Re: [RFC] VirtFS support on Xen

[Bob Liu <bob.liu@oracle.com>]

On 01/22/2016 06:50 PM, Wei Liu wrote:
> On Fri, Jan 22, 2016 at 06:45:30PM +0800, Bob Liu wrote:
>> Hi Wei,
>>
>> On 01/21/2016 06:59 PM, Wei Liu wrote:
>>> On Thu, Jan 21, 2016 at 10:50:08AM +0000, David Vrabel wrote:
>>>> On 21/01/16 10:28, Wei Liu wrote:
>>>>> [RFC] VirtFS support on Xen
>>>>>
>>>>> # Introduction
>>>>>
>>>>> QEMU/KVM supports file system passthrough via an interface called
>>>>> VirtFS [0]. VirtFS is in turn implemented with 9pfs protocol [1] and
>>>>> VirtIO transport.
>>>>>
>>>>> Xen used to have its own implementation of file system passthrough
>>>>> called XenFS, but that has been inactive for a few years. The latest
>>>>> update was in 2009 [2].
>>>>>
>>>>> This project aims to add VirtFS support on Xen. This is more
>>>>> sustainable than inventing our own wheel.#
>>>>
>>>> What's the use case for this?  Who wants this feature?
>>>>
>>>
>>> Anyone who wants file system passthrough.  More specifically, VM-based
>>> container solutions can share files from host file system.
>>>
>>
>> I'm a bit confused, can't we just use the VirtFS of Qemu?
>> E.g
>> ./configure --with-extra-qemuu-configure-args="--enable-virtfs"
>>
> 
> Yes, in theory you can -- with VirtIO transport. But I'm not sure if
> Virtio has been fixed to work with Xen.  That also means you need QEMU
> emulation, which we don't really need (or want) when running in PV or
> PVH mode.
> 

Just make sure if I get it right, in the KVM case:
Linux guest(v9fs-client) -> VirtIO transport -> Qemu(v9fs-server) -> Local file system in Host

And your plan is:
DomU(v9fs-client) -> XEN transport:grant map based -> Qemu(v9fs-server) -> Local file system in Dom0

Which means we need to implement a XEN-transport in linux/net/9p/, and also make Qemu can recognize this transport because we need Qemu to run as the v9fs-server anyway?

Bob