DISKBLOCKS(2) DISKBLOCKS(2)
NAME
Diskblocks: Block, Disk, tempfile - temporary storage of
variable-sized blocks
SYNOPSIS
include "diskblocks.m";
diskblocks := load Diskblocks Diskblocks->PATH;
Block: adt {
addr: big; # address on file
n: int; # size in bytes
};
Disk: adt {
init: fn(fd: ref Sys->FD, gran: int, maxblock: int): ref Disk;
new: fn(d: self ref Disk, n: int): ref Block;
release: fn(d: self ref Disk, b: ref Block);
read: fn(d: self ref Disk, b: ref Block,
a: array of byte, n: int): int;
write: fn(d: self ref Disk, b: ref Block,
a: array of byte, n: int): ref Block;
};
init: fn();
tempfile: fn(): ref Sys->FD;
DESCRIPTION
Diskblocks manages a set of variable-sized blocks on a tem-
porary file.
Init must be called before any other function in the module.
Each block has an address and a size in bytes, represented
by a value of type Block.
Each file is represented by the type Disk, providing the
following operations:
init(fd, gran, maxblock)
Initialises the file fd for use as temporary block stor-
age and returns a reference to a Disk to describe it.
Fd must be open for reading and writing, and must refer
to a file that allows random access. Blocks are allo-
cated in multiples of the granularity gran, in bytes;
the largest possible block is maxblock bytes, which must
be a multiple of gran.
d.new(n)
Allocate a block of n bytes on Disk d and return a ref-
erence to it.
d.release(b)
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DISKBLOCKS(2) DISKBLOCKS(2)
Free the Block b, making it available for reallocation.
d.write(b, a, n)
Write n bytes from array a to Block b on Disk d, return-
ing a reference to the resulting Block. If b is nil or
n exceeds b's current size, write allocates a new block
(releasing b). Thus the returned value might differ from
b, and must be used in subsequent IO requests.
d.read(b, a, n)
Read n bytes from Block b on Disk d into array a,
returning the number of bytes read. N must not exceed
b.n.
Tempfile returns a file descriptor referring to a newly-
created temporary file, suitable for use by Disk.init. The
file will be removed automatically when the file descriptor
is closed.
SOURCE
/appl/lib/diskblocks.b
DIAGNOSTICS
A function that returns an integer returns -1 on error; a
function that returns a reference returns nil on error. The
system error string is set in either case.
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