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From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	Jacob Pan <jacob.pan.linux@gmail.com>,
	Raj Ashok <ashok.raj@intel.com>, Jonathan Corbet <corbet@lwn.net>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Wu Hao <hao.wu@intel.com>, David Woodhouse <dwmw2@infradead.org>,
	Yi Sun <yi.y.sun@intel.com>
Subject: Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
Date: Thu, 24 Sep 2020 11:31:07 -0700	[thread overview]
Message-ID: <20200924113107.75379e6e@jacob-builder> (raw)
In-Reply-To: <20200924084015.GC27174@8bytes.org>

Hi Joerg,

On Thu, 24 Sep 2020 10:40:16 +0200, Joerg Roedel <joro@8bytes.org> wrote:

> > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel <joro@8bytes.org>
> > wrote: 
> > > On Fri, Sep 11, 2020 at 02:57:52PM -0700, Jacob Pan wrote:  
> > > > There can be multiple vendor-specific PASID data formats used in
> > > > UAPI structures. This patch adds enum type with a last entry which
> > > > makes range checking much easier.    
> > > 
> > > But it also makes it much easier to screw up the numbers (which are
> > > ABI) by inserting a new value into the middle. I prefer defines here,
> > > or alternativly BUILD_BUG_ON() checks for the numbers.
> > >   
> > I am not following, the purpose of IOMMU_PASID_FORMAT_LAST *is* for
> > preparing the future insertion of new value into the middle.
> > The checking against IOMMU_PASID_FORMAT_LAST is to protect ABI
> > compatibility by making sure that out of range format are rejected in
> > all versions of the ABI.  
> 
> But with the enum you could have:
> 
> enum {
> 	VTD_FOO,
> 	SMMU_FOO,
> 	LAST,
> };
> 
> which makes VTD_FOO==0 and SMMU_FOO==1, and when in the next version
> someone adds:
> 
> enum {
> 	VTD_FOO,
> 	VTD_BAR,
> 	SMMU_FOO,
> 	LAST,
> };
> 
> then SMMU_FOO will become 2 and break ABI. So I'd like to have this
> checked somewhere.
Got your point, will change to defines.

Thanks,

Jacob
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WARNING: multiple messages have this Message-ID (diff)
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Jacob Pan <jacob.pan.linux@gmail.com>,
	iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Eric Auger <eric.auger@redhat.com>, Yi Liu <yi.l.liu@intel.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>, Wu Hao <hao.wu@intel.com>,
	Yi Sun <yi.y.sun@intel.com>,
	jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
Date: Thu, 24 Sep 2020 11:31:07 -0700	[thread overview]
Message-ID: <20200924113107.75379e6e@jacob-builder> (raw)
In-Reply-To: <20200924084015.GC27174@8bytes.org>

Hi Joerg,

On Thu, 24 Sep 2020 10:40:16 +0200, Joerg Roedel <joro@8bytes.org> wrote:

> > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel <joro@8bytes.org>
> > wrote: 
> > > On Fri, Sep 11, 2020 at 02:57:52PM -0700, Jacob Pan wrote:  
> > > > There can be multiple vendor-specific PASID data formats used in
> > > > UAPI structures. This patch adds enum type with a last entry which
> > > > makes range checking much easier.    
> > > 
> > > But it also makes it much easier to screw up the numbers (which are
> > > ABI) by inserting a new value into the middle. I prefer defines here,
> > > or alternativly BUILD_BUG_ON() checks for the numbers.
> > >   
> > I am not following, the purpose of IOMMU_PASID_FORMAT_LAST *is* for
> > preparing the future insertion of new value into the middle.
> > The checking against IOMMU_PASID_FORMAT_LAST is to protect ABI
> > compatibility by making sure that out of range format are rejected in
> > all versions of the ABI.  
> 
> But with the enum you could have:
> 
> enum {
> 	VTD_FOO,
> 	SMMU_FOO,
> 	LAST,
> };
> 
> which makes VTD_FOO==0 and SMMU_FOO==1, and when in the next version
> someone adds:
> 
> enum {
> 	VTD_FOO,
> 	VTD_BAR,
> 	SMMU_FOO,
> 	LAST,
> };
> 
> then SMMU_FOO will become 2 and break ABI. So I'd like to have this
> checked somewhere.
Got your point, will change to defines.

Thanks,

Jacob

  reply	other threads:[~2020-09-24 18:29 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-11 21:57 [PATCH v9 0/7] IOMMU user API enhancement Jacob Pan
2020-09-11 21:57 ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 1/7] docs: IOMMU user API Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-16 18:26   ` Randy Dunlap
2020-09-16 18:26     ` Randy Dunlap
2020-09-18 19:44     ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 2/7] iommu/uapi: Add argsz for user filled data Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-18  9:44   ` Joerg Roedel
2020-09-18  9:44     ` Joerg Roedel
2020-09-18 17:11     ` Jacob Pan
2020-09-22 20:24       ` Jacob Pan
2020-09-22 20:24         ` Jacob Pan
2020-09-24  8:40       ` Joerg Roedel
2020-09-24  8:40         ` Joerg Roedel
2020-09-24 18:31         ` Jacob Pan [this message]
2020-09-24 18:31           ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 4/7] iommu/uapi: Use named union for user data Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 5/7] iommu/uapi: Rename uapi functions Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 6/7] iommu/uapi: Handle data and argsz filled by users Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-11 21:57 ` [PATCH v9 7/7] iommu/vt-d: Check UAPI data processed by IOMMU core Jacob Pan
2020-09-11 21:57   ` Jacob Pan
2020-09-18 10:02 ` [PATCH v9 0/7] IOMMU user API enhancement Joerg Roedel
2020-09-18 10:02   ` Joerg Roedel
2020-09-18 17:26   ` Jacob Pan
2020-09-18 17:26     ` Jacob Pan

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