Re: [PATCH 2/2] vduse: fix compat handling for VDUSE_IOTLB_GET_FD/VDUSE_VQ_GET_INFO

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Feb 02, 2026 at 11:54:17PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 2, 2026, at 17:45, Michael S. Tsirkin wrote:
> > On Mon, Feb 02, 2026 at 12:59:03PM +0100, Arnd Bergmann wrote:
> >
> > I think .compat_ioctl would be cleaner frankly. Just look at
> > all the ifdefery. And who knows what broken-ness userspace
> > comes up with with this approach. Better use the standard approach.
> 
> Sent now.
> 
> I'm not sure it's much better because there is quite a bit of
> code duplication, and reducing that would be a larger rework.

yes but on the flip side, we can put it all inside ifdef CONFIG_COMPAT
(which this code did not do, but should IMHO).

> It may be best to hold off on patch 2 for the coming merge window
> since the compat ioctl code has apparently always been broken for
> x86 here.

And it needs testing.

> I hope we can at least get patch 1/2 merged along with the
> new code though, otherwise it would get a lot harder to sort
> it out properly, with the v2 struct members overlapping the
> old padding fields.
> 
>      Arnd

Along with it or no, surely before the release.
Given 32 on 64 with this apparently has been broken forever,
I will merge this just based on even you did not bother testing compat, I am
inclined to say I am merging this but not rebasing because
of this.

Oh and we got lucky this didn't leak kernel stack info.

Eugenio, note for the future: please help make sure UAPI
structs do not have hidden padding.

-- 
MST