Re: [PATCH 06/21] vfio/pci: Retrieve preserved device files after Live Update

[Alex Mastro <amastro@fb.com>]

On Wed, Nov 26, 2025 at 07:35:53PM +0000, David Matlack wrote:
> From: Vipin Sharma <vipinsh@google.com>
>  static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_op_args *args)
>  {
> -	return -EOPNOTSUPP;
> +	struct vfio_pci_core_device_ser *ser;
> +	struct vfio_device *device;
> +	struct folio *folio;
> +	struct file *file;
> +	int ret;
> +
> +	folio = kho_restore_folio(args->serialized_data);
> +	if (!folio)
> +		return -ENOENT;

Should this be consistent with the behavior of pci_flb_retrieve() which panics
on failure? The short circuit failure paths which follow leak the folio,
which seems like a hygiene issue, but the practical significance is moot if
vfio_pci_liveupdate_retrieve() failure is catastrophic anyways?

> +
> +	ser = folio_address(folio);
> +
> +	device = vfio_find_device(ser, match_device);
> +	if (!device)
> +		return -ENODEV;
> +
> +	/*
> +	 * During a Live Update userspace retrieves preserved VFIO cdev files by
> +	 * issuing an ioctl on /dev/liveupdate rather than by opening VFIO
> +	 * character devices.
> +	 *
> +	 * To handle that scenario, this routine simulates opening the VFIO
> +	 * character device for userspace with an anonymous inode. The returned
> +	 * file has the same properties as a cdev file (e.g. operations are
> +	 * blocked until BIND_IOMMUFD is called), aside from the inode
> +	 * association.
> +	 */
> +	file = anon_inode_getfile_fmode("[vfio-device-liveupdate]",
> +					&vfio_device_fops, NULL,
> +					O_RDWR, FMODE_PREAD | FMODE_PWRITE);
> +
> +	if (IS_ERR(file)) {
> +		ret = PTR_ERR(file);
> +		goto out;
> +	}
> +
> +	ret = __vfio_device_fops_cdev_open(device, file);
> +	if (ret) {
> +		fput(file);
> +		goto out;
> +	}
> +
> +	args->file = file;
> +
> +out:
> +	/* Drop the reference from vfio_find_device() */
> +	put_device(&device->device);
> +
> +	return ret;
> +}