linux-kernel - Re: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW

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Date:   Fri, 19 May 2023 11:30:15 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
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        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: Re: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO

Hi Kevin,

On Fri, May 19, 2023 at 08:42:07AM +0000, Tian, Kevin wrote:

> > +};
> > +#define IOMMU_DEVICE_GET_HW_INFO _IO(IOMMUFD_TYPE,
> > IOMMUFD_CMD_DEVICE_GET_HW_INFO)
> >  #endif
> 
> Here we have a naming confusion.
> 
> 'IOMMU' is the prefix of iommufd ioctls.
> 
> 'DEVICE' is the subjective.
> 
> Then "GET_HW_INFO" implies getting hardware info related to
> this device. then it should not be restricted to the iommu info.
> 
> with that it's clearer to call it IOMMU_DEVICE_GET_IOMMU_INFO.

Though the entire ioctl is tied to the input "dev_id", I think
it isn't really about the device corresponding to the dev_id,
similar to the IOMMU_HWPT_ALLOC having a dev_id input too. So,
I think the "IOMMU_DEVICE" here should be interpreted simply
as "an iommu device". We could also highlight this somewhere
in the header.

With that being said, IOMMU_DEVICE_SET/UNSET_DATA should be
renamed to IOMMU_DEVICE_SET/UNSET_DEV_DATA -- "DEVICE" is the
iommu device while the "DEV_DATA" is a given device that's
behind the iommu.

> similarly for struct iommu_hw_info.
> 
> 'iommu' is the prefix for all iommufd ioctl structures.
> 
> then 'hw_info' is too broard.
> 
> iommu_device_iommu_info reads better? though having two
> iommu's in the name is a little bit annoying...

How about:
IOMMU_DEVICE_GET_FEATURES
struct iommu_device_features
?

Thanks
Nic