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                       The "Uncommon File System"



1.0  INTRODUCTION

The "Uncommon File System", or UFS, is an unsupported feature of TOPS-10
version  7.03  to  facilitate  sharing  a CI bus among several different
systems.  No sharing of disk units or files is provided by this feature.
This  feature  only  assists in preventing access to a disk unit by more
than one system.

(Allowing more than one system to access a disk unit leads  to  SAT  and
directory  differences,  causing  damage to new or existing data on that
disk unit.  Co-ordinating this access would  require  extensive  monitor
development which is not planned for TOPS-10 at this time.)



2.0  "DISK SETS"

Inherent in the design of UFS is the concept of a "disk  set".   A  disk
set  is  a  group  of  file structures which are related.  This relation
usually means they belong to the same system.  Disk sets are  especially
important  in  the  case of CI disks, which can be accessible to several
TOPS-10 systems at the same time.

There are thirty-eight different disk  sets.   These  are  the  numbered
sets,  1  through  36  (decimal),  the  "NO"  set,  and  the  "ALL" set.
Structures in the "NO" set are never mounted by a system, structures  in
the  "ALL"  set  are  always  mounted by a system, and structures in the
numbered sets are mounted by a  system  only  if  the  system  has  been
instructed to mount structures in one (or more) of the numbered sets.

As an example, if system "A" had a system pack called DSKA,  and  system
"B"  had  a  system  pack called DSKB, system A should not be allowed to
access DSKB, nor should system B be allowed to access DSKA.  Without UFS
there  is  no way to prevent TOPS-10 from trying to mount all structures
accessible at ONCE time to the system.  Using UFS, you can  define  DSKA
to be in set 1, and DSKB to be in set 2.  Further, you can tell system A
to only mount structures in set 1, and system B to only mount structures
in set 2.



3.0  PARTS OF UFS

Code to support UFS is contained in three places;  the  monitor,  TWICE,
and PULSAR.

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3.1  Monitor Support Of UFS

Whether or not the monitor supports UFS is determined by the conditional
assembly  option  "FTSETS",  defined  in  the F.MAC file produced by the
MONGEN "F" dialogue.  The default setting for this conditional  is  zero
(or  false).   By  responding  "NO"  to  the  MONGEN  question "Standard
settings" you can enter the dialogue to change the  default  setting  of
this conditional.

Once you have created a new F.MAC  you  must  re-compile  the  following
monitor modules:  F, COMMOD, ONCE, ONCMOD, and UUOCON.  You then proceed
to link the monitor as usual.  The result is a monitor with UFS support.



3.2  TWICE Support Of UFS

TWICE is a user-mode version of the ONCE dialogue.   The  ONCE  dialogue
allows  the operator to define or change disk parameters.  TWICE must be
re-built after re-building the  monitor,  as  TWICE  searches  F.UNV  to
obtain feature test settings.



3.3  GALAXY Support Of UFS

PULSAR has code to GETTAB the conditional feature test flag word in  the
monitor  which  indicates  whether  the  monitor  supports  UFS.  If the
monitor supports UFS, PULSAR will also, and vice versa.  No  re-assembly
of PULSAR is necessary, as this code exists in the distributed version.



4.0  DEFINING SET NUMBERS WHICH A SYSTEM MOUNTS

There are two ways to define which numbered  sets  are  mounted  by  the
system.   One  is  intended  to  be used when building monitors to set a
default, and the other is intended to be  used  during  system  start-up
when the default value is not acceptable.



4.1  Via MONGEN

The MONGEN parameter M.SETS defines a bit mask of  those  numbered  sets
which  are  to  be mounted by the system.  Bit 0 represents set 1, bit 1
represents set 2, ..., and bit 35 represents set 36.  If this  parameter
is  not  specified  in the optional octal dialogue, the monitor will not
mount any structures in the numbered sets (i.e., M.SETS defaults to zero
if not defined).

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4.2  During ONCE

The optional switch /SETS to the "Startup option" question allows you to
define at ONCE time which numbered sets are to be mounted to the system.
If /SETS  is  specified,  the  resulting  value  over-rides  the  MONGEN
parameter M.SETS.



5.0  DEFINING WHICH SET A STRUCTURE BELONGS TO

The set number is stored in the HOMe block of a disk.  The only  way  to
change  the  set number is by using the the TWICE program to change disk
parameters.  TWICE will ask if you want to change any  disk  parameters.
If  you  answer  YES,  you will be allowed to specify which set number a
structure belongs to.  A legal response is either "YES" or  "NO",  or  a
number between 1 and 36 (decimal).

The monitor will not allow you to access a disk  unit  during  the  ONCE
dialogue  which  belongs  to a disk set which is not normally mounted to
the system.  For this reason, you have to change the  set  number  using
TWICE.

By default, structures are defined as belonging to the "ALL" set;   that
is,  they will always be mounted by any system which can access the disk
unit(s) which contain that  structure.   When  defining  new  structures
which are contained on CI type disk units, if you plan to have more than
one system on the CI bus you should plan on putting that structure in  a
unique numbered set.

Structures which already exist will belong to the "ALL" set.