Re: Is libusb dead?

I sense a certain theme here...  :-)

On Sun, 22 Apr 2007, Greg KH wrote:

> > Something I've meant to ask for a while...  What about things that apply
> > to an entire interface or device, as opposed to a single endpoint?
> > 
> > In addition to sending or cancelling URBs, usbfs allows users to:
> > 
> > 	Issue a USB port reset to the device;
> > 
> > 	Find out the name of the driver bound to an interface;
> 
> Use sysfs

A little tricky, since it involves parsing the last component of a 
pathname stored in a symlink, but doable.

> > 	Unbind a kernel driver from an interface;
> 
> Use sysfs
> 
> > 	Find out the device's address and speed (although it doesn't
> > 	distinguish between full and high);
> 
> Use sysfs
> 
> > 	Change the altsetting for an interface;
> 
> Use sysfs

Actually this cannot be done using sysfs.  The bAlternateSetting attribute 
is read-only.  As it should be, since the altsetting is supposed to be 
determined by the driver owning the interface.

The case in question arises when a userspace driver owns the interface via 
usbfs.  The driver then needs a way to select an altsetting.

> > 	Change the device configuration;
> 
> Use sysfs
> 
> > 	Claim (bind usbfs to) an interface;
> 
> Use sysfs

Again, it can't be done.  You can use sysfs to bind a kernel driver to an 
interface, but you can't use it to bind a userspace program the way usbfs 
allows.

> > 	Release (unbind usbfs from) an interface.
> 
> Use sysfs

Likewise here.

> Let's not have a lot of duplication if we can help it :)

I agree.  Most of these things can indeed be done through sysfs.

The hardest aspect is matching up pathnames in usbfs with the
corresponding pathnames in sysfs.  Going from a usbfs name to a sysfs
path can be accomplished by looking in /sys/class/usb_device.  The other
direction is a little harder.  We have a "devnum" attribute but not a
"busnum" attribute.  Should I add one?

Alan Stern


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