Re: How to identify USB-video-devices

[Carsten Meier <cm@trexity.de>]

Am Thu, 15 Jan 2009 22:22:11 +0000
schrieb Pádraig Brady <P@draigBrady.com>:

> Carsten Meier wrote:
> > Storing device-file-names is also not an option because they are
> > created dynamicly.
> 
> You use udev rules to give persistent names.
> 
> Here is my /etc/udev/rules.d/video.rules file,
> which creates /dev/webcam and /dev/tvtuner as appropriate.
> 
> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
> NAME="video%n", SYMLINK+="tvtuner"
> 
> To find distinguishing attributes to match on use:
> 
> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
> 
> cheers,
> Pádraig.

This already came up on the pvrusb2-list and someone told me (I don't
know much about udev) that it might cause problems on disconnection of
a device with a file-descriptor open which then gets reconnected
and there are two device-files for it. I also don't like it,
because an average user (including me) usually can't or don't want to
write udev rules. Finally v4l2 already contains a very simple and
reliable mechanism for doing this (bus_info-field) which simply isn't
used correctly by the USB-drivers.

My app should simply scan for /dev/video*-files, read out capabilities
from them, present the user menus to select devices and edit device
settings, save settings to a file and apply them on demand. This would
work fine if bus_info was filled right, without root-privileges,
without special udev rules or other sysfs-magic.

Regards,
Carsten

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