Date: Mon, 17 Jan 2005 13:31:02 -0500
From: Mike Waychison <Michael.Waychison@Sun.COM>
Subject: Re: [RFC] shared subtrees
In-reply-to: <20050113221851.GI26051@parcelfarce.linux.theplanet.co.uk>
To: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Message-id: <41EC0466.9010509@sun.com>
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Al Viro wrote:
> 	3. bind
> 
> bind works almost identically to mount; new vfsmount is created for every
> place that gets propagation from mountpoint and propagation is set up to
> mirror that between the mountpoints.  However, there is a difference: unlike
> the case of mount, vfsmount we were going to attach (say it, A) has some
> history - it was created as a  copy of some pre-existing vfsmount V.  And
> that's where the things get interesting:
> 	* if V is contained in some p-node p, A is placed into the same
> p-node.  That may require merging one of the p-nodes we'd just created
> with p (that will be the counterpart of the p-node containing the mountpoint).
> 	* if V is owned by some p-node p, then A (or p-node containing A)
> becomes owned by p.
> 

Corner case: how do we handle the case where:

mount --make-shared /foo
mount --bind /foo /foo/bar

A nested --bind without sharing makes sense, but doesn't when sharing is
enabled (infinite loop).

How about a rule that states that for all Ai,Aj in p-node p, Ai must not
parent Aj in the vfsmount tree.  This can be enforced at graft time.

- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice

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