I'm not sure what series of events is leading up to this watch event
being received with no callback info and it should be investigated.
I'm triggering it somehow by registering an RTC device (which will
show up in a subsequent commit.)
Log:
- merge in latest xenbus from dfr's xenhvm
- fix race condition in xs_read_reply by converting tsleep to mtx_sleep
Log:
unmask evtchn in bind_{virq, ipi}_to_irq
Log:
- remove code for handling case of not being able to sleep
- eliminate tsleep - make sleeps atomic