Re: /sbin/hotplug invocation for USB devices in 2.5.40

[David Brownell <david-b@pacbell.net>]

Greg KH wrote:
> As almost no one noticed, I changed the environment variables that
> /sbin/hotplug is called with in 2.5.40 :)

I look at it just a bit differently ... where previously it only
issued calls for the first interface (typically that's all there is),
now it issues calls for every interface, _plus_ a call for a new kind
of thing never before seen through hotplug, a "usb device".

I really like the "event for each interface" change, though I'd
like it a bit better if we could tell this 2.5+ behavior apart
from earlier ones -- so hotplug agents can act accordingly.

Its that new type of hotplug event that makes recent kernels trigger
syslog messages about "Bad USB agent invocation".


> Now I know this overloads the existing DEVICE usage for USB devices, but
> I think we can determine what do properly (basically just test for
> DEVFS, and if it's not set, then we are looking at the driverfs entry
> for the device.)

I'd rather see these changes:

   - This new parameter to every (!!) hotplug event gets renamed to
     KFS_DEVICE (assuming that's the new driverfs name).

     Hotplug agents will need to access KFS data *and* talk to the
     device (and its drivers) using the DEVICE= path.  Plus, if this
     is present we know we don't need to ask 'usbmodules' to scan
     other interfaces for us.  (That often triggers other problems.)

   - Don't make hotplug calls for USB devices until we have something
     for them to do.  (Essentially these are a new class of event.)

     The example that comes to mind is policy agents using those
     events to choose a non-default device configuration.  But USB
     needs a bunch of work before such things become practical.

I think both of those would be simple changes to make.  They'd
greatly improve backward compatibility, while letting us do better
things on Linux Next Generation systems.



> I also created a lot of individual driverfs files for the USB device,
> basically everything that used to be specified by a environment variable
> in the call to /sbin/hotplug, is now a value in a file.  So ideally, we
> can get rid of those other variables for the USB call, and just rely on
> the info present in driverfs.

That'd only work if both KFS_DEVICE and DEVICE are simultaneously available.
See above ... :)  I wouldn't de-support the other parameters for quite
a while, though it's certainly good to have such improved flexibility.

By the way, what's the cost of a driverfs attribute on a 'struct device'?
Each USB device now has over a dozen of them.

- Dave





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