Re: [PATCH 10/10] tools/xenstored: Delay new transaction while Live-Update is pending

[Juergen Gross <jgross@xxxxxxxx>]

On 16.06.21 16:43, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> At the moment, Live-Update will, by default, not proceed if there are
> in-flight transactions. It is possible force it by passing -F but this
> will break any connection with in-flight transactions.
>
> There are PV drivers out that may never terminate some transaction. On
> host running such guest, we would need to use -F. Unfortunately, this
> also risks to break well-behaving guests (and even dom0) because
> Live-Update will happen as soon as the timeout is hit.
>
> Ideally, we would want to preserve transactions but this requires
> some work and a lot of testing to be able to use it in production.
>
> As a stop gap, we want to limit the damage of -F. This patch will delay
> any transactions that are started after Live-Update has been requested.
>
> If the request cannot be delayed, the connection will be stalled to
> avoid loosing requests.
>
> If the connection has already a pending transaction before Live-Update,
> then new transaction will not be delayed. This is to avoid the connection
> to stall.
>
> With this stop gap in place, domains with long running transactions will
> still break when using -F, but other domains which starts a transaction
> in the middle of Live-Update will continue to work.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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