Re: [PATCHv2 1/5] VFS: DazukoFS, stackable-fs, file access control

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

On Thu, Feb 12, 2009 at 04:59:41PM +0100, Jan Engelhardt wrote:
> 
> On Thursday 2009-02-12 16:31, Al Viro wrote:
> >On Thu, Feb 12, 2009 at 04:27:14PM +0100, Jan Engelhardt wrote:
> >
> >> This ought to be done better in light of the problem that one
> >> could issue `mount -t dazukofs /mnt /opt`
> >> In kernel code, I'm thinking something like
> >> 
> >> static int foofs_dothis(...)
> >> {
> >> 	buf = call d_path on sb->s_root
> >
> >Call what on what?  There is no such thing as the mountpoint of superblock.
> >
> In fs/namespace.c:do_new_mount there is 'path'. If 'path' was passed
> down to the filesystem, path->dentry, I would assume, could be used
> by the filesystem as a pointer to the original directory which
> dazuko is going to shadow.

It will not be passed dow to the filesystem, simply because said filesystem
can be silently moved elesewhere and whatever it used to be mounted on -
unmounted.

What's more, whatever it shadows might itself be mounted in any number of
places, so...