[PATCH 0/5] Dynamic Pseudo Root

[Trond Myklebust]

On Mon, 2008-02-18 at 12:13 -0500, J. Bruce Fields wrote:

> I agree that that's a problem.  It also seems unlikely in most setups,
> and easy to solve in those clients (for the special case of filehandles
> that are used only on mount).

No! You should not be relying on solving server brokenness on the
client. In a typical setup, the number of clients to upgrade would be
much larger, and the process tends to be more laborious since, for
instance, you may have to adapt and re-certify applications.

> ... I was assuming it would be cleaner and more flexible to construct
> a
> separate filesystem root for the psuedofilesystem.  What do you see as
> the advantages of using the real fs with masked out dentries?

     1. The fact that it provides a stable basis for constructing
        filehandles.
     2. No client changes.
     3. No mucking around with bind mounts and other namespace tricks
        that can go wrong.
     4. No races when the user decides to change the export table.
        Instead of having to reconstruct a namespace after clearing the
        in-kernel cache, mountd just sits there and continues to do its
        usual thing.
     5. It works for more complex topologies too, such as the example
        mentioned in section 7.3 of rfc3530: /a/b/c/d, where 'a' and 'c'
        are pseudo-filesystems, whereas 'b' and 'd' are real.

Trond