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Re: [PATCH v2 4/6] tools/oxenstored: Implement Domain.rebind_evtchn
- To: Christian Lindig <christian.lindig@xxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Thu, 1 Dec 2022 12:10:33 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Edwin Torok <edvin.torok@xxxxxxxxxx>, Rob Hoes <Rob.Hoes@xxxxxxxxxx>
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- Thread-topic: [PATCH v2 4/6] tools/oxenstored: Implement Domain.rebind_evtchn
On 01/12/2022 11:20, Christian Lindig wrote:
>
>> On 30 Nov 2022, at 16:54, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx> wrote:
>>
>> Generally speaking, the event channel local/remote port is fixed for the
>> lifetime of the associated domain object. The exception to this is a
>> secondary XS_INTRODUCE (defined to re-bind to a new event channel) which
>> pokes
>> around at the domain object's internal state.
>>
>> We need to refactor the evtchn handling to support live update, so start by
>> moving the relevant manipulation into Domain.
>>
>> No practical change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Christian Lindig <christian.lindig@xxxxxxxxxx>
>> CC: David Scott <dave@xxxxxxxxxx>
>> CC: Edwin Torok <edvin.torok@xxxxxxxxxx>
>> CC: Rob Hoes <Rob.Hoes@xxxxxxxxxx>
> Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
Thanks.
> The code makes changes around if-expressions and it is easy to get mislead by
> indentation which parts are covered by an if and which are not in the
> presence of sequential code. I would be more confident about this with
> automatic formatting (but also believe this is correct).
I can keep the being/end if you'd prefer.
Looking at the end result, it would actually shrink the patch, so is
probably worth doing anyway for clarity. The net result is:
diff --git a/tools/ocaml/xenstored/process.ml
b/tools/ocaml/xenstored/process.ml
index b2973aca2a82..1c80e7198dbe 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -569,8 +569,7 @@ let do_introduce con t domains cons data =
let edom = Domains.find domains domid in
if (Domain.get_mfn edom) = mfn &&
(Connections.find_domain cons domid) != con then begin
(* Use XS_INTRODUCE for recreating the
xenbus event-channel. *)
- edom.remote_port <- remote_port;
- Domain.bind_interdomain edom;
+ Domain.rebind_evtchn edom remote_port;
end;
edom
else try
I'm happy to adjust on commit.
When I started this, I tried rearranging things to avoid the "if exists
then find" pattern, but quickly got into a mess, then realised that this
is (almost) a dead logic path... I've got no idea why this is supported;
looking through history, I can't find a case where a redundant
XS_INTRODUCE was ever used, but its a common behaviour between C and O
so there was clearly some reason...
~Andrew
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