def mount_root(pool_name, device):
    root_pool_mnt = DEFAULT_MNT_DIR + pool_name
    if (is_share_mounted(pool_name)):
        return root_pool_mnt
    create_tmp_dir(root_pool_mnt)
    mnt_cmd = [MOUNT, '-t', 'btrfs', device, root_pool_mnt]
    run_command(mnt_cmd)
    return root_pool_mnt

def mount_share(share, mnt_pt):
    if (is_mounted(mnt_pt)):
        return
    mount_root(share.pool)
    pool_device = ('/dev/%s' % share.pool.disk_set.first().name)
    subvol_str = 'subvol=%s' % share.subvol_name
    create_tmp_dir(mnt_pt)
    mnt_cmd = [MOUNT, '-t', 'btrfs', '-o', subvol_str, pool_device, mnt_pt]
    return run_command(mnt_cmd)

def mount_share(share, pool_device, mnt_pt):
    if is_mounted(mnt_pt):
        return
    pool_device = "/dev/%s" % pool_device
    mount_root(share.pool, pool_device)
    subvol_str = "subvol=%s" % share.subvol_name
    create_tmp_dir(mnt_pt)
    mnt_cmd = [MOUNT, "-t", "btrfs", "-o", subvol_str, pool_device, mnt_pt]
    return run_command(mnt_cmd)

def mount_share(share, mnt_pt):
	if (is_mounted(mnt_pt)):
		return
	mount_root(share["pool"])
	pool_device = ('/dev/%s' % share["pool"]["disks"][0]["name"])
	subvol_str = 'subvol=%s' % share["subvol_name"]
	create_tmp_dir(mnt_pt)
	mnt_cmd = [MOUNT, '-t', 'btrfs', '-o', subvol_str, pool_device, mnt_pt]
	return run_command(mnt_cmd)

def add_snap(pool, share_name, snap_name, readonly=False):
    """
    create a snapshot
    """
    root_pool_mnt = mount_root(pool)
    share_full_path = ('%s/%s' % (root_pool_mnt, share_name))
    snap_dir = ('%s/.snapshots/%s' % (root_pool_mnt, share_name))
    create_tmp_dir(snap_dir)
    snap_full_path = ('%s/%s' % (snap_dir, snap_name))
    return add_snap_helper(share_full_path, snap_full_path, readonly)

def mount_root(pool):
    """
    Mounts a given pool at the default mount root (usually /mnt2/) using the
    pool.name as the final path entry. Ie pool.name = test-pool will be mounted
    at /mnt2/test-pool. Any mount options held in pool.mnt_options will be added
    to the mount command via the -o option as will a compress=pool.compression
    entry.
    N.B. Initially the mount target is defined by /dev/disk/by-label/pool.name,
    if this fails then an attempt to mount by each member of
    /dev/disk/by-id/pool.disk_set.all() but only if there are any members.
    If this second method also fails then an exception is raised, currently all
    but the last failed mount by device name is logged. If no disk members were
    reported by pool.disk_set.count() a separate Exception is raised.
    :param pool: pool object
    :return: either the relevant mount point or an Exception which either
    indicates 'no disks in pool' or 'Unknown Reason'
    """
    root_pool_mnt = DEFAULT_MNT_DIR + pool.name
    if (is_share_mounted(pool.name)):
        return root_pool_mnt
    # Creates a directory to act as the mount point.
    create_tmp_dir(root_pool_mnt)
    mnt_device = '/dev/disk/by-label/%s' % pool.name
    mnt_cmd = [MOUNT, mnt_device, root_pool_mnt, ]
    mnt_options = ''
    if (pool.mnt_options is not None):
        mnt_options = pool.mnt_options
    if (pool.compression is not None):
        if (re.search('compress', mnt_options) is None):
            mnt_options = ('%s,compress=%s' % (mnt_options, pool.compression))
    if (os.path.exists(mnt_device)):
        if (len(mnt_options) > 0):
            mnt_cmd.extend(['-o', mnt_options])
        run_command(mnt_cmd)
        return root_pool_mnt
    # If we cannot mount by-label, let's try mounting by device; one by one
    # until we get our first success.
    if (pool.disk_set.count() < 1):
        raise Exception('Cannot mount Pool(%s) as it has no disks in it.' % pool.name)
    last_device = pool.disk_set.last()
    for device in pool.disk_set.all():
        mnt_device = ('/dev/disk/by-id/%s' % device.name)
        if (os.path.exists(mnt_device)):
            mnt_cmd = [MOUNT, mnt_device, root_pool_mnt, ]
            if (len(mnt_options) > 0):
                mnt_cmd.extend(['-o', mnt_options])
            try:
                run_command(mnt_cmd)
                return root_pool_mnt
            except Exception, e:
                if (device.name == last_device.name):
                    # exhausted mounting using all devices in the pool
                    raise e
                logger.error('Error mounting: %s. Will try using another device.' % mnt_cmd)
                logger.exception(e)

def add_snap(pool, pool_device, share_name, snap_name, readonly=False):
    """
    create a snapshot
    """
    pool_device = "/dev/" + pool_device
    root_pool_mnt = mount_root(pool, pool_device)
    share_full_path = "%s/%s" % (root_pool_mnt, share_name)
    snap_dir = "%s/.snapshots/%s" % (root_pool_mnt, share_name)
    create_tmp_dir(snap_dir)
    snap_full_path = "%s/%s" % (snap_dir, snap_name)
    return add_snap_helper(share_full_path, snap_full_path, readonly)

def mount_snap(share, snap_name, pool_device, snap_mnt=None):
    pool_device = "/dev/%s" % pool_device
    share_path = "%s%s" % (DEFAULT_MNT_DIR, share.name)
    rel_snap_path = ".snapshots/%s/%s" % (share.name, snap_name)
    snap_path = "%s%s/%s" % (DEFAULT_MNT_DIR, share.pool.name, rel_snap_path)
    if snap_mnt is None:
        snap_mnt = "%s/.%s" % (share_path, snap_name)
    mount_share(share, pool_device[5:], share_path)
    if is_subvol(snap_path):
        create_tmp_dir(snap_mnt)
        return run_command([MOUNT, "-o", "subvol=%s" % rel_snap_path, pool_device, snap_mnt])

def mount_snap(share, snap_name, pool_device, snap_mnt=None):
    pool_device = ('/dev/%s' % pool_device)
    share_path = ('%s%s' % (DEFAULT_MNT_DIR, share.name))
    rel_snap_path = ('.snapshots/%s/%s' % (share.name, snap_name))
    snap_path = ('%s%s/%s' %
                 (DEFAULT_MNT_DIR, share.pool.name, rel_snap_path))
    if (snap_mnt is None):
        snap_mnt = ('%s/.%s' % (share_path, snap_name))
    mount_share(share, pool_device[5:], share_path)
    if (is_subvol(snap_path)):
        create_tmp_dir(snap_mnt)
        return run_command([MOUNT, '-o', 'subvol=%s' % rel_snap_path,
                            pool_device, snap_mnt])

def mount_root(pool, device):
    root_pool_mnt = DEFAULT_MNT_DIR + pool.name
    if is_share_mounted(pool.name):
        return root_pool_mnt
    create_tmp_dir(root_pool_mnt)
    mnt_device = "/dev/disk/by-label/%s" % pool.name
    if not os.path.exists(mnt_device):
        mnt_device = device
    mnt_cmd = [MOUNT, mnt_device, root_pool_mnt]
    mnt_options = ""
    if pool.mnt_options is not None:
        mnt_options = pool.mnt_options
    if pool.compression is not None:
        if re.search("compress", mnt_options) is None:
            mnt_options = "%s,compress=%s" % (mnt_options, pool.compression)
    if len(mnt_options) > 0:
        mnt_cmd.extend(["-o", mnt_options])
    run_command(mnt_cmd)
    return root_pool_mnt

def rollback_snap(snap_name, sname, subvol_name, pool, pool_device):
    """
    1. validate destination snapshot and umount the share
    2. remove the share
    3. move the snapshot to share location and mount it.
    """
    mnt_pt = "%s%s" % (DEFAULT_MNT_DIR, sname)
    snap_fp = "%s/%s/.snapshots/%s/%s" % (DEFAULT_MNT_DIR, pool.name, sname, snap_name)
    if not is_subvol(snap_fp):
        raise Exception("Snapshot(%s) does not exist. Rollback is not " "possible" % snap_fp)
    dpath = "/dev/%s" % pool_device
    mount_root(pool, dpath)
    if is_share_mounted(sname):
        umount_root(mnt_pt)
    remove_share(pool, pool_device, subvol_name)
    shutil.move(snap_fp, "%s/%s/%s" % (DEFAULT_MNT_DIR, pool.name, sname))
    create_tmp_dir(mnt_pt)
    subvol_str = "subvol=%s" % sname
    mnt_cmd = [MOUNT, "-t", "btrfs", "-o", subvol_str, dpath, mnt_pt]
    run_command(mnt_cmd)

def mount_root(pool, device):
    root_pool_mnt = DEFAULT_MNT_DIR + pool.name
    if (is_share_mounted(pool.name)):
        return root_pool_mnt
    create_tmp_dir(root_pool_mnt)
    mnt_device = '/dev/disk/by-label/%s' % pool.name
    if (not os.path.exists(mnt_device)):
        mnt_device = device
        if (re.match('/dev/', device) is None):
            mnt_device = ('/dev/%s' % mnt_device)
    mnt_cmd = [MOUNT, mnt_device, root_pool_mnt, ]
    mnt_options = ''
    if (pool.mnt_options is not None):
        mnt_options = pool.mnt_options
    if (pool.compression is not None):
        if (re.search('compress', mnt_options) is None):
            mnt_options = ('%s,compress=%s' % (mnt_options, pool.compression))
    if (len(mnt_options) > 0):
        mnt_cmd.extend(['-o', mnt_options])
    run_command(mnt_cmd)
    return root_pool_mnt

def mount_root(pool):
	root_pool_mnt = DEFAULT_MNT_DIR + pool["name"]
	if (is_share_mounted(pool["name"])):
		return root_pool_mnt
	create_tmp_dir(root_pool_mnt)
	mnt_device = '/dev/disk/by-label/%s' % pool["name"]
	mnt_cmd = [MOUNT, mnt_device, root_pool_mnt, ]
	mnt_options = ''
	if (pool["mnt_options"] is not None):
		mnt_options = pool["mnt_options"]
	if (pool["compression"] is not None):
		if (re.search('compress', mnt_options) is None):
			mnt_options = ('%s,compress=%s' % (mnt_options, pool["compression"]))
	if (os.path.exists(mnt_device)):
		if (len(mnt_options) > 0):
			mnt_cmd.extend(['-o', mnt_options])
		run_command(mnt_cmd)
		return root_pool_mnt

	# If we cannot mount by-label, let's try mounting by device one by one
	# until we get our first success.
	# ==============================================================================#
	if (len(pool["disks"]) < 1):
		raise Exception('Cannot mount Pool(%s) as it has no disks in it.' % pool["name"])
	last_device = pool["disks"][-1]
	for device in pool["disks"]:
		mnt_device = ('/dev/%s' % device["name"])
		if (os.path.exists(mnt_device)):
			mnt_cmd = [MOUNT, mnt_device, root_pool_mnt, ]
			if (len(mnt_options) > 0):
				mnt_cmd.extend(['-o', mnt_options])
			try:
				run_command(mnt_cmd)
				return root_pool_mnt
			except Exception, e:
				if (device["name"] == last_device["name"]):
					# exhausted mounting using all devices in the pool
					raise e
				logger.error('Error mouting: %s. Will try using another device.' % mnt_cmd)
				logger.exception(e)

def rollback_snap(snap_name, sname, subvol_name, pool):
    """
    1. validate destination snapshot and umount the share
    2. remove the share
    3. move the snapshot to share location and mount it.
    """
    mnt_pt = ('%s%s' % (DEFAULT_MNT_DIR, sname))
    snap_fp = ('%s/%s/.snapshots/%s/%s' % (DEFAULT_MNT_DIR, pool.name, sname,
                                           snap_name))
    if (not is_subvol(snap_fp)):
        raise Exception('Snapshot(%s) does not exist. Rollback is not '
                        'possible' % snap_fp)
    mount_root(pool)
    if (is_share_mounted(sname)):
        umount_root(mnt_pt)
    remove_share(pool, subvol_name, '-1/-1')
    shutil.move(snap_fp, '%s/%s/%s' % (DEFAULT_MNT_DIR, pool.name, sname))
    create_tmp_dir(mnt_pt)
    subvol_str = 'subvol=%s' % sname
    dpath = '/dev/%s' % pool.disk_set.first().name
    mnt_cmd = [MOUNT, '-t', 'btrfs', '-o', subvol_str, dpath, mnt_pt]
    run_command(mnt_cmd)

def mount_share(share_name, pool_device, mnt_pt):
    pool_device = '/dev/' + pool_device
    subvol_str = 'subvol=%s' % share_name
    create_tmp_dir(mnt_pt)
    mnt_cmd = [MOUNT, '-t', 'btrfs', '-o', subvol_str, pool_device, mnt_pt]
    return run_command(mnt_cmd)