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From: Alex Williamson <alex.williamson@redhat.com>
Date: Thu, 12 Nov 2015 07:16:59 -0700
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Subject: Re: [Qemu-devel] [PATCH] vfio: Fix handling VFIO_IOMMU_GET_INFO
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To: Pavel Fedin <p.fedin@samsung.com>
Cc: qemu-devel@nongnu.org

On Thu, 2015-11-12 at 10:16 +0300, Pavel Fedin wrote:
> Kernel headers define VFIO_IOMMU_INFO_PGSIZES flag, however it has
> actually been never used, probably by mistake which now became a part
> of the ABI. The kernel always sets info.flags to 0:

I don't see how this implies that it becomes part of the ABI.  In fact,
as the defacto userspace driver for vfio, QEMU honoring the flag and not
using the value the kernel provides implies the ABI is still valid.  We
should fix the kernel instead.  Thanks,

Alex

> http://lxr.free-electrons.com/source/drivers/vfio/vfio_iommu_type1.c?v=3.7#L675
> http://lxr.free-electrons.com/source/drivers/vfio/vfio_iommu_type1.c#L974
> 
> Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
> ---
>  hw/vfio/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 6797208..afc10c7 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -704,7 +704,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as)
>          info.argsz = sizeof(info);
>          ret = ioctl(fd, VFIO_IOMMU_GET_INFO, &info);
>          /* Ignore errors */
> -        if ((ret == 0) && (info.flags & VFIO_IOMMU_INFO_PGSIZES)) {
> +        if (ret == 0) {
>              container->iova_pgsizes = info.iova_pgsizes;
>          }
>      } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU)) {