Re: Xen 4.2 Release Plan / TODO

[Dario Faggioli <raistlin@linux.it>]

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On Tue, 2012-04-10 at 10:24 +0000, Ian Campbell wrote: 
> Lots more DONE this week, still a few big ticket items or items with no
> progress (that I've noticed) please let me know if the status of
> anything has changed.
>
Here I am. :-)

> tools, blockers:
>       * libxl stable API -- we would like 4.2 to define a stable API
>         which downstream's can start to rely on not changing. Aspects of
>         this are:
>               * Safe fork vs. fd handling hooks. Involves API changes
>                 (Ian J, patches posted)
>               * locking/serialization, e.g., for domain creation. As of
>                 now,  nothing is provided for this purpose, and
>                 downstream toolstacks have to put their own mechanisms
>                 in place. E.g., xl uses a fcntl() lock around the whole
>                 process of domain creation. It should OTOH be libxl job
>                 to offer a proper set of hooks --placed at the proper
>                 spots during the domain creation process-- for the
>                 downstreams to fill with the proper callbacks. (Dario
>                 Faggioli)
>                       * Thinking to defer this until 4.3?
>
Here's the point. This was raised for the following main reasons:
1. xl holds a lock during domain creation for way too long
2. checking for free memory in xl when it is Xen that will actually 
    allocate it after a while is prone to races (the classical TOCTTOU 
    condition)

We thought both these things to be addressable by messing around with
locks, but a more careful analysis revealed we can't solve 2. in a sane
enough way by just doing that (i.e., messing with lock, moving it
around, etc.).

That being the case, yes, I think we can move this forward toward 4.3
without much problems, and I propose doing so. Thoughts?

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)




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