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Date: 2005-05-25 (06:06)
From: Taras <taras.judge@s...>
Subject: partition tables and ocaml
Sven Luther wrote:

>On Mon, Apr 11, 2005 at 08:57:05AM -0400, Eric Cooper wrote:
>>On Mon, Apr 11, 2005 at 09:46:19AM +0200, Sven Luther wrote:
>>>I had plans to do a rewrite of GNU parted, a project which i am
>>>involved with, in ocaml, and am being blocked by a few issues.
>>>  1) most disk partition tables and filesystem have a mapping from a
>>>  given disk 512 byte sector to a descriptive structure.
>>>  [...]
>>>  or to have access functions which transform parts of
>>>  a byte array into values. The first one is ugly, as i was aiming
>>>  for a purely ocaml solution (so i can build and arch/plateform
>>>  independent bytecode tool), and the second would probably be a
>>>  disaster speed wise, and also somewhat ugly unless properly
>>>  encapsulated in an abstract module.
>>I would use the second approach.  I would define a logically
>>equivalent OCaml record or class, and conversion functions between
>>that object and a string + offset (or Bigarray of bytes, plus
>>offset).  Passing around an offset into a larger byte array can save a
>>lot of copying.
>>You can probably structure your code so that you only convert to/from
>>bytes in a few places, not likely to be performance-critical.
>Mmm, one could imagine a generic set of access function inside a byte array
>(would have to handle endianess and such though), and then a structure defined
>as a set of lazy values corresponding to the access functions in question, so
>only values actually accessed get computed.
>That said, 
Is a port of Parted to OCaml still in the works? In case you are still 
wondering, I would like to show out that OCaml can indeed deal with 
partitions in a painless manner.
See http://glek.net/subversion/os/kernel/modules/PartitionTable.ml
The read_tables function is capable of doing primary and extended 
partition table parsing in next to no code. Obviously Parted would need 
a bit more code than that, but things wouldn't get much hairier since 
partition entries are only 16 bytes and that code parses 6 of them :)