Re: [PATCH 1/4] VFS: Add a VFS helper function vfs_remote_path_lookup()

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

On Thu, Apr 02, 2009 at 06:16:25PM -0400, Trond Myklebust wrote:
> On Thu, 2009-04-02 at 21:54 +0100, Al Viro wrote:
> > > The other thing we'd need is a 'root' path argument to ensure that
> > > __vfs_follow_link() does the right thing when presented with an absolute
> > > symlink.
> > 
> > The only problem I see with this is that we'll get root vfsmount/dentry
> > refcount jerked on *all* lookups now, instead of just the absolute
> > ones...
> 
> How about using a LOOKUP_ROOT_SET nd->flag to switch between use of
> current->fs->root or nd->root? That allows you to keep the default
> behaviour of not changing the root refcount.

Eww...  Let's not.  First of all, the really useful part of nd->root for
normal case is that it allows to get ...->fs->root once.  So it's better
to *cache* ->fs->root in there.  At which point the flag disappears,
since it becomes simply nd->root.mnt != NULL.

The interesting part is keeping refcounting happy.  I'll see how to do
that - it's clearly useful on its own.  Hopefully will post later tonight...