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于 2018/9/25 上午12:14, Dr. David Alan Gilbert 写道:
> * Qixuan Wu (qixuan.wu at linux.alibaba.com) wrote:
>>
>>
>> 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.
>
> Please ask about your doubts; I'd like to make sure we have good
> answers to them.

My doubts are:

1. Is the Filesystem in Userspace (FUSE) used in Guest os or Host os?

2. As my understand, FUSE is the mechanism used between user space and
kernel space, not a protocal. So I cannot understand how create or
unlink command be transfered from guest to host over virtio. So i did
not understant "FUSE protocol over virtio".

3. Did you test the performance compared to 9P?

Thanks for replay and clarification very much.

Regards
Qixuan.