devfs vs udev/hotplug

[Dave Leimbach]

Matthew Dillon <dillon at xxxxxxxxxxxxxxxxxxxx> writes:

> : (Simon)
> :> What do people think of the udev/hotplug solution vs devfs? At first 
> :> inspection, udev appears to be a little more Dragonfly-ish because of 
> :> its placement in userland.
> :
> :I'd vote for udev (or something like it)
> :
> :-- 
> 
>     I think I would prefer udev over devfs.  It seems silly to try to manage
>     yet another fake filesystem in the kernel, just look at all the bugs 
>     that have cropped up in existing devfs and procfs implementations, not
>     to mention unionfs and nullfs!  You'd think we would have learned our
>     lesson by now!
> 
>     I would definitely prefer a userland demon which performs the work based
>     on what the kernels tells it to do.  The kernel can still assign dynamic
>     minor numbers for dynamic devices, and that is really the crux of the
>     functionality we want to have.

Doesn't this sort of design imply that the kernel is instructing a daemon
to make kernel calls to service the requests?  Isn't that a lot of 
address space crossing or do I not understand how a userland file "server"
would work?  I realize that this will be done with fast messages but such
designs leave me with "speed" doubts.  This might be a bad example for when
that speed matters though.

Dave