udavfs3/udavfs3

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# Usage: udavfs3 "host=dbhost dbname=database user=dbuser password=dbpass" <mountpoint> [-o mount_options]
# UdavFS mount_option:
#    blocksize=<bytes>
#    fssize=<size>[k|m|g|t]
#    fsid=<uniq_name>
#
# Option 'user_allow_other' MUST be set in /etc/fuse.conf

from __future__ import division, print_function, absolute_import

import os
import sys
import llfuse
import errno
import stat
import math
from time import time
import psycopg2
import psycopg2.extensions
import psycopg2.extras
import logging
from collections import defaultdict
from llfuse import FUSEError
from hashlib import sha1

log = logging.getLogger()
blocksize = 4096

class Operations(llfuse.Operations):
    def __init__(self, conn_str, fsid, bs, size):      
        super(Operations, self).__init__()
        self.blocksize = bs
        self.fssize = size
        self.fsid = fsid
        self.db = psycopg2.connect(conn_str)
        self.db.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
        self.cursor = self.db.cursor()        
        self.inode_open_count = defaultdict(int)
        try:
            if self.get_row('SELECT count(1) FROM fsinfo WHERE fsid=%s;', (self.fsid,))[0] == 0:
                self.init_fs()
        except:
            self.init_fs()
             
    def init_tables(self):
        '''Initialize file system tables'''
        
        self.cursor.execute("""
        CREATE TABLE fsinfo (
            id        SERIAL PRIMARY KEY,
            fsid      VARCHAR(40) NOT NULL,
            size      BIGINT NOT NULL,
            bs        INT NOT NULL,
            UNIQUE    (fsid)
        )
        """)
        
        self.cursor.execute("""
        CREATE TABLE inodes (
            id        BIGSERIAL PRIMARY KEY,
            fsid      VARCHAR(40) NOT NULL REFERENCES fsinfo (fsid) ON DELETE CASCADE,
            inode_id  BIGSERIAL,
            uid       INT NOT NULL,
            gid       INT NOT NULL,
            mode      INT NOT NULL,
            mtime     BIGINT NOT NULL,
            atime     BIGINT NOT NULL,
            ctime     BIGINT NOT NULL,
            target    BYTEA,
            size      BIGINT NOT NULL DEFAULT 0,
            rdev      INT NOT NULL DEFAULT 0,
            UNIQUE    (fsid, inode_id)
        )
        """)
        
        self.cursor.execute("""
        CREATE TABLE body (
            inode_id        BIGINT NOT NULL,
            fsid            VARCHAR(40) NOT NULL,
            block_no        INT NOT NULL DEFAULT 0,
            data            BYTEA,
            PRIMARY KEY     ( fsid, inode_id, block_no ),
            UNIQUE          ( fsid, inode_id, block_no),
            FOREIGN KEY     (fsid, inode_id) REFERENCES inodes (fsid, inode_id) ON DELETE CASCADE
        )
        """)
        
        self.cursor.execute("""
        CREATE TABLE contents (
            rowid     BIGSERIAL PRIMARY KEY,
            fsid      VARCHAR(40) NOT NULL,
            name      BYTEA NOT NULL,
            inode_id     BIGINT NOT NULL,
            parent_inode BIGINT NOT NULL,
            FOREIGN KEY( fsid, inode_id ) REFERENCES inodes( fsid, inode_id ) ON DELETE CASCADE,
            FOREIGN KEY( fsid, parent_inode ) REFERENCES inodes( fsid, inode_id ) ON DELETE CASCADE,
            UNIQUE (fsid, name, parent_inode)
        )""")
        
    def init_fs(self):
        if self.get_row('SELECT count(1) FROM information_schema.tables WHERE table_schema=\'public\' AND table_name=\'inodes\'')[0] == 0:
            self.init_tables()
        if self.get_row('SELECT count(1) FROM fsinfo WHERE fsid=%s;', (self.fsid,))[0] == 0:
            self.cursor.execute("INSERT INTO fsinfo (fsid, bs, size) VALUES (%s, %s,%s)",
                            (self.fsid, self.blocksize, self.fssize))
        # Insert root directory
        self.cursor.execute("INSERT INTO inodes (fsid,inode_id,mode,uid,gid,mtime,atime,ctime) "
                            "VALUES (%s,%s,%s,%s,%s,%s,%s,%s)",
                            (self.fsid, llfuse.ROOT_INODE, stat.S_IFDIR | stat.S_IRUSR | stat.S_IWUSR
                              | stat.S_IXUSR | stat.S_IRGRP | stat.S_IXGRP | stat.S_IROTH 
                              | stat.S_IXOTH, os.getuid(), os.getgid(), int(time() * 1e9), 
                              int(time() * 1e9), int(time() * 1e9)))
        self.cursor.execute("SELECT setval('inodes_inode_id_seq', %s);", (llfuse.ROOT_INODE + 1,))
        self.cursor.execute("INSERT INTO contents (fsid, name, parent_inode, inode_id) VALUES (%s,%s,%s,%s)",
                            (self.fsid, b'..', llfuse.ROOT_INODE, llfuse.ROOT_INODE))
        
    def get_row(self, *a, **kw):
        self.cursor.execute(*a, **kw) 
        row = self.cursor.fetchone()
        if row is None:
            raise NoSuchRowError()
        if self.cursor.fetchone() is None:
            pass
        else:
            raise NoUniqueValueError()

        return row
                    
    def lookup(self, inode_p, name, ctx):
        if name == b'.':
            inode = inode_p
        elif name == b'..':
            inode = self.get_row("SELECT parent_inode FROM contents WHERE inode_id=%s AND fsid=%s",
                                 (inode_p, self.fsid))[0]
        else:
            try:
                inode = self.get_row("SELECT inode_id FROM contents WHERE name=%s AND parent_inode=%s AND fsid=%s",
                                     (name, inode_p, self.fsid))[0]
            except NoSuchRowError:
                raise(llfuse.FUSEError(errno.ENOENT))
        
        return self.getattr(inode, ctx)
        
    def getattr(self, inode, ctx = None):
        cur = self.db.cursor(cursor_factory=psycopg2.extras.DictCursor)
        cur.execute('SELECT * FROM inodes WHERE inode_id=%s AND fsid=%s', (inode, self.fsid))
        row = cur.fetchone()
        entry = llfuse.EntryAttributes()
        entry.st_ino = inode
        entry.generation = 0
        entry.entry_timeout = 300
        entry.attr_timeout = 300
        entry.st_mode = row['mode']
        entry.st_nlink = self.get_row("SELECT COUNT(1) FROM contents WHERE inode_id=%s AND fsid=%s",
                                     (inode, self.fsid))[0]
        entry.st_uid = row['uid']
        entry.st_gid = row['gid']
        entry.st_rdev = row['rdev']
        entry.st_size = row['size']
        
        entry.st_blksize = self.blocksize
        entry.st_blocks = self.get_row("SELECT COUNT(1) FROM body WHERE inode_id=%s AND fsid=%s",
                                     (inode, self.fsid))[0]
        entry.st_atime_ns = row['atime']                          
        entry.st_mtime_ns = row['mtime']
        entry.st_ctime_ns = row['ctime']
        
        return entry

    def readlink(self, inode, ctx):
        return bytes(self.get_row('SELECT target FROM inodes WHERE inode_id=%s AND fsid=%s', (inode, self.fsid))[0])
    
    def opendir(self, inode, ctx):
        return inode

    def readdir(self, inode, off):
        if off == 0:
            off = -1
            
        cursor2 = self.db.cursor(cursor_factory=psycopg2.extras.DictCursor)
        cursor2.execute("SELECT * FROM contents WHERE parent_inode=%s "
                        'AND rowid > %s AND fsid=%s ORDER BY rowid', (inode, off, self.fsid))
        
        for row in cursor2.fetchall():
            yield (bytes(row['name']), self.getattr(row['inode_id']), row['rowid'])

    def unlink(self, inode_p, name, ctx):
        entry = self.lookup(inode_p, name, ctx)

        if stat.S_ISDIR(entry.st_mode):
            raise llfuse.FUSEError(errno.EISDIR)

        self._remove(inode_p, name, entry)

    def rmdir(self, inode_p, name, ctx):
        entry = self.lookup(inode_p, name, ctx)

        if not stat.S_ISDIR(entry.st_mode):
            raise llfuse.FUSEError(errno.ENOTDIR)

        self._remove(inode_p, name, entry)

    def _remove(self, inode_p, name, entry):
        if self.get_row("SELECT COUNT(1) FROM contents WHERE parent_inode=%s AND fsid=%s", 
                        (entry.st_ino, self.fsid))[0] > 0:
            raise llfuse.FUSEError(errno.ENOTEMPTY)

        self.cursor.execute("DELETE FROM contents WHERE name=%s AND parent_inode=%s AND fsid=%s",
                        (name, inode_p, self.fsid))
        
        if entry.st_nlink == 1 and entry.st_ino not in self.inode_open_count:
            self.cursor.execute("DELETE FROM inodes WHERE inode_id=%s AND fsid=%s", (entry.st_ino, self.fsid))
        

    def symlink(self, inode_p, name, target, ctx):
        mode = (stat.S_IFLNK | stat.S_IRUSR | stat.S_IWUSR | stat.S_IXUSR | 
                stat.S_IRGRP | stat.S_IWGRP | stat.S_IXGRP | 
                stat.S_IROTH | stat.S_IWOTH | stat.S_IXOTH)
        return self._create(inode_p, name, mode, ctx, target=target)

    def rename(self, inode_p_old, name_old, inode_p_new, name_new, ctx):
        entry_old = self.lookup(inode_p_old, name_old, ctx)

        try:
            entry_new = self.lookup(inode_p_new, name_new, ctx)
        except llfuse.FUSEError as exc:
            if exc.errno != errno.ENOENT:
                raise
            target_exists = False
        else:
            target_exists = True

        if target_exists:
            self._replace(inode_p_old, name_old, inode_p_new, name_new,
                          entry_old, entry_new)
        else:
            self.cursor.execute("UPDATE contents SET name=%s, parent_inode=%s WHERE name=%s "
                                "AND parent_inode=%s AND fsid=%s", (name_new, inode_p_new,
                                                       name_old, inode_p_old, self.fsid))
            

    def _replace(self, inode_p_old, name_old, inode_p_new, name_new,
                 entry_old, entry_new):
        if self.get_row("SELECT COUNT(1) FROM contents WHERE parent_inode=%s AND fsid=%s", 
                        (entry_new.st_ino, self.fsid))[0] > 0:
            raise llfuse.FUSEError(errno.ENOTEMPTY)
   
        self.cursor.execute("UPDATE contents SET inode_id=%s WHERE name=%s AND parent_inode=%s AND fsid=%s",
                            (entry_old.st_ino, name_new, inode_p_new, self.fsid))
        self.cursor.execute('DELETE FROM contents WHERE name=%s AND parent_inode=%s AND fsid=%s',
                        (name_old, inode_p_old, self.fsid))

        if entry_new.st_nlink == 1 and entry_new.st_ino not in self.inode_open_count:
            self.cursor.execute("DELETE FROM inodes WHERE inode_id=%s AND fsid=%s", (entry_new.st_ino, self.fsid))
        

    def link(self, inode, new_inode_p, new_name, ctx):
        entry_p = self.getattr(new_inode_p, ctx)
        if entry_p.st_nlink == 0:
            raise FUSEError(errno.EINVAL)

        self.cursor.execute("INSERT INTO contents (name, inode_id, parent_inode, fsid) VALUES(%s,%s,%s,%s)",
                            (new_name, inode, new_inode_p, self.fsid))
        
        return self.getattr(inode, ctx)
    def del_block(self, inode, num):
        self.cursor.execute("DELETE FROM body WHERE inode_id=%s AND block_no=%s AND fsid=%s", (inode, num, self.fsid))

    def setattr(self, inode, attr, fields, fh, ctx):

        if fields.update_size:
            size = self.get_row('SELECT size FROM inodes WHERE inode_id=%s AND fsid=%s', (inode, self.fsid))[0]
            if size is None:
                size = 0
            blocks = int(math.ceil(size / self.blocksize))
            end_len = size % self.blocksize
            if size < attr.st_size:
                dif_size = attr.st_size - size
                if dif_size <= (self.blocksize - end_len) and end_len > 0:
                    pass
                else:
                    addblocks = int(math.ceil(dif_size / self.blocksize))
                    for b in range(addblocks):
                        self.write(inode, (blocks + b) * self.blocksize , '\0' * self.blocksize)
            elif size > attr.st_size:
                dif_size = size - attr.st_size
                if dif_size < end_len:
                    self.write(inode, (blocks - 1) * self.blocksize,
                                    self.read(inode, (blocks - 1) * self.blocksize , 
                                              end_len - dif_size) + '\0' * (self.blocksize - (end_len - dif_size)))
                elif dif_size == end_len and end_len > 0:
                    self.del_block(inode, blocks - 1)
                elif dif_size > end_len:
                    if end_len > 0:
                        dif_size -= end_len
                        blocks -= 1
                        self.del_block(inode, blocks)
                    dif_blocks = int(math.ceil(dif_size / self.blocksize))
                    dif_end_len = dif_size % self.blocksize
                    if dif_end_len > 0:
                        dif_blocks -= 1
                    for b in range(dif_blocks):
                        blocks -= 1
                        self.del_block(inode, blocks)
                    if dif_end_len > 0:
                        self.write(inode, (blocks - 1) * self.blocksize,
                                    self.read(inode, (blocks - 1) * self.blocksize , 
                                                self.blocksize - dif_end_len) + '\0' * (self.blocksize - dif_end_len))
            if size == attr.st_size:
                pass
            else:
                self.cursor.execute("UPDATE inodes SET size=%s WHERE inode_id=%s AND fsid=%s",
                                (attr.st_size, inode, self.fsid))
        if fields.update_mode:
            self.cursor.execute('UPDATE inodes SET mode=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_mode, inode, self.fsid))

        if fields.update_uid:
            self.cursor.execute('UPDATE inodes SET uid=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_uid, inode, self.fsid))

        if fields.update_gid:
            self.cursor.execute('UPDATE inodes SET gid=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_gid, inode, self.fsid))

        if attr.st_rdev is not None:
            self.cursor.execute('UPDATE inodes SET rdev=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_rdev, inode, self.fsid))

        if fields.update_atime:
            self.cursor.execute('UPDATE inodes SET atime=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_atime_ns, inode, self.fsid))

        if fields.update_mtime:
            self.cursor.execute('UPDATE inodes SET mtime=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_mtime_ns, inode, self.fsid))

        if attr.st_ctime_ns is not None:
            self.cursor.execute('UPDATE inodes SET ctime=%s WHERE inode_id=%s AND fsid=%s',
                                (attr.st_ctime_ns, inode, self.fsid))
        
        return self.getattr(inode, ctx)

    def mknod(self, inode_p, name, mode, rdev, ctx):
        return self._create(inode_p, name, mode, ctx, rdev=rdev)

    def mkdir(self, inode_p, name, mode, ctx):
        return self._create(inode_p, name, mode, ctx)

    def statfs(self, ctx):
        stat_ = llfuse.StatvfsData()

        stat_.f_bsize = self.blocksize
        stat_.f_frsize = self.blocksize

        size = self.get_row('SELECT SUM(size) FROM inodes WHERE fsid=%s', (self.fsid,))[0]
        stat_.f_blocks = self.fssize // stat_.f_frsize
        stat_.f_bfree = int(stat_.f_blocks) - (size // stat_.f_frsize)
        stat_.f_bavail = stat_.f_bfree

        inodes = self.get_row('SELECT COUNT(1) FROM inodes WHERE fsid=%s', (self.fsid,))[0]
        stat_.f_files = inodes
        stat_.f_ffree = max(inodes , 100)
        stat_.f_favail = stat_.f_ffree

        return stat_

    def open(self, inode, flags, ctx):
        self.inode_open_count[inode] += 1
        return inode

    def access(self, inode, mode, ctx=None):
        if mode != os.F_OK and not self.__access(inode, mode, ctx):
            return False
        return True
    
    def __access(self, inode, flags, ctx):
        attrs = self.get_row("SELECT mode, uid, gid FROM inodes WHERE inode_id = %s AND fsid=%s",
                             (inode, self.fsid))
        uid, gid = (ctx.uid, ctx.gid)
        o = uid == attrs[1] # access by same user id?
        g = gid == attrs[2] and not o # access by same group id?
        # Note: "and not o" added after experimenting with EXT4.
        w = not (o or g) # anything else
        m = attrs[0]
        return (not (flags & os.R_OK) or ((o and (m & 0o0400)) or (g and (m & 0o0040)) or (w and (m & 0o0004)))) \
            and (not (flags & os.W_OK) or ((o and (m & 0o0200)) or (g and (m & 0o0020)) or (w and (m & 0o0002)))) \
            and (not (flags & os.X_OK) or ((o and (m & 0o0100)) or (g and (m & 0o0010)) or (w and (m & 0o0001))))

    def create(self, inode_parent, name, mode, flags, ctx):
        entry = self._create(inode_parent, name, mode, ctx)
        self.inode_open_count[entry.st_ino] += 1
        return (entry.st_ino, entry)

    def _create(self, inode_p, name, mode, ctx, rdev=0, target=None):             
        if self.getattr(inode_p, ctx).st_nlink == 0:
            raise FUSEError(errno.EINVAL)

        self.cursor.execute('INSERT INTO inodes (uid, gid, mode, mtime, atime, '
                            'ctime, target, rdev, fsid) VALUES(%s, %s, %s, %s, %s, %s, %s, %s, %s) RETURNING inode_id;',
                            (ctx.uid, ctx.gid, mode, int(time() * 1e9), int(time() * 1e9), int(time() * 1e9), target, rdev, self.fsid))

        inode = self.cursor.fetchone()[0]
        self.cursor.execute("INSERT INTO contents(name, inode_id, parent_inode, fsid) VALUES(%s,%s,%s,%s);",
                        (name, inode, inode_p, self.fsid))
        
        return self.getattr(inode, ctx)

    def block_info(self, offset, length):
        info = {}
        info['first_block'] =   int(offset / self.blocksize)
        info['start_idx']   =   offset % self.blocksize
        info['last_block']  =   int(math.ceil((offset + length) / self.blocksize)) - 1
        end                 =   (offset + length) % self.blocksize
        info['end_idx']     =   end > 0 and end or self.blocksize
        info['blocks']      =   info['last_block'] - info['first_block'] + 1
        return info

    def read(self, inode, offset, length):
        size = self.get_row('SELECT size FROM inodes WHERE inode_id=%s AND fsid=%s', (inode, self.fsid))[0]
        if offset < size:
            if offset + length > size:
                length = size - offset
            info = self.block_info(offset, length)
            self.cursor.execute('SELECT data FROM body WHERE inode_id=%s AND block_no>=%s AND block_no<=%s AND fsid=%s ORDER BY block_no ASC',
                               (inode, info['first_block'], info['last_block'], self.fsid))
            res = self.cursor.fetchall()
            if res is None:
                data = b''
            else:
                d = list()
                for r in res:
                    d.append(bytes(r[0]))
                d[-1] = d[-1][:info['end_idx']]
                d[0] = d[0][info['start_idx']:]
                data = b''.join(d)
        else:
            data = b''
        return data

    def write(self, fh, offset, buf):
        size = self.get_row('SELECT size FROM inodes WHERE inode_id=%s AND fsid=%s', (fh, self.fsid))[0]
        length = len(buf)
        old_info = self.block_info(0, size)
        write_info = self.block_info(offset, len(buf))
        gidx = 0
        for b in range(write_info['first_block'], write_info['last_block'] + 1):
            if b == write_info['first_block']:
                if b > old_info['last_block']:
                    old_block = b'\0' * self.blocksize
                else:
                    old_block = bytes(self.get_row('SELECT data FROM body WHERE inode_id=%s AND block_no=%s AND fsid=%s',
                               (fh, b, self.fsid))[0])
                if write_info['first_block'] == write_info['last_block']:
                    block = old_block[:write_info['start_idx']] + buf[write_info['start_idx']:write_info['end_idx']] + old_block[write_info['end_idx']:]
                else:
                    block = old_block[:write_info['start_idx']] + buf[write_info['start_idx']:self.blocksize]
                gidx += self.blocksize - write_info['start_idx']
            elif b == write_info['last_block']:
                if b > old_info['last_block']:
                    old_block = b'\0' * self.blocksize
                else:
                    old_block = bytes(self.get_row('SELECT data FROM body WHERE inode_id=%s AND block_no=%s AND fsid=%s',
                               (fh, b, self.fsid))[0])
                block = buf[gidx:gidx + write_info['end_idx']] + old_block[write_info['end_idx']:]
            else:
                block = buf[gidx:gidx + self.blocksize]
                gidx += self.blocksize
            if b > old_info['last_block']:
                self.cursor.execute("INSERT INTO body (inode_id,block_no,data, fsid)"
                            "VALUES (%s,%s,%s,%s)", (fh, b, psycopg2.Binary(block), self.fsid))
            else:
                self.cursor.execute('UPDATE body SET data=%s WHERE inode_id=%s AND fsid=%s',
                            (psycopg2.Binary(block), fh, self.fsid))

        if offset + length > size:
            self.cursor.execute('UPDATE inodes SET size=%s WHERE inode_id=%s AND fsid=%s',
                            (offset + length, fh, self.fsid))
        
        return length
   
    def release(self, fh):
        self.inode_open_count[fh] -= 1

        if self.inode_open_count[fh] == 0:
            del self.inode_open_count[fh]
            if self.getattr(fh).st_nlink == 0:
                self.cursor.execute("DELETE FROM inodes WHERE inode_id=%s AND fsid=%s", (fh, self.fsid))
                

class NoUniqueValueError(Exception):
    def __str__(self):
        return 'Query generated more than 1 result row'
    
    
class NoSuchRowError(Exception):
    def __str__(self):
        return 'Query produced 0 result rows'

def usage():
    raise SystemExit('''\
Usage: %s "host=dbhost dbname=database user=dbuser password=dbpass" <mountpoint> -o mount_options
UdavFS mount_option:
    fsid=<uniq_string>
    [locksize=<bytes>
    fssize=<size>[k|m|g|t] ]

Option 'user_allow_other' MUST be set in /etc/fuse.conf''' % sys.argv[0])

if __name__ == '__main__':
    
    if len(sys.argv) != 5:
        usage()
    if sys.argv[3] != '-o':
        usage()
    conn_str = sys.argv[1] + ' sslmode=\'require\''
    options = {x.split('=')[0].strip(): len(x.split('=')) > 1 and x.split('=')[1].strip() or True for x in sys.argv[4].split(',') }
    
    db = psycopg2.connect(conn_str)
    db.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
    cursor = db.cursor()
    
    if 'fsname' not in options.keys():
        print('fsname MUST be in mountoptions\n')
        usage()
    fsname = options['fsname']
    del options['fsname']
    fsid = sha1(bytes(fsname.strip(), 'UTF-8')).hexdigest()
    
    try:
        cursor.execute('SELECT bs, size FROM fsinfo WHERE fsid=%s', (fsid,))
        blocksize, fssize = cursor.fetchone()
        if options['fssize']: del options['fssize']
        if options['blocksize']: del options['blocksize']
    except:
        if 'blocksize' not in options.keys():
            print('blocksize mountoption MUST be specified\n')
            usage()
        if 'fssize' not in options.keys():
            print('fssize mountoption MUST be specified\n')
            usage()
        new_bs = int(options['blocksize'])
        blocksize = new_bs
        del options['blocksize']
        mod1 = {'k': 1024, 'm': 1024 ** 2, 'g': 1024 ** 3, 't': 1024 ** 4}
        fssize = options['fssize'].lower()
        del options['fssize']
        if fssize[-1].lower() in mod1.keys():
            fssize = math.ceil((int(fssize[:-1]) * mod1[fssize[-1]]) / blocksize) * blocksize
        if fssize < 4194304:
            raise SystemExit('Filesystem size less than 4MB.\n')
        
    db.close()
    del db
    
    m_params = [  'fsname=udavfs3', 'nonempty', 'default_permissions', 'allow_other' ]
    m_params.extend(options)
    mountpoint = os.path.abspath(sys.argv[2])
    
    if not os.path.isdir(mountpoint):
        raise SystemExit('Mountpoint "%s" not directory or does not exist!' % mountpoint)


# Start forking
    # First fork
    try:
        if os.fork() > 0:
            sys.exit(0)     # kill off parent
    except OSError as e:
        sys.stderr.write("fork #1 failed: (%d) %s\n" % (e.errno, e.strerror))
        sys.exit(1)
    os.setsid()
    os.chdir(os.getcwd())
    os.umask(0o022)

    # Second fork
    try:
        if os.fork() > 0:
            os._exit(0)
    except OSError as e:
        sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror))
        os._exit(1)
# End forking

    si = open('/dev/null', 'rb')
    so = open('/dev/null', 'ab+', 0)
    se = open('/dev/null', 'ab+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())
    sys.stdout, sys.stderr = so, se


    operations = Operations(conn_str, fsid, blocksize, fssize)
    llfuse.init(operations, mountpoint, m_params)

    
    try:
        llfuse.main(workers=None)
    except:
        llfuse.close(unmount=False)
        raise

    llfuse.close()