[Libguestfs] minor usability issue: confusing error message with guestmount + fuse errors

[Assaf Gordon]

Hello,

Using older libguestfs 1.34.6-2 (from Ubuntu's standard package),
I encountered this:

libguestfs fails with an error, but the error code is "success":

   $ sudo guestmount -m /dev/sda1 --ro \
                     -o allow_others \
                     -a data.qcow2 \
                     /media/foo
   fuse: unknown option `allow_others'
   libguestfs: error: fuse_new: /media/foo/: Success


Other fuse errors also cause the same behavior,
e.g. mounting to an already-mounted directory:

   $ sudo guestmount -m /dev/sda1 --ro -a data2.qcow2 /media/foo
   /media/foo mountpoint is not empty
   fuse: mountpoint is not empty
   fuse: if you are sure this is safe, use the 'nonempty' mount option
   libguestfs: error: fuse_mount: /media/foo: Success


I guess libguestfs uses the most recent 'errno'
to report the error string, but it is zero
(because the error was somewhere deeper, in fuse).


regards,
  - assaf