that device add/remove will work without usbd running. usbd is still
used for execing stuff, but that is all now. Ideally it could be replaced
by a devd some day. Until now, usbd had to be running so that the
USB_DISCOVER ioctl could be called to walk the tree when an attachment
status change was noticed.
Among the changes:
- when a detach happens, remove any pending 'attach' messages or the system
suffers from whiplash from exec moused / kill moused loops if you do lots
of attach/detach and later start usbd.
- tweaks related to kthread differences
- disable the select handler for the old interface (never return success).
I have not removed it yet or old usbd's will abort. That can get removed
later once usbd is cleaned up and things have stabilized for a few weeks.
- get Giant in the kthread.
- a couple of minor potential bug fixes (usb_nevents vs malloc failure etc)
Pre-approved by: n_hibma (ages and ages ago)
7b77e0fa50