Re: udev: Access permission of fw character device in which fw node includes unit handled by ALSA

[Lennart Poettering <mznyfn@0pointer.de>]

On Mo, 20.05.19 21:27, Takashi Sakamoto (o-takashi@sakamocchi.jp) wrote:

> Hi all,
>
> I'm an ALSA developer, mainly committing to drivers for audio and
> music units on IEEE 1394 bus (yes, it's legacy FireWire). I have a
> concern about access permission for fw character device.

I am not sure I understand firewire well enough to say something too
smart. But if I understand correctly, then we (in systemd upstream)
currently only have these four firewire specific rules in our tree:

  SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x00010*", GROUP="video"
  SUBSYSTEM=="firewire", ATTR{units}=="*0x00b09d:0x00010*", GROUP="video"
  SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x010001*", GROUP="video"
  SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x014001*", GROUP="video"

And all of these are handled by some firewire core driver? The devices
you care about, how would the rules look like for this?

In general, when it comes to auto-loading of drivers we usually expect
the kernel to add modalias metadata to .ko files.

In the hwdb usually mostly only "auxiliary" data is stored, i.e. stuff
that is great to have but is not essential for a device to work
basically.

Rules files should generally be kept short. i.e. if you add 3 more
rules for the devices you care about, that'd be fine — if you add 100,
then that's not so great however, and another approach should be
found.

Anyway, given that I am not a firewire pro, I figure you have to
decide yourself what the best approach is, and then prep a PR and we
can have a look. Without looking at an (maybe just RFC) patch I am not
sure I grok enugh to properly comment on it.

Lennart

--
Lennart Poettering, Berlin
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