[Libguestfs] guestfs_mount_local api test: have to 'mount' before calling it?

Hi I`ve been trying this guestfs_mount_local api for quite a few days, but still can`t get over it. Now it seems to have enter the fuse loop but have some problems with 'mount'， and stops at guestfs_mount_local_run(g). Here`s corresponding code in the test program: …… if(guestfs_mount_local(g,"/mnt/libg")==-1) exit(EXIT_FAILURE); else guestfs_mount_local_run(g); …… Below is a part of the debug dump information, …… version = 1.17.40.Root device: /dev/vda1 (this is test output) libguestfs: guestfs__mount_local: fuse_mount /mnt/libg libguestfs: guestfs__mount_local: fuse_new libguestfs: guestfs__mount_local: leaving fuse_mount_local libguestfs: guestfs__mount_local_run: entering fuse_loop libguestfs: send_to_daemon: 56 bytes: 00 00 00 34 | 20 00 f5 f5 | 00 00 00 04 | 00 00 00 35 | 00 00 00 00 | ... guestfsd: main_loop: proc 11 (lvs) took 0.04 seconds guestfsd: main_loop: new request, len 0x34 guestfsd: error: lstat_stub: you must call 'mount' first to mount the root filesystem guestfsd: main_loop: proc 53 (lstat) took 0.00 seconds libguestfs: recv_from_daemon: 116 bytes: 20 00 f5 f5 | 00 00 00 04 | 00 00 00 35 | 00 00 00 01 | 00 12 34 36 | ... libguestfs: error: lstat: lstat_stub: you must call 'mount' first to mount the root filesystem libguestfs: send_to_daemon: 56 bytes: 00 00 00 34 | 20 00 f5 f5 | 00 00 00 04 | 00 00 00 35 | 00 00 00 00 | ... guestfsd: main_loop: new request, len 0x34 …… Any idea what might be wrong with it?the fuse? Thanks Nok