Commit 719df469 authored May 06, 2005 by Roman Kagan Committed by Greg KH Jun 03, 2005

[PATCH] USB: update urb documentation



On Wed, May 04, 2005 at 01:37:30PM -0700, David Brownell wrote:
> On Wednesday 04 May 2005 12:19 pm, Roman Kagan wrote:
> > struct urb {
> > 	/* private, usb core and host controller only fields in the urb */
> > 	...
> > 	struct list_head urb_list;	/* list pointer to all active urbs */
> > 	...
> > };
> >
> > Is it safe to use it for driver's purposes when the driver owns the urb,
> > that is, starting from the completion routine until the urb is submitted
> > with usb_submit_urb()?
>
> Right now, it should be.

Great!  FWIW I've briefly tested a modified version of usbatm using
the list head in struct urb instead of creating a wrapper struct, and I
haven't seen any failures yet.  So I tend to believe that your "should
be" actually means "is" :)

> > If it is, can it be guaranteed in future, e.g.
> > by moving the list head into the public section of struct urb?
>
> In fact I'm not sure why it ever got called "private" to usbcore/hcds.
> I thought the idea was that it should be like urb->status, reserved for
> whoever controls the URB.

OK then how about the following (essentially documentation) patch?

Signed-off-by: Roman Kagan <rkagan@mail.ru>
Acked-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent 1724757e

include/linux/usb.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -796,6 +796,10 @@ typedef void (usb_complete_t)(struct urb , struct pt_regs *);
		* of the iso_frame_desc array, and the number of errors is reported in
		* error_count. Completion callbacks for ISO transfers will normally
		* (re)submit URBs to ensure a constant transfer rate.
		*
		* Note that even fields marked "public" should not be touched by the driver
		* when the urb is owned by the hcd, that is, since the call to
		* usb_submit_urb() till the entry into the completion routine.
		*/
		struct urb
		{
		@@ -803,12 +807,12 @@ struct urb
		struct kref kref; /* reference count of the URB */
		spinlock_t lock; /* lock for the URB */
		void hcpriv; / private data for host controller */
		struct list_head urb_list; /* list pointer to all active urbs */
		int bandwidth; /* bandwidth for INT/ISO request */
		atomic_t use_count; /* concurrent submissions counter */
		u8 reject; /* submissions will fail */

		/* public, documented fields in the urb that can be used by drivers */
		struct list_head urb_list; /* list head for use by the urb owner */
		struct usb_device dev; / (in) pointer to associated device */
		unsigned int pipe; /* (in) pipe information */
		int status; /* (return) non-ISO status */

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