RE: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd object

[Duan, Zhenzhong]

>-----Original Message-----
>From: Eric Auger <eric.auger@redhat.com>
>Sent: Thursday, November 16, 2023 4:33 PM
>Subject: Re: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd object
>
>Hi Zhenzhong,
>
>On 11/16/23 05:04, Duan, Zhenzhong wrote:
>> Hi Eric,
>>
>>> -----Original Message-----
>>> From: Eric Auger <eric.auger@redhat.com>
>>> Sent: Wednesday, November 15, 2023 8:53 PM
>>> Subject: Re: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd
>object
>>>
>>> Hi Zhenzhong,
>>>
>>> On 11/14/23 11:09, Zhenzhong Duan wrote:
>>>> From: Eric Auger <eric.auger@redhat.com>
>>>>
>>>> Introduce an iommufd object which allows the interaction
>>>> with the host /dev/iommu device.
>>>>
>>>> The /dev/iommu can have been already pre-opened outside of qemu,
>>>> in which case the fd can be passed directly along with the
>>>> iommufd object:
>>>>
>>>> This allows the iommufd object to be shared accross several
>>>> subsystems (VFIO, VDPA, ...). For example, libvirt would open
>>>> the /dev/iommu once.
>>>>
>>>> If no fd is passed along with the iommufd object, the /dev/iommu
>>>> is opened by the qemu code.
>>>>
>>>> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>> ---
>>>> v6: remove redundant call, alloc_hwpt, get/put_ioas
>>>>
>>>>  MAINTAINERS              |   7 ++
>>>>  qapi/qom.json            |  19 ++++
>>>>  include/sysemu/iommufd.h |  44 ++++++++
>>>>  backends/iommufd.c       | 228
>+++++++++++++++++++++++++++++++++++++++
>>>>  backends/Kconfig         |   4 +
>>>>  backends/meson.build     |   1 +
>>>>  backends/trace-events    |  10 ++
>>>>  qemu-options.hx          |  12 +++
>>>>  8 files changed, 325 insertions(+)
>>>>  create mode 100644 include/sysemu/iommufd.h
>>>>  create mode 100644 backends/iommufd.c
>>>>
>>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>>> index ff1238bb98..a4891f7bda 100644
>>>> --- a/MAINTAINERS
>>>> +++ b/MAINTAINERS
>>>> @@ -2166,6 +2166,13 @@ F: hw/vfio/ap.c
>>>>  F: docs/system/s390x/vfio-ap.rst
>>>>  L: qemu-s390x@nongnu.org
>>>>
>>>> +iommufd
>>>> +M: Yi Liu <yi.l.liu@intel.com>
>>>> +M: Eric Auger <eric.auger@redhat.com>
>>> Zhenzhong, don't you want to be added here?

Sorry, missed this comment.
My pleasure, I'll add myself in v7.

>>>> +S: Supported
>>>> +F: backends/iommufd.c
>>>> +F: include/sysemu/iommufd.h
>>>> +
>>>>  vhost
>>>>  M: Michael S. Tsirkin <mst@redhat.com>
>>>>  S: Supported
>>>> diff --git a/qapi/qom.json b/qapi/qom.json
>>>> index c53ef978ff..1fd8555a75 100644
>>>> --- a/qapi/qom.json
>>>> +++ b/qapi/qom.json
>>>> @@ -794,6 +794,23 @@
>>>>  { 'struct': 'VfioUserServerProperties',
>>>>    'data': { 'socket': 'SocketAddress', 'device': 'str' } }
>>>>
>>>> +##
>>>> +# @IOMMUFDProperties:
>>>> +#
>>>> +# Properties for iommufd objects.
>>>> +#
>>>> +# @fd: file descriptor name previously passed via 'getfd' command,
>>> "previously passed via 'getfd' command", I wonder if this applies here or
>whether
>>> it is copy/paste of
>>> RemoteObjectProperties.fd doc?
>> Maybe copied😊 I thinks this applies here because I use monitor_fd_param to
>get fd.
>> Or I miss anything?
>This is a bit cryptic to me and I don't really understand what it means.
>It does not mean it is not correct but I am curious about explanations
>if anybody has some ;-)

I have a weak understanding on this, may have errors😊
QMP support a command named 'getfd' to send a pre-opened fd with a name,
This fd is then stored in a fd list. Then we can use that name to reference the 
fd
In ths list.

Thanks
Zhenzhong