Re: Domain save/migrate issue

[Anthony Liguori <aliguori@us.ibm.com>]

Noam Taich wrote:
> We need the memory image of the domain to be static, So we can't allow
> the domain to run. So, the first idea is to use pause/unpause instead of
>   
Suspend does more than just canonicalize the p2m, it also provides 
callbacks for all of the devices so that they can canonicalize their own 
page references and set them self up to reinitialize upon resume.

While the save code can access the p2m table, it has no way of knowing 
the device information so just pausing isn't really an option (also, you 
could do bad things like checkpoint before a storage operation was 
committed or something like that).

Regards,

Anthony Liguori
> suspend.
>
> Now for the next (serious) problem:
> This seems to work fine (in live or non live settings) until the
> xc_linux_save() function reaches the part where it checks the frame
> number
> Of the suspend record, which makes sense, because now, we have NO
> suspend record. So, the second idea is to (simply?) write all that info
> on the io_fd
> The function gets ourselves. Just canonicalize the fns that suspend
> does,
> And write the appropriate info.
>
> The restore function does not have to change at all... it sees the same
> input.
>
> So, what do you think, is this a good idea? Even possible? Will it
> entail a lot?
>
> One of my concerns is this: the shared pages.
> Can Xen write to them while the guest is "only" paused? And if so, what 
> Can it (practically) write there while the guest is paused?
> Even if it CAN, is it Reasonable to expect it won't do that usually? 
>
>
> I'm not really troubled by the storage issues. This feature would be
> useful in many cases even with no solution to that problem.
>
> Sorry for the multiple messages on the original subject. It was an
> unfortunate misunderstanding.
>
>   
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