[libvirt-users] [libvirt] Add support for vhost-user-scsi-pci/vhost-user-blk-pci

[Li Feng]

Hi Cole & Michal,

I'm sorry for my late response, I just end my journey today.
Thank your response, your suggestion is very helpful to me.

I have added Michal in this mail, Michal helps me review my initial patchset.
(https://www.spinics.net/linux/fedora/libvir/msg191339.html)

All concern about this feature is the XML design.
My original XML design exposes more details of Qemu.

    <vhost-user-blk-pci type='unix'>
        <source type='bind' path='/tmp/vhost-blk.sock'>
            <reconnect enabled='yes' timeout='5' />
        </source>
        <queue num='4'/>
    </vhost-user-blk-pci>

As Cole's suggestion, the better design with all vhost-user-scsi/blk
features would like this:

vhost-user-blk:

<disk type='vhostuser' device='disk'>
   <source type='unix' path='/path/to/vhost-user-blk.sock' mode='client'>
       <reconnect enabled='yes' timeout='5' />
    </source>
   <target dev='vda' bus='virtio'/>
   <queue num='4'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</disk>

vhost-user-scsi:

<disk type='vhostuser' device='disk'>
   <source type='unix' path='/path/to/vhost-user-scsi.sock' mode='client'>
       <reconnect enabled='yes' timeout='5' />
   </source>
   <target dev='sda' bus='scsi'/>
   <queue num='4'/>
</disk>

Conclusion:
1. Add new type(vhostuser) for disk label;
2. Add queue sub-label for disk to support multiqueue(<queue
num='4'/>) or reusing the driver label
(<driver name='vhostuser' queues='4'), which one is better?
Qemu support multiqueue like this:
-device vhost-user-scsi-pci,id=scsi0,chardev=spdk_vhost_scsi0,num_queues=4
-device vhost-user-blk-pci,chardev=spdk_vhost_blk0,num-queues=4

Another question:
When qemu is connecting to a vhost-user-scsi controller[1],  there may
exist multiple LUNs under one target,
then one disklabel(<disk/>) will represent multiple SCSI LUNs,
the 'dev' property(<target dev='sda' bus='scsi'/>) will be ignored, right?
In other words, for vhost-user-scsi disk, it more likes a controller,
maybe the controller label is suitable.

I look forward to hearing from you as soon as possible.

[1]: https://spdk.io/doc/vhost.html

Feng Li

Cole Robinson <crobinso at redhat.com> 于2019年10月10日周四 上午6:48写道：
>
> Sorry for the late reply, and thanks Jano for pointing out elsewhere
> that this didn't receive a response.
>
> On 8/12/19 5:56 AM, Li Feng wrote:
> > Hi Guys,
> >
> > And I want to add the vhost-user-scsi-pci/vhost-user-blk-pci support
> > for libvirt.
> >
> > The usage in qemu like this:
> >
> > Vhost-SCSI
> > -chardev socket,id=char0,path=/var/tmp/vhost.0
> > -device vhost-user-scsi-pci,id=scsi0,chardev=char0
> > Vhost-BLK
> > -chardev socket,id=char1,path=/var/tmp/vhost.1
> > -device vhost-user-blk-pci,id=blk0,chardev=char1
> >
>
> Indeed that matches what I see for the qemu commits too:
>
> https://git.qemu.org/?p=qemu.git;a=commit;h=00343e4b54b
> https://git.qemu.org/?p=qemu.git;a=commit;h=f12c1ebddf7
>
> > What type should I add for libvirt.
> > Type1:
> >      <hostdev mode='subsystem' type='vhost-user'>
> >          <source protocol='vhost-user-scsi' path='/tmp/vhost-scsi.sock'></source>
> >          <alias name="vhost-user-scsi-disk1"/>
> >      </hostdev>
> >
> >
> > Type2:
> >
> >      <disk type='network' device='disk'>
> >        <driver name='qemu' type='raw' cache='none' io='native'/>
> >        <source protocol='vhost-user' path='/tmp/vhost-scsi.sock'>
> >        </source>
> >        <target dev='sdb' bus='vhost-user-scsi'/>
> >        <boot order='3'/>
> >        <alias name='scsi0-0-0-1'/>
> >        <address type='drive' controller='0' bus='0' target='0' unit='1'/>
> >      </disk>
> >
> >
> >      <disk type='network' device='disk'>
> >        <driver name='qemu' type='raw' cache='none' io='native'/>
> >        <source protocol='vhost-user' path='/tmp/vhost-blk.sock'>
> >        </source>
> >        <target dev='vda' bus='vhost-user-blk'/>
> >        <boot order='1'/>
> >        <alias name='virtio-disk0'/>
> >        <address type='pci' domain='0x0000' bus='0x00' slot='0x07'
> > function='0x0'/>
> >      </disk>
> >
>
> I think wiring this into <disk> makes more sense. <hostdev> is really an
> abstraction for assigning a (typically) physical host device to the VM,
> so it handles things like hiding a PCI device from the host, and passing
> that exact device to the VM.
>
> In the vhost-user-scsi/blk case, the host device is just a special
> process running on the other side of a socket, and the device
> represented to the guest is a typical virtio device. So to me it makes
> more sense as a <disk> with a <source> that points at that socket.
>
> target bus=virtio vs bus=scsi is already used to distinguish between
> virtio-blk and virtio-scsi, so I think we can keep that bit as is, with
> the <address type=drive|pci> to match. We just need to differentiate
> between plain virtio and vhost-user
>
> network devices already have vhostuser support:
>
>    <interface type='vhostuser'>
>      <source type='unix' path='/tmp/vhost1.sock' mode='server|client'/>
>      <model type='virtio'/>
>    </interface>
>
> Internally that <source> is a virDomainChrSourceDefPtr which is our
> internal representation of a chardev. So I think something akin to this
> is the way to go. It will likely require updating a LOT of places in the
> code that check disk type= field, probably most places that care about
> whether type=NETWORK or type=!NETWORK will need to be mirrored for the
> new type.
>
> <disk type='vhostuser' device='disk'>
>    <source type='unix' path='/path/to/vhost-user-blk.sock' mode='client'/>
>    <target dev='vda' bus='virtio'/>
> </disk>
>
> <disk type='vhostuser' device='disk'>
>    <source type='unix' path='/path/to/vhost-user-scsi.sock' mode='client'/>
>    <target dev='sda' bus='scsi'/>
> </disk>
>
> - Cole

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