Re: How to identify USB-video-devices

[Carsten Meier <cm@trexity.de>]

Am Fri, 16 Jan 2009 00:40:47 +0100
schrieb "Markus Rechberger" <mrechberger@gmail.com>:

> On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de> wrote:
> > 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.
> >
> 
> check the device serial for this one. I don't know if the pvrusb2
> devices have it set up properly
> I know some manufacturers don't do!
> Be flexible with the node, but not with the serial.
> 
> cat /sys/class/video4linux/video0/device/serial
> 080702001788
> 
> you have the nodename in it, there are many ways to retrieve the
> nodename.

If I do a "ls /sys/class/video4linux/video0/" it simply prints:

dev  index  name  power  subsystem  uevent

and it will end up with many differnet cases to consider by any app. I
stay at my opinion that current bus_info-impl is broken. This *is* a
driver issue that needs fixing.

> 
> > 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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