Re: hotplug arch. and apps

[Greg KH <greg@kroah.com>]

On Thu, Nov 15, 2001 at 12:38:03PM -0800, Scott Cuyle Fritzinger wrote:
> 
> Hey hotplug developers! My name is Scott Fritzinger, a developer with the
> gPhoto project (www.gphoto.org)
> 
> In pushing out our newest version (2.0), we are coming up with ideas as to
> how to make digital cameras truly "plug and play" (when the user plugs in
> the camera, it's ready to use). We have come up with the following
> solution:
> 
> Using a hotplug script (/etc/hotplug/usb/camera), we either set the
> ownership of the device (/proc/bus/usb/001/003 for example) to that of the
> locally logged in user in the case of a non-mass-storage camera, or we
> mount the mass-storage camera to /camera0 and set ownership again to the
> locally logged in user. this alleviates all the problems with permissions,
> and make the camera ready to use right away.

Sounds great.

> the base of this is of course a hotplug script. there is a catch though:
> how does hotplug know which cameras gphoto (or other applications)
> support? we can easily go through and append the ID's to
> /etc/hotplug/usb.handmap|usb.usermap, but what about when gphoto is
> updated with a new camera list? we'd have to go back through find out
> which entries are there, and then add new ones. and removing an ID would
> be a bit tough too.
> 
> I've come up with an idea that would make this REALLY easy to do, and it
> is only slightly different than what hotplug currently does. instead of
> just relying on usb.handmap or usb.usermap, why not create a directory
> /etc/hotplug/usb.map/ and place files in there that contain the ID's for
> the supported devices? the hotplug agent can open each file, look for ID's
> and then run the corresponding scripts.

This needs to play nice with the automated
/lib/modules/<kernel_version>/modules.usbmap files too (these are
automatically built by depmod so the hotplug scripts know what kernel
drivers match what devices.

But I suppose if no match is found in the kernel driver list, searching
a directory is a good idea.

> like, you can place all the HID device "lines" in /etc/hotplug/usb.map/hid

These should be covered by the modules.usbmap file.

> in our (gphoto's) case, we can place everything in
> /etc/hotplug/usb.map/camera for all known (still) camera ID's. This will
> be a VERY generic file, not gphoto specific at all, but rather supportive
> of all apps out there. this file will cause the agent to run the
> /etc/hotplug/usb/camera script, which will then mount (usb mass storage)
> or set permissions on the device. 

What would you expect the /etc/hotplug/usb.map/camera file to look like?
Would it have all usb product/vendor ids that gphoto2 works with, or
would there be single file for ever product/vendor pair?

> this design allows for other applications that implement user-land drivers
> via libusb to set up proper permissions on the device when it is plugged
> in. 

That is a great idea, and as more USB devices are supported by user
space programs (like gphoto) instead of kernel drivers, this will become
more important.

> is it possible alter the usb agent to work in this way? the downside would
> be disk hits for each file in /etc/hotplug/usb.map/* (a little slower),
> but the flexibility is that each application can EASILY update the devices
> it supports by just placing a file in there instead of having to search
> through a single file and replace (usb.handmap).

Don't worrry about the speed hit, the flexibility is much more important
(I don't think a user minds that a device takes an extra second or so to
initialize everything when it is plugged in.)

> ideas? thoughts?

I think it's a great idea, and am interested in further implementation
details.

thanks,

greg k-h

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