Re: [linux-cifs-client] Re: mount options for selectively disabling parts of CIFS Unix Extensions

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Tue, 2007-07-17 at 07:57 -0400, Jeff Layton wrote:
> NFS has just gone through a not too dissimilar situation (mounting the
> same export twice with different options). It now fails with -EBUSY in
> that situation. A new mount option was also introduced (nosharedcache)
> that makes it fall back on the previous behavior (not sharing
> superblocks between mounts of the same export).

Well... The NFS situation was different. NFS has always supported
different mount options for different filesystems. What we were having
issues with was that people were asking to mount the _same_ filesystem
in different places with different mount options.

In CIFS parlance, the equivalent would be to mount \\SERVER\SHAREA\foo
and \\SERVER\SHAREA\bar with different mount options: I'm not sure that
is really what Steve is proposing.

Anyhow, the issue with that is you have to deal with potentially caching
the same file on two different super blocks if, say foo/a and bar/b
happen to be hard linked. We punted on dealing with the dragons hidden
in that sort of issue by requiring that users mount with nosharedcache
if and only if they know that this is safe.

Cheers
  Trond