Re: [RFC] provide an API to userspace doing memory snapshot

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On Tue, Apr 16, 2013 at 03:54:15PM +0800, Wenchao Xia wrote:
> 于 2013-4-16 13:51, Stefan Hajnoczi 写道:
> >On Mon, Apr 15, 2013 at 09:03:36PM +0800, Wenchao Xia wrote:
> >>   I'd like to add/export an function which allow userspace program
> >>to take snapshot for a region of memory. Since it is not implemented yet
> >>I will describe it as C APIs, it is quite simple now and if it is worthy
> >>I'll improve the interface later:
> >
> >We talked about a simple approach using fork(2) on IRC yesterday.
> >
> >Is this email outdated?
> >
> >Stefan
> >
>   No, after the discuss on IRC, I agree that fork() is a simpler
> method to do it, which can comes to qemu fast, since user wants it.
>   With a more consideration, still I think a KVM's mem snapshot would
> be an long term solution for it:
>   The source of the problem comes from acceleration module, kvm.ko, when
> qemu does not use it, no troubles. This means an acceleration module
> missed a function while caller requires. My instinct idea is: when
> acceleration module replace a pure software one, it should try provide
> all parts or not stop software filling the gap, and doing so brings
> benefits, so hope to add it.
>   My API description is old, the core is COW pages, maybe redesign if
> reasonable.

QEMU is a userspace process that has guest RAM mmapped.  You want to
snapshot that mmap region but there is no Linux system call to do that.
Maybe a new mremap(2) flag is what you want.

But I don't see the connection to kvm.ko which you mention.  The feature
you're wishing for has nothing to do with kvm.ko.

Stefan
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