Re: [RFC v3 18/18] vfio/as: Allow the selection of a given iommu backend

[Jason Gunthorpe]

On Tue, Jan 31, 2023 at 09:53:05PM +0100, Eric Auger wrote:
> Now we support two types of iommu backends, let's add the capability
> to select one of them. This depends on whether an iommufd object has
> been linked with the vfio-pci device:
> 
> if the user wants to use the legacy backend, it shall not
> link the vfio-pci device with any iommufd object:
> 
> -device vfio-pci,host=0000:02:00.0
> 
> This is called the legacy mode/backend.
> 
> If the user wants to use the iommufd backend (/dev/iommu) it
> shall pass an iommufd object id in the vfio-pci device options:
> 
>  -object iommufd,id=iommufd0
>  -device vfio-pci,host=0000:02:00.0,iommufd=iommufd0
> 
> Note the /dev/iommu device may have been pre-opened by a
> management tool such as libvirt. This mode is no more considered
> for the legacy backend. So let's remove the "TODO" comment.

The vfio cdev should also be pre-openable like iommufd?

Jason