USB_POISON_URB(9)                         USB Core APIs                         USB_POISON_URB(9)



NAME
       usb_poison_urb - reliably kill a transfer and prevent further use of an URB

SYNOPSIS
       void usb_poison_urb(struct urb * urb);

ARGUMENTS
       urb
           pointer to URB describing a previously submitted request, may be NULL

DESCRIPTION
       This routine cancels an in-progress request. It is guaranteed that upon return all
       completion handlers will have finished and the URB will be totally idle and cannot be
       reused. These features make this an ideal way to stop I/O in a disconnect callback. If the
       request has not already finished or been unlinked the completion handler will see
       urb->status == -ENOENT.

       After and while the routine runs, attempts to resubmit the URB will fail with error
       -EPERM. Thus even if the URB's completion handler always tries to resubmit, it will not
       succeed and the URB will become idle.

       The URB must not be deallocated while this routine is running. In particular, when a
       driver calls this routine, it must insure that the completion handler cannot deallocate
       the URB.

       This routine may not be used in an interrupt context (such as a bottom half or a
       completion handler), or when holding a spinlock, or in other situations where the caller
       can't schedule.

       This routine should not be called by a driver after its disconnect method has returned.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                         USB_POISON_URB(9)