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    SubjectRe: [RFC] shared subtrees
    On Thu, Jan 13, 2005 at 06:30:50PM -0500, Mike Waychison wrote:
    > > 1) each p-node corresponds to a group of 1 or more vfsmounts.
    > > 2) there is at most 1 p-node containing a given vfsmount.
    > > 3) each p-node owns a possibly empty set of p-nodes and vfsmounts
    > > 4) no p-node or vfsmount can be owned by more than one p-node
    > > 5) only vfsmounts that are not contained in any p-nodes might be owned.
    > > 6) no p-node can own (directly or via intermediates) itself (i.e. the
    > > graph of p-node ownership is a forest).
    > >
    > > These guys define propagation:
    > > a) if vfsmounts A and B are contained in the same p-node, events
    > > propagate from A to B
    > > b) if vfsmount A is contained in p-node p, vfsmount B is contained
    > > in p-node q and p owns q, events propagate from A to B
    > > c) if vfsmount A is contained in p-node p and vfsmount B is owned
    > > by p, events propagate from A to B
    > How is (c) different from (a)? Is there a distinction between
    > 'containing' and 'owning' here?

    Yes. See (3) and (1) above. Consider the following:
    p = {A, B}
    p owns C

    Then we have propagation between A and B _and_ from either to C.

    > > * we can mark a subtree slave. That removes all vfsmounts in
    > > the subtree from their p-nodes and makes them owned by said p-nodes.
    > > p-nodes that became empty will disappear and everything they used to
    > > own will be repossessed by their owners (if any).
    > Would this be better read as "That removes each vfsmount A in the
    > subtree from its respective p-node p and makes it contained by a new
    > p-node p' (containing only A), and p' becomes 'owned' by p." ?

    No. "Belongs to a single-element p-node" != "doesn't belong to any
    p-node". The former means "share on copy" (and might have slaves).
    The latter is noone's master. Again, see the propagation rules and
    behaviour on clone/rbind.

    > > * 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.
    > I don't follow this. I still don't see the distinction between being
    > owned and being contained. Also, for statements like 'A belongs to B',
    > which is it?

    "V owned by p" == "V is a slave of (equivelent) members of p"
    "p contains V" == "V is one of the members of p, whatever happens to it
    will happen to all of them".

    "element belongs to set" means what it usually means ;-) (again, p-nodes
    are sets of vfsmounts).
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