On Tue, Jul 27, 2021 at 08:09:41PM -0300, Jason Gunthorpe wrote:

On Tue, Jul 27, 2021 at 03:54:40PM -0600, Alex Williamson wrote:

quoted

I'm still not happy with how this is likely to break users and even
downstreams when upgrading to a Kconfig with this change.

I've never heard of Kconfig as stable ABI. Christoph/Arnd, have you
heard of any cases where we want to keep it stable?

It isn't an ABI, but we really do try to avoid breaking if we can and
I rember Linus shouting at people if they did that for common options.

However lately for example the completely silly s/THUNDERBOLT/USB4/
change did slip through and did break my test setup with a vfio passed
through external nvme drive :(

Which might reasonably be from an old kernel. 'make oldconfig' prompts:

VFIO Non-Privileged userspace driver framework (VFIO) [Y/n/m/?] y
  VFIO No-IOMMU support (VFIO_NOIOMMU) [Y/n/?] y
  VFIO support for PCI devices (VFIO_PCI_CORE) [N/m/y/?] (NEW) 

Which is completely fine, IMHO.

Why do we need to have VFIO_PCI_CORE as a user visible option?
I'd just select it.