On Wednesday 18 July 2012 11:42:50 Alan Stern wrote:
> On Wed, 18 Jul 2012, Oliver Neukum wrote:
>
> > 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.
>
> Everything userspace does is a race.
Therefore some things should be done in kernel space ;-)
Regards
Oliver
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