udev and usb.agent

udev and usb.agent

[Greg Bell]

Hi Developers,

On my FC4 system, hotplug calls /etc/hotplug/usb.agent (and therefore my 
/etc/hotplug/usb/camera script).  However, it doesn't run udev until 
AFTER, so my /dev/sd?1 mapping to /dev/camera hasn't happened yet when my 
camera script is running.

What am I doing wrong?  Is there a way to get hotplug to call udev to do 
the device mapping BEFORE usb.agent gets called?

Thanks,

~greg bell


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Re: udev and usb.agent

[Kay Sievers]

On Sat, Oct 15, 2005 at 04:14:29PM +1000, Greg Bell wrote:
> 
> Hi Developers,
> 
> On my FC4 system, hotplug calls /etc/hotplug/usb.agent (and therefore my 
> /etc/hotplug/usb/camera script).  However, it doesn't run udev until 
> AFTER, so my /dev/sd?1 mapping to /dev/camera hasn't happened yet when my 
> camera script is running.
> 
> What am I doing wrong?  Is there a way to get hotplug to call udev to do 
> the device mapping BEFORE usb.agent gets called?

The "camera script" is probably triggered by the usb device event, not the
block device event. Use an explicit udev rule that matches the block device
and the usb properties of the camera. The old agent crap should no longer
be used.

Btw: HAL which should be running on your box is expected to manage that
in conjunction with your desktop session. Modern desktop setups don't
need to fiddle around with device id's and scripts to make your camera
just work.

Kay


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Re: udev and usb.agent

[Greg Bell]

>> What am I doing wrong?  Is there a way to get hotplug to call udev to do
>> the device mapping BEFORE usb.agent gets called?
>
> The "camera script" is probably triggered by the usb device event, not the
> block device event. Use an explicit udev rule that matches the block device
> and the usb properties of the camera.

But the udev, whether the rule is for USB or SCSI, is getting run after 
the usb.agent stuff...

> The old agent crap should no longer
> be used.

But udev only does device creation, not scripts.

> Modern desktop setups don't
> need to fiddle around with device id's and scripts to make your camera
> just work.

Sure, they 'just work', but they don't do the fun stuff I'm hoping to 
script up...

So, again, why does hotplug call udev *after* it calls usb.agent? 
usb.agent can't do much since it doesn't have a nice static name for the 
newly inserted usb device until after udev runs...

~gb


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Re: udev and usb.agent

[Kay Sievers]

On Sun, Oct 16, 2005 at 09:33:39AM +1000, Greg Bell wrote:
> >>What am I doing wrong?  Is there a way to get hotplug to call udev to do
> >>the device mapping BEFORE usb.agent gets called?
> >
> >The "camera script" is probably triggered by the usb device event, not the
> >block device event. Use an explicit udev rule that matches the block device
> >and the usb properties of the camera.
> 
> But the udev, whether the rule is for USB or SCSI, is getting run after 
> the usb.agent stuff...

Probably, but usb.agent has nothing to do with the block device event!
These are completely different events...

> >The old agent crap should no longer
> >be used.
> 
> But udev only does device creation, not scripts.

Catch up! udev does _all_ hotplug today. Everything that runs on hotplug
events is managed by udev. You can plug into any stage of the event
processing with udev rules and run an unlimited number of scripts...

> >Modern desktop setups don't
> >need to fiddle around with device id's and scripts to make your camera
> >just work.
> 
> Sure, they 'just work', but they don't do the fun stuff I'm hoping to 
> script up...
> 
> So, again, why does hotplug call udev *after* it calls usb.agent? 

Again, udev calls _everything_, also the agent stuff. Use the right
event, and everything will work!

> usb.agent can't do much since it doesn't have a nice static name for the 
> newly inserted usb device until after udev runs...

Matching on the right event will carry DEVNAME in the environment, which
is the name of the node.

Good luck,
Kay


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Re: udev and usb.agent

[Greg Bell]

> Catch up! udev does _all_ hotplug today.

Oh, oops.  OK I've done some more reading.  However the FAQ at
   http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev-FAQ

...says/implies that udev is for creating the /dev nodes and not much else 
because that's where devfs went wrong (trying to do too much).  They even 
refer the reader to HAL for the fancier more desktopy stuff.

I see the PROGRAM= feature, but it seems that's run before the dev node 
gets created, and is intended for using a script to figure out what the 
node should be named, rather than reacting after the node's been created.

Maybe I'm looking at a multiple line udev.rules entry.  I'm used to the 
main part of the event matching being a BUS= or KERNEL=.

My understanding of what goes on is:

1) device is plugged in
2) USB event occurs
3) udev or usb.agent inserts SCSI module (sr_mod)
4) SCSI event occurs
5) udev creates /dev/camera (my rule)
6) ??? reacts and runs script to automatically slurp pictures off, etc.

Its step 6 I'm having trouble with.

~gb


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Re: udev and usb.agent

[Kay Sievers]

On Mon, Oct 17, 2005 at 10:42:20AM +1000, Greg Bell wrote:
> 
> >Catch up! udev does _all_ hotplug today.
> 
> Oh, oops.  OK I've done some more reading.  However the FAQ at
>   http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev-FAQ
> 
> ...says/implies that udev is for creating the /dev nodes and not much else 
> because that's where devfs went wrong (trying to do too much).  They even 
> refer the reader to HAL for the fancier more desktopy stuff.
> 
> I see the PROGRAM= feature, but it seems that's run before the dev node 
> gets created, and is intended for using a script to figure out what the 
> node should be named, rather than reacting after the node's been created.

PROGRAM is for naming the node and therefore runs before the node is
created. RUN is for postprocessing.

> Maybe I'm looking at a multiple line udev.rules entry.  I'm used to the 
> main part of the event matching being a BUS= or KERNEL=.
> 
> My understanding of what goes on is:
> 
> 1) device is plugged in
> 2) USB event occurs
> 3) udev or usb.agent inserts SCSI module (sr_mod)
> 4) SCSI event occurs
> 5) udev creates /dev/camera (my rule)
> 6) ??? reacts and runs script to automatically slurp pictures off, etc.
> 
> Its step 6 I'm having trouble with.

Yeah, 6 runs along with 3, that's your trouble. :)
2 and 4 are different events, 2 will have finished before 4 even starts.
What you are looking for is 7, the block device event, which creates the
node.

Kay


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Re: udev and usb.agent

[Olivier Blin]

Greg Bell <gregbell@znet.com> writes:

>> Catch up! udev does _all_ hotplug today.
>
> Oh, oops.  OK I've done some more reading.  However the FAQ at
>   http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev-FAQ
>
> ...says/implies that udev is for creating the /dev nodes and not much else 
> because that's where devfs went wrong (trying to do too much).  They even 
> refer the reader to HAL for the fancier more desktopy stuff.

Maybe the udev FAQ should be updated then.
It's quite confusing to read this:
"udev is for managing /dev, not loading kernel drivers."

-- 
Olivier Blin
Mandriva



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Re: udev and usb.agent

[Kay Sievers]

On Thu, Oct 27, 2005 at 12:36:27PM +0200, Olivier Blin wrote:
> Greg Bell <gregbell@znet.com> writes:
> 
> >> Catch up! udev does _all_ hotplug today.
> >
> > Oh, oops.  OK I've done some more reading.  However the FAQ at
> >   http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev-FAQ
> >
> > ...says/implies that udev is for creating the /dev nodes and not much else 
> > because that's where devfs went wrong (trying to do too much).  They even 
> > refer the reader to HAL for the fancier more desktopy stuff.
> 
> Maybe the udev FAQ should be updated then.
> It's quite confusing to read this:
> "udev is for managing /dev, not loading kernel drivers."

Done.

Thanks,
Kay


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