[libvirt] [PATCH 07/13] qemu: Add hotpluging support for PCI devices on S390 guests

[Cornelia Huck]

On Mon, 28 May 2018 16:26:57 +0800
Xiao Feng Ren <renxiaof at linux.vnet.ibm.com> wrote:

> On 5/25/2018 6:22 PM, Bjoern Walk wrote:
> > Cornelia Huck <cohuck at redhat.com> [2018-05-24, 06:25PM +0200]:  
> >> On Thu, 24 May 2018 14:24:32 +0200
> >> Xiao Feng Ren <renxiaof at linux.vnet.ibm.com> wrote:
> >>  
> >>> From: Yi Min Zhao <zyimin at linux.ibm.com>
> >>>
> >>> This commit adds hotplug support for PCI devices on S390 guests.
> >>> There's no need to implement hot unplug for zPCI as QEMU implements
> >>> an unplug callback which will unplug both PCI and zPCI device in a
> >>> cascaded way.
> >>> Currently, the following PCI devices are supported:
> >>>    virtio-blk-pci
> >>>    virtio-net-pci
> >>>    virtio-rng-pci
> >>>    virtio-input-host-pci
> >>>    virtio-keyboard-pci
> >>>    virtio-mouse-pci
> >>>    virtio-tablet-pci
> >>>    vfio-pci
> >>>    Shmem device
> >>>    SCSIVhost device  
> >> Hm, how did you arrive at this list? Is it 'anything that uses msi-x'?  
> > I guess it's just any device that libvirt actually supports hotplug for,
> > with a few exceptions (cf. patch 3 and 6). Not familiar wuth msi-x.  
> 
> The list should be the devices that support MSI-X and have realized the 
> hotplug in qemu,
> we support the hotplug for them in the libvirt.  So the list will be 
> updated to:
> 
>    virtio-blk-pci
>    virtio-net-pci
>    virtio-input-host-pci
>    virtio-keyboard-pci
>    virtio-mouse-pci
>    virtio-tablet-pci
>    vfio-pci
>    SCSIVhost device

Ok, that makes sense.

I also checked that libvirt only allows setting the vectors property
for virtio-serial and shmem (vectors == 0 turns msi-x off), so that
should be fine.

> 
> As the model of Shmem is not support in qemu, the rng device doesn't 
> support MSI-X.  So remove them.

So, should qemu add support for msi-x with virtio-rng-pci in the
future, we'd want to update libvirt as well, correct?

> 
> 
> In addition, the bug found need to be fixed for the hotplug of tablet, 
> in the virDomainDeviceIsUSB()
> if ((t == VIR_DOMAIN_DEVICE_DISK &&
>           dev->data.disk->bus == VIR_DOMAIN_DISK_BUS_USB) ||
>          (t == VIR_DOMAIN_DEVICE_INPUT &&
>           dev->data.input->type == VIR_DOMAIN_INPUT_BUS_USB) ||  
> ---------->dev->data.input->bus == VIR_DOMAIN_INPUT_BUS_USB  
>          (t == VIR_DOMAIN_DEVICE_HOSTDEV &&
> I will send the fix if this bug is agreed.
>