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

[Greg KH <greg@kroah.com>]

On Tue, Oct 08, 2002 at 10:02:59AM -0700, David Brownell wrote:
> 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.

What needs to be different?

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

Hey, it's not my fault you have good error checking :)

Seriously, we're going to have to upgrade the hotplug scripts for 2.5
anyway, so this problem will go away soon enough.

> >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).

I like Pat's suggestion of DEV_PATH.  Does anyone object to this?

>     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.)

Wait, why does anyone need to use the usbfs path (what is specified by
DEVICE= in the usb code)?  All of the info that usbmodules used to get
is now present in DEV_PATH, right?  If not, let me know.

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

Why not?  That lets us load drivers based on vendor and product id.  The
interface specific calls let us load protocol specific drivers, giving
us a semblance of heirachy that a lot of people used to want a few years
ago (and Johannes provided a patch for a long time ago.)

And if the hotplug scripts don't want to do anything with this event,
it's quite easy to ignore :)

>     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.

The USB core needs it?  Or the hotplug scripts?

I'm curious about this, as I'm looking at a device that might need to
have it's second configuration enabled if it's running on Linux, yet the
default config is for when running on Windows.

> >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.

Well, with a rename to DEV_PATH that should work out fine.

Also, any reason to keep the DEVFS variable?  It's wrongly named, and
doesn't look like anyone uses it.

thanks,

greg k-h


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