fuse: device fd clone

Allow an open fuse device to be "cloned".  Userspace can create a clone by:

      newfd = open("/dev/fuse", O_RDWR)
      ioctl(newfd, FUSE_DEV_IOC_CLONE, &oldfd);

At this point newfd will refer to the same fuse connection as oldfd.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 25084a0..c9aca04 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -755,4 +755,7 @@
 	uint64_t	dummy4;
 };
 
+/* Device ioctls: */
+#define FUSE_DEV_IOC_CLONE	_IOR(229, 0, uint32_t)
+
 #endif /* _LINUX_FUSE_H */