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

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Mar 23, 2023 at 03:15:20AM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, March 22, 2023 9:43 PM
> > 
> > On Wed, Mar 22, 2023 at 01:33:09PM +0000, Liu, Yi L wrote:
> > 
> > > Thanks. So this new _INFO only reports a limited scope instead of
> > > the full list of affected devices. Also, it is not static scope since device
> > > may be opened just after the _INFO returns.
> > 
> > Yes, it would be simplest for qemu to do the query after it gains a
> > new dev_id and then it can add the new dev_id with the correct reset
> > group.
> 
> I see. QEMU can decide. For now, it seems like QEMU doesn't store
> such the info return by the existing _INFO ioctl. It is used in the hot
> reset helper and freed before it returns. Though, I'm not sure whether
> QEMU will store the dev_id info returned by the new _INFO. Perhaps
> Alex can give some guidance.

That seems a bit confusing, qemu should take the reset group
information and encode it so that the guest can know it as well.

If all it does is blindly invoke the hot_reset with the right
parameters then what was the point of all this discussion?
 
> btw.  Another question about this new _INFO ioctl. If there are affected
> devices that have not been bound to vfio driver yet, should this new _INFO
> ioctl fail all the same with EPERM? 

Yeah, it should EPERM the same as the normal hot reset if it can't
marshal the device list.

Jason