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

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu at 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'