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SubjectRe: [RFC] shared subtrees
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On Mon, 2005-01-31 at 23:02, Mike Waychison wrote:
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> Ram wrote:
> > On Fri, 2005-01-28 at 14:31, Mike Waychison wrote:
> >
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> >>Al Viro wrote:
> >>
> >>
> >>>OK, here comes the first draft of proposed semantics for subtree
> >>>sharing. What we want is being able to propagate events between
> >>>the parts of mount trees. Below is a description of what I think
> >>>might be a workable semantics; it does *NOT* describe the data
> >>>structures I would consider final and there are considerable
> >>>areas where we still need to figure out the right behaviour.
> >>>
> >>
> >>Okay, I'm not convinced that shared subtrees as proposed will work well
> >>with autofs.
> >>
> >>The idea discussed off-line was this:
> >>
> >>When you install an autofs mountpoint, on say /home, a daemon is started
> >>to service the requests. As far as the admin is concerned, an fs is
> >>mounted in the current namespace, call it namespaceA. The daemon
> >>actually runs in it's one private namespace: call it namespaceB.
> >>namespaceB receives a new autofs filesystem: call it autofsB. autofsB
> >>is in it's own p-node. namespaceA gets an autofsA on /home as well, and
> >>autofsA is 'owned' by autofsB's p-node.
> >
> >
> > Mike, multiple parsing through the problem definition, still did not
> > make the problem clear. What problem is autofs trying to solve using
> > namespaces?
> >
> > My guess is you dont want to see a automount taking place in namespaceA,
> > when a automount takes place in namespaceB, even though
> > the automount-point is in a shared subtree?
> >
> > Sorry don't understand automount's requirement in the first place,
> > RP
>
> The major concern for automounting is that currently, if you start an
> automount daemon in the primary namespace, and some process clones off
> into a new namespace with clone(CLONE_NS), then there is no way for the
> daemon running in the first namespace to automount (let alone expire)
> any mounts in the second namespace. There doesn't exist a way for the
> daemon to mount(2) nor umount(2) across namespaces.
>
> The proposed solution for this is to use shared and private subtrees to
> have the daemon run in it's own namespace, with the primary and any
> derivative namespaces inheriting the automounts. I'm not convinced that
> it'd work though.
>
> Does this clarify?

Yes it does clarify the problem and motivates the reason behind using
shared subtree.

However going back to your original problem 1:

you have a daemon running in namespaceB, and a process running in
namespaceA and it acceses a auto-mountpoint /home.

The expected behavior in this case should be: the autofs-daemon must
mount the corresponding device at that mount point '/home' on all
existing namespaces(provided that part of the subtree is shared). Right?
So in this case it should mount the device in both the namespaces, i.e
namespaceA and namespaceB. But you seem to be saying that you want to
block the auto-mount in namespaceA?

RP
>
> - --
> Mike Waychison
> Sun Microsystems, Inc.
> 1 (650) 352-5299 voice
> 1 (416) 202-8336 voice
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> NOTICE: The opinions expressed in this email are held by me,
> and may not represent the views of Sun Microsystems, Inc.
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