Re: [PATCH] virtio_pci: fix macro exported in uapi

From: Rusty Russell
Date: Sun May 19 2013 - 22:36:29 EST

David Howells <dhowells@xxxxxxxxxx> writes:
> Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
>> Macro still isn't usable, because userspace can't know whether it's the
>> new or old.
>> We need to either remove it from UAPI, or rename it to
> Surely, if userspace is using it as is, you can't remove it, rename it or
> alter it?

The point of the patch is that it's unusable:

#define VIRTIO_PCI_CONFIG(dev) ((dev)->msix_enabled ? 24 : 20)

ie. it's accessing a member of the kernel's virtio_pci_dev structure.

In theory, userspace could have a structure with the same field and be
using it now, but that's unlikely (qemu certainly doesn't). No harm no

In theory it's actually a useful macro, so we could expose it to
userspace, but we'd need to have a new name so userspace can #ifdef for
older headers...

Hope that clarifies,
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