Re: [Intel-gfx] [PATCH v7 8/9] vfio/pci: Extend VFIO_DEVICE_GET_PCI_HOT_RESET_INFO for vfio device cdev

Jason Gunthorpe
2023-06-13T17:40:20Z

On Tue, Jun 13, 2023 at 08:32:29AM -0600, Alex Williamson wrote:
> On Tue, 13 Jun 2023 12:50:43 +0000
> "Liu, Yi L" <yi.l.liu@intel.com> wrote:
>
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Tuesday, June 13, 2023 7:47 PM
> > >
> > > On Fri, Jun 02, 2023 at 05:15:14AM -0700, Yi Liu wrote:
> > > > +/*
> > > > + * Return devid for a device which is affected by hot-reset.
> > > > + * - valid devid > 0 for the device that is bound to the input
> > > > + * iommufd_ctx.
> > > > + * - devid == VFIO_PCI_DEVID_OWNED for the device that has not
> > > > + * been bound to any iommufd_ctx but other device within its
> > > > + * group has been bound to the input iommufd_ctx.
> > > > + * - devid == VFIO_PCI_DEVID_NOT_OWNED for others. e.g. device
> > > > + * is bound to other iommufd_ctx etc.
> > > > + */
> > > > +int vfio_iommufd_device_hot_reset_devid(struct vfio_device *vdev,
> > > > + struct iommufd_ctx *ictx)
> > > > +{
> > > > + struct iommu_group *group;
> > > > + int devid;
> > > > +
> > > > + if (vfio_iommufd_device_ictx(vdev) == ictx)
> > > > + return vfio_iommufd_device_id(vdev);
> > > > +
> > > > + group = iommu_group_get(vdev->dev);
> > > > + if (!group)
> > > > + return VFIO_PCI_DEVID_NOT_OWNED;
> > > > +
> > > > + if (iommufd_ctx_has_group(ictx, group))
> > > > + devid = VFIO_PCI_DEVID_OWNED;
> > > > + else
> > > > + devid = VFIO_PCI_DEVID_NOT_OWNED;
> > > > +
> > > > + iommu_group_put(group);
> > > > +
> > > > + return devid;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(vfio_iommufd_device_hot_reset_devid);
> > >
> > > This function really should not be in the core iommufd.c file - it is
> > > a purely vfio-pci function - why did you have to place it here?
> >
> > Put it here can avoid calling iommufd_ctx_has_group() in vfio-pci,
> > which requires to import IOMMUFD_NS. If this reason is not so
> > strong I can move it back to vfio-pci code.
>
> The PCI-isms here are the name of the function and the return value,
> otherwise this is simply a "give me the devid for this device in this
> context". The function name is trivial to change and we can define the
> internal errno usage such that the vfio-pci-core code can interpret the
> correct uAPI value. For example, -EXDEV ("Cross-device link") could
> maybe be interpreted as owned and any other errno is not-owned, -ENODEV
> maybe being the default.

Yeah, this approach seems logical

If the function is called

vfio_iommufd_get_dev_id(struct vfio_device *vdev, struct iommufd_ctx *ictx)

Then maybe
ENOENT = device is owned but there is no Id
ENODEV = device is not owned

EXDEV is good too, nice symmetry with ENODEV - it doesn't really
matter since there is only one caller and there is no embedded errno
propogation.

Jason