Re: [9fans] Acme mailreader - now: User mode filesystems in linux

[Russ Cox <russcox@gmail.com>]

> [Lots of good arguments]

You're stuck with the operating system you have,
not the operating system you'd like to have.  If one were
designing the system from scratch one could always do
better.  Sadly this Coda discussion is about how to deal with
what's already available on Unix.

> I don't have much knowledge of/experience with Plan9, but I've read
> that the system is designed so that it's very easy to port drivers
> between user-space and kernel-space.  Is this correct?  

No, it's not.  It's not hard (I can't think of any system-level
programming task I'd characterize as "hard" using Plan 9)
but it's not trivial either.

> In a "standard" setup, how many of the drivers are (mostly) in user-space?

Anything that touches hardware is typically in the kernel, though
in the case of particularly complicated hardware (like vga and usb),
the kernel part just makes it possible for user-mode programs to
get at the hardware and do the complicated stuff.

On the other hand, file system drivers are typically outside the
kernel, and the network and graphics devices have moved back
and forth a few times.

Russ