User mode drivers (Honest does not pay here ...)

[Pete Zaitcev]

> I may be showing my ignorance here (won't be the first time) but this makes
> me wonder if Linux could provide a way to do "user level drivers".

It is a question often asked in comp.os.linux.development.system.
If performance penalties and security problems are no obstacle,
a lot of hardware can be serviced with a user mode driver, except
one that requires interrupts to operate. There is no way to deliver
an interrupt safely to the user mode, because a device specific
deactivation or ack-ing must be performed before interrupts are
enabled (on i386 at least). Other problems can be worked around
with ioperm and friends.

-- Pete