Re: [PATCH] virt: vbox: Implement passing requestor info to the host for VirtualBox 6.0.x

[Hans de Goede]

Hi,

On 20-03-19 19:19, Greg Kroah-Hartman wrote:
> On Wed, Mar 20, 2019 at 10:52:05AM +0100, Hans de Goede wrote:
> > Hi,
> >
> > On 20-03-19 10:46, Greg Kroah-Hartman wrote:
> > > On Wed, Mar 20, 2019 at 10:35:19AM +0100, Hans de Goede wrote:
> > > > VirtualBox 6.0.x has a new feature where the guest kernel driver passes
> > > > info about the origin of the request (e.g. userspace or kernelspace) to
> > > > the hypervisor.
> > > >
> > > > If we do not pass this information then when running the 6.0.x userspace
> > > > guest-additions tools on a 6.0.x host, some requests will get denied
> > > > with a VERR_VERSION_MISMATCH error, breaking vboxservice.service and
> > > > the mounting of shared folders marked to be auto-mounted.
> > > >
> > > > This commit implements passing the requestor info to the host, fixing this.
> > > >
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > >
> > > This feels like support for a "new feature", so why would this need to
> > > go to older kernels?
> > >
> > > It's not our fault that vb implemented a non-backwards-compatible change
> > > for their new release, right?  So why should we be forced to add new
> > > features to stable kernels?
> >
> >  From a technical point of view I completely agree with you and I'm unhappy
> > with this breakage after vb agreed with me to keep ABI compatibility so
> > that we could add a version of the vboxguest driver to the mainline kernel.
>
> So they broke that agreement, ugh.  That implies they will do it again?

Well they did not really broke the ABI, they started using a reserved
field and a 6.0.x host will happily work with 5.2.x guest-extensions
(with the mainline vboxguest driver) the same way around, 5.2.x host
als works with 6.0.x guest-extensions user-space bits + mainline kernel
module.

Things break when using a 6.0.x host + 6.0.x guest-extensions userspace
parts combined with the mainline kernel module. The 6.0.x + 6.0.x combi
seems to assume that there is a 6.0.x vboxguest driver which fills in
the reserved field. I believe this is an oversight and not a deliberate
breakage. Perhaps this is even something which the VirtualBox devs can
fix in a future 6.0.x update...  Michael ?

> > OTOH this is going to bite users out there, which is why I added the Cc:
> > stable. But this is entirely your call.
>
> Let me think about it...
>
> > > I have no problem to add this for 5.2, but not for older stuff.
> >
> > Can we at least at it as a fix to 5.1 ? It is not very adventurous.
>
> Sure, let me go review it now.

Thank you for the review, I will reply to it tomorrow (and prep a v2).

Regards,

Hans