While DAL3 created and enforced a distinction among directory blocks, file blocks, and data blocks (along with providing an easy interface to directory blocks and files blocks), DAL4 introduces the concept of linking all of these blocks together and giving names to directories and files. While still primitive, the file system is now unified and allows more advanced abstractions to be built on top of it.
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from math import ceil
################################################################################
class DAL3(dal_3.DAL3):
# Get Configuration Information
def info(self):
return self.__blocks, self.__size
################################################################################
class DAL4:
# CONSTANTS
MAX_BLOCKS = (2 ** 16) - 2
MAX_SIZE = (2 ** 16)
STATUS = dal_3.enum('closed', 'directory', 'file', 'block')
# Disk Abstraction Layer
def __init__(self, blocks, size):
assert type(blocks) is int and 0 < blocks <= self.MAX_BLOCKS
assert type(size) is int and 4 < size <= self.MAX_SIZE
assert int(ceil(float((blocks + 1) * (size + 1)) / size)) \
<= self.MAX_SIZE
self.__disk = DAL3(blocks, size)
self.__blocks, self.__size = self.__disk.info()
block = self.__disk.open_directory()
assert block == 1
self.__disk.write_directory(block, '\x00\x00\x00')
# Make New Directory
def make_directory(self, block, name):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(name) is str and 1 <= len(name) <= 255
assert self.status(block) == self.STATUS.directory
assert self.find(block, name) == 0
root = self.__disk.read_directory(block)
new_directory = self.__disk.open_directory()
root += chr(new_directory >> 8) + chr(new_directory & 0xFF)
self.__disk.write_directory(block, root)
data = chr(block >> 8) + chr(block & 0xFF) + chr(len(name)) + name
self.__disk.write_directory(new_directory, data)
return new_directory
# Remove Old Directory
def remove_directory(self, block):
assert type(block) is int and 2 <= block <= self.__blocks
assert self.status(block) == self.STATUS.directory
assert self.empty(block)
temp = self.__disk.read_directory(block)
root = (ord(temp[0]) << 8) + ord(temp[1])
data = self.__disk.read_directory(root)
size = ord(data[2])
header = data[:size+3]
contents = data[size+3:]
pointers = [(ord(contents[index*2]) << 8) + ord(contents[index*2+1]) \
for index in range(len(contents) / 2)]
assert block in pointers
pointers.remove(block)
assert block not in pointers
contents = ''.join([chr(pointer >> 8) + chr(pointer & 0xFF) \
for pointer in pointers])
data = header + contents
self.__disk.write_directory(root, data)
self.__disk.close_directory(block)
return root
# Make New File
def make_file(self, block, name):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(name) is str and 1 <= len(name) <= 255
assert self.is_directory(block)
assert not self.exists(block, name)
root = self.__disk.read_directory(block)
new_file = self.__disk.open_file()
root += chr(new_file >> 8) + chr(new_file & 0xFF)
self.__disk.write_directory(block, root)
data = chr(block >> 8) + chr(block & 0xFF)
data += chr(len(name)) + name
data += '\x00' * 4
self.__disk.write_file(new_file, data)
return new_file
# Remove Old File
def remove_file(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
assert self.is_file(block)
data = self.__disk.read_file(block)
size = ord(data[2])
blocks = data[size+3+4:]
pointers = [(ord(blocks[index*2]) << 8) + ord(blocks[index*2+1]) \
for index in range(len(blocks) / 2)]
for pointer in pointers:
self.__disk.close_block(pointer)
self.__disk.close_file(block)
root = (ord(data[0]) << 8) + ord(data[1])
data = self.__disk.read_directory(root)
size = ord(data[2])
header = data[:size+3]
contents = data[size+3:]
pointers = [(ord(contents[index*2]) << 8) + ord(contents[index*2+1]) \
for index in range(len(contents) / 2)]
assert block in pointers
pointers.remove(block)
assert block not in pointers
contents = ''.join([chr(pointer >> 8) + chr(pointer & 0xFF) \
for pointer in pointers])
data = header + contents
self.__disk.write_directory(root, data)
return root
# Read From File
def read_file(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
assert self.is_file(block)
data = self.__disk.read_file(block)
size = ord(data[2])
stream_length = (ord(data[size+3]) << 24) + (ord(data[size+4]) << 16)
stream_length += (ord(data[size+5]) << 8) + ord(data[size+6])
contents = data[size+3+4:]
pointers = [(ord(contents[index*2]) << 8) + ord(contents[index*2+1]) \
for index in range(len(contents) / 2)]
stream = ''.join([self.__disk.read_block(pointer) \
for pointer in pointers])
return stream[:stream_length]
# Write To File
def write_file(self, block, data):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(data) is str
assert self.is_file(block)
length = len(data)
file_data = self.__disk.read_file(block)
size = ord(file_data[2])
header = file_data[:size+3]
blocks = file_data[size+3+4:]
file_map = [(ord(blocks[index*2]) << 8) + ord(blocks[index*2+1]) \
for index in range(len(blocks) / 2)]
if len(data) % self.__size:
blocks = len(data) / self.__size + 1
else:
blocks = len(data) / self.__size
blocks = [data[index*self.__size:index*self.__size+self.__size] \
for index in range(blocks)]
while len(file_map) > len(blocks):
self.__disk.close_block(file_map[-1])
del file_map[-1]
while len(file_map) < len(blocks):
file_map.append(self.__disk.open_block())
if blocks:
if len(blocks) == 1:
data = blocks[0]
data = data + chr(0) * (self.__size - len(data))
self.__disk.write_block(file_map[0], data)
else:
self.__disk.write_block(file_map[0], blocks[0])
index = 1
while blocks[index] is not blocks[-1]:
self.__disk.write_block(file_map[index], blocks[index])
index += 1
data = blocks[-1]
data = data + chr(0) * (self.__size - len(data))
self.__disk.write_block(file_map[-1], data)
length = chr(length >> 24) + chr((length >> 16) & 0xFF) + \
chr((length >> 8) & 0xFF) + chr(length & 0xFF)
blocks = ''.join([chr(pointer >> 8) + chr(pointer & 0xFF) \
for pointer in file_map])
data = header + length + blocks
self.__disk.write_file(block, data)
return block
# Get Directory Contents
def list_directory(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
assert self.status(block) == self.STATUS.directory
directory = self.__disk.read_directory(block)
size = ord(directory[2])
contents = directory[3+size:]
pointers = [(ord(contents[index*2]) << 8) + ord(contents[index*2+1]) \
for index in range(len(contents) / 2)]
return pointers
# Check If Empty
def empty(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.status(block)
assert status == self.STATUS.directory or status == self.STATUS.file
if status == self.STATUS.directory:
data = self.__disk.read_directory(block)
else:
data = self.__disk.read_file(block)
size = ord(data[2])
data = data[3+size:]
if status == self.STATUS.directory:
return not bool(data)
else:
return len(data) == 4
# Looks For Name
def find(self, block, name):
pointers = self.list_directory(block)
names = [self.name(pointer) for pointer in pointers]
for block, temp_name in zip(pointers, names):
if temp_name == name:
return block
return 0
# Returns Directory/File Name
def name(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.status(block)
assert status == self.STATUS.directory or status == self.STATUS.file
if status == self.STATUS.directory:
data = self.__disk.read_directory(block)
else:
data = self.__disk.read_file(block)
size = ord(data[2])
name = data[3:3+size]
return name
# Changes Directory/File Name
def rename(self, block, name):
assert type(block) is int and 2 <= block <= self.__blocks
assert type(name) is str and 1 <= len(name) <= 255
status = self.status(block)
assert status == self.STATUS.directory or status == self.STATUS.file
if status == self.STATUS.directory:
data = self.__disk.read_directory(block)
else:
data = self.__disk.read_file(block)
size = ord(data[2])
root = data[:2]
contents = data[size+3:]
new_name = chr(len(name)) + name
data = root + new_name + contents
if status == self.STATUS.directory:
self.__disk.write_directory(block, data)
else:
self.__disk.write_file(block, data)
return block
# Test For Existance
def exists(self, block, name):
return self.find(block, name) != 0
# Check If File
def is_file(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
return self.status(block) == self.STATUS.file
# Check If Directory
def is_directory(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
return self.status(block) == self.STATUS.directory
# Read Block Status
def status(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.__disk.status(block)
if status == self.__disk.STATUS.closed:
return self.STATUS.closed
elif self.__disk.STATUS.d1 <= status <= self.__disk.STATUS.dZ:
return self.STATUS.directory
elif self.__disk.STATUS.f1 <= status <= self.__disk.STATUS.fZ:
return self.STATUS.file
else:
return self.STATUS.block
# Seed Control Interface
def seed(self, data=None):
return self.__disk.seed(data)
# Probability Of Failure
def fail(self, probability):
self.__disk.fail(probability)
# Dump To File
def dump(self, name):
self.__disk.dump(name)
# Load From File
def load(self, name, abstract):
assert type(abstract) is bool
self.__disk.load(name, abstract)
self.__blocks, self.__size = self.__disk.info()
if abstract:
self.__soft()
else:
self.__hard()
# Fix All Errors
def __soft(self):
# Not Yet Implemented
pass
# Find Any Error
def __hard(self):
# Not Yet Implemented
pass
################################################################################
def test():
# Not Yet Implemented
pass
################################################################################
if __name__ == '__main__':
test()
|
This recipe is part of a group of recipes that demonstrate the implementation of an abstract file system. dal_3.py can be found at http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/492211
Tags: files
