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> We're currently experimenting with something a bit different;
> we've got a setup that uses a modified version of the FUSE protocol
> running over vhost-user;  it's:
>    a) Got the filesystem access split out of qemu into a separate daemon
>        - that's just a modified version of a normal FUSE filesystem daemon
>        with the nice bit being that since it's a separate process you
>        can do whatever isolation on it you want.
>    b) But the latency is low because vhost-user means the daemon can read
>       the request queue straight out of the guest memory
>    c) We've got a setup with DAX so that the files are mapped straight
>       into guest address space, so the overhead is very low for large
>       files.
That's so cool. I guess it will not use virtio. And this way maybe the 
new para-virtualization method, it's specific about the file system for 
the data shared between guest and host.

>    d) We've got a caching scheme for metadata, which again removes a lot
>       of latency.
>    e) We've got some patches to use it in KATA; I can start a basic KATA
>       guest with it.
>
> This is the first public mention of it because I didn't want you waiting
> for a reply; but our code is still rather messy and experimental; give
> us a few weeks and as soon as it survives some smoke tests we'll make
> the code public.
>
> Because we're reusing both FUSE and vhost-user the kernel changes are
> quite small, as are the qemu changes.
>
> I realise that's not much detail yet; we're starting to write some of it
> up; feel free to ask any specifics.
>

Thank for the replay. Seems that the file data are mmapping direct, but 
the control plane, like metadata are still using some other simple 
protocal, maybe new protocal ? Because 9p and nfs are very complex, they 
are not developed for the file sharing between guest and host. I always 
hope there is a simple file sharing protocal. I am very looking forward 
for the code. :-).

Thanks & Regards
Qixuan Wu.