Hi Warner, On Thursday 19 February 2009, M. Warner Losh wrote: > In message: <200902190926.42992.hsela...@c2i.net> > > Hans Petter Selasky <hsela...@c2i.net> writes: > : Do you understand why probe and attach is currently partially deferred in > : some drivers? It has to do with the ability to quickly recover if a > : device is suddenly detached when doing multiple sequential USB operations > : towards a USB device. I have the impression that you are not thinking > : about failure cases like constant timeouts. What makes the picture > : additionaly complicated is that there are multiple sources of detach, > : that do not all go through the USB stack. > : > : kldunload does not go through the USB stack. > : set_config does. > : device_detach does. > > You are doing something wrong then. All of these *DO* go through > newbus for proper drivers. If not, then that's a bug in newbus and > should be fixed there, not kludged around.
Yes, but they do not go through the USB stack [thread]. When you are running kldunload then the kldunload process is doing the detach(). This can crash with the USB explore thread adding and removing devices. Last time I checked the newbus attach/detach was only protected by "Giant" which is exited when an operation is sleeping. This Giant needs to be replaced by a sleep-enabled lock, like a SX lock, which will not get exited when we are calling msleep(), pause() or cv_wait(). > > None of this prevents the usb stack from signaling when the > probe/attach is done. It is not a problem to do a synchronous enumeration of the USB stack before mountroot. It just wastes time in my opinion. > You can't expect mountroot to wait forever. > Also, there are times when there's multiple disks available that could > be root. Just waiting for root is also bad because that root might > not ever get there. There has to be some sanity timeout. Yes, you have a point there. I think that fallback options should only kick in after a reasonable timeout. The first non-fallback disk to present itself is selected within a tuneable delay. > By properly > signaling that the operation is complete, you can have better > semantics. Yes, I can make such a function for USB. We know how many USB busses there are after attach and we can keep a refcount which cause a callback when the refcount reaches zero. Does such a function or API already exist that USB can call? And what should such a function do? Should it just signal that it is time to go trying secondary boot options? > All the other drivers in the system can accommodate this > paradigm. What makes usb so special? There is nothing special about USB. > > These sound like they might be bugs in newbus. Can you elaborate on > the details? See top of e-mail. --HPS _______________________________________________ freebsd-usb@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-usb To unsubscribe, send any mail to "freebsd-usb-unsubscr...@freebsd.org"
