LMI REMOTE DISK PROTOCOL

Purpose: Used to read and write arbitrary disk blocks. 
         The disks are refered to by a <unit-number> and may be actual or simulated disk
         drives.

TCP: Using PORT 101 decimal. (presently DOD assigned to random useless purpose).

Operation as seen from user side:

 * Connect to the server on the PORT.
 * Invoke operations as defined.
 * close the connection when done.

Operation as seen from the server side:
 * listen for a connection on the PORT.
 * read opcode and execute data as defined.
 * EXIT when connection is closed.

Data Transmission format:

Integer: a 32bit integer. Sent as four bytes, low byte first.

String: Length sent as 32B, then data of string as 8 bit bytes.

A disk block is 1024 bytes.


Operations as seen from user side:

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NOTIFY:

Transmit-character: N
Transmit-String: <notification message>
Receive-Character: R

Purpose: To print <notification message> on operator console at server host.
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---------------------------------------------
DISK-READ:

Transmit-character:  R
Transmit-Integer:    <unit-number>
Transmit-Integer:    <number-of-blocks>
Transmit-Integer:    <block-number>
Receive-Character:   R
Receive-String:      <data, result of disk-read>

Purpose: To read <number-of-blocks> of disk data starting at <block-number>.
---------------------------------------------


---------------------------------------------
DISK-WRITE

Transmit-character: W
Transmit-Integer:   <unit-number>
Transmit-Integer:   <number-of-blocks>
Transmit-Integer:   <block-number>
Transmit-String:    <data, to be written to disk>
Receive-Character: R

Purpose: To write <number-of-blocks> of data to disk starting at <block-number>.
---------------------------------------------


Details of disk data, the LABEL.

Starting a block 0 there is a datastructure called the disk label.
Integers in the datastructure are 32 bits, low byte first.
Strings in the datastructure are padded with nulls.
The label may extend over more than one block, in which case it uses even blocks, 0,2,4... etc.

 WORD   Data-Type  Description/Value
 0      STRING      the characters "LABL" or 1279410508 as an integer.
 1      INTEGER     label version number, must be 1.
 2      INTEGER     number of cylinders
 3      INTEGER     number of data heads.
 4      INTEGER     number of blocks per track.
 5      INTEGER     number of blocks per cylinder.
 6      STRING      name of default microcode.
 7      STRING      name of default load.
 8-15   STRING      drive name (manufacturers description, e.g. Fujistu Eagle)
 16-23  STRING      pack name.
 24-48  STRING      comment
 128    INTEGER     number of partitions.
 129    INTEGER     number of words per partition descriptor = (PN+1).
 130    INTEGER     start of partition descriptor table.

Partition Descriptor entry:
 
 WORD   Data-Type  Description/Value
 0      STRING     partition name
 1      INTEGER    starting block address
 2      INTEGER    size in blocks.
 3-PN   STRING     comment.


The cylinder/head/track information is meaningful for real disks and may be used to
in a model of head-movement rotational/latency optimization. The mapping of logical
block numbers to [cylinder,head,track] coordinates is...

The default microcode,load,drive-name,pack-name, and comment fields can be left blank.

Suggested initial values for a simulated or virtual disk of N blocks.

 WORD    Data-Type   Value
 0       STRING      "LABL"
 1       INTEGER     1
 2       INTEGER     1 (cylinder)
 3       INTEGER     1 (head)
 4       INTEGER     N (blocks per track)
 5       INTEGER     N (blocks per cylinder)
 6       STRING      ""
 7       STRING      ""
 8-15    STRING      "virtual disk drive"
 16-23   STRING      "anonymous"
 24-48   STRING      ""
 128     INTEGER     1
 129     INTEGER     7
 130     STRING      "DATA"
 131     INTEGER     6
 132     INTEGER     N-6
 133-139 STRING      "empty partition"