What is the libmount equivalent function to mount a FUSE file-system. I understand that FUSE is not a real file system and my strace of mount.fuse shows opening a /dev/fuse file and doing some complicated manipulations.
I tried seeing how the mount.fuse works by reading it's source code but not only it is needlessly complicated by string manipulations in C, it is a GPL program.
My question is, am I missing the obvious API to mount fuse file systems?
The kernel interface for mounting a FUSE filesystem is described in "linux/Documentation/filesystems/fuse.txt" (for example, see here).
In a nutshell, you call mount(2) as you would to mount any filesystem. However, the key difference is that you must provide a mount option fd=n where n is a file descriptor you've obtained by opening /dev/fuse and which will be used by the userspace process implementing the filesystem to respond to kernel requests.
In particular, this means that the mount is actually performed by the user space program that implements the filesystem. Specifically, most FUSE filesystems use libfuse and call the function fuse_main or fuse_session_mount to perform the mount (which eventually call the internal function fuse_mount_sys in mount.c that contains the actual mount(2) system call).
So, if you want to mount a FUSE filesystem programmatically, the correct way to do this is to fork and exec the corresponding FUSE executable (e.g., sshfs) and have it handle the mount on your behalf.
Note that /sbin/mount.fuse doesn't actually mount anything itself. It's just a wrapper to allow you to mount FUSE filesystems via entries in "/etc/fstab" via the mount command line utility or at boot time. That's why you can't find any mounting code there. It mounts FUSE filesystems the same way I described above, by running the FUSE executable for the filesystem in question to perform the actual mount.