[review request] New config.5 manual page

[Joseph Koshy]

The attached manual page documents the syntax for the kernel configuration
files as understood by the config(8) program in 5-CURRENT.  This syntax has 
diverged from the syntax understood by the original 4.4BSD config(8) program,
and it is perhaps time for a new manual page.

This manual entry is to be added to section 5 (file formats) of the 
FreeBSD manual.

Could you please review and send in your comments?

----
Joseph Koshy                           <jkoshy at freebsd.org>
Developer, The FreeBSD Project         http://people.freebsd.org/~jkoshy/
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.\" Copyright (c) 2003	Joseph Koshy
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.\" $FreeBSD: src/share/man/man5/quota.user.5,v 1.3 2002/12/12 17:25:57 ru Exp 
$
.\"
.Dd June 03, 2003
.Dt CONFIG 5
.Os
.Sh NAME
.Nm config
.Nd kernel configuration file format
.Sh DESCRIPTION
A kernel configuration file specifies the configuration of a
.Fx
kernel.
It is processed by
.Xr config 8
to create a build environment where a kernel may be built using
.Xr make 1 .
.Sh LEXICAL STRUCTURE
A kernel configuration file comprises a sequence of specification
directives.
.Pp
A specification directive starts with a keyword at the beginning
of the line and is followed by additional parameters.
.Pp
A specification directive may be terminated by a semicolon
.Ql \&;
or by a newline.
Long input lines may be broken into shorter lines by
starting the second and subsequent lines with a white
space character.
.Pp
Case is significant,
.Ql machine
and
.Ql MACHINE
are different tokens.
.Pp
A double quote character
.Ql \&\*q
starts a quoted string.
All characters up to the next quote character form the value
of the quoted string.
A
.Ql \&\*q
character may be inserted into a quoted string by
using the sequence
.Ql \e\*q .
.Pp
Number are specified using
.Li C Ns No -style
syntax.
.Pp
A
.Ql #
character starts a comment; all characters from the
.Ql #
character till end of line are ignored.
.Pp
Whitespace between tokens is ignored, except inside quoted strings.
Whitespace following a comment line is ignored.
.Sh CONFIGURATION DIRECTIVES
Kernel configuration directives may appear in any order
in a kernel configuration file.
Directives are processed in order of appearance with subsequent
directive lines overriding the effect of prior ones.
.Pp
The list of keywords and their meanings are as follows:
.Bl -tag -width "makeoptions"
.\" -------- CPU --------
.It Cm cpu Ar cputype
Specify the CPU this kernel will run on.
There can be more than one
.Li cpu
directives in a configuration file.
The allowed list of cpu names is architecture specific and is
defined in the file
.Pa "sys/conf/options." Ns Ar arch .
.\" -------- DEVICE --------
.It Cm device Ar name Op count
Configures device
.Ar name
for inclusion into the kernel image.
If
.Ar count
is specified, the device is configured for
.Ar count
instances.
The list of valid device names is architecture specific and are
defined in the files
.Pa "sys/conf/files"
and
.Pa "sys/conf/files." Ns Ar arch .
.\" -------- ENV --------
.It Cm env Ar filename
Specifies a filename containing a kernel environment definition.
The kernel normally uses an environment prepared for it at boot time
by
.Xr loader 8 .
This directive makes the kernel ignore the boot environment and use
the compiled in environment instead.
.Pp
This directive is useful for setting kernel tunables in
embedded environments that do not start from
.Xr loader 8 .
.\" -------- HINTS --------
.It Cm hints Ar filename
Specifies a file to load a static device configuration specification
from.
From
.Fx 5.0
onwards, the kernel picks up the device configuration at boot time
(see
.Xr device.hints 5 Ns ).
This directive configures the kernel to use the static device configuration
listed in
.Ar filename.
.Ar filename
must conform to
.Xr device.hints 5
syntax.
.\" -------- IDENT --------
.It Cm ident Ar name
Set the kernel name to
.Ar name .
At least one
.Cm ident
directive is required.
.\" -------- INCLUDE --------
.It Cm include Ar filename
Read subsequent text from file
.Ar filename
and return to the current file after
.Ar filename
is successfully processed.
.\" -------- MACHINE --------
.It Cm machine Ar arch
Specifies the architecture of the machine the kernel is being
compiled for.
Legal values for
.Ar arch
include:
.Bl -hang -compact
.It alpha
The DEC Alpha architecture.
.It amd64
The AMD x86-64 architecture.
.It i386
The IBM PC architecture.
.It ia64
The Intel IA64 architecture.
.It pc98
The pc96 architecture.
.It powerpc
The IBM PowerPC architecture.
.It sparc64
The Sparc64 architecture.
.El
.Pp
At least one machine architecture must be specified.
.\" -------- MAKEOPTION --------
.It Cm makeoptions Ar options
Add
.Ar options
to the generated makefile.
.Pp
.Ar options
is a comma separated list of one or more option
specifications.
Each option specification has the form
.D1 Ar MakeVariableName Op = Ar Value
and results in the appropriate
.Xr make 1
variable definition
being inserted into the generated makefile.
If only the name of the
.Xr make 1
variable is specified,
.Ar value
is assumed to be the empty string.
.Pp
Example:
.Bd -unfilled -offset indent -compact
.Li makeoptions MYOPTION = \*qfoobar\*q
.Li makeoptions MYNULLOPTION
.Ed
.\" -------- MAXUSERS --------
.It Cm maxusers Ar number
This optional directive is used to configure the size
of some kernel data structures.
.Ar number
should be an integer between 2 and 512, or can
be 0.
From
.Fx 4.5
onwards, the kernel will automatically size its tables
according to the available physical memory if
.Cm maxusers
is not specified or is specified to be 0.
As explained in
.Xr tuning 7 ,
this tunable can also be set on a running kernel
using
.Xr sysctl 8 .
.\" -------- NOMAKEOPTION --------
.It Cm nomakeoption Ar name
Removes previously defined
.Xr make 1
option
.Ar name
from the kernel build.
.\" -------- NOOPTION --------
.It Cm nooption Ar kerneloptionname
Remove kernel option
.Ar kerneloptionname
from the list of previously defined options.
.\" -------- OPTIONS --------
.It Cm options Ar optionspecs
Add compile time kernel options to the kernel build.
.Ar optionspecs
is a comma separated list of option specifications.
Each option specification has the form
.D1 Ar KernelOptionName Op = Ar OptionValue
If
.Ar OptionValue
is not specified, it is assumed to be NULL.
The list of allowed options is architecture specific and
are specified in the files
.Pa "sys/conf/options"
and
.Pa "sys/conf/options." Ns Ar arch .
.\" -------- PROFILE --------
.It Cm profile Ar number
Enables kernel profiling if
.Ar number
is non-zero.
If
.Ar number
is 2 or greater, the kernel is configured for
high-resolution profiling.
Kernels can also be built for profiling using the
.Fl -p
option to
.Xr config 8 .
.El
.Sh OBSOLETE DIRECTIVES
The following kernel configuration directives are obsolete.
.Bl -tag -width "makeoptions" -compact
.\" -------- CONFIG --------
.It Cm config
This directive was used to specify the device to be used for the root
filesystem.
From
.Fx 4.0
onwards, this information is passed to a booting kernel by
.Xr loader 8 .
.El
.Sh FILES
.Bl -tag -width "XXXXXXXXXXXXXXXXXXXXXXXXX" -compact
.It Pa "sys/compile/" Ns Ar NAME
Compile directory created from a kernel configuration.
.It Pa "sys/conf/Makefile." Ns Ar arch
Architecture specific
.Pa Makefile
fragments.
.It Pa "sys/conf/files"
Devices common to all architectures.
.It Pa "sys/conf/files." Ns Ar arch
Devices for architecture
.Ar arch .
.It Pa "sys/conf/options"
Options common to all architectures.
.It Pa "sys/conf/options." Ns Ar arch
Options for architecture
.Ar arch .
.El
.Sh SEE ALSO
.Xr kenv 1 ,
.Xr make 1 ,
.Xr device.hints 5 ,
.Xr loader.conf 5 ,
.Xr config 8 ,
.Xr kldload 8 ,
.Xr loader 8
.Rs
.%T "Building 4.4BSD Kernels with Config"
.%A Samuel J. Leffler
.%A Michael J. Karels
.Re
.Sh HISTORY
.Xr config 8
first appeared in
.Bx 4.1 ,
and was subsequently revised in
.Bx 4.4 .
The
.Fx
the kernel configuration mechanism changed further in
.Fx 4.0
and
.Fx 5.0 ,
moving towards an architecture supporting dynamic (boot time
and runtime) kernel configuration.