[GRLUG] GRLUG Potluck and Udev

[Ben Rousch]

On Wed, Dec 23, 2009 at 10:34 AM, Michael Mol <mikemol at gmail.com> wrote:
> On Wed, Dec 23, 2009 at 9:54 AM, Ben Rousch <brousch at gmail.com> wrote:
>> I had a great time at the GRLUG potluck last night. Thanks again,
>> Casey, for letting us take over your garage!
>>
>> Someone asked a question about disabling a device that had been
>> activated by udev, and I don't remember a conclusive answer
>> being reached. This interesting article [1] showed up in my
>> feed reader today, and it has a little information about udev.
>> A little further reading courtesy of the Arch Linux wiki [2]
>> makes me think that disabling the device after it has already
>> been detected and running would require a device-specific
>> command. Now you could prevent it from loading in the first
>> place by using a udev rule, but I don't know that you can use
>> udev to actually cripple it afterwards.
>
> The general topic at that moment was the webcam built into laptops,
> and how could one effectively disable the webcam without physically
> removing or modifying the device.

There is a package for my EeePC that gives me a menu where I can
enable and disable the webcam, wifi, bluetooth, and SD card slot. You
can see a screenshot of it, and see the source code at [3]. I could
not get the git to clone, but there is a tarball available.

[3]  http://greg.geekmind.org/eee-control/

>
> Granted, a software method isn't going to be as effective, but the key
> question is how do you get a behavior analogous to the device control
> you get under Windows? (In particular, go to Control Panel -> System
> -> Device Manager.  You can enable and disable devices at the kernel
> level from in there.)
>
> The problem with the approaches discussed at first, such as removing
> the /dev/video0 node, aren't ideal, because /dev/video0 is merely a
> device node with a particular major/minor number binding it to a
> particular device from the kernel's perspective. Anyone who can run
> mknod can create a device node with the same capabilities just about
> anywhere else and give it the same major/minor number.
>
> Most specifically, the the question becomes "how can one disable and
> enable a particular USB UVC (that webcame) device in software?"  Most
> generally, the question becomes "how can one disable and enable an
> arbitrary device found in sysfs, in software?"
>
> I haven't finished reading through the linked articles.
>
> --
> :wq
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-- 
  Ben Rousch
  brousch at gmail.com
  http://ishmilok.blogspot.com/
  http://tech-ishmilok.blogspot.com/