Disk Abstraction Layer 3 provides a more useful framework for secondary memory and provides an abstract interface for implementing a generic file system. It renumbers the blocks on the hard drive to start at block 1 so that block 0 can be considered a NULL reference. At a lower level, block 0 would be seen to be where the OS can keep a seed for its random number generator (interface provided).
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from math import ceil
################################################################################
class DAL2(dal_2.DAL2):
# Get Configuration Information
def info(self):
return self.__blocks, self.__disk.SIZE
# Change Status Information
def edit(self, block, status):
assert type(block) is int and 0 <= block < self.__blocks
assert type(status) is int and 1 <= status <= 255
assert self.__BIT[block] != 0
self.__BIT[block] = status
################################################################################
class Seed:
# Random Seed Generator
def __init__(self, data):
if type(data) is int:
assert 1 <= data <= 65536
self.__data = [0 for index in range(data)]
elif type(data) is str:
assert 1 <= len(data) <= 65536
self.__data = [ord(c) for c in data]
else:
raise TypeError
self.__active = True
self.__index = 0
# Seed Control Interface
def __call__(self, data=None):
if data is None:
return ''.join([chr(i) for i in self.__data])
elif type(data) is bool:
self.__active = data
elif type(data) is str:
if self.__active:
for c in data:
self.__data[self.__index] ^= ord(c)
self.__index = (self.__index + 1) % len(self.__data)
else:
raise TypeError
################################################################################
# Create Enumeration Objects
def enum(*names):
class enum:
def __setattr__(self, name, value):
raise AttributeError
def __delattr__(self, name):
raise AttributeError
temp = enum()
for value, name in enumerate(names):
temp.__dict__[name] = value
return temp
################################################################################
class DAL3:
# CONSTANTS
MAX_BLOCKS = (2 ** 16) - 2
MAX_SIZE = (2 ** 16)
STATUS = enum('closed', 'd1', 'dA', 'dB', 'dZ', \
'f1', 'fA', 'fB', 'fZ', 'b1', 's1')
# 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
blocks += 1
assert int(ceil(float(blocks * (size + 1)) / size)) <= self.MAX_SIZE
self.__disk = DAL2(blocks, size)
self.__blocks, self.__size = self.__disk.info()
self.__blocks -= 1
self.__seed = Seed(self.__size)
self.__disk.open(self.STATUS.s1)
# Open A Directory
def open_directory(self):
return self.__disk.open(self.STATUS.d1)
# Read A Directory
def read_directory(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.__disk.status(block)
assert self.STATUS.d1 <= status <= self.STATUS.dZ
if status == self.STATUS.d1:
temp = self.__disk.read(block)
size = (ord(temp[0]) << 8) + ord(temp[1])
return temp[2:size+2]
else:
while self.__disk.status(block) != self.STATUS.dA:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
temp = self.__disk.read(block)
size = (ord(temp[0]) << 8) + ord(temp[1])
data = temp[2:-2]
block = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(block) == self.STATUS.dB:
temp = self.__disk.read(block)
data += temp[2:-2]
block = (ord(temp[-2]) << 8) + ord(temp[-1])
temp = self.__disk.read(block)
return data + temp[2:size-len(data)+2]
# Write A Directory
def write_directory(self, block, data):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(data) is str and len(data)
status = self.__disk.status(block)
assert self.STATUS.d1 <= status <= self.STATUS.dZ
self.__seed(data)
dir_map = [block]
if status == self.STATUS.dA:
temp = self.__disk.read(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [block]
while self.__disk.status(block) == self.STATUS.dB:
temp = self.__disk.read(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [block]
elif status == self.STATUS.dB:
temp = self.__disk.read(block)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [dirA] + dir_map
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [dirZ]
while self.__disk.status(dirA) == self.STATUS.dB:
temp = self.__disk.read(dirA)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [dirA] + dir_map
while self.__disk.status(dirZ) == self.STATUS.dB:
temp = self.__disk.read(dirZ)
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [dirZ]
elif status == self.STATUS.dZ:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [block] + dir_map
while self.__disk.status(block) == self.STATUS.dB:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [block] + dir_map
size = self.__size - 4
if len(data) % size:
blocks = len(data) / size + 1
else:
blocks = len(data) / size
blocks = [data[index*size:index*size+size] for index in range(blocks)]
while len(dir_map) > len(blocks):
self.__disk.close(dir_map[-1])
del dir_map[-1]
while len(dir_map) < len(blocks):
dir_map.append(self.__disk.open(255))
if len(blocks) == 1:
temp = len(data)
size = chr(temp >> 8) + chr(temp & 0xFF)
blocks[0] = size + blocks[0] + size
else:
temp = len(data)
size = chr(temp >> 8) + chr(temp & 0xFF)
temp = dir_map[1]
next = chr(temp >> 8) + chr(temp & 0xFF)
blocks[0] = size + blocks[0] + next
index = 1
while blocks[index] is not blocks[-1]:
temp = dir_map[index - 1]
last = chr(temp >> 8) + chr(temp & 0xFF)
temp = dir_map[index + 1]
next = chr(temp >> 8) + chr(temp & 0xFF)
blocks[index] = last + blocks[index] + next
index += 1
temp = dir_map[index - 1]
last = chr(temp >> 8) + chr(temp & 0xFF)
blocks[index] = last + blocks[index] + size
if len(blocks) == 1:
self.__disk.write(dir_map[0], blocks[0] + chr(0) * \
(self.__size - len(blocks[0])))
self.__disk.edit(dir_map[0], self.STATUS.d1)
else:
self.__disk.write(dir_map[0], blocks[0])
self.__disk.edit(dir_map[0], self.STATUS.dA)
index = 1
while blocks[index] is not blocks[-1]:
self.__disk.write(dir_map[index], blocks[index])
self.__disk.edit(dir_map[index], self.STATUS.dB)
index += 1
self.__disk.write(dir_map[index], blocks[index] + chr(0) * \
(self.__size - len(blocks[index])))
self.__disk.edit(dir_map[index], self.STATUS.dZ)
# Close A Directory
def close_directory(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.__disk.status(block)
assert self.STATUS.d1 <= status <= self.STATUS.dZ
if status == self.STATUS.dA:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(block) == self.STATUS.dB:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
self.__disk.close(block)
elif status == self.STATUS.dB:
temp = self.__disk.read(block)
self.__disk.close(block)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(dirA) == self.STATUS.dB:
temp = self.__disk.read(dirA)
self.__disk.close(dirA)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
self.__disk.close(dirA)
while self.__disk.status(dirZ) == self.STATUS.dB:
temp = self.__disk.read(dirZ)
self.__disk.close(dirZ)
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
self.__disk.close(dirZ)
elif status == self.STATUS.dZ:
temp = self.__disk.read(block)
self.__disk.blose(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
while self.__disk.status(block) == self.STATUS.dB:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
self.__disk.close(block)
else:
self.__disk.close(block)
# Open A File
def open_file(self):
return self.__disk.open(self.STATUS.f1)
# Read A File
def read_file(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.__disk.status(block)
assert self.STATUS.f1 <= status <= self.STATUS.fZ
if status == self.STATUS.f1:
temp = self.__disk.read(block)
size = (ord(temp[0]) << 8) + ord(temp[1])
return temp[2:size+2]
else:
while self.__disk.status(block) != self.STATUS.fA:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
temp = self.__disk.read(block)
size = (ord(temp[0]) << 8) + ord(temp[1])
data = temp[2:-2]
block = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(block) == self.STATUS.fB:
temp = self.__disk.read(block)
data += temp[2:-2]
block = (ord(temp[-2]) << 8) + ord(temp[-1])
temp = self.__disk.read(block)
return data + temp[2:size-len(data)+2]
# Write A File
def write_file(self, block, data):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(data) is str and len(data)
status = self.__disk.status(block)
assert self.STATUS.f1 <= status <= self.STATUS.fZ
self.__seed(data)
dir_map = [block]
if status == self.STATUS.fA:
temp = self.__disk.read(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [block]
while self.__disk.status(block) == self.STATUS.fB:
temp = self.__disk.read(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [block]
elif status == self.STATUS.fB:
temp = self.__disk.read(block)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [dirA] + dir_map
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [dirZ]
while self.__disk.status(dirA) == self.STATUS.fB:
temp = self.__disk.read(dirA)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [dirA] + dir_map
while self.__disk.status(dirZ) == self.STATUS.fB:
temp = self.__disk.read(dirZ)
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
dir_map = dir_map + [dirZ]
elif status == self.STATUS.fZ:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [block] + dir_map
while self.__disk.status(block) == self.STATUS.fB:
temp = self.__disk.read(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
dir_map = [block] + dir_map
size = self.__size - 4
if len(data) % size:
blocks = len(data) / size + 1
else:
blocks = len(data) / size
blocks = [data[index*size:index*size+size] for index in range(blocks)]
while len(dir_map) > len(blocks):
self.__disk.close(dir_map[-1])
del dir_map[-1]
while len(dir_map) < len(blocks):
dir_map.append(self.__disk.open(255))
if len(blocks) == 1:
temp = len(data)
size = chr(temp >> 8) + chr(temp & 0xFF)
blocks[0] = size + blocks[0] + size
else:
temp = len(data)
size = chr(temp >> 8) + chr(temp & 0xFF)
temp = dir_map[1]
next = chr(temp >> 8) + chr(temp & 0xFF)
blocks[0] = size + blocks[0] + next
index = 1
while blocks[index] is not blocks[-1]:
temp = dir_map[index - 1]
last = chr(temp >> 8) + chr(temp & 0xFF)
temp = dir_map[index + 1]
next = chr(temp >> 8) + chr(temp & 0xFF)
blocks[index] = last + blocks[index] + next
index += 1
temp = dir_map[index - 1]
last = chr(temp >> 8) + chr(temp & 0xFF)
blocks[index] = last + blocks[index] + size
if len(blocks) == 1:
self.__disk.write(dir_map[0], blocks[0] + chr(0) * \
(self.__size - len(blocks[0])))
self.__disk.edit(dir_map[0], self.STATUS.f1)
else:
self.__disk.write(dir_map[0], blocks[0])
self.__disk.edit(dir_map[0], self.STATUS.fA)
index = 1
while blocks[index] is not blocks[-1]:
self.__disk.write(dir_map[index], blocks[index])
self.__disk.edit(dir_map[index], self.STATUS.fB)
index += 1
self.__disk.write(dir_map[index], blocks[index] + chr(0) * \
(self.__size - len(blocks[index])))
self.__disk.edit(dir_map[index], self.STATUS.fZ)
# Close A File
def close_file(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
status = self.__disk.status(block)
assert self.STATUS.f1 <= status <= self.STATUS.fZ
if status == self.STATUS.fA:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(block) == self.STATUS.fB:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[-2]) << 8) + ord(temp[-1])
self.__disk.close(block)
elif status == self.STATUS.fB:
temp = self.__disk.read(block)
self.__disk.close(block)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
while self.__disk.status(dirA) == self.STATUS.fB:
temp = self.__disk.read(dirA)
self.__disk.close(dirA)
dirA = (ord(temp[0]) << 8) + ord(temp[1])
self.__disk.close(dirA)
while self.__disk.status(dirZ) == self.STATUS.fB:
temp = self.__disk.read(dirZ)
self.__disk.close(dirZ)
dirZ = (ord(temp[-2]) << 8) + ord(temp[-1])
self.__disk.close(dirZ)
elif status == self.STATUS.fZ:
temp = self.__disk.read(block)
self.__disk.blose(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
while self.__disk.status(block) == self.STATUS.fB:
temp = self.__disk.read(block)
self.__disk.close(block)
block = (ord(temp[0]) << 8) + ord(temp[1])
self.__disk.close(block)
else:
self.__disk.close(block)
# Open A Block
def open_block(self):
return self.__disk.open(self.STATUS.b1)
# Read A Block
def read_block(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
assert self.__disk.status(block) == self.STATUS.b1
return self.__disk.read(block)
# Write A Block
def write_block(self, block, data):
assert type(block) is int and 1 <= block <= self.__blocks
assert type(data) is str and len(data) == self.__size
assert self.__disk.status(block) == self.STATUS.b1
self.__seed(data)
self.__disk.write(block, data)
# Close A Block
def close_block(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
assert self.__disk.status(block) == self.STATUS.b1
self.__disk.close(block)
# Get Status Information
def status(self, block):
assert type(block) is int and 1 <= block <= self.__blocks
return self.__disk.status(block)
# Seed Control Interface
def seed(self, data=None):
return self.__seed(data)
# Probability Of Failure
def fail(self, probability):
self.__disk.fail(probability)
# Dump To File
def dump(self, name):
self.__disk.write(0, self.__seed())
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()
self.__blocks -= 1
assert 0 < self.__blocks <= self.MAX_BLOCKS
assert 4 < self.__size <= self.MAX_SIZE
self.__seed = Seed(self.__disk.read(0))
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 presented from a collection of recipes that outline the creation of a custom file system. dal_2.py can be found at http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/492210
Tags: files
