[Intel-gfx] [PATCH v6 12/24] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

[Liu, Yi L]

> From: Alex Williamson <alex.williamson at redhat.com>
> Sent: Wednesday, March 22, 2023 6:48 AM
> 
> On Tue, 21 Mar 2023 19:20:37 -0300
> Jason Gunthorpe <jgg at nvidia.com> wrote:
> 
> > On Tue, Mar 21, 2023 at 03:01:12PM -0600, Alex Williamson wrote:
> >
> > > > Though it would be nice if qemu didn't need two implementations so Yi
> > > > I'd rather see a new info in this series as well and qemu can just
> > > > consistently use dev_id and never bdf in iommufd mode.
> > >
> > > We also need to consider how libvirt determines if QEMU has the kernel
> > > support it needs to pass file descriptors.  It'd be a lot cleaner if
> > > this aligned with the introduction of vfio cdevs.
> >
> > Yes, that would be much better if it was one package.
> >
> > But this is starting to grow and we have so many threads that need to
> > progress blocked on this cdev enablement :(
> >
> > Could we go forward with the cdev main patches and kconfig it to
> > experimental or something while the rest of the parts are completed
> > and tested through qemu? ie move the vfio-pci reset enablment to after
> > the cdev patches?
> 
> We need to be able to guarantee that there cannot be any significant
> builds of the kernel with vfio cdev support if our intention is to stage
> it for libvirt.  We don't have a global EXPERIMENTAL config option any
> more.  Adding new code under BROKEN seems wrong.  Fedora ships with
> STAGING enabled.  A sternly worded Kconfig entry is toothless.  What is
> the proposed mechanism to make this not look like a big uncompiled code
> dump?  Thanks,

Just out of curious, is the BDF mapping gap only for cdev or it also
exists in the traditional group path? IMHO, if it is only a gap for cdev, maybe
we can use CONFIG_VFIO_DEVICE_CDEV to stage it. This kconfig is N by
default. I think it won't change until one day the whole ecosystem is
updated.

Anyhow, I'll also see the complexity of adding a new _INFO ioctl. It should
return a set of dev_id to user rather than the bdf info in the existing _INFO
ioctl. Is it?

Regards,
Yi Liu