RE: [PATCH v5 09/19] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

Tian, Kevin
2023-03-08T07:27:10Z

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Tuesday, March 7, 2023 9:29 PM
>
> >
> > I really prefer the 'use the iommufd option' still exist, it is so
> > much cleaner and easier for the actual users of this API. We've lost
> > the point by worrying about no iommu.
>
> Hmmm, so you are suggesting to have both the device fd approach
> and the zero-length array approach, let user to select the best way
> based on their wisdom. Is it? how about something like below in the
> uapi header.
>
> /**
> * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
> * struct vfio_pci_hot_reset)
> *
> * Userspace requests hot reset for the devices it uses. Due to the
> * underlying topology, multiple devices may be affected in the reset.
> * The affected devices may have been opened by the user or by other
> * users or not opened yet. Only when all the affected devices are
> * either opened by the current user or not opened by any user, should
> * the reset request be allowed. Otherwise, this request is expected
> * to return error. group_fds array can accept either group fds or
> * device fds. Users using iommufd (valid fd), could also passing a
> * zero-length group_fds array to indicate using the bound iommufd_ctx
> * for ownership check to the affected devices that are opened.
> *
> * Return: 0 on success, -errno on failure.
> */
> struct vfio_pci_hot_reset {
> __u32 argsz;
> __u32 flags;
> __u32 count;
> __s32 group_fds[];
> };
>

* Userspace requests hot reset for the devices it uses. Due to the
* underlying topology, multiple devices can be affected in the reset
* while some might be opened by another user. To avoid interference
* the calling user must ensure all affected devices, if opened, are
* owned by itself.
*
* The ownership can be proved in three ways:
* - An array of group fds
* - An array of device fds
* - A zero-length array
*
* In the last case all affected devices which are opened by this user must
* have been bound to a same iommufd_ctx.

and with this change let's rename 'group_fds' to 'fds'