Comment 3 for bug 1891906

I'm afraid I don't know the answer but I can give some pointers to the code
so you can work out what's going on:

https://github.com/libguestfs/libguestfs/blob/master/fuse/guestmount.c

This is the program that is supposed to parse the -o options from
the command line. It adds them to a list of options (fuse_options)
that are passed to the libguestfs mount_local_* APIs. You should be
able to see the arguments being passed through to the API if you use
guestmount -x

https://github.com/libguestfs/libguestfs/blob/master/lib/fuse.c

This is where the API gets implemented. It's supposed to only pass
the options through to fuse_opt_add_arg where fuse does the rest.