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于 2018/9/24 下午11:53, Dr. David Alan Gilbert 写道:
> * Qixuan Wu (qixuan.wu at linux.alibaba.com) wrote:
>>> 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.
>
> It does use virtio!  It's basically just the existing FUSE protocol
> carried over virtio; it's got some tweaks to allow the direct mappings
> and to deal with some difference sin the setup.
> It uses the existing vhost-user implementation of virtio (just like
> vhost-user for network does virtio for dpdk).
>
>>>     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 ?
>
> The control plane again is basically just the existing FUSE protocol;
> but we've got a shared mmap'd region for a fast lookup for some of the
> metadata.
>
>> 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.
>> :-).
>
> Glad you like the sound of it;  we'll try and get it out ASAP.
>

Though has some doubts about it, anyway, seems like it's faster and 
simpler than 9pfs and nfs+vsock. It's a good news for kata user.

Thanks & Regards
Qixuan.