Re: [RFC] VirtFS support on Xen

[Wei Liu <wei.liu2@citrix.com>]

On Sat, Jan 23, 2016 at 10:35:44AM -0500, Konrad Rzeszutek Wilk wrote:
> 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?
> 

That goes back to the old topic of how to make VirtIO work on Xen (PV in
particular). It's not easy task by any means.

Wei.

> >Wei.
> >
> >> Bob
> >
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> 
>