[Qemu-devel] Sharing virtio-devices between several kvm virtual machines over network

[Qemu-devel] Sharing virtio-devices between several kvm virtual machines over network

[Leib, David]

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Hi,
I am trying to share devices between vm's. For example I want to use a cdrom-drive who is exposed to a vm from another vm over the network.
In addition to this I want to use virtio for this idea.
What I am trying to do step by step:
1.      If virtqueue_pop is called on the KVM 2 I take the iovec structure information
2.      I send it over to the KVM 1
3.      KVM 1 put it into the own virtqueue_pop
4.      KVM 1 wait for virtqueue_push
5.      KVM 1 take the information from virtqueue_push
6.      KVM 1 send it over to KVM 2
7.      KVM 2 put it into the virtqueue push

                 |----------------------|                    |--------------------|
                 |                      |                    |                    |
                 |        KVM 1         |                    |       KVM 2        |
                 |                      |                    |                    |
                 |                      |                    |                    |
                 |----------------------|                    |--------------------|
                   |      |    |                                       | |       |
                   |      |    |                                       | |       |
                   |      |    |                                       | |       |
                   |    /--------\<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</-----\     |
 First virtqueue   |    |        |  TCP/IP Connection                |     |  Second Virtqueue
                   |    |        |>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>|     |     |
                   |     \-------/                                   \_____/     |
                   |        | |                                                  |
                   |        | |                             _______________________
                 -----------------------                    |                      |
                 |                     |                    |                      |
                 |                     |                    |                      |
                 |     Host 1          |                    |                      |
                 |                     |                    |       Host 2         |
                 |______               |                    |                      |
                 |      |              |                    |                      |
                 | CDROM|              |                    |                      |
                 |______|______________|                    |----------------------|

I tried it already slightly different by stopping KVM 1 and only waiting for request of KVM 2 but there are some problems with the iovec buffer address I am not able to use as a address of the buffer.
Has somebody experience with that or an idea of doing this maybe in a more smarter way or is it generally possible to do that?
Thank you for your help



David Leib
SAP Research Belfast
SAP (UK) Limited   I   The Concourse   I   Queen's Road   I   Queen's Island   I   Belfast BT3 9DT

mailto: david.leib@sap.com<mailto:mary.clarke@sap.com>  I   www.sap.com/research<http://www.sap.com/research>

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Re: [Qemu-devel] Sharing virtio-devices between several kvm virtual machines over network

[Stefan Hajnoczi]

On Tue, Nov 15, 2011 at 5:37 PM, Leib, David <david.leib@sap.com> wrote:
> I am trying to share devices between vm’s. For example I want to use a
> cdrom-drive who is exposed to a vm from another vm over the network.

The normal way of doing this would be to export the CD-ROM using
NFS/CIFS or iSCSI.  It has nothing to do with virtualization.

> In addition to this I want to use virtio for this idea.

Why?  It's not clear what problem you are trying to solve and why you
want to use virtio.

> What I am trying to do step by step:
>
> If virtqueue_pop is called on the KVM 2 I take the iovec structure
> information
> I send it over to the KVM 1
> KVM 1 put it into the own virtqueue_pop
> KVM 1 wait for virtqueue_push
> KVM 1 take the information from virtqueue_push
> KVM 1 send it over to KVM 2
> KVM 2 put it into the virtqueue push
> I tried it already slightly different by stopping KVM 1 and only waiting for
> request of KVM 2 but there are some problems with the iovec buffer address I
> am not able to use as a address of the buffer.
> Has somebody experience with that or an idea of doing this maybe in a more
> smarter way or is it generally possible to do that?

In theory it would be possible to implement a virtio TCP/IP transport.
 The protocol needs to support virtqueue operations (push, pop),
notify, configuration space, and device lifecycle.  Then it would be
possible to launch a virtio-blk server on machine A and attach to the
device from machine B.

But back to my first two points: what are you really trying to do?

Stefan