Re: [PATCH v3 08/24] vfio/pci: Retrieve preserved device files after Live Update

[Yi Liu <yi.l.liu@intel.com>]

On 3/24/26 07:58, David Matlack wrote:
> From: Vipin Sharma <vipinsh@google.com>
> 
> Enable userspace to retrieve preserved VFIO device files from VFIO after
> a Live Update by implementing the retrieve() and finish() file handler
> callbacks.
> 
> Use an anonymous inode when creating the file, since the retrieved
> device file is not opened through any particular cdev inode, and the
> cdev inode does not matter in practice.

do we have a list of struct file fields that do not matter?

> 
> For now the retrieved file is functionally equivalent a opening the
> corresponding VFIO cdev file. Subsequent commits will leverage the
> preserved state associated with the retrieved file to preserve bits of
> the device across Live Update.
> 
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> Co-developed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>   drivers/vfio/device_cdev.c             | 59 ++++++++++++++++++++++----
>   drivers/vfio/pci/vfio_pci_liveupdate.c | 52 ++++++++++++++++++++++-
>   drivers/vfio/vfio_main.c               | 13 ++++++
>   include/linux/vfio.h                   | 11 +++++
>   4 files changed, 124 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index 8ceca24ac136..edf322315a41 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -2,6 +2,7 @@
>   /*
>    * Copyright (c) 2023 Intel Corporation.
>    */
> +#include <linux/anon_inodes.h>
>   #include <linux/vfio.h>
>   #include <linux/iommufd.h>
>   
> @@ -16,15 +17,10 @@ void vfio_init_device_cdev(struct vfio_device *device)
>   	device->cdev.owner = THIS_MODULE;
>   }
>   
> -/*
> - * device access via the fd opened by this function is blocked until
> - * .open_device() is called successfully during BIND_IOMMUFD.
> - */
> -int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
> +static int vfio_device_cdev_open(struct vfio_device *device, struct file **filep)
>   {
> -	struct vfio_device *device = container_of(inode->i_cdev,
> -						  struct vfio_device, cdev);
>   	struct vfio_device_file *df;
> +	struct file *file = *filep;
>   	int ret;
>   
>   	/* Paired with the put in vfio_device_fops_release() */
> @@ -37,22 +33,67 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
>   		goto err_put_registration;
>   	}
>   
> -	filep->private_data = df;
> +	/*
> +	 * Simulate opening the character device using an anonymous inode. The
> +	 * returned file has the same properties as a cdev file (e.g. operations
> +	 * are blocked until BIND_IOMMUFD is called).
> +	 */
> +	if (!file) {
> +		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 err_free_device_file;
> +		}
> +
> +		*filep = file;
> +	}
> +
> +	file->private_data = df;
>   
>   	/*
>   	 * Use the pseudo fs inode on the device to link all mmaps
>   	 * to the same address space, allowing us to unmap all vmas
>   	 * associated to this device using unmap_mapping_range().
>   	 */
> -	filep->f_mapping = device->inode->i_mapping;
> +	file->f_mapping = device->inode->i_mapping;
>
>   	return 0;
>   
> +err_free_device_file:
> +	kvfree(df);

any reason to use kvfree()?

Regards,
Yi Liu