From mboxrd@z Thu Jan  1 00:00:00 1970
From: viro@parcelfarce.linux.theplanet.co.uk
Subject: Re: [some sanity for a change] possible design issues for hybrids
Date: Thu, 26 Aug 2004 23:53:08 +0100
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Cc: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>,
	Rik van Riel <riel@redhat.com>, Diego Calleja <diegocg@teleline.es>,
	jamie@shareable.org, christophe@saout.de, christer@weinigel.se,
	spam@tnonline.net, akpm@osdl.org, wichert@wiggy.net, jra@samba.org,
	reiser@namesys.com, hch@lst.de, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, flx@namesys.com,
	reiserfs-list@namesys.com
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To: Linus Torvalds <torvalds@osdl.org>
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On Thu, Aug 26, 2004 at 03:45:09PM -0700, Linus Torvalds wrote:
> No, lookup would just return the dentry, but the dentry would already be 
> filled in with the mount-point information.
> 
> And you can do that with a simple vfs helper function, ie the filesystem 
> itself would just need to do
> 
> 	pseudo_mount(dentry, inode);
> 
> thing - which just fills in dentry->d_mountpoint with a new vfsmount
> thing. It would allocate a new root dentry (for the pseudo-mount) and a
> new vfsmount, and make dentry->d_mountpoint point to it.

What dentry->d_mountpoint?  No such thing...

Note that we can't get vfsmount by dentry - that's the point of having these
guys in the first place.  So I'm not sure what you are trying to do here -
dentry + inode is definitely not enough to attach any vfsmounts anywhere.

That's not about namespaces - same fs mounted in several places will give
the same problem - one dentry, many vfsmounts.  And we obviously *can't*
have one vfsmount for all of them - if the same fs is mounted on /foo and
/bar, we will have the same dentry for /foo/splat and /bar/splat.  So
what should we get for /foo/splat/. and /bar/splat/.?  Same dentry *and*
same vfsmount?  I'd expect .. from the former to give /foo and from the
latter - /bar...