 2011 16:55:39 +0200,
Kay Sievers wrote:
> 
> On Thu, Jun 16, 2011 at 16:48, Takashi Iwai <tiwai@suse.de> wrote:
> > At Thu, 16 Jun 2011 16:28:08 +0200,
> > Kay Sievers wrote:
> >>
> >> On Thu, Jun 16, 2011 at 16:12, David Henningsson
> >> <david.henningsson@canonical.com> wrote:
> >> > One missing piece for userspace (PulseAudio etc) to actually be able to use
> >> > the jack input devices that ALSA create, is that these devices are
> >> > accessible by root only. This patch makes the input device nodes accessible
> >> > by the same users that can access the sound card: the current logged in
> >> > user, as well as users in the audio group.
> >> >
> >> > One thing I was thinking about, was that the udev-acl rule actually grants
> >> > read-write access to the input device node, where probably only read access
> >> > is needed. Is this dangerous?
> >>
> >> Takashi, wasn't there already something else to use from ALSA than the
> >> artificial input devices?
> >
> > These input devices are just notification from the sound driver at
> > jack plugging, so basically it's read-only indeed, and setting the
> > file permission RO would make sense.
> 
> Na, I mean, I remember you talking about some other channel of
> notifications about jack changes.

Ah, yeah, it's still possible to implement via ALSA control API, too.
Just add a new control element for jack notification, and the apps can
listen to it via normal ALSA API like the mixer elements.

> Didn't the input devices get replaced by something on the control
> device? Or was that just a plan?

I had some patches for it years ago, but never got merged.
If apps prefer it, I can revisit it.  Meanwhile, the jack-input stuff
is already present, so it might not be worth for it.


Takashi