Re: [RFC PATCH] USB: enable "power/wakeup" to control remote wakeup in the runtime suspend

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On Wednesday 18 July 2012 10:54:20 Alan Stern wrote:
> On Wed, 18 Jul 2012, Lan Tianyu wrote:
> 
> > On 2012/7/18 22:19, Alan Stern wrote:
> > > An alternative to her suggestion would be to disconnect the device when
> > > the port goes off.  When the port is powered back on, the device will
> > > be rediscovered and probed again.
> > hi alan:
> > 	Reprobe may cause the devnum change. Userspace will treat it a
> > different device from previous one. e.g app held the device node fd,
> > After port went off and on, device reprobed and the fd became invalid.
> 
> That's right.  Your argument suggests that power-off should be 
> controlled by userspace, not by the kernel, and it should happen only 
> when no app is holding the device node open.

That is a race. And it is basically unsolvable in user space if the device
is available to everybody.

	Regards
		Oliver

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