Re: [Xen-devel] [PATCH 6/6] libxl: events: Document and enforce actual callbacks restriction

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-11-27 at 18:27 +0000, Ian Jackson wrote:
> libxl_event_register_callbacks cannot reasonably be called while libxl
> is busy (has outstanding operations and/or enabled events).
> 
> This is because the previous spec implied (although not entirely
> clearly) that event hooks would not be called for existing fd and
> timeout interests.  There is thus no way to reliably ensure that libxl
> would get told about fds and timeouts which it became interested in
> beforehand.
> 
> So there have to be no such fds or timeouts, which means that the
> callbacks must only be registered or changed when the ctx is idle.
> 
> Document this restriction, and enforce it with a pair of asserts.
> 
> (It would be nicer, perhaps, to say that the application may not call
> libxl_osevent_register_hooks other than right after creating the ctx.
> But there are existing callers, including libvirt, who do it later -
> even after doing major operations such as domain creation.)
> 
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>



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