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

[Duan, Zhenzhong]

>-----Original Message-----
>From: Jason Gunthorpe <jgg@nvidia.com>
>Sent: Thursday, September 7, 2023 9:11 AM
>To: Alex Williamson <alex.williamson@redhat.com>
>Subject: Re: [PATCH v1 21/22] vfio/pci: Allow the selection of a given iommu
>backend
>
>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

Thanks for point out this issue.
I can think of two choices:
1. squash this patch to PATCH16
2. keep this patch separate and to pull fd passing related change from PATCH16 
into this one
Please kindly suggest which way is preferred in community.

Btw: I only enable fd passing for vfio pci device, let me know if it's preferred
to include all other vfio devices in this series, then I'll add them.

>>
>> > 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

Good idea, will fix.

Thanks
Zhenzhong