Re: [PATCH V2 1/3] usb: add kerneldoc for usb_get_hub_child_device function

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

On 2012/5/16 22:33, Alan Stern wrote:
> On Wed, 16 May 2012, Lan Tianyu wrote:
>
> > > Ick, no, again, make it an iterator, as that's what you really want,
> > > right?
> > Sorry. That's not really I want. If make it an iterator, how to get one hub's child?
>
> You can write both an iterator and a single-access function.
Yeah. I will do it.
> > As you know, I will also work on power off mechanism. In some places, I need
> > to get one port's child or check whether there is a device on the port. So
> > an iterator doesn't work.
> >
> > An more question: If I make an iterator, different places have different
> > process way. That means to add an callback param?
> >
> > usb_hub_children_iterator(hdev, callback)
> > {
> > 	struct usb_hub *hub = hdev_to_hub(hdev);
> > 	struct usb_device *child;
> > 	int port1;
> > 	
> > 	for(port1 = 1; port1<  hdev->maxchild; port1++) {
> > 		child = usb_get_dev(hub->port_data[port1 - 1].child);
> >
> > 		if (child) {
> > 			usb_lock_device(child);
> > 			callback(child);
> > 			usb_unlock_device(child);
> > 			usb_put_dev(child);
> > 		}				
> > 	}
> > }
> > right?
>
> IMO it would be better to copy the pattern used by list_for_each(), if
> you can.  That pattern doesn't use a callback.
>
> Also, you should check to see whether the usb_lock_device() call is
> really needed.  If the caller already owns the lock for the parent hub
> then you don't need to lock the child -- you don't even need the
> usb_{get,put}_dev() calls.

How about this?
#define usb_get_hub_each_child(hdev, port1, child) \
	for (port1 = 1, child = usb_get_hub_child(hdev, port1); \
		port1 <= hdev->maxchild; child = \
	 	usb_get_hub_child(hdev, ++port1))

usb_get_hub_child(hdev, port1)
{
	struct usb_hub *hub = hdev_to_hub(hdev);
 	return usb_get_dev(hub->port_data[port1 - 1].child);
}

For more general, usb_get_hub_child() increases child refcount
to prevent child from being removed during processing and the caller
should invoke usb_put_dev() when child will never be used.

> Alan Stern


--
Best Regards
Tianyu Lan
linux kernel enabling team
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