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Date:   Thu, 6 Feb 2020 10:22:47 -0800
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     Auger Eric <eric.auger@redhat.com>
Cc:     iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Yi Liu <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Jonathan Cameron <jic23@kernel.org>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH 1/3] iommu/uapi: Define uapi version and capabilities
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        <699faadb-e714-e36d-152a-5b650c0a403f@redhat.com>
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On Thu, 6 Feb 2020 11:14:27 +0100
Auger Eric <eric.auger@redhat.com> wrote:

> 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@intel.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.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.
make sense.

> > + *
> > + * 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
will fix.

> > + *    results in version bump up.  
> in a version number increment?
sounds good, more specific.

> > + *
> > + * 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
>