Re: [PATCH v3 12/12] vfio/pci: Report dev_id in VFIO_DEVICE_GET_PCI_HOT_RESET_INFO

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Apr 17, 2023 at 02:06:42PM -0600, Alex Williamson wrote:
> On Mon, 17 Apr 2023 16:31:56 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Mon, Apr 17, 2023 at 01:01:40PM -0600, Alex Williamson wrote:
> > > Yes, it's not trivial, but Jason is now proposing that we consider
> > > mixing groups, cdevs, and multiple iommufd_ctxs as invalid.  I think
> > > this means that regardless of which device calls INFO, there's only one
> > > answer (assuming same set of devices opened, all cdev, all within same
> > > iommufd_ctx).  Based on what I explained about my understanding of INFO2
> > > and Jason agreed to, I think the output would be:
> > > 
> > > flags: NOT_RESETABLE | DEV_ID
> > > {
> > >   { valid devA-id,  devA-BDF },
> > >   { valid devC-id,  devC-BDF },
> > >   { valid devD-id,  devD-BDF },
> > >   { invalid dev-id, devE-BDF },
> > > }
> > > 
> > > Here devB gets dropped because the kernel understands that devB is
> > > unopened, affected, and owned.  It's therefore not a blocker for
> > > hot-reset.  
> > 
> > I don't think we want to drop anything because it makes the API
> > ill suited for the debugging purpose.
> > 
> > devb should be returned with an invalid dev_id if I understand your
> > example. Maybe it should return with -1 as the dev_id instead of 0, to
> > make the debugging a bit better.
> > 
> > Userspace should look at only NOT_RESETTABLE to determine if it
> > proceeds or not, and it should use the valid dev_id list to iterate
> > over the devices it has open to do the config stuff.
> 
> If an affected device is owned, not opened, and not interfering with
> the reset, what is it adding to the API to report it for debugging
> purposes?

It lets it print the entire group of devices, this is the only way
something can learn the actual list of all BDFs affected.

dev_id can just return 0, we don't need a complex bitmap. Userspace
looks at the flag, if !NOT_RESETABLE then it ignores dev_id=0.

Jason