Hi, On 07/28/2012 06:33 PM, Peter Stuge wrote: > Hans de Goede wrote: >> This patch fixes libusb_detach_kernel_driver to only detach "real" >> kernel drivers and not the special usbfs driver > > Ignoring the race for now?
Yes, the race is mostly theoretical thing, where as one libusb app stealing the device from another is very much a real issue, it is for example the root cause of: https://bugzilla.redhat.com/show_bug.cgi?id=820205 > What's the situation of kernel support to > make the operations race free? Quoting from: http://marc.info/?l=libusb-devel&m=128655552910330&w=2 "I agree that it makes sense for libusb to be aware of a device's current driver before trying to detach it. It might also be desirable to avoid ever detaching the usbfs driver -- however this is a matter to be settled by the designers and users of libusb. It should not be enforced by the kernel. Certainly libusb-0.1's ability to report the name of the current driver shouldn't be given up in libusb-1.0. That's a backward step. Alan Stern" So Alan believes, and I agree, that the policy of handling the detaching of usbfs in a special way is a userspace decision. Note that we've 2 racy things here btw: 1) Testing if a driver is bound and then doing a detach This can be fixed (in apps) by simply doing the unbind always and ignore the ERROR_NOT_FOUND return 2) Testing if the driver is usbfs, and if it is not then unbind the kernel driver (which my patch does / adds). This is racy too and cannot simply be fixed. The only solution I can come up with is adding a "USBDEVFS_NO_USBFS_DISCONNECT" flag with a value of 0x80000000 which can be or-ed together with the interface number passed to the USBDEVFS_DISCONNECT ioctl to make it not unbind the usbfs driver in a non racy way. Combined with a new capability flag for this (I assume you've seen my capability patches). I must say I find this kind of ugly though, if people think this is a good idea, I'll try to push it upstream, but I believe the race window is so small, it is not really an issue. Regards, Hans ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
