config_intrhook_drain will remove the hook from the list as
config_intrhook_disestablish does if the hook hasn't been called. If it has,
config_intrhook_drain will wait for the hook to be disestablished in the normal
course (or expedited, it's up to the driver to decide how and when
to call config_intrhook_disestablish).
This is intended for removable devices that use config_intrhook and might be
attached early in boot, but that may be removed before the kernel can call the
config_intrhook or before it ends. To prevent all races, the detach routine will
need to call config_intrhook_train.
Sponsored by: Netflix, Inc
Reviewed by: jhb, mav, gde (in D29006 for man page)
Differential Revision: https://reviews.freebsd.org/D29005
it automatically after it runs.
The config_intrhook mechanism allows a driver to stall the boot process
until device(s) required for booting are available, by not allowing system
inits to proceed until all intrhook functions have been unregistered.
Virtually all existing code simply unregisters from within the hook function
when it gets called.
This new function makes that common usage more convenient. Instead of
allocating and filling in a struct, passing it to a function that might (in
theory) fail, and checking the return code, now a driver can simply call
this cannot-fail routine, passing just the intrhook function and its arg.
Differential Revision: https://reviews.freebsd.org/D11963
