








               BBuuiillddiinngg NNeettBBSSDD KKeerrnneellss wwiitthh CCoonnffiigg


             _S_a_m_u_e_l _J_. _L_e_f_f_l_e_r _a_n_d _M_i_c_h_a_e_l _J_. _K_a_r_e_l_s


                            _A_B_S_T_R_A_C_T

          This  document  describes  the use of _c_o_n_f_i_g(1) to
     configure and create bootable NetBSD system images.  It
     discusses  the  structure of system configuration files
     and how to configure systems with non-standard hardware
     configurations.   Sections describing the preferred way
     to add new code to the  system  and  how  the  system's
     autoconfiguration  process  operates  are included.  An
     appendix contains a summary of the rules  used  by  the
     system  in  calculating  the size of system data struc-
     tures, and also indicates some of the  standard  system
     size limitations and how to change them.  Other config-
     uration options are also listed.


     Revised July 5, 1993

     Revised for NetBSD beginning July 5, 2014






11..  IINNTTRROODDUUCCTTIIOONN

     _C_o_n_f_i_g is a tool used in building  BSD  kernel  images.   It
takes a file describing the tunable parameter settings, features,
and drivers to include, and generates a collection of files which
are  then  used to build a copy of the kernel appropriate to that
configuration.  _C_o_n_f_i_g simplifies system maintenance by isolating
system dependencies in a single, easy to understand, file.

     This  document  describes  the  content and format of system
configuration files and the rules which  must  be  followed  when
creating  these  files.   Example  configuration  files  are con-
structed and discussed.

     Later sections suggest guidelines to be  used  in  modifying
system source and explain some of the inner workings of the auto-
configuration process.  Appendix D summarizes the rules  used  in
calculating  the  most important system data structures and indi-
cates some inherent system data structure size  limitations  (and










Command Reference Documents   Building NetBSD Kernels with Config


how to go about modifying them).

22..  CCOONNFFIIGGUURRAATTIIOONN FFIILLEE CCOONNTTEENNTTSS

     A  system  configuration must include at least the following
pieces of information:

+o  machine type

+o  cpu type

+o  system identification

+o  timezone

+o  maximum number of users

+o  location of the root file system

+o  available hardware

     _C_o_n_f_i_g allows multiple system images to be generated from  a
single  configuration  description.  Each system image is config-
ured for identical hardware, but may have different locations for
the root file system and, possibly, other system devices.

22..11..  MMaacchhiinnee ttyyppee

     The _m_a_c_h_i_n_e _t_y_p_e indicates if the system is going to operate
on  a  DEC  VAX-11[+]  computer,  or  some other machine on which
NetBSD operates.  The machine type is used to locate certain data
files  which  are machine specific, and also to select rules used
in constructing the resultant configuration files.

22..22..  CCppuu ttyyppee

     The _c_p_u _t_y_p_e indicates which, of possibly  many,  cpu's  the
system  is  to  operate  on.  For example, if the system is being
configured for a VAX-11, it could  be  running  on  a  VAX  8600,
VAX-11/780,  VAX-11/750,  VAX-11/730  or MicroVAX II.  (Other VAX
cpu types, including the 8650, 785 and 725, are configured  using
the  cpu designation for compatible machines introduced earlier.)
Specifying more than one cpu type implies that the system  should
be  configured  to  run  on any of the cpu's specified.  For some
types of machines this is not possible and _c_o_n_f_i_g  will  print  a
diagnostic indicating such.

22..33..  SSyysstteemm iiddeennttiiffiiccaattiioonn

     The  _s_y_s_t_e_m _i_d_e_n_t_i_f_i_c_a_t_i_o_n is a moniker attached to the sys-
tem, and often the machine on which the system is  to  run.   For
-----------
[+] DEC, VAX, UNIBUS, MASSBUS and MicroVAX are  trade-
marks of Digital Equipment Corporation.









Building NetBSD Kernels with Config   Command Reference Documents


example,  at  Berkeley we have machines named Ernie (Co-VAX), Kim
(No-VAX), and so on.  The system identifier selected is  used  to
create a global C ``#define'' which may be used to isolate system
dependent pieces of code in the  kernel.   For  example,  Ernie's
Varian driver used to be special cased because its interrupt vec-
tors were wired together.  The code in the  driver  which  under-
stood  how to handle this non-standard hardware configuration was
conditionally compiled in only if the system was for Ernie.

     The system identifier ``GENERIC'' is given to a system which
will  run  on any cpu of a particular machine type; it should not
otherwise be used for a system identifier.

22..44..  TTiimmeezzoonnee

     The timezone in which the system is to run is used to define
the  information  returned  by  the  _g_e_t_t_i_m_e_o_f_d_a_y(2) system call.
This value is specified as the number of hours east  or  west  of
GMT.   Negative  numbers indicate a value east of GMT.  The time-
zone specification may also indicate the type of daylight savings
time rules to be applied.

22..55..  MMaaxxiimmuumm nnuummbbeerr ooff uusseerrss

     The  system  allocates  many  system data structures at boot
time based on the maximum number of users the  system  will  sup-
port.  This number is normally between 8 and 40, depending on the
hardware and expected job mix.  The rules used to calculate  sys-
tem data structures are discussed in Appendix D.

22..66..  RRoooott ffiillee ssyysstteemm llooccaattiioonn

     When  the system boots it must know the location of the root
of the file system tree.  This location and the  part(s)  of  the
disk(s)  to  be used for paging and swapping must be specified in
order to create a  complete  configuration  description.   _C_o_n_f_i_g
uses  many  rules to calculate default locations for these items;
these are described in Appendix B.

     When a generic system is configured, the root file system is
left  undefined  until  the  system is booted.  In this case, the
root file system need not be specified, only that the system is a
generic system.

22..77..  HHaarrddwwaarree ddeevviicceess

     When  the  system boots it goes through an _a_u_t_o_c_o_n_f_i_g_u_r_a_t_i_o_n
phase.  During this period, the system  searches  for  all  those
hardware  devices which the system builder has indicated might be
present.  This probing sequence requires certain pieces of infor-
mation  such  as  register  addresses, bus interconnects, etc.  A
system's hardware may be configured in a very flexible manner  or
be  specified without any flexibility whatsoever.  Most people do
not configure hardware devices into the system  unless  they  are









Command Reference Documents   Building NetBSD Kernels with Config


currently  present  on  the machine, expect them to be present in
the near future, or are simply guarding against a hardware  fail-
ure  somewhere else at the site (it is often wise to configure in
extra disks in case  an  emergency  requires  moving  one  off  a
machine which has hardware problems).

     The  specification  of hardware devices usually occupies the
majority of the configuration file.  As such, a large portion  of
this  document  will be spent understanding it.  Section 6.3 con-
tains a description  of  the  autoconfiguration  process,  as  it
applies  to  those  planning to write, or modify existing, device
drivers.

22..88..  PPsseeuuddoo ddeevviicceess

     Several system facilities are configured in  a  manner  like
that  used  for hardware devices although they are not associated
with specific hardware.  These system options are  configured  as
_p_s_e_u_d_o_-_d_e_v_i_c_e_s.   Some pseudo devices allow an optional parameter
that sets the limit on the number of instances of the device that
are active simultaneously.

22..99..  SSyysstteemm ooppttiioonnss

     Other  than  the  mandatory  pieces of information described
above, it is also possible to  include  various  optional  system
facilities or to modify system behavior and/or limits.  For exam-
ple, NetBSD can be configured to support binary compatibility for
programs  built  under Linux and FreeBSD.  Also, optional support
is provided for disk quotas and tracing the  performance  of  the
virtual  memory subsystem.  Any optional facilities to be config-
ured into the system are specified  in  the  configuration  file.
The  resultant  files  generated  by  _c_o_n_f_i_g  will  automatically
include the necessary pieces of the system.

33..  SSYYSSTTEEMM BBUUIILLDDIINNGG PPRROOCCEESSSS

     In this section we consider the steps necessary to  build  a
bootable system image.  We assume the system source is located in
the ``/usr/src'' directory and that,  initially,  the  system  is
being configured from source code.

     Under  normal  circumstances there are 5 steps in building a
system.

1) Create a configuration file for the system.

2) Make a directory for the system to be constructed in.

3) Run _c_o_n_f_i_g on the configuration file  to  generate  the  files
   required to compile and load the system image.

4) Construct  the  source code interdependency rules for the con-
   figured system with _m_a_k_e _d_e_p_e_n_d using _m_a_k_e(1).









Building NetBSD Kernels with Config   Command Reference Documents


5) Compile and link the system with _m_a_k_e.

     Steps 1 and 2 are usually done only  once.   When  a  system
configuration  changes  it usually suffices to just run _c_o_n_f_i_g on
the modified configuration file, rebuild the source  code  depen-
dencies,  and  remake the system.  Sometimes, however, configura-
tion dependencies may not be noticed in which case it  is  neces-
sary  to  clean out the object files saved in the system's direc-
tory; this will be discussed later.

33..11..  CCrreeaattiinngg aa ccoonnffiigguurraattiioonn ffiillee

     Configuration  files  normally  reside  in   the   directory
``conf''  in  the architecture-specific subtree of the kernel for
the machine type in use.  (For example, configuration  files  for
64-bit x86 machines live in ``/usr/src/sys/arch/amd64/conf''.)  A
configuration file is  most  easily  constructed  by  copying  an
existing configuration file and modifying it.  The NetBSD distri-
bution contains assorted standard configuration files for differ-
ent  machine  types  and varieties.  Start with ``GENERIC'' if no
other is more appropriate.

     The configuration file must have the same name as the direc-
tory  in  which  the  configured system is to be built.  Further,
_c_o_n_f_i_g assumes this directory is located  under  the  ``compile''
directory  at  the  same level as the ``conf'' directory in which
it is run.  For example, the generic 64-bit x86 system has a con-
figuration  file  ``/usr/src/sys/arch/amd64/conf/GENERIC'' and an
accompanying   directory   named   ``/usr/src/sys/arch/amd64/com-
pile/GENERIC''.   Although  it  is  not  required that the system
sources and configuration files reside in ``/usr/src,'' the  con-
figuration  and  compilation  procedure  depends  on the relative
locations of directories within that hierarchy, as  most  of  the
system  code and the files created by _c_o_n_f_i_g use pathnames of the
form ``../''.

     When building the configuration file, be sure to include the
items  described  in section 2.  In particular, the machine type,
cpu type, timezone, system identifier, maximum  users,  and  root
device  must  be  specified.   The  specification of the hardware
present may take a bit of work; particularly if your hardware  is
configured  at non-standard places (e.g. device registers located
at funny places or devices not supported by the system).  Section
4 of this document gives a detailed description of the configura-
tion file syntax, section 5 explains  some  sample  configuration
files, and section 6 discusses how to add new devices to the sys-
tem.  If the devices to be configured are not  already  described
in  one  of the existing configuration files you should check the
section 4 manual pages.  For each supported  device,  the  manual
page synopsis entry gives a sample configuration line.

     Once the configuration file is complete, run it through _c_o_n_-
_f_i_g and look for any errors.  Never try and use  a  system  which
_c_o_n_f_i_g  has complained about; the results are unpredictable.  For









Command Reference Documents   Building NetBSD Kernels with Config


the most part, _c_o_n_f_i_g's error diagnostics are  self  explanatory.
It  may  be  the  case that the line numbers given with the error
messages are off by one.

     A successful run of _c_o_n_f_i_g on your configuration  file  will
generate a number of files in the configuration directory.  These
files are:

+o  A file to be used by _m_a_k_e(1) in compiling and loading the sys-
   tem, _M_a_k_e_f_i_l_e.

+o  One  file  for  each  possible  system image for this machine,
   _s_w_a_p_x_x_x_._c, where _x_x_x is the name of the  system  image,  which
   describes where swapping, the root file system, and other mis-
   cellaneous system devices are located.

+o  A collection of header files, one per possible device the sys-
   tem supports, which define the hardware configured.

+o  A  file  containing  the  I/O configuration tables used by the
   system during its _a_u_t_o_c_o_n_f_i_g_u_r_a_t_i_o_n phase, _i_o_c_o_n_f_._c.

+o  An assembly language file of interrupt vectors  which  connect
   interrupts  from the machine's external buses to the main sys-
   tem path for handling interrupts, and  a  file  that  contains
   counters and names for the interrupt vectors.

     Unless  you  have reason to doubt _c_o_n_f_i_g, or are curious how
the system's autoconfiguration scheme  works,  you  should  never
have to look at any of these files.

33..22..  CCoonnssttrruuccttiinngg ssoouurrccee ccooddee ddeeppeennddeenncciieess

     When  _c_o_n_f_i_g  is done generating the files needed to compile
and link your system it will terminate with a message of the form
``Don't forget to run make depend''.  This is a reminder that you
should change over to the configuration directory for the  system
just  configured and type ``make depend'' to build the rules used
by _m_a_k_e to recognize interdependencies in the system source code.
This will insure that any changes to a piece of the system source
code will result in the proper modules being recompiled the  next
time _m_a_k_e is run.

     This  step  is  particularly  important  if  your site makes
changes to the system include files.  The rules generated specify
which  source  code  files  are dependent on which include files.
Without these rules, _m_a_k_e will not recognize when it must rebuild
modules  due  to  the  modification of a system header file.  The
dependency rules are generated by a pass of  the  C  preprocessor
and  reflect  the  global  system  options.   This  step  must be
repeated when the configuration file is  changed  and  _c_o_n_f_i_g  is
used to regenerate the system makefile.











Building NetBSD Kernels with Config   Command Reference Documents


33..33..  BBuuiillddiinngg tthhee ssyysstteemm

     The makefile constructed by _c_o_n_f_i_g should allow a new system
to be rebuilt by simply typing ``make''.  Alternate system  image
names are used when the root file system location and/or swapping
configuration is done in more than one way.  The  makefile  which
_c_o_n_f_i_g  creates has entry points for each system image defined in
the configuration file.  Thus, if you have configured  ``netbsd''
to  be a system with the root file system on an ``hp'' device and
``hknetbsd'' to be a system with  the  root  file  system  on  an
``hk'' device, then ``make netbsd hknetbsd'' will generate binary
images for each.  As the system will generally use the disk  from
which it is loaded as the root filesystem, separate system images
are only required to support different swap configurations.

     Note that the name of a bootable image is different from the
system  identifier.   All  bootable images are configured for the
same system; only the information about the root file system  and
paging devices differ.  (This is described in more detail in sec-
tion 4.)

     The last step in the system building process is to rearrange
certain  commonly  used symbols in the symbol table of the system
image;  the makefile generated by _c_o_n_f_i_g does this  automatically
for  you.   This  is advantageous for programs such as _n_e_t_s_t_a_t(1)
and _v_m_s_t_a_t(1), which run much faster when the symbols  they  need
are located at the front of the symbol table.  Remember also that
many programs expect the currently executing system to  be  named
``/netbsd''.   If  you install a new system and name it something
other than ``/netbsd'', many programs are likely to give  strange
results.

33..44..  SShhaarriinngg oobbjjeecctt mmoodduulleess

     If  you  have  many  systems which are all built on a single
machine there are at least  two  approaches  to  saving  time  in
building  system images.  The best way is to have a single system
image which is run on all machines.  This is attractive since  it
minimizes  disk  space  used and time required to rebuild systems
after making changes.  However, it is often the case that one  or
more  systems  will require a separately configured system image.
This may be due to limited memory (building a  system  with  many
unused  device  drivers  can  be  expensive), or to configuration
requirements (one machine may be a development machine where disk
quotas  are  not  needed,  while  another is a production machine
where they are), etc.  In these cases it is possible  for  common
systems to share relocatable object modules which are not config-
uration dependent.

     To share object modules, a generic system should  be  built.
Then,  for each system configure the system as before, but before
recompiling and linking the system, type ``make  links''  in  the
system  compilation  directory.  This will cause the system to be
searched for source modules  which  are  safe  to  share  between









Command Reference Documents   Building NetBSD Kernels with Config


systems  and  generate symbolic links in the current directory to
the appropriate object modules in the  directory  ``../GENERIC''.
A  shell script, ``makelinks'' is generated with this request and
may be checked for correctness.  The  file  ``/sys/conf/defines''
contains  a  list  of symbols which we believe are safe to ignore
when checking the source code for modules which  may  be  shared.
Note  that  this list includes the definitions used to condition-
ally compile in the virtual memory tracing  facilities,  and  the
trace  point support used only rarely (even at Berkeley).  It may
be necessary to modify this file to reflect  local  needs.   Note
further  that interdependencies which are not directly visible in
the source code are not caught.  This means  that  if  you  place
per-system dependencies in an include file, they will not be rec-
ognized and the shared code may  be  selected  in  an  unexpected
fashion.

33..55..  BBuuiillddiinngg pprrooffiilleedd ssyysstteemmss

     It  is simple to configure a system which will automatically
collect profiling information as it operates.  The profiling data
may  be  collected  with  _k_g_m_o_n(8) and processed with _g_p_r_o_f(1) to
obtain information regarding the  system's  operation.   Profiled
systems maintain histograms of the program counter as well as the
number of invocations of each routine.  The  _g_p_r_o_f  command  will
also  generate  a  dynamic call graph of the executing system and
propagate time spent in each routine along the arcs of  the  call
graph  (consult  the  _g_p_r_o_f  documentation for elaboration).  The
program counter sampling can be driven by the system clock, or if
you  have  an  alternate  real time clock, this can be used.  The
latter is highly recommended, as use of  the  system  clock  will
result in statistical anomalies, and time spent in the clock rou-
tine will not be accurately attributed.

     To configure a profiled system, the --pp option should be sup-
plied  to _c_o_n_f_i_g.  A profiled system is about 5-10% larger in its
text space due to the calls to count the subroutine  invocations.
When  the  system  executes,  the  profiling  data is stored in a
buffer which is 1.2 times the size of the text space.  The  over-
head  for  running a profiled system varies; under normal load we
see anywhere from 5-25% of the system time spent in the profiling
code.

     Note  that  systems  configured  for profiling should not be
shared as described above unless all the other shared systems are



















Building NetBSD Kernels with Config   Command Reference Documents


also to be profiled.

44..  CCOONNFFIIGGUURRAATTIIOONN FFIILLEE SSYYNNTTAAXX

     In this section we consider the specific rules used in writ-
ing a configuration file.  A complete grammar for the input  lan-
guage  can be found in Appendix A and may be of use if you should
have problems with syntax errors.

     A configuration file is broken up into three logical pieces:

+o  configuration parameters global to all system images specified
   in the configuration file,

+o  parameters specific to each system image to be generated, and

+o  device specifications.

44..11..  GGlloobbaall ccoonnffiigguurraattiioonn ppaarraammeetteerrss

     The global configuration parameters are the type of machine,
cpu  types,  options,  timezone,  system  identifier, and maximum
users.  Each is specified with a separate line in the  configura-
tion file.

mmaacchhiinnee _t_y_p_e
     The system is to run on the machine type specified.  No more
     than one machine type can appear in the configuration  file.
     Legal values are vvaaxx and ssuunn.

ccppuu ``_t_y_p_e''
     This  system is to run on the cpu type specified.  More than
     one cpu type specification can  appear  in  a  configuration
     file.   Legal  types  for a vvaaxx machine are VVAAXX88660000, VVAAXX778800,
     VVAAXX775500, VVAAXX773300 and VVAAXX663300 (MicroVAX II).  The 8650 is listed
     as an 8600, the 785 as a 780, and a 725 as a 730.

ooppttiioonnss _o_p_t_i_o_n_l_i_s_t
     Compile  the  listed optional code into the system.  Options
     in this list are separated by commas.  Possible options  are
     listed  at  the  top of the generic makefile.  A line of the
     form ``options FUNNY,HAHA''  generates  global  ``#define''s
     -DFUNNY  -DHAHA in the resultant makefile.  An option may be
     given a value by following its name  with  ``=='',  then  the
     value  enclosed in (double) quotes.  The following are major
     options are currently in use: COMPAT (include code for  com-
     patibility  with 4.1BSD binaries), INET (Internet communica-
     tion protocols), NS (Xerox NS communication protocols),  and
     QUOTA  (enable  disk quotas).  Other kernel options control-
     ling system sizes and  limits  are  listed  in  Appendix  D;
     options  for the network are found in Appendix E.  There are
     additional options which are associated with certain periph-
     eral  devices;  those  are listed in the Synopsis section of
     the manual page for the device.









Command Reference Documents   Building NetBSD Kernels with Config


mmaakkeeooppttiioonnss _o_p_t_i_o_n_l_i_s_t
     Options that are used within the system makefile and  evalu-
     ated  by _m_a_k_e are listed as _m_a_k_e_o_p_t_i_o_n_s.  Options are listed
     with   their   values   with    the    form    ``makeoptions
     name=value,name2=value2.''   The  values must be enclosed in
     double quotes if they include numerals or begin with a dash.

ttiimmeezzoonnee _n_u_m_b_e_r [ ddsstt [ _n_u_m_b_e_r ] ]
     Specifies the timezone used by the system.  This is measured
     in the number of hours your timezone is west of GMT.  EST is
     5  hours  west  of GMT, PST is 8.  Negative numbers indicate
     hours east of GMT.  If you  specify  ddsstt,  the  system  will
     operate under daylight savings time.  An optional integer or
     floating point number may be included to specify a  particu-
     lar  daylight  saving time correction algorithm; the default
     value is 1, indicating the United States.  Other values are:
     2  (Australian style), 3 (Western European), 4 (Middle Euro-
     pean), and 5 (Eastern European).   See  _g_e_t_t_i_m_e_o_f_d_a_y(2)  and
     _c_t_i_m_e(3) for more information.

iiddeenntt _n_a_m_e
     This  system is to be known as _n_a_m_e.  This is usually a cute
     name like ERNIE (short for Ernie  Co-Vax)  or  VAXWELL  (for
     Vaxwell  Smart).   This  value  is defined for use in condi-
     tional compilation, and is also used to locate  an  optional
     list of source files specific to this system.

mmaaxxuusseerrss _n_u_m_b_e_r
     The maximum expected number of simultaneously active user on
     this system is _n_u_m_b_e_r.  This number is used to size  several
     system data structures.

44..22..  SSyysstteemm iimmaaggee ppaarraammeetteerrss

     Multiple  bootable  images may be specified in a single con-
figuration file.  The systems will have the same global  configu-
ration  parameters and devices, but the location of the root file
system and other system specific devices  may  be  different.   A
system image is specified with a ``config'' line:

     ccoonnffiigg _s_y_s_n_a_m_e _c_o_n_f_i_g_-_c_l_a_u_s_e_s

The  _s_y_s_n_a_m_e  field is the name given to the loaded system image;
almost everyone names their  standard  system  image  ``netbsd''.
The configuration clauses are one or more specifications indicat-
ing where the root file system is  located  and  the  number  and
location  of  paging  devices.   The device used by the system to
process argument lists during _e_x_e_c_v_e(2) calls may also be  speci-
fied, though in practice this is almost always selected by _c_o_n_f_i_g
using one of its rules for selecting default locations for system
devices.

     A configuration clause is one of the following










Building NetBSD Kernels with Config   Command Reference Documents


     rroooott [ oonn ] _r_o_o_t_-_d_e_v_i_c_e
     sswwaapp [ oonn ] _s_w_a_p_-_d_e_v_i_c_e [ aanndd _s_w_a_p_-_d_e_v_i_c_e ] ...
     dduummppss [ oonn ] _d_u_m_p_-_d_e_v_i_c_e
     aarrggss [ oonn ] _a_r_g_-_d_e_v_i_c_e

(the  ``on''  is  optional.)   Multiple configuration clauses are
separated by white space; _c_o_n_f_i_g allows specifications to be con-
tinued  across  multiple lines by beginning the continuation line
with a tab character.  The ``root'' clause  specifies  where  the
root  file system is located, the ``swap'' clause indicates swap-
ping and paging area(s), the ``dumps''  clause  can  be  used  to
force  system  dumps  to be taken on a particular device, and the
``args'' clause can be used to specify that  argument  list  pro-
cessing for _e_x_e_c_v_e should be done on a particular device.

     The device names supplied in the clauses may be fully speci-
fied as a device, unit, and file system partition; or underspeci-
fied  in  which  case  _c_o_n_f_i_g  will  use  builtin rules to select
default unit numbers and file system partitions.  The  defaulting
rules  are a bit complicated as they are dependent on the overall
system configuration.  For example, the swap  area  need  not  be
specified  at  all  if the root device is specified; in this case
the swap area is placed in the ``b'' partition of the  same  disk
where  the  root  file  system is located.  Appendix B contains a
complete list of the defaulting rules used  in  selecting  system
configuration devices.

     The device names are translated to the appropriate major and
minor  device  numbers  on  a   per-machine   basis.    A   file,
``/sys/conf/devices.machine''  (where  ``machine'' is the machine
type specified in the configuration  file),  is  used  to  map  a
device  name  to its major block device number.  The minor device
number is calculated using the standard disk partitioning  rules:
on  unit 0, partition ``a'' is minor device 0, partition ``b'' is
minor device 1, and so on; for units other than 0,  add  8  times
the unit number to get the minor device.

     If  the default mapping of device name to major/minor device
number is incorrect for your configuration, it can be replaced by
an  explicit  specification  of  the major/minor device.  This is
done by substituting

     mmaajjoorr _x mmiinnoorr _y

where the device name would normally be found.  For example,

     ccoonnffiigg kernel rroooott oonn mmaajjoorr 99 mmiinnoorr 1

     Normally, the areas configured for swap space are  sized  by
the  system  at  boot time.  If a non-standard size is to be used
for one or more swap areas (less than the full  partition),  this
can also be specified.  To do this, the device name specified for
a swap area should have a ``size'' specification  appended.   For
example,









Command Reference Documents   Building NetBSD Kernels with Config


     ccoonnffiigg kernel rroooott oonn hp0 sswwaapp oonn hp0b ssiizzee 1200

would force swapping to be done in partition ``b'' of ``hp0'' and
the swap partition size would be set to  1200  sectors.   A  swap
area  sized  larger than the associated disk partition is trimmed
to the partition size.

     To create a generic configuration, only  the  clause  ``swap
generic''  should  be  specified; any extra clauses will cause an
error.

44..33..  DDeevviiccee ssppeecciiffiiccaattiioonnss

     Each device attached to a machine must be specified to  _c_o_n_-
_f_i_g so that the system generated will know to probe for it during
the autoconfiguration process carried out at boot time.  Hardware
specified  in  the  configuration need not actually be present on
the machine where the generated system is to be  run.   Only  the
hardware  actually found at boot time will be used by the system.

     The specification of hardware devices in  the  configuration
file parallels the interconnection hierarchy of the machine to be
configured.  On the VAX, this means  that  a  configuration  file
must  indicate  what MASSBUS and UNIBUS adapters are present, and
to which _n_e_x_i they might be connected.*  Similarly,  devices  and
controllers  must be indicated as possibly being connected to one
or more adapters.  A device description may  provide  a  complete
definition  of  the  possible  configuration parameters or it may
leave certain parameters undefined and make the system probe  for
all  the possible values.  The latter allows a single device con-
figuration list to match many possible  physical  configurations.
For example, a disk may be indicated as present at UNIBUS adapter
0, or at any UNIBUS adapter which  the  system  locates  at  boot
time.   The latter scheme, termed _w_i_l_d_c_a_r_d_i_n_g, allows more flexi-
bility in the physical configuration of a system; if a disk  must
be  moved around for some reason, the system will still locate it
at the alternate location.

     A device specification takes one of the following forms:

     mmaasstteerr _d_e_v_i_c_e_-_n_a_m_e _d_e_v_i_c_e_-_i_n_f_o
     ccoonnttrroolllleerr _d_e_v_i_c_e_-_n_a_m_e _d_e_v_i_c_e_-_i_n_f_o [ _i_n_t_e_r_r_u_p_t_-_s_p_e_c ]
     ddeevviiccee _d_e_v_i_c_e_-_n_a_m_e _d_e_v_i_c_e_-_i_n_f_o _i_n_t_e_r_r_u_p_t_-_s_p_e_c
     ddiisskk _d_e_v_i_c_e_-_n_a_m_e _d_e_v_i_c_e_-_i_n_f_o
     ttaappee _d_e_v_i_c_e_-_n_a_m_e _d_e_v_i_c_e_-_i_n_f_o

A ``master'' is a MASSBUS tape controller; a ``controller'' is  a
disk  controller, a UNIBUS tape controller, a MASSBUS adapter, or
a UNIBUS adapter.  A ``device'' is  an  autonomous  device  which
connects  directly  to  a UNIBUS adapter (as opposed to something
-----------
* While VAX-11/750's and VAX-11/730  do  not  actually
have  nexi, the system treats them as having _s_i_m_u_l_a_t_e_d
_n_e_x_i to simplify device configuration.









Building NetBSD Kernels with Config   Command Reference Documents


like a disk which connects through a disk controller).   ``Disk''
and  ``tape'' identify disk drives and tape drives connected to a
``controller'' or ``master.''

     The _d_e_v_i_c_e_-_n_a_m_e is one of  the  standard  device  names,  as
indicated  in  section 4 of the UNIX Programmers Manual, concate-
nated with the _l_o_g_i_c_a_l unit number to be assigned the device (the
_l_o_g_i_c_a_l  unit number may be different than the _p_h_y_s_i_c_a_l unit num-
ber indicated on the front of something like a disk; the  _l_o_g_i_c_a_l
unit number is used to refer to the UNIX device, not the physical
unit number).  For example, ``hp0'' is logical unit 0 of a  MASS-
BUS  storage  device,  even though it might be physical unit 3 on
MASSBUS adapter 1.

     The _d_e_v_i_c_e_-_i_n_f_o clause specifies how the  hardware  is  con-
nected  in the interconnection hierarchy.  On the VAX, UNIBUS and
MASSBUS adapters are connected to the internal system bus through
a  _n_e_x_u_s.   Thus,  one  of  the following specifications would be
used:

     ccoonnttrroolllleerr     mba0      aatt nneexxuuss _x
     ccoonnttrroolllleerr     uba0      aatt nneexxuuss _x

To tie a controller to a specific nexus, ``x'' would be  supplied
as  the number of that nexus; otherwise ``x'' may be specified as
``?'', in which case the system will probe all nexi present look-
ing for the specified controller.

     The remaining interconnections on the VAX are:

+o  a  controller  may  be connected to another controller (e.g. a
   disk controller attached to a UNIBUS adapter),

+o  a master  is  always  attached  to  a  controller  (a  MASSBUS
   adapter),

+o  a  tape  is  always  attached  to  a  master (for MASSBUS tape
   drives),

+o  a disk is always attached to a controller, and

+o  devices are always attached to controllers (e.g.  UNIBUS  con-
   trollers attached to UNIBUS adapters).

The following lines give an example of each of these interconnec-
tions:

     ccoonnttrroolllleerr     hk0       aatt uba0 ...
     mmaasstteerr         ht0       aatt mba0 ...
     ddiisskk           hp0       aatt mba0 ...
     ttaappee           tu0       aatt ht0 ...
     ddiisskk           rk1       aatt hk0 ...
     ddeevviiccee         dz0       aatt uba0 ...










Command Reference Documents   Building NetBSD Kernels with Config


Any piece of hardware which may be connected to a  specific  con-
troller may also be wildcarded across multiple controllers.

     The  final piece of information needed by the system to con-
figure devices is some indication of where or how a  device  will
interrupt.   For  tapes and disks, simply specifying the _s_l_a_v_e or
_d_r_i_v_e number is sufficient to locate the control status  register
for  the  device.   _D_r_i_v_e  numbers  may  be wildcarded on MASSBUS
devices, but not on disks  on  a  UNIBUS  controller.   For  con-
trollers,  the  control status register must be given explicitly,
as well the number of interrupt vectors used and the names of the
routines  to  which they should be bound.  Thus the example lines
given above might be completed as:

     ccoonnttrroolllleerr     hk0       aatt uba0 ccssrr 0177440vveeccttoorr rkintr
     mmaasstteerr         ht0       aatt mba0 ddrriivvee 0
     ddiisskk           hp0       aatt mba0 ddrriivvee ?
     ttaappee           tu0       aatt ht0 ssllaavvee 0
     ddiisskk           rk1       aatt hk0 ddrriivvee 1
     ddeevviiccee         dz0       aatt uba0 ccssrr 0160100vveeccttoorr dzrint dzxint

     Certain device drivers require extra information  passed  to
them  at  boot time to tailor their operation to the actual hard-
ware present.  The line printer driver,  for  example,  needs  to
know  how  many  columns  are  present  on each non-standard line
printer (i.e. a line printer with other than  80  columns).   The
drivers  for  the  terminal multiplexors need to know which lines
are attached to modem lines so that no one will be allowed to use
them  unless  a connection is present.  For this reason, one last
parameter may be specified to a _d_e_v_i_c_e, a _f_l_a_g_s  field.   It  has
the syntax

     ffllaaggss _n_u_m_b_e_r

and is usually placed after the _c_s_r specification.  The _n_u_m_b_e_r is
passed directly to the associated driver.  The  manual  pages  in
section  4  should be consulted to determine how each driver uses
this value (if at all).  Communications  interface  drivers  com-
monly use the flags to indicate whether modem control signals are
in use.

     The exact syntax for each specific device is  given  in  the
Synopsis section of its manual page in section 4 of the manual.

44..44..  PPsseeuuddoo--ddeevviicceess

     A number of drivers and software subsystems are treated like
device drivers without any associated hardware.  To  include  any
of  these pieces, a ``pseudo-device'' specification must be used.
A specification for a pseudo device takes the form

     ppsseeuuddoo--ddeevviiccee  _d_e_v_i_c_e_-_n_a_m_e [ _h_o_w_m_a_n_y ]











Building NetBSD Kernels with Config   Command Reference Documents


     Examples of pseudo devices  are  ppttyy,  the  pseudo  terminal
driver  (where the optional _h_o_w_m_a_n_y value indicates the number of
pseudo terminals to configure, 32 default), and lloooopp,  the  soft-
ware loopback network pseudo-interface.  Other pseudo devices for
the network include iimmpp (required when a CSS or ACC imp  is  con-
figured) and eetthheerr (used by the Address Resolution Protocol on 10
Mb/sec Ethernets).  More information on configuring each of these
can also be found in section 4 of the manual.

55..  SSAAMMPPLLEE CCOONNFFIIGGUURRAATTIIOONN FFIILLEESS

     In  this  section we will consider how to configure a sample
VAX-11/780 system on which the hardware can  be  reconfigured  to
guard  against various hardware mishaps.  We then study the rules
needed to configure a VAX-11/750 to run in a networking  environ-
ment.

55..11..  VVAAXX--1111//778800 SSyysstteemm

     Our  VAX-11/780  is  configured with hardware recommended in
the document ``Hints on Configuring a VAX for 4.2BSD''  (this  is
one of the high-end configurations).  Table 1 lists the pertinent
hardware to be configured.


+---------------------+---------+------------+--------+-----------+
|Item                 | Vendor  | Connection | Name   | Reference |
+---------------------+---------+------------+--------+-----------+
|cpu                  | DEC     |            | VAX780 |           |
|MASSBUS controller   | Emulex  | nexus ?    | mba0   | hp(4)     |
|disk                 | Fujitsu | mba0       | hp0    |           |
|disk                 | Fujitsu | mba0       | hp1    |           |
|MASSBUS controller   | Emulex  | nexus ?    | mba1   |           |
|disk                 | Fujitsu | mba1       | hp2    |           |
|disk                 | Fujitsu | mba1       | hp3    |           |
|UNIBUS adapter       | DEC     | nexus ?    |        |           |
|tape controller      | Emulex  | uba0       | tm0    | tm(4)     |
|tape drive           | Kennedy | tm0        | te0    |           |
|tape drive           | Kennedy | tm0        | te1    |           |
|terminal multiplexor | Emulex  | uba0       | dh0    | dh(4)     |
|terminal multiplexor | Emulex  | uba0       | dh1    |           |
|terminal multiplexor | Emulex  | uba0       | dh2    |           |
+---------------------+---------+------------+--------+-----------+

             Table 1.  VAX-11/780 Hardware support.

We will call this machine ANSEL  and  construct  a  configuration
file one step at a time.

     The first step is to fill in the global configuration param-
eters.  The machine is a VAX, so the _m_a_c_h_i_n_e _t_y_p_e is ``vax''.  We
will  assume  this system will run only on this one processor, so
the _c_p_u _t_y_p_e is ``VAX780''.  The options are empty since this  is
going  to  be  a  ``vanilla''  VAX.   The  system  identifier, as









Command Reference Documents   Building NetBSD Kernels with Config


mentioned before, is ``ANSEL,'' and the maximum number  of  users
we  plan  to support is about 40.  Thus the beginning of the con-
figuration file looks like this:

     #
     # ANSEL VAX (a picture perfect machine)
     #
     machine        vax
     cpu            VAX780
     timezone       8 dst
     ident          ANSEL
     maxusers       40


     To this we must then add the specifications for three system
images.   The  first will be our standard system with the root on
``hp0'' and swapping on the same drive as the root.   The  second
will  have  the  root  file system in the same location, but swap
space interleaved among drives on each controller.  Finally,  the
third  will  be  a generic system, to allow us to boot off any of
the four disk drives.

     config         kernel    root on hp0
     config         hpkernel  root on hp0 swap on hp0 and hp2
     config         genkernel swap generic


     Finally, the hardware must be specified.  Let us first  just
try transcribing the information from Table 1.

     controller     mba0      at nexus ?
     disk           hp0       at mba0 disk 0
     disk           hp1       at mba0 disk 1
     controller     mba1      at nexus ?
     disk           hp2       at mba1 disk 2
     disk           hp3       at mba1 disk 3
     controller     uba0      at nexus ?
     controller     tm0       at uba0 csr 0172520vector tmintr
     tape           te0       at tm0 drive 0
     tape           te1       at tm0 drive 1
     device         dh0       at uba0 csr 0160020vector dhrint dhxint
     device         dm0       at uba0 csr 0170500vector dmintr
     device         dh1       at uba0 csr 0160040vector dhrint dhxint
     device         dh2       at uba0 csr 0160060vector dhrint dhxint


(Oh,  I  forgot  to mention one panel of the terminal multiplexor
has modem control, thus the ``dm0'' device.)

     This will suffice, but leaves us  with  little  flexibility.
Suppose  our  first disk controller were to break.  We would like
to recable the drives normally on the second controller  so  that
all  our disks could still be used without reconfiguring the sys-
tem.  To do this we wildcard the MASSBUS adapter connections  and









Building NetBSD Kernels with Config   Command Reference Documents


also  the slave numbers.  Further, we wildcard the UNIBUS adapter
connections in case we decide some time in the future to purchase
another  adapter  to offload the single UNIBUS we currently have.
The revised device specifications would then be:

     controller     mba0      at nexus ?
     disk           hp0       at mba? disk ?
     disk           hp1       at mba? disk ?
     controller     mba1      at nexus ?
     disk           hp2       at mba? disk ?
     disk           hp3       at mba? disk ?
     controller     uba0      at nexus ?
     controller     tm0       at uba? csr 0172520vector tmintr
     tape           te0       at tm0 drive 0
     tape           te1       at tm0 drive 1
     device         dh0       at uba? csr 0160020vector dhrint dhxint
     device         dm0       at uba? csr 0170500vector dmintr
     device         dh1       at uba? csr 0160040vector dhrint dhxint
     device         dh2       at uba? csr 0160060vector dhrint dhxint


The completed configuration file for ANSEL is shown  in  Appendix
C.

55..22..  VVAAXX--1111//775500 wwiitthh nneettwwoorrkk ssuuppppoorrtt

     Our VAX-11/750 system will be located on two 10Mb/s Ethernet
local area networks and also the DARPA Internet.  The system will
have  a  MASSBUS  drive  for  the root file system and two UNIBUS
drives.  Paging is interleaved among all three drives.   We  have
sold  our  standard  DEC terminal multiplexors since this machine
will be accessed solely through the network.  This machine is not
intended to have a large user community, it does not have a great
deal of memory.  First the global parameters:

     #
     # UCBVAX (Gateway to the world)
     #
     machine        vax
     cpu            "VAX780"
     cpu            "VAX750"
     ident          UCBVAX
     timezone       8 dst
     maxusers       32
     options        INET
     options        NS


     The multiple cpu types allow us to  replace  UCBVAX  with  a
more powerful cpu without reconfiguring the system.  The value of
32 given for the maximum number of users is  done  to  force  the
system  data  structures to be over-allocated.  That is desirable
on this machine because, while it is not expected to support many
users,  it  is  expected  to  perform  a great deal of work.  The









Command Reference Documents   Building NetBSD Kernels with Config


``INET'' indicates that we plan to use the DARPA standard  Inter-
net  protocols  on this machine, and ``NS'' also includes support
for Xerox NS protocols.  Note that  unlike  4.2BSD  configuration
files,  the network protocol options do not require corresponding
pseudo devices.

     The system images and disks are configured next.

     config         kernel    root on hp swap on hp and rk0 and rk1
     config         upkernel  root on up
     config         hkkernel  root on hk swap on rk0 and rk1

     controller     mba0      at nexus ?
     controller     uba0      at nexus ?
     disk           hp0       at mba? drive 0
     disk           hp1       at mba? drive 1
     controller     sc0       at uba? csr 0176700vector upintr
     disk           up0       at sc0 drive 0
     disk           up1       at sc0 drive 1
     controller     hk0       at uba? csr 0177440 vector rkintr
     disk           rk0       at hk0 drive 0
     disk           rk1       at hk0 drive 1


     UCBVAX requires heavy interleaving of  its  paging  area  to
keep  up with all the mail traffic it handles.  The limiting fac-
tor on this system's performance is usually the  number  of  disk
arms,  as opposed to memory or cpu cycles.  The extra UNIBUS con-
troller, ``sc0'', is in case the MASSBUS controller breaks and  a
spare  controller  must be installed (most of our old UNIBUS con-
trollers have been replaced with the newer  MASSBUS  controllers,
so we have a number of these around as spares).

     Finally,  we  add  in the network devices.  Pseudo terminals
are needed to allow users to log in across the network  (remember
the  only hardwired terminal is the console).  The software loop-
back device is used for on-machine communications.   The  connec-
tion to the Internet is through an IMP, this requires yet another
_p_s_e_u_d_o_-_d_e_v_i_c_e (in addition to the actual hardware device used  by
the  IMP  software).   And,  finally,  there are the two Ethernet
devices.  These use a special protocol,  the  Address  Resolution
Protocol  (ARP),  to map between Internet and Ethernet addresses.
Thus, yet another _p_s_e_u_d_o_-_d_e_v_i_c_e is needed.  The additional device
specifications are show below.

     pseudo-device  pty
     pseudo-device  loop
     pseudo-device  imp
     device         acc0      at uba? csr 0167600vector accrint accxint
     pseudo-device  ether
     device         ec0       at uba? csr 0164330vector ecrint eccollide ecxint
     device         il0       at uba? csr 0164000vector ilrint ilcint











Building NetBSD Kernels with Config   Command Reference Documents


The  completed configuration file for UCBVAX is shown in Appendix
C.

55..33..  MMiisscceellllaanneeoouuss ccoommmmeennttss

     It should be noted in these examples that neither system was
configured  to  use disk quotas or the 4.1BSD compatibility mode.
To use these optional facilities, and others, we  would  probably
clean out our current configuration, reconfigure the system, then
recompile and relink the system image(s).  This could, of course,
be  avoided  by  figuring  out which relocatable object files are
affected by the reconfiguration, then reconfiguring and recompil-
ing  only those files affected by the configuration change.  This
technique should be used carefully.

66..  AADDDDIINNGG NNEEWW SSYYSSTTEEMM SSOOFFTTWWAARREE

     This section is not for the novice, it describes some of the
inner workings of the configuration process as well as the perti-
nent parts  of  the  system  autoconfiguration  process.   It  is
intended  to  give  those people who intend to install new device
drivers and/or other system facilities sufficient information  to
do  so  in the manner which will allow others to easily share the
changes.

     This section is broken into four parts:

+o  general guidelines to be followed in modifying system code,

+o  how to add non-standard system facilities to NetBSD, and

+o  how to add a device driver to NetBSD.

66..11..  MMooddiiffyyiinngg ssyysstteemm ccooddee

     If you wish to make site-specific modifications to the  sys-
tem it is best to bracket them with

     #ifdef SITENAME
     ...
     #endif

to allow your source to be easily distributed to others, and also
to simplify _d_i_f_f(1) listings.  It is recommended  that  you  save
the old code with something of the form:

     #ifndef SITENAME
     ...
     #endif


     Machine-specific  code should be placed in existing machine-
specific files, or added as new files in machine-specific  source
directories.     The   use   of   machine-specific   preprocessor









Command Reference Documents   Building NetBSD Kernels with Config


conditionals is discouraged.

66..22..  AAddddiinngg nnoonn--ssttaannddaarrdd ssyysstteemm ffaacciilliittiieess

     This section considers the work needed to  augment  _c_o_n_f_i_g's
data  base files for non-standard system facilities.  _C_o_n_f_i_g uses
a set of files that list the source modules that may be  required
when  building  a system.  The data bases are taken from standard
locations    in    the    system    source     tree,     normally
``/usr/src/sys/conf''.   Three  such  files  may  be used: _f_i_l_e_s,
_f_i_l_e_s.machine, and _f_i_l_e_s.ident.  The first is common to all  sys-
tems,  the second contains files unique to a single machine type,
and the third is an optional list of modules for use  on  a  spe-
cific machine.  This last file may override specifications in the
first two.  The format of the _f_i_l_e_s file has grown somewhat  com-
plex over time.  Entries are normally of the form

     _d_i_r_/_s_o_u_r_c_e_._c   _t_y_p_e  _o_p_t_i_o_n_-_l_i_s_t _m_o_d_i_f_i_e_r_s

for example,

     _v_a_x_u_b_a_/_f_o_o_._c   ooppttiioonnaall  foo  ddeevviiccee--ddrriivveerr

The  _t_y_p_e  is one of ssttaannddaarrdd or ooppttiioonnaall.  Files marked as stan-
dard are included in all system  configurations.   Optional  file
specifications  include a list of one or more system options that
together require the inclusion of this module.   The  options  in
the  list  may be either names of devices that may be in the con-
figuration file, or the names  of  system  options  that  may  be
defined.  An optional file may be listed multiple times with dif-
ferent options; if all of the options for any of the entries  are
satisfied, the module is included.

     If  a file is specified as a _d_e_v_i_c_e_-_d_r_i_v_e_r, any special com-
pilation options for device drivers will be invoked.  On the  VAX
this  results  in  the  use of the --ii option for the C optimizer.
This is required when pointer references are made to memory loca-
tions in the VAX I/O address space.

     Two  other  optional  keywords modify the usage of the file.
_C_o_n_f_i_g understands that certain files  are  used  especially  for
kernel  profiling.   These files are indicated in the _f_i_l_e_s files
with a _p_r_o_f_i_l_i_n_g_-_r_o_u_t_i_n_e keyword.  For example, the current  pro-
filing  subroutines  are  sequestered off in a separate file with
the following entry:

     _s_y_s_/_s_u_b_r___m_c_o_u_n_t_._c   ooppttiioonnaall  pprrooffiilliinngg--rroouuttiinnee

The _p_r_o_f_i_l_i_n_g_-_r_o_u_t_i_n_e keyword forces _c_o_n_f_i_g not  to  compile  the
source file with the --ppgg option.

     The  second keyword which can be of use is the _c_o_n_f_i_g_-_d_e_p_e_n_-
_d_e_n_t keyword.  This causes _c_o_n_f_i_g to compile the indicated module
with  the  global  configuration parameters.  This allows certain









Building NetBSD Kernels with Config   Command Reference Documents


modules, such as _m_a_c_h_d_e_p_._c to size system data  structures  based
on the maximum number of users configured for the system.

66..33..  AAddddiinngg ddeevviiccee ddrriivveerrss ttoo NNeettBBSSDD

     The I/O system and _c_o_n_f_i_g have been designed to easily allow
new device support to be added.  The  system  source  directories
are organized as follows:


     /usr/src/sys/sys               machine independent include files
     /usr/src/sys/kern              machine-independent system source files
     /usr/src/sys/conf              machine-independent configuration data
     /usr/src/sys/net               network-protocol-independent, but network-related code
     /usr/src/sys/netinet           DARPA Internet code
     /usr/src/sys/dev               machine-independent device drivers
     /usr/src/sys/arch              machine-dependent code
     /usr/src/sys/arch/amd64        machine-dependent code for 64-bit x86
     /usr/src/sys/arch/i386         machine-dependent code for 32-bit x86
     /usr/src/sys/arch/x86          machine-dependent code shared between x86 types
     /usr/src/sys/arch/amd64/conf   site configuration files and basic templates
     (and so on)



     Existing  block  and  character  device  drivers for the VAX
reside in ``/usr/src/sys/dev''.  Any new device drivers should be
placed  in  the appropriate source code directory and named so as
not to conflict with existing devices.  Normally, definitions for
things like device registers are placed in a separate file in the
same directory.  For example,  the  ``auixp''  device  driver  is
named  ``auixp.c''  and  its  associated  include  file  is named
``auixpreg.h''. There is also an  ``auixpvar.h''  which  contains
data  structures  and other external declarations that the driver
needs to expose.

     Once the source for the device driver has been placed  in  a
directory,  the  file ``/usr/src/sys/conf/files'' should be modi-
fied.  The _f_i_l_e_s files in the conf directory contain a  line  for
each  C  source  or  binary-only file in the system.  Those files
which    are    machine    independent     are     located     in
``/usr/src/sys/conf/files,'' while machine specific files for the
``foo''  port  are  in  ``/usr/src/sys/arch/foo/conf/files.foo''.
The  ``devices.foo''  file  is  used to map device names to major
block device numbers.  If the device driver being added  provides
support  for  a  new  disk you will want to modify this file (the
format is obvious).

     In addition to including the driver in the  _f_i_l_e_s  file,  it
must also be added to the device configuration tables.  These are
located in ``/sys/vax/conf.c'', or  similar  for  machines  other
than  the VAX.  If you don't understand what to add to this file,
you should study an entry for an existing driver.  Remember  that
the  position  in  the  device  table  specifies the major device









Command Reference Documents   Building NetBSD Kernels with Config


number.    The   block   major   number   is   needed   in    the
``devices.machine'' file if the device is a disk.

     With the configuration information in place, your configura-
tion file appropriately modified, and a system  reconfigured  and
rebooted  you  should  incorporate  the  shell commands needed to
install the  special  files  in  the  file  system  to  the  file
``/dev/MAKEDEV'' or ``/dev/MAKEDEV.local''.  This is discussed in
the document ``Installing and Operating 4.4BSD''.






















































Building NetBSD Kernels with Config   Command Reference Documents


             AAPPPPEENNDDIIXX AA.. CCOONNFFIIGGUURRAATTIIOONN FFIILLEE GGRRAAMMMMAARR


     The following grammar is a compressed  form  of  the  actual
_y_a_c_c(1)  grammar  used  by  _c_o_n_f_i_g  to parse configuration files.
Terminal symbols are  shown  all  in  upper  case,  literals  are
emboldened;  optional clauses are enclosed in brackets, ``['' and
``]'';  zero or more instantiations are denoted with ``*''.

Configuration ::=  [ Spec ;; ]*

Spec ::= Config_spec
     | Device_spec
     | ttrraaccee
     | /* lambda */

/* configuration specifications */

Config_spec ::=  mmaacchhiinnee ID
     | ccppuu ID
     | ooppttiioonnss Opt_list
     | iiddeenntt ID
     | System_spec
     | ttiimmeezzoonnee [ -- ] NUMBER [ ddsstt [ NUMBER ] ]
     | ttiimmeezzoonnee [ -- ] FPNUMBER [ ddsstt [ NUMBER ] ]
     | mmaaxxuusseerrss NUMBER

/* system configuration specifications */

System_spec ::= ccoonnffiigg ID System_parameter [ System_parameter ]*

System_parameter ::=  swap_spec | root_spec | dump_spec | arg_spec

swap_spec ::=  sswwaapp [ oonn ] swap_dev [ aanndd swap_dev ]*

swap_dev ::=  dev_spec [ ssiizzee NUMBER ]

root_spec ::=  rroooott [ oonn ] dev_spec

dump_spec ::=  dduummppss [ oonn ] dev_spec

arg_spec ::=  aarrggss [ oonn ] dev_spec

dev_spec ::=  dev_name | major_minor

major_minor ::=  mmaajjoorr NUMBER mmiinnoorr NUMBER

dev_name ::=  ID [ NUMBER [ ID ] ]

/* option specifications */

Opt_list ::=  Option [ ,, Option ]*

Option ::=  ID [ == Opt_value ]









Command Reference Documents   Building NetBSD Kernels with Config


Opt_value ::=  ID | NUMBER

Mkopt_list ::=  Mkoption [ ,, Mkoption ]*

Mkoption ::=  ID == Opt_value

/* device specifications */

Device_spec ::= ddeevviiccee Dev_name Dev_info Int_spec
     | mmaasstteerr Dev_name Dev_info
     | ddiisskk Dev_name Dev_info
     | ttaappee Dev_name Dev_info
     | ccoonnttrroolllleerr Dev_name Dev_info [ Int_spec ]
     | ppsseeuuddoo--ddeevviiccee Dev [ NUMBER ]

Dev_name ::=  Dev NUMBER

Dev ::=  uubbaa | mmbbaa | ID

Dev_info ::=  Con_info [ Info ]*

Con_info ::=  aatt Dev NUMBER
     | aatt nneexxuuss NUMBER

Info ::=  ccssrr NUMBER
     | ddrriivvee NUMBER
     | ssllaavvee NUMBER
     | ffllaaggss NUMBER

Int_spec ::=  vveeccttoorr ID [ ID ]*
     | pprriioorriittyy NUMBER


LLeexxiiccaall CCoonnvveennttiioonnss

The terminal symbols are loosely defined as:

ID
     One or more alphabetics, either upper  or  lower  case,  and
     underscore, ``_''.

NUMBER
     Approximately  the  C  language specification for an integer
     number.  That is, a leading ``0x'' indicates  a  hexadecimal
     value,  a  leading ``0'' indicates an octal value, otherwise
     the number is expected to be a decimal  value.   Hexadecimal
     numbers may use either upper or lower case alphabetics.

FPNUMBER
     A  floating point number without exponent.  That is a number
     of the form ``nnn.ddd'', where the fractional  component  is
     optional.











Building NetBSD Kernels with Config   Command Reference Documents


In  special  instances a question mark, ``?'', can be substituted
for a ``NUMBER'' token.  This is used to  effect  wildcarding  in
device interconnection specifications.

Comments  in configuration files are indicated by a ``#'' charac-
ter at the beginning of the line; the remainder of  the  line  is
discarded.

A  specification is interpreted as a continuation of the previous
line if the first character of the line is tab.





















































Command Reference Documents   Building NetBSD Kernels with Config


         AAPPPPEENNDDIIXX BB.. RRUULLEESS FFOORR DDEEFFAAUULLTTIINNGG SSYYSSTTEEMM DDEEVVIICCEESS


     When _c_o_n_f_i_g processes a ``config'' rule which does not fully
specify  the  location  of  the root file system, paging area(s),
device for system dumps, and device for argument list  processing
it  applies  a  set of rules to define those values left unspeci-
fied.  The following list of rules are used in defaulting  system
devices.

1) If a root device is not specified, the swap specification must
   indicate a ``generic'' system is to be built.

2) If the root device does not specify a unit number, it defaults
   to unit 0.

3) If the root device does not include a partition specification,
   it defaults to the ``a'' partition.

4) If no swap area is specified, it defaults to the ``b''  parti-
   tion of the root device.

5) If  no  device is specified for processing argument lists, the
   first swap partition is selected.

6) If no device is chosen for system dumps, the first swap parti-
   tion is selected (see below to find out where dumps are placed
   within the partition).

     The  following  table  summarizes  the  default   partitions
selected when a device specification is incomplete, e.g. ``hp0''.


     Type    Partition
     ------------------
     root    ``a''
     swap    ``b''
     args    ``b''
     dumps   ``b''



MMuullttiippllee sswwaapp//ppaaggiinngg aarreeaass

     When multiple swap  partitions  are  specified,  the  system
treats  the  first  specified as a ``primary'' swap area which is
always used.  The remaining partitions are then interleaved  into
the  paging  system  at the time a _s_w_a_p_o_n(2) system call is made.
This is normally done at boot time with a call to _s_w_a_p_o_n(8)  from
the /etc/rc file.













Building NetBSD Kernels with Config   Command Reference Documents


SSyysstteemm dduummppss

     System  dumps  are automatically taken after a system crash,
provided the device driver  for  the  ``dumps''  device  supports
this.  The dump contains the contents of memory, but not the swap
areas.  Normally the dump device is a  disk  in  which  case  the
information is copied to a location at the back of the partition.
The dump is placed in the back of the partition because the  pri-
mary  swap  and dump device are commonly the same device and this
allows the system to be rebooted without immediately  overwriting
the  saved  information.   When  a  dump has occurred, the system
variable _d_u_m_p_s_i_z_e is set to a non-zero value indicating the  size
(in  bytes) of the dump.  The _s_a_v_e_c_o_r_e(8) program then copies the
information from the dump partition to  a  file  in  a  ``crash''
directory  and  also makes a copy of the system which was running
at the time of the crash (usually ``/kernel'').   The  offset  to
the  system dump is defined in the system variable _d_u_m_p_l_o (a sec-
tor offset from the front of the dump partition).   The  _s_a_v_e_c_o_r_e
program  operates by reading the contents of _d_u_m_p_l_o, _d_u_m_p_d_e_v, and
_d_u_m_p_m_a_g_i_c from /dev/kmem, then comparing the value  of  _d_u_m_p_m_a_g_i_c
read  from /dev/kmem to that located in corresponding location in
the dump area of the  dump  partition.   If  a  match  is  found,
_s_a_v_e_c_o_r_e  assumes  a  crash  occurred and reads _d_u_m_p_s_i_z_e from the
dump area of the dump partition.  This  value  is  then  used  in
copying  the system dump.  Refer to _s_a_v_e_c_o_r_e(8) for more informa-
tion about its operation.

     The value _d_u_m_p_l_o is calculated to be

     _d_u_m_p_d_e_v_-_s_i_z_e - _m_e_m_s_i_z_e

where _d_u_m_p_d_e_v_-_s_i_z_e is the size of the disk partition where system
dumps  are to be placed, and _m_e_m_s_i_z_e is the size of physical mem-
ory.  If the disk partition is not large enough to  hold  a  full
dump, _d_u_m_p_l_o is set to 0 (the start of the partition).




























Command Reference Documents   Building NetBSD Kernels with Config


             AAPPPPEENNDDIIXX CC.. SSAAMMPPLLEE CCOONNFFIIGGUURRAATTIIOONN FFIILLEESS


     The  following  configuration files are developed in section
5; they are included here for completeness.


#
# ANSEL VAX (a picture perfect machine)
#
machine        vax
cpu            VAX780
timezone       8 dst
ident          ANSEL
maxusers       40

config         kernel    root on hp0
config         hpkernel  root on hp0 swap on hp0 and hp2
config         genkernel swap generic

controller     mba0      at nexus ?
disk           hp0       at mba? disk ?
disk           hp1       at mba? disk ?
controller     mba1      at nexus ?
disk           hp2       at mba? disk ?
disk           hp3       at mba? disk ?
controller     uba0      at nexus ?
controller     tm0       at uba? csr 0172520vector tmintr
tape           te0       at tm0 drive 0
tape           te1       at tm0 drive 1
device         dh0       at uba? csr 0160020vector dhrint dhxint
device         dm0       at uba? csr 0170500vector dmintr
device         dh1       at uba? csr 0160040vector dhrint dhxint
device         dh2       at uba? csr 0160060vector dhrint dhxint





























Building NetBSD Kernels with Config   Command Reference Documents


#
# UCBVAX - Gateway to the world
#
machine        vax
cpu            "VAX780"
cpu            "VAX750"
ident          UCBVAX
timezone       8 dst
maxusers       32
options        INET
options        NS

config         kernel    root on hp swap on hp and rk0 and rk1
config         upkernel  root on up
config         hkkernel  root on hk swap on rk0 and rk1

controller     mba0      at nexus ?
controller     uba0      at nexus ?
disk           hp0       at mba? drive 0
disk           hp1       at mba? drive 1
controller     sc0       at uba? csr 0176700vector upintr
disk           up0       at sc0 drive 0
disk           up1       at sc0 drive 1
controller     hk0       at uba? csr 0177440vector rkintr
disk           rk0       at hk0 drive 0
disk           rk1       at hk0 drive 1
pseudo-device  pty
pseudo-device  loop
pseudo-device  imp
device         acc0      at uba? csr 0167600vector accrint accxint
pseudo-device  ether
device         ec0       at uba? csr 0164330vector ecrint eccollide ecxint
device         il0       at uba? csr 0164000vector ilrint ilcint






























Command Reference Documents   Building NetBSD Kernels with Config


       AAPPPPEENNDDIIXX DD.. VVAAXX KKEERRNNEELL DDAATTAA SSTTRRUUCCTTUURREE SSIIZZIINNGG RRUULLEESS


     Certain system data structures are  sized  at  compile  time
according  to  the maximum number of simultaneous users expected,
while others are calculated at boot time based  on  the  physical
resources present, e.g. memory.  This appendix lists both sets of
rules and also includes some hints on changing  built-in  limita-
tions on certain data structures.

CCoommppiillee ttiimmee rruulleess

     The  file  _/_s_y_s_/_c_o_n_f_/_p_a_r_a_m_._c  contains  the  definitions  of
almost all data structures sized at compile time.  This  file  is
copied into the directory of each configured system to allow con-
figuration-dependent rules and values to  be  maintained.   (Each
copy  normally depends on the copy in /sys/conf, and global modi-
fications cause the file to be recopied unless  the  makefile  is
modified.)   The  rules  implied  by  its contents are summarized
below (here MAXUSERS refers to the value defined in the  configu-
ration  file in the ``maxusers'' rule).  Most limits are computed
at compile time and stored in global variables for use  by  other
modules; they may generally be patched in the system binary image
before rebooting to test new values.

nnpprroocc
     The maximum number of processes which may be running at  any
     time.   It is referred to in other calculations as NPROC and
     is defined to be

          20 + 8 * MAXUSERS


nntteexxtt
     The maximum number of active shared text segments.  The con-
     stant  is  intended  to allow for network servers and common
     commands that remain in the table.  It is defined as

          36 + MAXUSERS.


nniinnooddee
     The maximum number of files in the file system which may  be
     active at any time.  This includes files in use by users, as
     well as directory files being read or written by the  system
     and  files  associated  with  bound  sockets in the UNIX IPC
     domain.  It is defined as

          (NPROC + 16 + MAXUSERS) + 32


nnffiillee
     The number of ``file table''  structures.   One  file  table
     structure  is used for each open, unshared, file descriptor.









Building NetBSD Kernels with Config   Command Reference Documents


     Multiple file descriptors may reference a single file  table
     entry  when  they  are created through a _d_u_p call, or as the
     result of a _f_o_r_k.  This is defined to be

          16 * (NPROC + 16 + MAXUSERS) / 10 + 32


nnccaalllloouutt
     The number of ``callout'' structures.  One callout structure
     is  used  per  internal system event handled with a timeout.
     Timeouts are used for terminal delays, watchdog routines  in
     device  drivers,  protocol timeout processing, etc.  This is
     defined as

          16 + NPROC


nncclliisstt
     The number of ``c-list'' structures.  C-list structures  are
     used  in  terminal  I/O, and currently each holds 60 charac-
     ters.  Their number is defined as

          60 + 12 * MAXUSERS


nnmmbbcclluusstteerrss
     The maximum number of pages which may be  allocated  by  the
     network.  This is defined as 256 (a quarter megabyte of mem-
     ory) in /sys/h/mbuf.h.  In practice, the network rarely uses
     this  much  memory.  It starts off by allocating 8 kilobytes
     of memory, then requesting more  as  required.   This  value
     represents an upper bound.

nnqquuoottaa
     The  number of ``quota'' structures allocated.  Quota struc-
     tures are present only when disc quotas  are  configured  in
     the  system.  One quota structure is kept per user.  This is
     defined to be

          (MAXUSERS * 9) / 7 + 3


nnddqquuoott
     The number of ``dquot'' structures allocated.  Dquot  struc-
     tures  are  present  only when disc quotas are configured in
     the system.  One dquot structure is required per  user,  per
     active  file system quota.  That is, when a user manipulates
     a file on a file system on which  quotas  are  enabled,  the
     information  regarding the user's quotas on that file system
     must be in-core.  This information is cached,  so  that  not
     all  information must be present in-core all the time.  This
     is defined as











Command Reference Documents   Building NetBSD Kernels with Config


          NINODE + (MAXUSERS * NMOUNT) / 4

     where NMOUNT is the maximum number of  mountable  file  sys-
     tems.

In  addition to the above values, the system page tables (used to
map virtual memory in the kernel's address space)  are  sized  at
compile   time   by   the   SYSPTSIZE   definition  in  the  file
/sys/vax/vmparam.h.  This is defined to be

     20 + MAXUSERS

pages of page tables.  Its definition affects the  size  of  many
data  structures allocated at boot time because it constrains the
amount of virtual memory which may be addressed  by  the  running
system.   This  is  often  the limiting factor in the size of the
buffer cache, in which case a message is printed when the  system
configures at boot time.

RRuunn--ttiimmee ccaallccuullaattiioonnss

     The  most  important  data  structures sized at run-time are
those used in the buffer cache.  Allocation is done by allocating
physical memory (and system virtual memory) immediately after the
system has been started up; look in the file  /sys/vax/machdep.c.
The  amount  of  physical  memory  which  may be allocated to the
buffer cache is constrained  by  the  size  of  the  system  page
tables,  among  other  things.   While the system may calculate a
large amount of memory to be allocated to the  buffer  cache,  if
the  system  page  table is too small to map this physical memory
into the virtual address space of the system, only as much as can
be mapped will be used.

     The  buffer cache is comprised of a number of ``buffer head-
ers'' and a pool of pages  attached  to  these  headers.   Buffer
headers  are divided into two categories: those used for swapping
and paging, and those used for normal file I/O.  The system tries
to  allocate 10% of the first two megabytes and 5% of the remain-
ing available physical memory for the buffer cache (where  _a_v_a_i_l_-
_a_b_l_e  does not count that space occupied by the system's text and
data segments).  If this results in fewer than 16 pages of memory
allocated,  then  16  pages are allocated.  This value is kept in
the initialized variable _b_u_f_p_a_g_e_s so that it may  be  patched  in
the  binary  image  (to allow tuning without recompiling the sys-
tem), or the default may be overridden with a  configuration-file
option.   For  example, the option ooppttiioonnss BBUUFFPPAAGGEESS==""33220000"" causes
3200 pages (3.2M bytes) to be used by the buffer cache.  A suffi-
cient  number  of  file  I/O buffer headers are then allocated to
allow each to hold 2 pages each.  Each buffer maps 8K bytes.   If
the  number  of  buffer pages is larger than can be mapped by the
buffer headers, the number of pages is reduced.   The  number  of
buffer  headers  allocated is stored in the global variable _n_b_u_f,
which may be patched before the system  is  booted.   The  system
option  ooppttiioonnss  NNBBUUFF==""11000000"" forces the allocation of 1000 buffer









Building NetBSD Kernels with Config   Command Reference Documents


headers.  Half as many  swap  I/O  buffer  headers  as  file  I/O
buffers are allocated, but no more than 256.

SSyysstteemm ssiizzee lliimmiittaattiioonnss

     As  distributed,  the  sum of the virtual sizes of the core-
resident processes is limited to 256M bytes.   The  size  of  the
text  segment  of  a  single  process  is currently limited to 6M
bytes.  It may be increased to no greater than the  data  segment
size  limit  (see below) by redefining MAXTSIZ.  This may be done
with  a   configuration   file   option,   e.g.   ooppttiioonnss   MMAAXXTT--
SSIIZZ==""((1100**11002244**11002244))"" to set the limit to 10 million bytes.  Other
per-process limits discussed here may  be  changed  with  similar
options  with  names given in parentheses.  Soft, user-changeable
limits are set to 512K bytes for stack (DFLSSIZ) and 6M bytes for
the  data segment (DFLDSIZ) by default; these may be increased up
to the hard limit with the _s_e_t_r_l_i_m_i_t(2) system  call.   The  data
and stack segment size hard limits are set by a system configura-
tion option to one of 17M, 33M or 64M bytes.  One of these  sizes
is chosen based on the definition of MAXDSIZ; with no option, the
limit   is   17M   bytes;   with   an   option   ooppttiioonnss    MMAAXXDD--
SSIIZZ==""((3322**11002244**11002244))""  (or  any  value  between  17M and 33M), the
limit is increased to 33M  bytes,  and  values  larger  than  33M
result  in  a  limit  of 64M bytes.  You must be careful in doing
this that you have adequate paging space.  As normally configured
,  the  system has 16M or 32M bytes per paging area, depending on
disk size.  The best way to get more space is to  provide  multi-
ple,  thereby  interleaved, paging areas.  Increasing the virtual
memory limits results in interleaving of  swap  space  in  larger
sections (from 500K bytes to 1M or 2M bytes).

     By  default, the virtual memory system allocates enough mem-
ory for system page tables mapping user page tables to allow  256
megabytes  of  simultaneous  active virtual memory.  That is, the
sum of the virtual memory  sizes  of  all  (completely-  or  par-
tially-)  resident  processes  can not exceed this limit.  If the
limit is exceeded, some process(es)  must  be  swapped  out.   To
increase  the  amount of resident virtual space possible, you can
alter the constant USRPTSIZE (in /sys/vax/vmparam.h).  Each  page
of  system page tables allows 8 megabytes of user virtual memory.

     Because the file system block numbers are stored in page ta-
ble  _p_g___b_l_k_n_o  entries, the maximum size of a file system is lim-
ited to 2^24 1024 byte blocks.  Thus no file system can be larger
than 8 gigabytes.

     The  number  of  mountable  file systems is set at 20 by the
definition of NMOUNT in /sys/h/param.h.  This  should  be  suffi-
cient; if not, the value can be increased up to 255.  If you have
many disks, it makes sense to make some of them single file  sys-
tems, and the paging areas don't count in this total.

     The  limit  to  the  number of files that a process may have
open simultaneously is set to 64.   This  limit  is  set  by  the









Command Reference Documents   Building NetBSD Kernels with Config


NOFILE  definition  in /sys/h/param.h.  It may be increased arbi-
trarily, with the caveat that the user  structure  expands  by  5
bytes  for each file, and thus UPAGES (/sys/vax/machparam.h) must
be increased accordingly.

     The amount of physical memory is currently limited to 64  Mb
by  the size of the index fields in the core-map (/sys/h/cmap.h).
The limit may be increased by following instructions in that file
to enlarge those fields.






















































Building NetBSD Kernels with Config   Command Reference Documents


            AAPPPPEENNDDIIXX EE.. NNEETTWWOORRKK CCOONNFFIIGGUURRAATTIIOONN OOPPTTIIOONNSS


     The  network  support  in  the  kernel  is  self-configuring
according to the protocol support options (INET and NS)  and  the
network  hardware discovered during autoconfiguration.  There are
several changes that may be made to  customize  network  behavior
due  to  local  restrictions.   Within the Internet protocol rou-
tines, the following options set in the system configuration file
are supported:

GGAATTEEWWAAYY
     The  machine  is  to be used as a gateway.  This option cur-
     rently makes only minor changes.  First,  the  size  of  the
     network routing hash table is increased.  Secondly, machines
     that have only a single hardware network interface will  not
     forward  IP  packets;  without  this  option, they will also
     refrain from sending any error indication to the  source  of
     unforwardable  packets.   Gateways with only a single inter-
     face are assumed to have missing or broken  interfaces,  and
     will  return  ICMP  unreachable errors to hosts sending them
     packets to be forwarded.

TTCCPP__CCOOMMPPAATT__4422
     This option forces the  system  to  limit  its  initial  TCP
     sequence  numbers to positive numbers.  Without this option,
     4.4BSD systems may have problems  with  TCP  connections  to
     4.2BSD  systems  that  connect but never transfer data.  The
     problem is a bug in the 4.2BSD TCP.

IIPPFFOORRWWAARRDDIINNGG
     Normally, 4.4BSD machines with multiple  network  interfaces
     will  forward  IP  packets received that should be resent to
     another host.  If the line ``options  IPFORWARDING="0"''  is
     in  the system configuration file, IP packet forwarding will
     be disabled.

IIPPSSEENNDDRREEDDIIRREECCTTSS
     When forwarding IP packets,  4.4BSD  IP  will  note  when  a
     packet  is  forwarded  using  the same interface on which it
     arrived.  When this is noted, if the source  machine  is  on
     the  directly-attached  network, an ICMP redirect is sent to
     the source host.  If the packet was forwarded using a  route
     to a host or to a subnet, a host redirect is sent, otherwise
     a network redirect is sent.  The generation of redirects may
     be   inhibited   with  the  configuration  option  ``options
     IPSENDREDIRECTS="0".''

SSUUBBNNEETTSSAARREELLOOCCAALL
     TCP calculates a maximum segment size to use for  each  con-
     nection, and sends no datagrams larger than that size.  This
     size will be no larger than that supported on  the  outgoing
     interface.   Furthermore,  if  the destination is not on the
     local network, the size will be no larger  than  576  bytes.









Command Reference Documents   Building NetBSD Kernels with Config


     For this test, other subnets of a directly-connected subnet-
     ted network are considered  to  be  local  unless  the  line
     ``options  SUBNETSARELOCAL="0"''  is used in the system con-
     figuration file.

The following options are supported by the Xerox NS protocols:

NNSSIIPP
     This option allows NS IDP datagrams to  be  encapsulated  in
     Internet IP packets for transmission to a collaborating NSIP
     host.  This may be used to pass IDP packets through  IP-only
     link layer networks.  See _n_s_i_p(4P) for details.

TTHHRREEEEWWAAYYSSHHAAKKEE
     The  NS  Sequenced Packet Protocol does not require a three-
     way handshake before considering a connection to be  in  the
     established  state.   (A  three-way  handshake consists of a
     connection request, an acknowledgement of the request  along
     with  a symmetrical opening indication, and then an acknowl-
     edgement of the reciprocal  opening  packet.)   This  option
     forces  a three-way handshake before data may be transmitted
     on Sequenced Packet sockets.






































