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 <redacted>
---
 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;
+};