[PATCH 0/5] Dynamic Pseudo Root

[Trond Myklebust]

On Tue, 2008-02-19 at 10:04 -0500, Steve Dickson wrote:
> Sorry for the delayed response...Dealing with a sick kid, among
> other things... :-\
> 
> Neil Brown wrote:
> > Some comments on the comments on this.....
> > 
> > 
> > 1/ The use of volatile file handles as required by the use of tmpfs.
> > 
> >    Now I don't much care which way we go:  remove them from the spec
> >    or implement them.  But refusing the allow them while they remain
> >    in the spec just seems dishonest to me.
> I have to agree with this. Just because nobody else can't support
> something does not mean we should not... I bet if we started handling
> out volatile filehandles and client started dropping, the support
> would come pretty quickly... ;-)

Feel free to contribute the code. I see volatile filehandles as being
completely incompatible with POSIX semantics and have zero interest in
implementing support for them in the client.

The one exception I might see as being useful is the 'volatile on
migration' case, but even that is going to be a nightmare. Take, for
instance the case where a file is renamed on the server, while you have
it open, and the filesystem is then migrated...

> > 2/ We don't actually need to use TMPFS for the suggested
> >    implementation.  We could use an ext2 filesystem loop-mounted on
> >    some file, or even just part of the /var filesystem with
> >    subtree_check set to avoid accessing other parts of the tree.
> >    Then filehandles would be stable.
> I agree. Trond's point of not being able to guarantee stable filehandles
> is very valid, which is the main problem with the current design... 
> but I'm not convinced using ext2 is the answer either.

You and Neil are trying to solve a problem of _access_ rights on the
filesystem by redesigning the topology of the entire filesystem. I have
yet to see an argument for why this is a good thing other than 'it can
be done'.

> I have to disagree with Trond (and a few other people I respect) that 
> putting hooks into the lookup and readdir paths may not be the best 
> approach for the Linux server implementation . It is a proven implementation
> and we ultimately might end up there, but I just think we can come up
> with a clearer and less invasive way of support dynamic pseudo roots.

Redesigning the top-level filesystem topology is not 'less invasive' or
'cleaner' in my book. It is simply not the way we solve problems of
defining access rights.