Re: [RFC] VirtFS support on Xen

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On January 23, 2016 9:50:30 AM EST, Wei Liu <wei.liu2@citrix.com> wrote:
>On Sat, Jan 23, 2016 at 01:33:40PM +0800, Bob Liu wrote:
>> 
>> 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
>> 
>
>Yes. Your understanding is correct.
>
>> 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?
>> 
>
>Yes. There will be code in both QEMU and Linux kernel.
>

Why not just make the VirtIO MMIO implementation work with Xen? That would give you what you need right?

>Wei.
>
>> Bob
>
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