FreeBSD/cddl/contrib/opensolaris/cmd/zfs/zfs_main.c
/*
 * zfs unmount -a
 * zfs unmount filesystem
 *
 * Unmount all filesystems, or a specific ZFS filesystem.
 */
zfs unmount -a
zfs unmount filesystem

Unmount all filesystems, or a specific ZFS filesystem.
zfs unmount - a zfs unmount filesystem Unmount all filesystems or a specific ZFS filesystem .
static int
zfs_do_unmount(int argc, char **argv)
{
	return (unshare_unmount(OP_MOUNT, argc, argv));
}
static int zfs_do_unmount ( int argc , char * * argv ) { return ( unshare_unmount ( OP_MOUNT , argc , argv ) ) ; }
zfs unmount -a
 zfs unmount filesystem
zfs unmount - a zfs unmount filesystem