linux-kernel - Re: [PATCH 1/3] iommu/uapi: Define uapi version and capabilities

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Date:   Thu, 6 Feb 2020 11:14:27 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     Yi Liu <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH 1/3] iommu/uapi: Define uapi version and capabilities

Hi Jacob,
On 1/29/20 7:02 AM, Jacob Pan wrote:
> Define a unified UAPI version to be used for compatibility
> checks between user and kernel.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  include/uapi/linux/iommu.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
> 
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index fcafb6401430..65a26c2519ee 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -8,6 +8,54 @@
>  
>  #include <linux/types.h>
>  
> +/**
> + * Current version of the IOMMU user API. This is intended for query
> + * between user and kernel to determine compatible data structures.
> + *
> + * Having a single UAPI version to govern the user-kernel data structures
> + * makes compatibility check straightforward. On the contrary, supporting
> + * combinations of multiple versions of the data can be a nightmare.
I would rather put the above justification in the commit msg and not here.
> + *
> + * UAPI version can be bumped up with the following rules:
> + * 1. All data structures passed between user and kernel space share
> + *    the same version number. i.e. any extension to to any structure
s/to to/to
> + *    results in version bump up.
in a version number increment?
> + *
> + * 2. Data structures are open to extension but closed to modification.> + *    New fields must be added at the end of each data structure with
> + *    64bit alignment. Flag bits can be added without size change but
> + *    existing ones cannot be altered.
> + *
> + * 3. Versions are backward compatible.
> + *
> + * 4. Version to size lookup is supported by kernel internal API for each
> + *    API function type. @version is mandatory for new data structures
> + *    and must be at the beginning with type of __u32.
> + */
> +#define IOMMU_UAPI_VERSION	1
> +static inline int iommu_get_uapi_version(void)
> +{
> +	return IOMMU_UAPI_VERSION;
> +}
> +
> +/*
> + * Supported UAPI features that can be reported to user space.
> + * These types represent the capability available in the kernel.
> + *
> + * REVISIT: UAPI version also implies the capabilities. Should we
> + * report them explicitly?
> + */
> +enum IOMMU_UAPI_DATA_TYPES {
> +	IOMMU_UAPI_BIND_GPASID,
> +	IOMMU_UAPI_CACHE_INVAL,
> +	IOMMU_UAPI_PAGE_RESP,
> +	NR_IOMMU_UAPI_TYPE,
> +};
> +
> +#define IOMMU_UAPI_CAP_MASK ((1 << IOMMU_UAPI_BIND_GPASID) |	\
> +				(1 << IOMMU_UAPI_CACHE_INVAL) |	\
> +				(1 << IOMMU_UAPI_PAGE_RESP))
> +
>  #define IOMMU_FAULT_PERM_READ	(1 << 0) /* read */
>  #define IOMMU_FAULT_PERM_WRITE	(1 << 1) /* write */
>  #define IOMMU_FAULT_PERM_EXEC	(1 << 2) /* exec */
> 
Thanks

Eric