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

[Alex Williamson]

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, 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,

Alex