Everyone has convinced me that there's no point in making usbdev->serialize an rw-semaphore, so that's out. A big relief to some people, no doubt :-)
I still have a problem with marking devices as soon as we know they are unplugged. Even using David's scheme where this is done using a separate unprotected flag in struct usb_device, I can't see any way to make it work without introducing a new lock. The problem is that when the "unplugged" flag is set for a hub, it must be set recursively for all the children as well. This requires reading through the list of the hub's children, but it takes place asynchronously with respect to other tasks that may be updating the list. It's not enough to say those other tasks should check the hub's unplugged flag before they update anything; setting and checking a flag does not constitute a true synchronization operation. Either a spinlock or a semaphore is required. Basically the new lock would have to be held while adding or removing a device from a hub's list of children and while the recursive set-the-unplugged-flag takes place. This doesn't seem likely to create a lot of contention, but still, if anyone can think of a way to do this without a lock I would be pleased to hear it. Alan Stern ------------------------------------------------------- The SF.Net email is sponsored by EclipseCon 2004 Premiere Conference on Open Tools Development and Integration See the breadth of Eclipse activity. February 3-5 in Anaheim, CA. http://www.eclipsecon.org/osdn _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
