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usb_poison_urb(9) [centos man page]

USB_POISON_URB(9)						   USB Core APIs						 USB_POISON_URB(9)

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 3.10 June 2014 USB_POISON_URB(9)

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USB_BULK_MSG(9) 						   USB Core APIs						   USB_BULK_MSG(9)

usb_bulk_msg - Builds a bulk urb, sends it off and waits for completion SYNOPSIS
int usb_bulk_msg(struct usb_device * usb_dev, unsigned int pipe, void * data, int len, int * actual_length, int timeout); ARGUMENTS
usb_dev pointer to the usb device to send the message to pipe endpoint "pipe" to send the message to data pointer to the data to send len length in bytes of the data to send actual_length pointer to a location to put the actual length transferred in bytes timeout time in msecs to wait for the message to complete before timing out (if 0 the wait is forever) CONTEXT
!in_interrupt () DESCRIPTION
This function sends a simple bulk message to a specified endpoint and waits for the message to complete, or timeout. Don't use this function from within an interrupt context, like a bottom half handler. If you need an asynchronous message, or need to send a message from within interrupt context, use usb_submit_urb If a thread in your driver uses this call, make sure your disconnect method can wait for it to complete. Since you don't have a handle on the URB used, you can't cancel the request. Because there is no usb_interrupt_msg and no USBDEVFS_INTERRUPT ioctl, users are forced to abuse this routine by using it to submit URBs for interrupt endpoints. We will take the liberty of creating an interrupt URB (with the default interval) if the target is an interrupt endpoint. RETURN
If successful, 0. Otherwise a negative error number. The number of actual bytes transferred will be stored in the actual_length paramater. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 USB_BULK_MSG(9)
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