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Re: [Xen-devel] [PATCH] Convert shutdown to use xenstore

To: Dan Smith <danms@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Convert shutdown to use xenstore
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Date: Fri, 05 Aug 2005 12:09:50 +1000
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On Thu, 2005-08-04 at 08:35 -0700, Dan Smith wrote:
> 2. Includes Anthony's xenstore notification code, and

There are subtleties here.  We do need a notifier, because in domain 0,
the store gets started long after boot (when xenstored starts).
However, we don't need a notifier for domU code, because the store
exists from the moment we boot.

ie. for domU, this notifier chain is a noop, and I think the name should
reflect that, otherwise we'll have innocent drivers thinking registering
is the right thing.  register_dom0_xenstore_start()?

Or we could hide the whole thing, and simply call the notifier
immediately in the dom0/store-already-up case:

/* Only required if your code runs in dom0 as well as domU */
static int register_xenstore_notifier(struct notifier_block *notifier)
        int ret = 0;

        if (xen_start_info.evtchn)
                ret = notifier.notifier_call(notifier, 0, NULL);
                notifier_chain_register(&xenstore_chain, nb);
        return ret;

Implementation detail: just use the xenbus_lock rather than another
lock, and make sure you hold it while traversing, not just registering!

A bad analogy is like a leaky screwdriver -- Richard Braakman

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