linux-kernel - Re: [PATCH 04/11] remove usb

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Date:	Thu, 07 Jun 2012 17:03:43 +0200
From:	Stefani Seibold <stefani@...bold.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
	oneukum@...e.de, alan@...rguk.ukuu.org.uk,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH 04/11] remove usb_interface pointer

Am Donnerstag, den 07.06.2012, 10:28 -0400 schrieb Alan Stern:
> On Thu, 7 Jun 2012, Stefani Seibold wrote:
> 
> > I tried to implement your idea to kick away the usb_device pointer, but
> > i think it is impossible. The skel_delete() function needs the
> > usb_device pointer for calling usb_put, which is called from
> > skel_disconnect() or skel_release().
>   
> Does skel_delete() really need to call usb_put_dev()?  I suspect that  
> the driver doesn't need to take a reference to either the device or the
> interface.
>  

I think it will be needed, since usb core will decrement the reference
when the device go away. Lock every access to the usb core if a tedious
thing and will waste a lot of code.

The problem with hotpluging is not the plug, it is the unplug, which can
happen any time.

BTW: An interface have no reference count.

> > A call of interface_to_usbdev(dev->intf) results in a udev pointer, but
> > this pointer is only valid if it was called trough kref_put() from
> > skel_disconnect().
> > 
> > For an already opened devices, the call will come from skel_release()
> > and in this case the interface pointer could be already owned by an
> > other driver and no more longer handle by the skeleton driver.
> > 
> > So i think we need both.
> 
> If skel_delete is changed then we don't need the usb_device pointer.
> 

I have no idea how to do this. Every USB driver i know stores the
usb_device pointer.

Maybe you have an idea?

Steffi


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