Re: [PATCH] VFS: fix recent breakage of FS_REVAL_DOT

[Al Viro <viro@ZenIV.linux.org.uk>]

On Mon, May 24, 2010 at 12:21:22PM -0400, Trond Myklebust wrote:
> > Can an nfs4 server e.g. have /x/y being a symlink that resolves to /a/b and
> > allow mounting of both /x/y/c and /a/b/c?  Which path would it return to
> > client that has mounted both, walked to some referral point and called
> > nfs_do_refmount(), triggering nfs4_proc_fs_locations()?
> > 
> > Trond, Neil?
> 
> When mounting /x/y/c in your example above, the NFSv4 protocol requires
> the client itself to resolve the symlink, and then walk down /a/b/c
> (looking up component by component), so it will in practice not see
> anything other than /a/b/c.
> 
> If it walks down to a referral, and then calls nfs_do_refmount, it will
> do the same thing: obtain a path /e/f/g on the new server, and then walk
> down that component by component while resolving any symlinks and/or
> referrals that it crosses in the process.

Ho-hum...  What happens if the same fs is mounted twice on server?  I.e.
have ext2 from /dev/sda1 mounted on /a and /b on server, then on the client
do mount -t nfs foo:/a /tmp/a; mount -t nfs foo:/b /tmp/b.  Which path
would we get from GETATTR with fs_locations requested, if we do it for
/tmp/a/x and /tmp/b/x resp.?  Dentry will be the same, since fsid would
match.

Or would the server refuse to export things that way?