Date: Sun, 20 Oct 1996 14:53:33 -0700 From: Julian Elischer <julian@whistle.com> To: hackers@freebsd.org Subject: DEVFS progress report Message-ID: <326A9F5D.2781E494@whistle.com>
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Well here's a progress report on devfs..
One of my original design goals was to do away with the
mechanism in the kernel known as "device vnode aliasing".
The theory was that if all references to the same device
ended up at the same vnode, then that would allow the vnode aliasing
code (messy stuff) to simply be elliminated.
Unfortunatly there is one problem about this that just cannot be
gotten around. If there is just one vnode for all instances for
a device, then all fstats on that vnode must return the same value.
no matter where it was openned from, even if the original
path looked as though it had a different set of attributes.
I've tried many ways to get around this but it's just too
hard to get "expected" unix semantics. The only way to achieve it
is to use a scheme that ends up looking exactly like
vnode aliasing, which is what I was trying to get away from in the
first place..
After trying for a year, I've basically decided that I can't
achieve this (laudable) goal. this has produced many complication
in the devfs design, and stopped me from doing many "obvious"
things. I will be changing devfs inthe near future to
re-allign it with the design now that I have removed that
one goal. hopefully this will allow the following to happen easier..
1/ mounting root from the devfs (you'd be surprised how this is
affected)
2/ translucent attribute storage
(I've been worrying how to do this.. this makes it more possible).
3/ resolution of the problems with unmounting
filesystems mounted from devfs
4/ assisting the ability to change permissions
for a device in one devfs without compromising another. (don't ask)
I hope you will all bear with me as I make these changes.
(or is that "bare"?)
julian
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