failing to force-claim USB interface

failing to force-claim USB interface

[Martin F Krafft]

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I am trying to make use of the usbfs USBDEVFS_DISCONNECT ioctl, and
I am failing. Here is the code:

  struct usb_device *dev;
  [...]
  sprintf(path, "/proc/bus/usb/%s/%s", dev->bus->dirname, dev->filename);
  int fd = open(path);
  struct usbdevfs_ioctl command = { 0, USBDEVFS_DISCONNECT, 0 };
  ioctl (fd, USBDEVFS_IOCTL, &command) < 0

However, the ioctl always fails. I am not sure whether I am using
the right values for the file descriptor passed to ioctl(), or what
the interface number (first parameter of usbdevfs_ioctl) is.

Maybe someone could offer me some advice or tell me to RTFM (but
please specify TM to FR).

Thanks,

-- 
Martin F. Krafft                Artificial Intelligence Laboratory
Ph.D. Student                   Department of Information Technology
Email: krafft@ailab.ch          University of Zurich
Tel: +41.(0)1.63-54323          Andreasstrasse 15, Office 2.20
http://ailab.ch/people/krafft   CH-8050 Zurich, Switzerland
 
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[solved] failing to force-claim USB interface

[martin f krafft]

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also sprach Martin F Krafft <krafft@ailab.ch> [2004.01.19.1646 +0100]:
>   struct usb_device *dev;
>   [...]
>   sprintf(path, "/proc/bus/usb/%s/%s", dev->bus->dirname, dev->filename);
>   int fd = open(path);
>   struct usbdevfs_ioctl command = { 0, USBDEVFS_DISCONNECT, 0 };
>   ioctl (fd, USBDEVFS_IOCTL, &command) < 0

I was using the wrong fd. The following works:

  struct usb_device *dev;
  [...]
  struct usb_device_handle udev = usb_open(dev);
  struct usbdevfs_ioctl command = { 0, USBDEVFS_DISCONNECT, 0 };
  ioctl(udev->fd, USBDEVFS_IOCTL, &command)

Now the only thing left to figure out is how the libusb library
expects us to do this, because struct usb_device_handle; is not
implemented in the exported interface.

I guess the solution is to implement the above functionality in
libusb itself.

-- 
martin;              (greetings from the heart of the sun.)
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Re: failing to force-claim USB interface

[David Brownell]

> I am trying to make use of the usbfs USBDEVFS_DISCONNECT ioctl, and
> I am failing.

Appended, see a snippet of code which worked reliably way back on
the original 2.4 patch.  Maybe you tripped on the precondition?
Or maybe this is just broken so far in 2.6.

A fair amount of usbfs code is at least slightly broken in 2.6;
some usbcore driver model changes are still needed in the area
of this particular ioctl.  (Which got mangled more than most
during its evolution.)  Was this with a 2.6.1 kernel?

I'm thinking this kind of thing ought to be generically doable
with sysfs, maybe with symlink/unlink syscalls between device
and driver nodes.

- Dave


     if (ioctl (fd, USBDEVFS_CLAIMINTERFACE, &ifno) < 0) {
#ifdef  USBDEVFS_DISCONNECT
         int                             saved_errno = errno;
         struct usbdevfs_ioctl           command;
         int                             retval;

         /*
          * maybe we need to boot a kernel driver off before we
          * can bind to this.  a "polite" unbind might be nice;
          * for now we expect apps to adopt a reasonble policy,
          * checking if it's claimed already (when it matters).
          */
         if (saved_errno != EBUSY)
             return -errno;
         command.ifno = ifno;
         command.ioctl_code = USBDEVFS_DISCONNECT;
         command.data = 0;
         retval = ioctl (fd, USBDEVFS_IOCTL, &command);
         if (retval < 0)
             return -saved_errno;

         if (ioctl (fd, USBDEVFS_CLAIMINTERFACE, &ifno) < 0)
             return -errno;
#else
         return -errno;
#endif
     }
     return 0;