Subject: Re: Detaching devices
To: Bill Studenmund <email@example.com>
From: Jason Thorpe <firstname.lastname@example.org>
Date: 06/28/1999 12:46:18
On Mon, 28 Jun 1999 12:05:45 -0700 (PDT)
Bill Studenmund <email@example.com> wrote:
> that's what reference counting is for. :-) What you/we need to do is add
> foo_addref and foo_delref routines. When all the references have been
> deleted, the memory goes away.
guys, this is not that hard...
(1) USB controller gets "status event", and wakes up USB
controller's "event thread".
(2) USB controller's "event thread" determines the type of status
event (i.e. "removal" in this case). Do this in process context
(i.e. the "event thread") so you can sleep while this happens.
"Event thread" calls a USB stack interface function to the
device (i.e. some pointer in a function switch, *not*
(3) Device driver takes appropriate action, e.g. vdevgone()'s the
devices, sets a flag in its softc "dying", or whatever. Any
things asleep in the driver are now awakened.
(4) As things are awakened, they see the "dying" bit set, and return
errors. When the last of these things is awakened, there are
no more references to the device (open/read/write fail, close
is stub'd to a "OK! WORKED!" in deadfs, because of the
vdevgone()). At this point, you can config_detach() (either
directly or via a callback into the USB controller code; probably
the latter so it can know "ok, it's really gone now").
Anyhow, this mechanism can probably be cleaned up a little, but you get the
-- Jason R. Thorpe <firstname.lastname@example.org>