Date: Mon, 17 Jan 2005 16:21:28 -0500
To: Mike Waychison <Michael.Waychison@Sun.COM>
Cc: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] shared subtrees
Message-ID: <20050117212128.GJ24830@fieldses.org>
References: <20050113221851.GI26051@parcelfarce.linux.theplanet.co.uk> <41EC0466.9010509@sun.com> <20050117190028.GF24830@fieldses.org> <41EC1253.8080902@sun.com> <20050117193206.GH24830@fieldses.org> <41EC1BE6.1030506@sun.com>
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From: "J. Bruce Fields" <bfields@fieldses.org>
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On Mon, Jan 17, 2005 at 03:11:18PM -0500, Mike Waychison wrote:
> I don't think that solves the problem.  B should receive copies (with
> shared semantics if called for) of all mountpoints C1,..,Cn that are
> children of A if A->A.  This is regardless of whether or not propagation
> occurs before or after the attach.

Consider this situation:
# #make new vfsmounts at /foo and /bar:
# mount --bind /foo /foo
# mount --bind /bar /bar
# # mount /bar under /foo, *then* put /bar and /mnt2 in the same p-node:
# mount --bind /bar /foo/mnt1
# mount --make-shared /foo
# mount --bind /foo /mnt2
# find # and I think this is what you'll get:
.
./foo
./bar
./bar/file_in_bar
./foo/mnt1
./foo/mnt1/file_in_bar
./mnt2/
./mnt2/mnt1/

Since /mnt2 and /foo are in the same p-node, any mounts we may make
under them later will be shared.  But the mount under under /foo/mnt1 is
*not* automatically propagated to /mnt2/mnt1, and /mnt1 is still in its
own little p-node (so mounts under it won't be replicated).

At least, I think I have that right.

In any case, setting up propagation between two vfsmounts needn't force
propagation of preexisting mounts, it need only affect mounts made later.

--b.
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