On Wed, 3 Mar 2004, Ragnar Sundblad wrote:

Background:

We are depending on the file system AFS in our environment

of different unix flavours. The AFS client is, as I

understand it, very much a stacked file system.

What you would do, is create a brand new file system, that's not layered, and use UNIX sockets to do all file IO through a userland daemon, ala webdav. This would remove any need for a layered file system.

My questions:

Could this be implemented at all without using a stacked

file system, and what would be the apple recommended way

of doing it? (Of course one could use a separate cache

See above...

I'd be happy if someone could explain both of these statements

from Q&A 1242:

"

... it's not possible to create a stacking VFS plug-in that:

1. works reliably,

Writing file systems is never a fun task, there are a lot of locking issues involved and any minor mess up here and you'll be KP'ing some place or another. They can also be *very* hard to track down.

2. does not severely impinge on system performance

In a layered file system, you consume resources more quickly. The kernel keeps N vnodes alive at any given time, if you're doing a layered file system then each vnode really now uses 2 vnodes, so you've effectively changed N to N/2.

3. has any hope of binary (or even source-level) compatibility

with future systems.

Apple makes no promises not to completely change how all this stuff works at some future date. The only Kernel interface that is not going to change drastically I believe is the IOKit.

Would a stacking file system have (significantly) more

compatibility problems than a non stacking file system?

I've written a stacking file system in Mac OS X, we've not really seen any more issues than I think I'd see w/a non-stacked file system, but I must just have been lucky so far...

Wasn't there some ideas about a cleaner and more static

file system api for darwin?

It would be nice if Apple decided how they wanted it to work, and then implelemnted it. Though I really doubt we'll see anything for 10.4. --- Marek Kozubal marek@portents.com _______________________________________________ darwin-kernel mailing list | darwin-kernel@lists.apple.com Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/darwin-kernel Do not post admin requests to the list. They will be ignored.