Re: [Xen-devel] [PATCH 20/29] libxl: cancellation: Note that driver domain task cannot be usefully cancelled

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [Xen-devel] [PATCH 20/29] libxl: cancellation: Note 
that driver domain task cannot be usefully cancelled"):
> On Tue, 2015-02-10 at 20:10 +0000, Ian Jackson wrote:
> > In practice, cancelling this task will cause all subsequent actual
> > backend operations to fail, but will not actually cause the
> > libxl_device_events_handler operation to complete.
...
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> This is an unfortunate short-coming though, and I presume one which
> could be fixed by updates to the toolstack<->driver domain protocol?

It could be fixed by updates to the code inside libxl for the driver
domain task.  But it is not clear that the benefit would be large, and
the memory management in the driver domain task means that it would be
tricky to implement - there would have to be more tracking of what
operations are ongoing.

The behaviour of a driver domain service task which is in the process
of being cancelled is not anything that you would want, so a
cancel-and-restart isn't a nice operation anyway.

Ian.

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