Re: New hotplug interface is not working right for me

[Kay Sievers <kay.sievers@vrfy.org>]

On Fri, 2005-03-11 at 08:38 -0500, Eric S. Raymond wrote:
> Kay Sievers <kay.sievers@vrfy.org>:
> > Yeah, I'm all for doing this with udev rules. It is already working on
> > my box. We just need to agree if and how we should do that. The plan is
> > to add hotplug scripts with udev rules and execute scripts based on the
> > same rule logic we use to name the device node.
> > 
> > Your hook into hotplug with a udev rule would look like this:
> >   ACTION="add", SYSFS{vendor}="GPS", SYSFS{product}="0815", NAME="gps", HOTPLUG="/usr/bin/gps-something"
> 
> Hmm, this looks interesting.  I'm looking at the udev man page, and it looks
> as though rules like this might work:

No, not today, not with the current version. We are just thought about
adding rule based program execution, cause it is similar to all the
match logic to name a device and it would be more elegant than the
current directory searching.

> # The Prolific Technology 2303 (commonly in tandem with SiRF chips)
> BUS="usb" ACTION="add" SYSFS{vendor}="067b" SYSFS{product}="2303" \
> 		NAME="gps%e" \
> 		HOTPLUG="/usr/bin/gps-probe"
> # FTDI 8U232AM
> BUS="usb" ACTION="add" SYSFS{vendor}="0403" SYSFS{product}="6001" \
> 		NAME="gps%e" \
> 		HOTPLUG="/usr/bin/gps-probe"
> # Cypress M8/CY7C64013 (DeLorme uses these)
> BUS="usb" ACTION="add" SYSFS{vendor}="1163" SYSFS{product}="0100" \
> 		NAME="gps%e" \
> 		HOTPLUG="/usr/bin/gps-probe"
> 
> 1. Am I correct that when triggered, these would create a device called
>    /dev/gpsN for some enumerated N?

Yes, this would be correct, if we decide to support the HOTPLUG key. For
now you need to put a script in /etc/dev.d/* that needs to check if a
DEVNAME=gps* is in the environment.

And the enumeration %e is an ugly thing in a world where devices can
come and go at any time. The result is unpredictable if you don't
connect and probe in the same order every time and under all situations
like suspend/resume, reboot, later plug-in.
If possible, these simple kind of enumerations should be avoided and the
names should depend on a unique attribute like a device serial number or
similar. Or the physical location can possibly be included in the device
node name if there is no better attribute.

> 2. What is the lifetime of that device?  Under what circumstances is it
>    removed?

The device will stay there as long as the kernel represents the device.
If the kernel discovers a USB-disconnect the node will be removed and a
newly connected device will get the lowest free %e number in the node
name.

Kay



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