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. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
