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

[Nok]

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