Re: work-around for video4linux sysfs

[Kees Cook <kees@outflux.net>]

On Fri, Aug 03, 2007 at 12:30:12AM +0200, Kay Sievers wrote:
> > I have no problem changing it to be more in line with what you'd like
> > to see; I just want to solve the problem.  :)  Can you make some
> > suggestions on what a clean solution would look like?
> 
> Can there be more than one device of the same type at the same pci
> instance? If not why not just have:
>   pci-0000:01:06.0-video -> ../../video0
>   pci-0000:01:07.0-video -> ../../video1
> 
> For USB devices it could just look like:
>   pci-0000:00:1d.2-usb-0:1:1.0-video -> ../../video0
>   pci-0000:00:1d.2-usb-0:1:1.0-radio -> ../../radio0

Unfortunately, you can have multiple of the same type for the same PCI
instance, which I worked around in the original patch.  This is related
to how some v4l drivers deal with multiple output modes from the same
card[1] (e.g. MPEG2 encoder output, YUV output, audio only output, etc,
are associated with an offset minor number).  It's really ugly.  :(

What I did was limit the by-path links to only the first 10 video
devices:

+# This is limited to the first 10 video devices to avoid per-driver 
+# device duplication (like ivtv), since we have no way to distinguish
+# interfaces via sysfs in a driver-agnostic way yet.  If OPTIONS allowed
+# replacement, we could set link_priority to -%m to give preference to the
+# first v4l interface per physical device.
+ENV{ID_PATH}="?*", KERNEL="video[0-9]", SYMLINK+="v4l/by-path/$env{ID_PATH}"

If %m was expanded in OPTIONS, then preference in links could be given
to the first interface a driver assigned for a given card.  Beyond that,
I could only think to avoid ivtv's minor id assignment ugliness by just
not support having >10 video cards in the same system, which didn't seem
like too bad of a compromise.

-Kees

[1] http://ivtvdriver.org/index.php/FAQ

-- 
Kees Cook                                            @outflux.net

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