Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

usb_init_urb(9) [centos man page]

USB_INIT_URB(9) 						   USB Core APIs						   USB_INIT_URB(9)

NAME
usb_init_urb - initializes a urb so that it can be used by a USB driver SYNOPSIS
void usb_init_urb(struct urb * urb); ARGUMENTS
urb pointer to the urb to initialize DESCRIPTION
Initializes a urb so that the USB subsystem can use it properly. If a urb is created with a call to usb_alloc_urb it is not necessary to call this function. Only use this if you allocate the space for a struct urb on your own. If you call this function, be careful when freeing the memory for your urb that it is no longer in use by the USB core. Only use this function if you _really_ understand what you are doing. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 USB_INIT_URB(9)

Check Out this Related Man Page

USB_UNLINK_URB(9)						   USB Core APIs						 USB_UNLINK_URB(9)

NAME
usb_unlink_urb - abort/cancel a transfer request for an endpoint SYNOPSIS
int usb_unlink_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. URBs complete only once per submission, and may be canceled only once per submission. Successful cancellation means termination of urb will be expedited and the completion handler will be called with a status code indicating that the request has been canceled (rather than any other code). Drivers should not call this routine or related routines, such as usb_kill_urb or usb_unlink_anchored_urbs, after their disconnect method has returned. The disconnect function should synchronize with a driver's I/O routines to insure that all URB-related activity has completed before it returns. This request is always asynchronous. Success is indicated by returning -EINPROGRESS, at which time the URB will probably not yet have been given back to the device driver. When it is eventually called, the completion function will see urb->status == -ECONNRESET. Failure is indicated by usb_unlink_urb returning any other value. Unlinking will fail when urb is not currently "linked" (i.e., it was never submitted, or it was unlinked before, or the hardware is already finished with it), even if the completion handler has not yet run. UNLINKING AND ENDPOINT QUEUES
[The behaviors and guarantees described below do not apply to virtual root hubs but only to endpoint queues for physical USB devices.] Host Controller Drivers (HCDs) place all the URBs for a particular endpoint in a queue. Normally the queue advances as the controller hardware processes each request. But when an URB terminates with an error its queue generally stops (see below), at least until that URB's completion routine returns. It is guaranteed that a stopped queue will not restart until all its unlinked URBs have been fully retired, with their completion routines run, even if that's not until some time after the original completion handler returns. The same behavior and guarantee apply when an URB terminates because it was unlinked. Bulk and interrupt endpoint queues are guaranteed to stop whenever an URB terminates with any sort of error, including -ECONNRESET, -ENOENT, and -EREMOTEIO. Control endpoint queues behave the same way except that they are not guaranteed to stop for -EREMOTEIO errors. Queues for isochronous endpoints are treated differently, because they must advance at fixed rates. Such queues do not stop when an URB encounters an error or is unlinked. An unlinked isochronous URB may leave a gap in the stream of packets; it is undefined whether such gaps can be filled in. Note that early termination of an URB because a short packet was received will generate a -EREMOTEIO error if and only if the URB_SHORT_NOT_OK flag is set. By setting this flag, USB device drivers can build deep queues for large or complex bulk transfers and clean them up reliably after any sort of aborted transfer by unlinking all pending URBs at the first fault. When a control URB terminates with an error other than -EREMOTEIO, it is quite likely that the status stage of the transfer will not take place. COPYRIGHT
Kernel Hackers Manual 2.6. July 2010 USB_UNLINK_URB(9)
Man Page

Featured Tech Videos