Re: [PATCH v1 21/22] vfio/pci: Allow the selection of a given iommu backend

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Sep 06, 2023 at 01:09:26PM -0600, Alex Williamson wrote:
> On Wed, 6 Sep 2023 15:10:39 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Wed, Aug 30, 2023 at 06:37:53PM +0800, Zhenzhong Duan wrote:
> > > 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.  
> > 
> > Can you show an example of that syntax too?
> 
> Unless you're just looking for something in the commit log, 

Yeah, I was thinking the commit log

> patch 16/ added the following to the qemu help output:
> 
> +#ifdef CONFIG_IOMMUFD
> +    ``-object iommufd,id=id[,fd=fd]``
> +        Creates an iommufd backend which allows control of DMA mapping
> +        through the /dev/iommu device.
> +
> +        The ``id`` parameter is a unique ID which frontends (such as
> +        vfio-pci of vdpa) will use to connect withe the iommufd backend.
> +
> +        The ``fd`` parameter is an optional pre-opened file descriptor
> +        resulting from /dev/iommu opening. Usually the iommufd is shared
> +        accross all subsystems, bringing the benefit of centralized
> +        reference counting.
> +#endif
>  
> > Also, the vfio device should be openable externally as well
> 
> Appears to be added in the very next patch in the series.  Thanks,

Indeed, I got confused because this removed the TODO - that could
reasonably be pushed to the next patch and include a bit more detail
in the commit message

Jason