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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