Re: [Qemu-devel] [PATCH] vfio: Fix handling VFIO_IOMMU_GET_INFO results

[Pavel Fedin]

 Hello!

> > 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.

 Well... I intentionally put two links to LXR. From the very beginning, this 
ioctl returned valid page sizes. And it never set this flag. We simply cannot 
have a kernel which does not report page sizes.
 If we fix qemu, it will automatically start working with all available kernels 
which are there in the wild. If we fix kernel, older versions will still not 
work, however they can.
 That's why i think that we should adapt qemu to what already exists. But, 
well, you are The Boss, so you can just say "i don't care". So, just let me now 
if you strongly disagree with this.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia