Re: [PATCH] Driver core: Don't ignore bus_attach_device() retval

[Alan Stern]

On Mon, 9 Oct 2006, Cornelia Huck wrote:

> From: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> 
> Check for return value of bus_attach_device() in device_add(). Add a
> function bus_delete_device() that undos the effects of bus_add_device().
> bus_remove_device() now undos the effects of bus_attach_device() only.
> device_del() now calls bus_remove_device(), kobject_uevent(),
> bus_delete_device() which makes it symmetric to the call sequence in
> device_add().

You know, I'm not so sure device registration should fail when 
bus_attach_device() returns an error.

After all, the device really is there even if it's not working properly.  
In the Windows device manager it would show up with a big red X through 
it, but it _would_ show up.

Furthermore there are subtle problems that can arise.  In effect, the
device is registered for a brief time (while the driver is probed) and
then unregistered without giving the bus subsystem a chance to prepare for
the removal.  With USB this can lead to problems; if the driver called
usb_set_interface() then child devices would be created below the one
being probed -- and they would never get removed.

Has this question been raised before?  Is there any reason not to 
register a device even when probing fails?

In fact, we might want to separate driver probing from device_add()  
entirely.  That is, make them available as two separate function calls.  
That way the subsystem driver will have a chance to create attribute files
before a uevent is generated and a driver is loaded.  (That should help
udev to work better.)  This would require a larger change, though --
probably requiring an alternate version of device_add().

Alan Stern


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