Video devices

Video devices

[Paul Check]

Hi: I have a webcam and a pvr350 capture card (modules pwc and ivtv 
resp) attached to my machine, running 2.6.16 kernel and udev. The 
classic problem is that these modules get assigned to /dev/video0 and 
/dev/video1 in seemingly arbitrary ways. I've tried forcing module 
loading at boot time but still can't seem to get one to load first 
consistently.

So, I turned to writing udev rules and followed the "writing udev rules" 
document. My goal would be to have udev just symlink

/dev/webcam0   to   /dev/videoM

and

/dev/pvr0 to /dev/videoN,

where M and N are 0 and 1, assignmed however the system so chooses.

I've tried writing udev rules to symlink, but they didn't work. Upon 
further investigation I don't actually see any rules to create the video 
devices in the /etc/udev/rules.d/ directory. And yet, they are created. 
Also, I see they are mentioned in /etc/udev/devfs.rules, but there is no 
symlink to this file in the rules.d/ directory.

So, how do the video devices get created here? Is there some devfs 
left-over? Perhaps if I knew where the /dev/video?'s are being created 
I'd be able to figure out how to symlink to them?! I'm running debian 
unstable, fully updated.

Thanks, Paul


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Re: Video devices

[Kay Sievers]

On Mon, 2006-07-10 at 21:09 -0400, Paul Check wrote:
> Hi: I have a webcam and a pvr350 capture card (modules pwc and ivtv 
> resp) attached to my machine, running 2.6.16 kernel and udev. The 
> classic problem is that these modules get assigned to /dev/video0 and 
> /dev/video1 in seemingly arbitrary ways. I've tried forcing module 
> loading at boot time but still can't seem to get one to load first 
> consistently.
> 
> So, I turned to writing udev rules and followed the "writing udev rules" 
> document. My goal would be to have udev just symlink
> 
> /dev/webcam0   to   /dev/videoM
> 
> and
> 
> /dev/pvr0 to /dev/videoN,
> 
> where M and N are 0 and 1, assignmed however the system so chooses.
> 
> I've tried writing udev rules to symlink, but they didn't work. Upon 
> further investigation I don't actually see any rules to create the video 
> devices in the /etc/udev/rules.d/ directory. And yet, they are created. 
> Also, I see they are mentioned in /etc/udev/devfs.rules, but there is no 
> symlink to this file in the rules.d/ directory.
> 
> So, how do the video devices get created here? Is there some devfs 
> left-over? Perhaps if I knew where the /dev/video?'s are being created 
> I'd be able to figure out how to symlink to them?! I'm running debian 
> unstable, fully updated.

Udev does not need any rule to work, it just uses as the default the
kernel device name and creates the node owned by root.

Kay



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Re: Video devices

[Paul Check]

Kay Sievers wrote:

>On Mon, 2006-07-10 at 21:09 -0400, Paul Check wrote:
>  
>
>>Hi: I have a webcam and a pvr350 capture card (modules pwc and ivtv 
>>resp) attached to my machine, running 2.6.16 kernel and udev. The 
>>classic problem is that these modules get assigned to /dev/video0 and 
>>/dev/video1 in seemingly arbitrary ways. I've tried forcing module 
>>loading at boot time but still can't seem to get one to load first 
>>consistently.
>>
>>So, I turned to writing udev rules and followed the "writing udev rules" 
>>document. My goal would be to have udev just symlink
>>
>>/dev/webcam0   to   /dev/videoM
>>
>>and
>>
>>/dev/pvr0 to /dev/videoN,
>>
>>where M and N are 0 and 1, assignmed however the system so chooses.
>>
>>I've tried writing udev rules to symlink, but they didn't work. Upon 
>>further investigation I don't actually see any rules to create the video 
>>devices in the /etc/udev/rules.d/ directory. And yet, they are created. 
>>Also, I see they are mentioned in /etc/udev/devfs.rules, but there is no 
>>symlink to this file in the rules.d/ directory.
>>
>>So, how do the video devices get created here? Is there some devfs 
>>left-over? Perhaps if I knew where the /dev/video?'s are being created 
>>I'd be able to figure out how to symlink to them?! I'm running debian 
>>unstable, fully updated.
>>    
>>
>
>Udev does not need any rule to work, it just uses as the default the
>kernel device name and creates the node owned by root.
>
>Kay
>
>  
>
Hi Kay: Thanks for the reply. I really don't understand what you mean 
though.

Let me show what I did:

I created /etc/udev/local-late.rules containing:

KERNEL="ivtv", SYMLINK+="pvr0", GROUP="video"
KERNEL="pwc", SYMLINK+="webcam0", GROUP="video"

then created a symlink in /etc/udev/rules.d to that file:

z10_local-late.rules -> ../local-late.rules

and yet the /dev/webcam0 and /dev/pvr0 are not created.

Am I missing something there? I thought that perhaps since the video 
devices are created as part of the MAKEDEV script my symlinks wouldn't 
work. If not that, then why not, or...how to fix?

Thanks, Paul



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Re: Video devices

[Kay Sievers]

On Mon, 2006-07-10 at 22:08 -0400, Paul Check wrote:
> Kay Sievers wrote:
> 
> >On Mon, 2006-07-10 at 21:09 -0400, Paul Check wrote:
> >  
> >
> >>Hi: I have a webcam and a pvr350 capture card (modules pwc and ivtv 
> >>resp) attached to my machine, running 2.6.16 kernel and udev. The 
> >>classic problem is that these modules get assigned to /dev/video0 and 
> >>/dev/video1 in seemingly arbitrary ways. I've tried forcing module 
> >>loading at boot time but still can't seem to get one to load first 
> >>consistently.
> >>
> >>So, I turned to writing udev rules and followed the "writing udev rules" 
> >>document. My goal would be to have udev just symlink
> >>
> >>/dev/webcam0   to   /dev/videoM
> >>
> >>and
> >>
> >>/dev/pvr0 to /dev/videoN,
> >>
> >>where M and N are 0 and 1, assignmed however the system so chooses.
> >>
> >>I've tried writing udev rules to symlink, but they didn't work. Upon 
> >>further investigation I don't actually see any rules to create the video 
> >>devices in the /etc/udev/rules.d/ directory. And yet, they are created. 
> >>Also, I see they are mentioned in /etc/udev/devfs.rules, but there is no 
> >>symlink to this file in the rules.d/ directory.
> >>
> >>So, how do the video devices get created here? Is there some devfs 
> >>left-over? Perhaps if I knew where the /dev/video?'s are being created 
> >>I'd be able to figure out how to symlink to them?! I'm running debian 
> >>unstable, fully updated.
> >>    
> >>
> >
> >Udev does not need any rule to work, it just uses as the default the
> >kernel device name and creates the node owned by root.

> Let me show what I did:
> 
> I created /etc/udev/local-late.rules containing:
> 
> KERNEL="ivtv", SYMLINK+="pvr0", GROUP="video"
> KERNEL="pwc", SYMLINK+="webcam0", GROUP="video"
> 
> then created a symlink in /etc/udev/rules.d to that file:
> 
> z10_local-late.rules -> ../local-late.rules
> 
> and yet the /dev/webcam0 and /dev/pvr0 are not created.

Is "ivtv" and "pwc" really a kernel name (existing node)?
Don't you need to link to "video0" and "video1"?

You may want to try:
  udevinfo -a -p /class/video4linux/video0

select properties which identify the device and create a rule like:
  KERNEL="video*", SYSFS{idProduct}="a511", SYSFS{idVendor}="05a9", SYMLINK+="webcam0"

Kay



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