Re: [PATCH 0/5] ALSA: firewire-tascam: add MIDI functionality

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

On Oct 20 Takashi Sakamoto wrote:
> When using polkit correctly, I guess users doesn't need to join in
> 'audio' group, so as PulseAudio achieved with polkit.

With regard to access to /dev/fw* files, this is true with the existing
FFADO rules too.  60-ffado.rules sets ENV{ID_FFADO}="1", and
consolekit's 70-udev-acl.rules recognizes ID_FFADO and runs udev-acl on
the device.

(I.e. the current "console" owner is granted access to the character
device file via access control list (ACL), which is a mechanism in
parallel to Unix permission flags.)

The console owner policy and ACL mechanism are not a complete replacement
for the group mechanism though:
  - There may be headless systems and other occasions at which the audio
    user is not console owner.
  - Processes involved in capture or playback, i.e. applications beyond
    mixers, may require realtime scheduling class privilege and memlocking
    privilege, which are traditionally configured for Unix groups and
    users (typically for a group).  Not sure whether a mechanism exists
    which can implement a console owner policy for realtime and memlock
    privileges.
-- 
Stefan Richter
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http://arcgraph.de/sr/