Add demos/tetris build script for GCC

[helenos.git] / tools / mkext2.py

#!/usr/bin/env python
#
# Copyright (c) 2011 Martin Sucha
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# - Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# - The name of the author may not be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

"""
EXT2 creator
"""

import sys
import os
import xstruct
import array
import time
import uuid
from imgutil import *

if sys.version >= '3':
        xrange = range

GDE_SIZE = 32

STRUCT_DIR_ENTRY_HEAD = """little:
        uint32_t inode       /* inode number */
        uint16_t skip        /* byte offset to the next record */
        uint8_t  name_length /* file attributes */
        uint8_t  inode_type  /* type of the referenced inode */
"""

STRUCT_SUPERBLOCK = """little:
        uint32_t total_inode_count    /* Total number of inodes */
        uint32_t total_block_count    /* Total number of blocks */
        uint32_t reserved_block_count /* Total number of reserved blocks */
        uint32_t free_block_count     /* Total number of free blocks */
        uint32_t free_inode_count     /* Total number of free inodes */
        uint32_t first_block          /* Block containing the superblock */
        uint32_t block_size_log2      /* log_2(block_size) */
        int32_t  fragment_size_log2   /* log_2(fragment size) */
        uint32_t blocks_per_group     /* Number of blocks in one block group */
        uint32_t fragments_per_group  /* Number of fragments per block group */
        uint32_t inodes_per_group     /* Number of inodes per block group */
        uint32_t mount_time           /* Time when the filesystem was last mounted */
        uint32_t write_time           /* Time when the filesystem was last written */
        uint16_t mount_count          /* Mount count since last full filesystem check */
        uint16_t max_mount_count      /* Number of mounts after which the fs must be checked */
        uint16_t magic                /* Magic value */
        uint16_t state                /* State (mounted/unmounted) */
        uint16_t error_behavior       /* What to do when errors are encountered */
        uint16_t rev_minor            /* Minor revision level */
        uint32_t last_check_time      /* Unix time of last fs check */
        uint32_t max_check_interval   /* Max unix time interval between checks */
        uint32_t os                   /* OS that created the filesystem */
        uint32_t rev_major            /* Major revision level */
        padding[4] /* default reserved uid and gid */
        
        /* Following is for ext2 revision 1 only */
        uint32_t first_inode
        uint16_t inode_size
        uint16_t block_group_number /* Block group where this SB is stored */
        uint32_t features_compatible
        uint32_t features_incompatible
        uint32_t features_read_only
        char     uuid[16]
        char     volume_name[16]
"""

STRUCT_BLOCK_GROUP_DESCRIPTOR = """little:
        uint32_t block_bitmap_block      /* Block ID for block bitmap */
        uint32_t inode_bitmap_block      /* Block ID for inode bitmap */
        uint32_t inode_table_first_block /* Block ID of first block of inode table */
        uint16_t free_block_count        /* Count of free blocks */
        uint16_t free_inode_count        /* Count of free inodes */
        uint16_t directory_inode_count   /* Number of inodes allocated to directories */
"""

STRUCT_INODE = """little:
        uint16_t mode
        uint16_t user_id
        uint32_t size
        uint32_t access_time
        uint32_t creation_time
        uint32_t modification_time
        uint32_t deletion_time
        uint16_t group_id
        uint16_t usage_count /* Hard link count, when 0 the inode is to be freed */
        uint32_t reserved_512_blocks /* Size of this inode in 512-byte blocks */
        uint32_t flags
        padding[4]
        uint32_t direct_blocks[12] /* Direct block ids stored in this inode */
        uint32_t indirect_blocks[3]
        uint32_t version
        uint32_t file_acl
        uint32_t size_high /* For regular files in version >= 1, dir_acl if dir */
        padding[6]
        uint16_t mode_high /* Hurd only */
        uint16_t user_id_high /* Linux/Hurd only */
        uint16_t group_id_high /* Linux/Hurd only */
"""

# The following is here to handle byte-order conversion in indirect block lookups
STRUCT_BLOCK_REFERENCE = """little:
        uint32_t block_id /* Referenced block ID */
"""

class Filesystem:       
        def __init__(self, filename, block_groups, blocks_per_group, inodes_per_group, block_size, inode_size, reserved_inode_count):
                "Initialize the filesystem writer"
                
                outf = open(filename, "w+b")
                # Set the correct size of the image, so that we can read arbitrary position
                outf.truncate(block_size * blocks_per_group * block_groups)
                self.outf = outf
                self.uuid = uuid.uuid4()
                self.block_size = block_size
                self.inode_size = inode_size
                self.block_groups = block_groups
                self.blocks_per_group = blocks_per_group
                self.inodes_per_group = inodes_per_group
                self.reserved_inode_count = reserved_inode_count
                self.gdt_blocks = count_up(block_groups * GDE_SIZE, block_size)
                self.inode_table_blocks_per_group = (inodes_per_group * inode_size) // block_size
                self.inode_bitmap_blocks_per_group = count_up(inodes_per_group // 8, block_size)
                self.block_bitmap_blocks_per_group = count_up(blocks_per_group // 8, block_size)
                self.total_block_count = self.blocks_per_group * self.block_groups
                self.total_inode_count = self.inodes_per_group * self.block_groups
                self.inode_table_blocks = count_up(self.total_inode_count * inode_size, block_size)
                self.inodes = {}
                self.superblock_at_block = 2047 // block_size
                self.block_ids_per_block = self.block_size // 4
                self.indirect_limits = [12, None, None, None]
                self.indirect_blocks_per_level = [1, None, None, None]
                for i in range(1,4):
                        self.indirect_blocks_per_level[i] = self.indirect_blocks_per_level[i-1] * self.block_ids_per_block
                        self.indirect_limits[i] = self.indirect_limits[i-1] + self.indirect_blocks_per_level[i]
                self.block_allocator = Allocator(0, self.total_block_count)
                self.inode_allocator = Allocator(1, self.total_inode_count)
                self.init_gdt()
                # Set the callbacks after GDT has been initialized
                self.block_allocator.mark_cb = self.mark_block_cb
                self.inode_allocator.mark_cb = self.mark_inode_cb
                self.block_allocator.mark_used_all(range(self.superblock_at_block))
                self.inode_allocator.mark_used_all(range(1, self.reserved_inode_count + 1))
                self.root_inode = Inode(self, 2, Inode.TYPE_DIR)
                self.gdt[0].directory_inode_count += 1
                self.lost_plus_found = Inode(self, self.inode_allocator.alloc(directory=True), Inode.TYPE_DIR)
                lpf_dir = DirWriter(self.lost_plus_found)
                lpf_dir.add(self.lost_plus_found.as_dirent('.'))
                lpf_dir.add(self.root_inode.as_dirent('..'))
                lpf_dir.finish()
        
        def init_gdt(self):
                "Initialize block group descriptor table"
                
                self.superblock_positions = []
                self.gdt = []
                consumed_blocks_per_group = (1 + self.gdt_blocks +
                            self.inode_bitmap_blocks_per_group +
                            self.block_bitmap_blocks_per_group +
                            self.inode_table_blocks_per_group)
                initial_free_blocks = self.blocks_per_group - consumed_blocks_per_group
                for bg in range(self.block_groups):
                        base = bg * self.blocks_per_group
                        if (bg == 0):
                                base = self.superblock_at_block
                                self.superblock_positions.append(1024)
                        else:
                                self.superblock_positions.append(base * self.block_size)
                        self.block_allocator.mark_used_all(range(base, base+consumed_blocks_per_group))
                        pos = base + 1 + self.gdt_blocks
                        gde = xstruct.create(STRUCT_BLOCK_GROUP_DESCRIPTOR)
                        gde.block_bitmap_block = pos
                        pos += self.block_bitmap_blocks_per_group
                        gde.inode_bitmap_block = pos
                        pos += self.inode_bitmap_blocks_per_group
                        gde.inode_table_first_block = pos
                        gde.free_block_count = initial_free_blocks
                        gde.free_inode_count = self.inodes_per_group
                        gde.directory_inode_count = 0
                        self.gdt.append(gde)
        
        def mark_block_cb(self, block):
                "Called after a block has been allocated"
                
                self.gdt[block // self.blocks_per_group].free_block_count -= 1
        
        def mark_inode_cb(self, index, directory=False):
                "Called after an inode has been allocated"
                
                index -= 1
                gde = self.gdt[index // self.inodes_per_group]
                gde.free_inode_count -= 1
                if directory:
                        gde.directory_inode_count += 1          
        
        def seek_to_block(self, block, offset=0):
                "Seek to offset bytes after the start of the given block"
                
                if offset < 0 or offset > self.block_size:
                        raise Exception("Invalid in-block offset")
                self.outf.seek(block * self.block_size + offset)
        
        def seek_to_inode(self, index):
                "Seek to the start of the inode structure for the inode number index"
                
                index -= 1
                if index < 0:
                        raise Exception("Invalid inode number")
                gde = self.gdt[index // self.inodes_per_group]
                base_block = gde.inode_table_first_block
                offset = (index % self.inodes_per_group) * self.inode_size
                block = base_block + (offset // self.block_size)
                self.seek_to_block(block, offset % self.block_size)     
        
        def subtree_add(self, inode, parent_inode, dirpath, is_root=False):
                "Recursively add files to the filesystem"
                
                dir_writer = DirWriter(inode)   
                dir_writer.add(inode.as_dirent('.'))
                dir_writer.add(parent_inode.as_dirent('..'))
                
                if is_root:
                        dir_writer.add(self.lost_plus_found.as_dirent('lost+found'))

                for item in listdir_items(dirpath):
                        newidx = self.inode_allocator.alloc(directory = item.is_dir)
                        if item.is_file:
                                child_inode = Inode(self, newidx, Inode.TYPE_FILE)
                                for data in chunks(item, self.block_size):
                                        child_inode.write(data)
                        elif item.is_dir:
                                child_inode = Inode(self, newidx, Inode.TYPE_DIR)
                                self.subtree_add(child_inode, inode, item.path)
                
                        dir_writer.add(child_inode.as_dirent(item.name))
                        self.write_inode(child_inode)

                dir_writer.finish()
        
        def write_inode(self, inode):
                "Write inode information into the inode table"
                
                self.seek_to_inode(inode.index)
                self.outf.write(inode.pack())

        def write_gdt(self):
                "Write group descriptor table at the current file position"
                
                for gde in self.gdt:
                        data = bytes(gde.pack())
                        self.outf.write(data)
                        self.outf.seek(GDE_SIZE-len(data), os.SEEK_CUR)
        
        def write_superblock(self, block_group):
                "Write superblock at the current position"
                
                sb = xstruct.create(STRUCT_SUPERBLOCK)
                sb.total_inode_count = self.total_inode_count
                sb.total_block_count = self.total_block_count
                sb.reserved_block_count = 0
                sb.free_block_count = self.block_allocator.free
                sb.free_inode_count = self.inode_allocator.free
                sb.first_block = self.superblock_at_block
                sb.block_size_log2 = num_of_trailing_bin_zeros(self.block_size) - 10
                sb.fragment_size_log2 = sb.block_size_log2
                sb.blocks_per_group = self.blocks_per_group
                sb.fragments_per_group = self.blocks_per_group
                sb.inodes_per_group = self.inodes_per_group
                curtime = int(time.time())
                sb.mount_time = curtime
                sb.write_time = curtime
                sb.mount_count = 0
                sb.max_mount_count = 21
                sb.magic = 0xEF53
                sb.state = 5 # clean
                sb.error_behavior = 1 # continue on errors
                sb.rev_minor = 0
                sb.last_check_time = curtime
                sb.max_check_interval = 15552000 # 6 months
                sb.os = 0 # Linux
                sb.rev_major = 1
                sb.first_inode = self.reserved_inode_count + 1
                sb.inode_size = self.inode_size
                sb.block_group_number = block_group
                sb.features_compatible = 0
                sb.features_incompatible = 2 # filetype
                sb.features_read_only = 0
                sb.uuid = self.uuid.bytes_le
                sb.volume_name = 'HelenOS rdimage\0'
                self.outf.write(bytes(sb.pack()))
        
        def write_all_metadata(self):
                "Write superblocks, block group tables, block and inode bitmaps"
                
                bbpg = self.blocks_per_group // 8
                bipg = self.inodes_per_group // 8
                def window(arr, index, size):
                        return arr[index * size:(index + 1) * size]
                
                for bg_index in xrange(len(self.gdt)):
                        sbpos = self.superblock_positions[bg_index]
                        sbblock = (sbpos + 1023) // self.block_size
                        gde = self.gdt[bg_index]
                        
                        self.outf.seek(sbpos)
                        self.write_superblock(bg_index)
                        
                        self.seek_to_block(sbblock+1)
                        self.write_gdt()
                        
                        self.seek_to_block(gde.block_bitmap_block)
                        self.outf.write(window(self.block_allocator.bitmap, bg_index, bbpg))
                        
                        self.seek_to_block(gde.inode_bitmap_block)
                        self.outf.write(window(self.inode_allocator.bitmap, bg_index, bipg))
        
        def close(self):
                "Write all remaining data to the filesystem and close the file"
                
                self.write_inode(self.root_inode)
                self.write_inode(self.lost_plus_found)
                self.write_all_metadata()
                self.outf.close()

class Allocator:
        def __init__(self, base, count):
                self.count = count
                self.base = base
                self.free = count
                self.nextidx = 0
                self.bitmap = array.array('B', [0] * (count // 8))
                self.mark_cb = None
        
        def __contains__(self, item):
                "Check if the item is already used"
                
                bitidx = item - self.base
                return get_bit(self.bitmap[bitidx // 8], bitidx % 8)
        
        def alloc(self, **options):
                "Allocate a new item"
                
                while self.nextidx < self.count and (self.base + self.nextidx) in self:
                        self.nextidx += 1
                if self.nextidx == self.count:
                        raise Exception("No free item available")
                item = self.base + self.nextidx
                self.nextidx += 1
                self.mark_used(item, **options)
                return item
        
        def mark_used(self, item, **options):
                "Mark the specified item as used"
                
                bitidx = item - self.base
                if item in self:
                        raise Exception("Item already used: " + str(item))
                self.free -= 1
                index = bitidx // 8
                self.bitmap[index] = set_bit(self.bitmap[index], bitidx % 8)
                if self.mark_cb:
                        self.mark_cb(item, **options)
        
        def mark_used_all(self, items, **options):
                "Mark all specified items as used"
                
                for item in items:
                        self.mark_used(item, **options)

class Inode:
        TYPE_FILE = 1
        TYPE_DIR = 2
        TYPE2MODE = {TYPE_FILE: 8, TYPE_DIR: 4}
        
        def __init__(self, fs, index, typ):
                self.fs = fs
                self.direct = [None] * 12
                self.indirect = [None] * 3
                self.pos = 0
                self.size = 0
                self.blocks = 0
                self.index = index
                self.type = typ
                self.refcount = 0
        
        def as_dirent(self, name):
                "Return a DirEntry corresponding to this inode"
                self.refcount += 1
                return DirEntry(name, self.index, self.type)
        
        def new_block(self, data=True):
                "Get a new block index from allocator and count it here as belonging to the file"
                
                block = self.fs.block_allocator.alloc()
                self.blocks += 1
                return block
        
        def get_or_add_block(self, block):
                "Get or add a real block to the file"
                
                if block < 12:
                        return self.get_or_add_block_direct(block)
                return self.get_or_add_block_indirect(block)
        
        def get_or_add_block_direct(self, block):
                "Get or add a real block to the file (direct blocks)"
                
                if self.direct[block] == None:
                        self.direct[block] = self.new_block()
                return self.direct[block]
        
        def get_or_add_block_indirect(self, block):
                "Get or add a real block to the file (indirect blocks)"
                
                # Determine the indirection level for the desired block
                level = None
                for i in range(4):
                        if block < self.fs.indirect_limits[i]:
                                level = i
                                break

                assert level != None
        
                # Compute offsets for the topmost level
                block_offset_in_level = block - self.fs.indirect_limits[level-1];
                if self.indirect[level-1] == None:
                        self.indirect[level-1] = self.new_block(data = False)
                current_block = xstruct.create(STRUCT_BLOCK_REFERENCE)
                current_block.block_id = self.indirect[level-1]
                offset_in_block = block_offset_in_level // self.fs.indirect_blocks_per_level[level-1]
        
                # Navigate through other levels
                while level > 0:                
                        assert offset_in_block < self.fs.block_ids_per_block
                        
                        level -= 1
                        
                        self.fs.seek_to_block(current_block.block_id, offset_in_block*4)
                        current_block.unpack(self.fs.outf.read(4))
                        
                        if current_block.block_id == 0:
                                # The block does not exist, so alloc one and write it there
                                self.fs.outf.seek(-4, os.SEEK_CUR)
                                current_block.block_id = self.new_block(data=(level==0))
                                self.fs.outf.write(current_block.pack())
                
                        # If we are on the last level, break here as
                        # there is no next level to visit
                        if level == 0:
                                break
                
                        # Visit the next level
                        block_offset_in_level %= self.fs.indirect_blocks_per_level[level];
                        offset_in_block = block_offset_in_level // self.fs.indirect_blocks_per_level[level-1]

                return current_block.block_id
        
        def do_seek(self):
                "Perform a seek to the position indicated by self.pos"
                
                block = self.pos // self.fs.block_size
                real_block = self.get_or_add_block(block)
                offset = self.pos % self.fs.block_size
                self.fs.seek_to_block(real_block, offset)
                
        def write(self, data):
                "Write a piece of data (arbitrarily long) as the contents of the inode"
                
                data_pos = 0            
                while data_pos < len(data):
                        bytes_remaining_in_block = self.fs.block_size - (self.pos % self.fs.block_size)
                        bytes_to_write = min(bytes_remaining_in_block, len(data)-data_pos)
                        self.do_seek()
                        self.fs.outf.write(data[data_pos:data_pos + bytes_to_write])
                        self.pos += bytes_to_write
                        data_pos += bytes_to_write
                        self.size = max(self.pos, self.size)
        
        def align_size_to_block(self):
                "Align the size of the inode up to block size"
                
                self.size = align_up(self.size, self.fs.block_size)
        
        def align_pos(self, bytes):
                "Align the current position up to bytes boundary"
                
                self.pos = align_up(self.pos, bytes)
        
        def set_pos(self, pos):
                "Set the current position"
                
                self.pos = pos
        
        def pack(self):
                "Pack the inode structure and return the result"
                
                data = xstruct.create(STRUCT_INODE)
                data.mode = (Inode.TYPE2MODE[self.type] << 12)
                data.mode |= 0x1ff # ugo+rwx
                data.user_id = 0
                data.size = self.size & 0xFFFFFFFF
                data.group_id = 0
                curtime = int(time.time())
                data.access_time = curtime
                data.modification_time = curtime
                data.creation_time = curtime
                data.deletion_time = 0
                data.usage_count = self.refcount
                data.reserved_512_blocks = self.blocks * (self.fs.block_size // 512)
                data.flags = 0
                blockconv = lambda x: 0 if x == None else x
                data.direct_blocks = list(map(blockconv, self.direct))
                data.indirect_blocks = list(map(blockconv, self.indirect))
                data.version = 0
                data.file_acl = 0
                if self.type == Inode.TYPE_FILE:
                        data.size_high = (self.size >> 32)
                else:
                        # size_high represents dir_acl in this case
                        data.size_high = 0
                data.mode_high = 0
                data.user_id_high = 0
                data.group_id_high = 0
                return data.pack()
                
class DirEntry:
        "Represents a linked list directory entry"
        
        def __init__(self, name, inode, typ):
                self.name = name.encode('UTF-8')
                self.inode = inode
                self.skip = None
                self.type = typ
        
        def size(self):
                "Return size of the entry in bytes"
                
                return align_up(8 + len(self.name)+1, 4)
        
        def write(self, inode):
                "Write the directory entry into the inode"
                
                head = xstruct.create(STRUCT_DIR_ENTRY_HEAD)
                head.inode = self.inode
                head.skip = self.skip
                head.name_length = len(self.name)
                head.inode_type = self.type
                inode.write(head.pack())
                inode.write(self.name+'\0'.encode())
                inode.align_pos(4)

class DirWriter:
        "Manages writing directory entries into an inode (alignment, etc.)"
        
        def __init__(self, inode):
                self.pos = 0
                self.inode = inode
                self.prev_entry = None
                self.prev_pos = None
        
        def prev_write(self):
                "Write a previously remembered entry"
                
                if self.prev_entry:
                        self.prev_entry.skip = self.pos - self.prev_pos
                        if self.inode:
                                self.prev_entry.write(self.inode)
                                self.inode.set_pos(self.pos)
        
        def add(self, entry):
                "Add a directory entry to the directory"
                
                size = entry.size()
                block_size = self.inode.fs.block_size
                if align_up(self.pos, block_size) < align_up(self.pos + size, block_size):
                        self.pos = align_up(self.pos, block_size)
                self.prev_write()
                self.prev_entry = entry
                self.prev_pos = self.pos
                self.pos += size
        
        def finish(self):
                "Write the last entry and finish writing the directory contents"
                
                if not self.inode:
                        return
                self.pos = align_up(self.pos, self.inode.fs.block_size)
                self.prev_write()
                self.inode.align_size_to_block()

def subtree_stats(root, block_size):
        "Recursively calculate statistics"
        
        blocks = 0
        inodes = 1
        dir_writer = DirWriter(None)
        
        for item in listdir_items(root):
                inodes += 1
                if item.is_file:
                        blocks += count_up(item.size, block_size)
                elif item.is_dir:
                        subtree_blocks, subtree_inodes = subtree_stats(item.path, block_size)
                        blocks += subtree_blocks
                        inodes += subtree_inodes
        
        dir_writer.finish()
        blocks += count_up(dir_writer.pos, block_size)
        return (blocks, inodes)

def usage(prname):
        "Print usage syntax"
        print(prname + " <EXTRA_BYTES> <PATH> <IMAGE>")

def main():
        if (len(sys.argv) < 4):
                usage(sys.argv[0])
                return
        
        if (not sys.argv[1].isdigit()):
                print("<EXTRA_BYTES> must be a number")
                return
        
        extra_bytes = int(sys.argv[1])
        
        path = os.path.abspath(sys.argv[2])
        if (not os.path.isdir(path)):
                print("<PATH> must be a directory")
                return
        
        block_size = 4096
        inode_size = 128
        reserved_inode_count = 10
        blocks_per_group = 1024
        inodes_per_group = 512
        
        blocks, inodes = subtree_stats(path, block_size)
        blocks += count_up(extra_bytes, block_size)
        inodes += reserved_inode_count
        
        inodes_per_group = align_up(inodes_per_group, 8)
        blocks_per_group = align_up(blocks_per_group, 8)
        
        inode_table_blocks_per_group = (inodes_per_group * inode_size) // block_size
        inode_bitmap_blocks_per_group = count_up(inodes_per_group // 8, block_size)
        block_bitmap_blocks_per_group = count_up(blocks_per_group // 8, block_size)
        free_blocks_per_group = blocks_per_group
        free_blocks_per_group -= inode_table_blocks_per_group
        free_blocks_per_group -= inode_bitmap_blocks_per_group
        free_blocks_per_group -= block_bitmap_blocks_per_group
        free_blocks_per_group -= 10 # one for SB and some reserve for GDT
        
        block_groups = max(count_up(inodes, inodes_per_group), count_up(blocks, free_blocks_per_group))
        
        fs = Filesystem(sys.argv[3], block_groups, blocks_per_group, inodes_per_group,
                                block_size, inode_size, reserved_inode_count)
        
        fs.subtree_add(fs.root_inode, fs.root_inode, path, is_root=True)
        fs.close()
        
if __name__ == '__main__':
        main()