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From: Oliver Neukum <oliver@neukum.org>
To: Hans de Goede <hdegoede@redhat.com>
Subject: Re: USB mini-summit at LinuxCon Vancouveroliver
Date: Fri, 5 Aug 2011 09:59:00 +0200
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Cc: Greg KH <greg@kroah.com>, Mauro Carvalho Chehab <mchehab@infradead.org>,
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Am Freitag, 5. August 2011, 09:45:56 schrieb Hans de Goede:
> This is the issue on which I feel a bit stonewalled. Simple putting your
> fingers in your ears and singing la la la do it in userspace is not going
> to cut it here. There is no way to do this race free in userspace, unless
> all possible callers of mount get modified. Moreover 99% of the necessary
> accounting for this is already done in the kernel. We already have the notion
> of a block device being in use. We simply need to add some code to pass
> this notion to the usb mass storage driver, and add a new try_disconnect
> callback for usb drivers. I'm not saying this is going to be completely
> straight forward, but it ain't rocket science either. And it so very
> obviously is the right thing to do, that I'm getting very tired of
> the do it in userspace song I keep hearing.

Doing a try_disconnect() would also solve the dual camera issue.
But it doesn't really interfere with the user space vs. kernel space
issue. You simply have to expand the ioctl interface to have
an ioctl that triggers this API call in the kernel.

A V4L2 device would return an error if its device node is opened,
otherwise disconnect.

	Regards
		Oliver