Re: [RFC v2 4/4] vduse: Add new ioctl VDUSE_GET_RECONNECT_INFO

[Jason Wang]

On Tue, Sep 12, 2023 at 11:01 AM Cindy Lu <lulu@xxxxxxxxxx> wrote:
>
> In VDUSE_GET_RECONNECT_INFO, the Userspace App can get the map size
> and The number of mapping memory pages from the kernel. The userspace
> App can use this information to map the pages.
>
> Signed-off-by: Cindy Lu <lulu@xxxxxxxxxx>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 15 +++++++++++++++
>  include/uapi/linux/vduse.h         | 15 +++++++++++++++
>  2 files changed, 30 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 680b23dbdde2..c99f99892b5c 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1368,6 +1368,21 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
>                 ret = 0;
>                 break;
>         }
> +       case VDUSE_GET_RECONNECT_INFO: {
> +               struct vduse_reconnect_mmap_info info;
> +
> +               ret = -EFAULT;
> +               if (copy_from_user(&info, argp, sizeof(info)))
> +                       break;
> +
> +               info.size = PAGE_SIZE;
> +               info.max_index = dev->vq_num + 1;
> +
> +               if (copy_to_user(argp, &info, sizeof(info)))
> +                       break;
> +               ret = 0;
> +               break;
> +       }
>         default:
>                 ret = -ENOIOCTLCMD;
>                 break;
> diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> index d585425803fd..ce55e34f63d7 100644
> --- a/include/uapi/linux/vduse.h
> +++ b/include/uapi/linux/vduse.h
> @@ -356,4 +356,19 @@ struct vhost_reconnect_vring {
>         _Bool avail_wrap_counter;
>  };
>
> +/**
> + * struct vduse_reconnect_mmap_info
> + * @size: mapping memory size, always page_size here
> + * @max_index: the number of pages allocated in kernel,just
> + * use for check
> + */
> +
> +struct vduse_reconnect_mmap_info {
> +       __u32 size;
> +       __u32 max_index;
> +};

One thing I didn't understand is that, aren't the things we used to
store connection info belong to uAPI? If not, how can we make sure the
connections work across different vendors/implementations. If yes,
where?

Thanks

> +
> +#define VDUSE_GET_RECONNECT_INFO \
> +       _IOWR(VDUSE_BASE, 0x1b, struct vduse_reconnect_mmap_info)
> +
>  #endif /* _UAPI_VDUSE_H_ */
> --
> 2.34.3
>