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

[Cindy Lu <lulu@redhat.com>]

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@redhat.com>
---
 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;
+};
+
+#define VDUSE_GET_RECONNECT_INFO \
+	_IOWR(VDUSE_BASE, 0x1b, struct vduse_reconnect_mmap_info)
+
 #endif /* _UAPI_VDUSE_H_ */
-- 
2.34.3