Re: [Qemu-devel] [RFC] virtio-fc: draft idea of virtual fibre channel HBA

[Stefan Hajnoczi]

On Wed, Feb 15, 2017 at 12:15:02AM -0700, Lin Ma wrote:
> Hi all,
>  
> We know that libvirt can create fibre channels vHBA on host
> based on npiv, and present the LUNs to guest.
>  
> I'd like to implement a virtual fibre channel HBA for qemu,
> I havn't investigate it deeply yet. The idea presents a fc
> vHBA in guest, interact with remote fc switch through npiv,
> The LUNs will be recognized inside guest. I sent this email
> here to see if you are in agreement with this approach and
> hope to get some ideas/suggestions.
>  
> The frontend is based on virtio, say virtio-fc-pci; the backend
> is based on npiv of physical fc hba on host.
> The implementation of this virtual fc hba doesn't support Fc-al,
> only supports Fabric. It wrappers scsi data info fc frames, then
> forwards them to backend, sounds like scsi over fc.
> (maybe I can re-use some of virtio-scsi code/idea to deal with scsi data)
>  
> The minimum invocation may look like:
> qemu-system-x86_64 \
> ...... \
> -object fibrechannel-backend,id=fcdev0,host=0000:81:00.0 \
> -device 
> virtio-fc-pci,id=vfc0,fc_backend=fcdev0,wwpn=1000000000000001,wwnn=1100000000000001
>  \
> ......
>  
> BTW, I have no idea how to make migration works:
> How to deal with the BDF during migration?
> How to deal with the Fabric ID during migration?
>  
> It's a draft idea, There are lots of related code I need to
> investigate, Currently this is all thoughts I have.
>  
> Hello Paolo and Stefan, You are the authors of virtio-scsi,
> and had some in-depth discuss about virtio-scsi in 2011
> with Hannes, May I have your ideas/thoughts?

I'm not sure it's necessary for the guest to have FC access.  Fam Zheng
and Paolo are working on virtio-scsi FC NPIV enhancements.  It should
make NPIV work better without adding a whole new FC device.

https://lkml.org/lkml/2017/1/16/439

The plan is:

1. libvirt listens to udev events on the host so it can add/remove
   QEMU SCSI LUNs.

2. virtio-scsi is extended to include a WWPN that the guest can see.

The guest doesn't do any FC fabric level stuff, it just does virtio-scsi
as usual.

It supports live migration by swapping between a pair of WWPNs across
migration.

What are the benefits of having FC access from the guest?

Stefan

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