Messages in this thread | | | Date | Thu, 24 Sep 2020 11:31:07 -0700 | From | Jacob Pan <> | Subject | Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format |
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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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