[PATCH v5] xenstore: extend the xenstore ring with a 'closing' signal

[Ian Jackson <Ian.Jackson@eu.citrix.com>]

David Scott writes ("[PATCH v5] xenstore: extend the xenstore ring with a 'closing' signal"):
> Hvmloader uses the xenstore ring and then tries to reset it back
> to its initial state before booting the guest. Occasionally xenstored
> will read the ring while it is being zeroed and conclude it has
> been corrupted. This prevents PV drivers from loading in the guest.
> 
> This patch updates the xenstore ring protocol definition, enabling
> a server to advertise additional features to the guest. One such feature
> is defined: the ability to cleanly reset the ring including the
> higher-level protocol, like an enhanced RESET_WATCHES for rings.
> 
> This patch implements the ring reconnection features in oxenstored
> and hvmloader, fixing the bug.
> 
> This patch also defines an 'invalid' xenstore packet type and uses this
> to poison the ring over a reconnect. This will make diagnosing this
> bug much easier in future.
> 
> Signed-off-by: David Scott <dave.scott@citrix.com>

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

I'm happy to take this from you without really reviewing the ocaml
code.

To be applied this needs a freeze exception.  You should make the case
(explaining why the feature is important and why it is low risk) to
Konrad.

Ian.