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[Xen-devel] Re: [PATCH] Require that xenstored writes to a domain complete in a single chunk

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: David Edmondson <dme@xxxxxxx>
  • Date: Mon, 26 Feb 2007 17:48:25 +0000
  • Cancel-lock: sha1:kd12HeBmvA8UlvLcbAFyfHW8hPQ=
  • Delivery-date: Mon, 26 Feb 2007 09:46:05 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

* keir@xxxxxxxxxxxxx [2007-02-26 17:20:34]
> This seems dubious. There's no reason we might not have payloads
> bigger than the ring size (which is only 1kB).


> The right fix would be in the guest, which should already be
> stopping any transactions or commands across save/restore. Does this
> problem occur when xenstored sends an asynchronous watch-fired
> message?

All of the cases I examined (a few dozen) were for watch events.

> Probably the packet-reading thread should be interrupted
> and put to sleep before suspending.

I'll look at this.

> For older guest compatibility perhaps we can take a variant of your
> patch that only waits for enough space is the entire message fits in
> the ring in one go. This would be 'best-effort' at compatibility
> while not precluding use of larger messages in general.

Is the implication that you think that this problem could occur with a
Linux guest (I've never seen it, though have tested much less)?

David Edmondson, Sun Microsystems, http://www.dme.org

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