Re: [Xen-devel] [PATCH v5] xenstore: extend the xenstore ring with a 'closing' signal

[Dave Scott <Dave.Scott@xxxxxxxxxx>]

On 26 Sep 2014, at 15:00, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:

> 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@xxxxxxxxxx>
> 
> Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Thanks!

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

Jon: could you take another look at the OCaml code? It’s slightly modified
from the previous one you reviewed. This version allows the Reconnect
exception to bubble up to the oxenstored connection handler and allows
oxenstored to reset all the state (ring, requests, watches, transactions
etc)
 
> 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.

Understood.

Cheers,
Dave


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