Avi Kivity <[email protected]> wrote:
> > We cannot get a complete snapshot without mmu_lock; if the guest faults on
> > the Nth page during xchg'ing i = 1, 2, ... then the i = N alone will
> > become newer.
>
> Ah, so there is no data corruption (missed dirty bits), just the display
> is updated inconsistently?
Yes, no data corruption and just a matter of ... feeling.
The basic rule I wrote in the comment in this patch should be enough to
not lose dirty bits.
> I don't think we can get a consistent snapshot anyway, since the guest
> can update the framebuffer while userspace is processing it.
Yes, nothing will be broken. I was just not sure what the API should promise
to the userspace.
To some extent the inconsistency may be felt more than before.
> Understood. I don't think we can get a consistent vga snapshot without
> stopping the guest, and even then, it depends on how the guest updates
> the framebuffer.
OKay, I will not care about this from now.
> > So I want to see how much improvement the proposed API can achieve.
> >
> > I thought this might be a good GSoC project but ...
>
> It may be too involved for GSoC, the issues are difficult.
I am now checking QEMU code closely - rather readable than before!
Though I can make experimental KVM patches for the student, just changing
QEMU's live migration code seems to be difficult - but not sure now.
Anyway, we should try this before deciding the new API: I mean if I cannot
find anyone who want to try this, no need to be a student, I may do instead
at some point.
Takuya
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