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Re: [PATCH v1 21/22] vfio/pci: Allow the selection of a given iommu back
From: |
Jason Gunthorpe |
Subject: |
Re: [PATCH v1 21/22] vfio/pci: Allow the selection of a given iommu backend |
Date: |
Wed, 6 Sep 2023 22:10:40 -0300 |
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