.TH CONF 9
.SH NAME
conf \- native and hosted kernel configuration file
.SH DESCRIPTION
Plan 9 kernels are built for a given target
.I platform
using platform-specific code in directory
.BI /sys/src/9/ platform
and portable code in
.BR /sys/src/9/port ,
.B /sys/src/9/ip
and elsewhere.
Existing
.I platforms
include
.B alphapc
for the DEC Alpha,
.B iPAQ
for the Compaq iPAQ,
.B pc
for the Intel x86,
and
.B ppc
for the IBM/Motorola PowerPC.
Each
.I platform
can have several different kernels with different configurations.
A given configuration is built in the platform's directory using the
.IR mk (1)
command:
.IP
.EX
mk 'CONF=\fIconf\fP'
.EE
.PP
where
.I conf
is a text file that specifies drivers, protocols and other parameters for that
particular kernel:
a parts list.
The result of a successful
.I mk
is
an executable or bootable file with a name determined by the
.IR platform 's
.BR mkfile ,
typically
.BI 9 conf.
.PP
A kernel configuration file has several sections of the form
.IP
.EX
.I "label"
.IR "	item" " [ " "subitem ..." " ]"
\&	...
.EE
.PP
Each section begins with a
.I label
at the start of a line, which names a configuration
category, followed by
a list of each
.I item
to select from that category,
one line per item, with white space (ie, blank or tab) at the start of the line.
An
.I item
line can optionally list one or more
.I subitems
that must be included in the kernel to support it.
A line that starts with a
.L #
is a comment.
Empty lines are ignored.
.PP
.I Labels
are chosen from the following set, listed in the order
in which they conventionally appear in a configuration file:
.TF etherxx
.TP
.B dev
Device drivers
.TP
.B ip
IP protocols (native kernels only) taken from
.B ../ip
.TP
.B link
Hardware-specific parts of device drivers.
.TP
.B misc
Architecture-specific files; specific VGA and SCSI interfaces
.TP
.B lib
Libraries to link with the kernel
.TP
.B port
C code and declarations to include as-is in the generated configuration file
.TP
.B boot
Configuration for
.IR boot (8)
.TP
.B bootdir
List of files and directories to put in the
.B boot
directory of
.IR root (3).
.PD
.PP
When an
.I item
is listed
under a given
.I label
it causes a corresponding component to be included in the kernel.
The details depend on the
.IR label ,
as discussed below.
Each
.I subitem
represents a kernel subcomponent required by the corresponding
.IR item .
Both items and subitems can be either portable (platform-independent)
or platform-specific.
The source file for a given item or subitem
is sought in the platform-directory
(for platform-specific code), and
in directories
.BR ../port
and
.BR ../ip ,
under control of the platform's
.BR mkfile
and
.B ../port/portmkfile
(which is included by
.BR mkfile ).
Resulting object files are left in the
.I platform
directory.
.PP
Outside the
.B dev
section,
each item and subitem
.I x
causes the kernel image to include the code compiled from
.IB x .c ,
(or
.IB x .s
for assembly-language support),
or
.IB portdir / x .c ,
where
.I portdir
is one of the portable directories mentioned above.
In the
.B dev
section, an item
.I x
corresponds instead to the driver source file
.BI dev x .c
in the current (platform-specific)
directory or a portable driver
.IB portdir /dev x .c .
Subitems are handled as in any other section.
Typically they are auxiliary files that are needed by the associated driver.
.PP
For instance, in a native kernel
the portable driver for the
.B draw
device uses platform-specific code from
.BR screen.c .
That can be represented as follows:
.IP
.EX
dev
	draw	screen
.EE
.PP
Each item
.I x
in the
.B ip
section
corresponds to a protocol implementation compiled from
.BI ../ip/ x .c .
Any subitems
are dealt with in the same way as in the
.B dev
section.
.PP
The
.B link
section provides a way for hardware-specific
parts of drivers to link at runtime to the hardware-invariant part of a device
drivers.
For each item
.IR x ,
the kernel will call the function
.IB x link
during its initialisation.
Typically that function makes itself known to the device driver by
calling a function provided by that driver,
passing the address of a interface-specific data structure or linkage table.
For example,
.B ethersmc
is an interface-specific component:
.IP
.EX
link
	\fR...\fP
	ethersmc
.EE
.PP
and its source file
.B ethersmc.c
provides a function
.B ethersmclink
that
calls
.B addethercard
in the interface-invariant part of the driver,
.BR devether.c :
.IP
.EX
void
ethersmclink(void)
{
	addethercard("smc91cXX", reset);
}
.EE
.PP
The
.B boot
section configures
.IR boot (8),
the first user program run by the kernel.
Each line in the section names a possible boot method (see
.IR boot (8)
for the current list).
The first will be the default.
Also by default,
.B /boot
will run
.B /bin/termrc
from
.IR cpurc (8),
with
.B bootdisk
set to
.BR #S/sdC0/ .
To change the defaults, the line (or lines) containing a
.B boot
label can be given some options:
.RS
.TP
.B "boot cpu"
.br
The kernel is a cpu server: run
.B /bin/cpurc
not
.B /bin/termrc
(see
.IR cpurc (8)).
.TP
.BI "boot cpu boot " disk
Use
.I disk
as the default
.BR bootdisk .
.RE
.PP
The
.B lib
section lists the libraries to include when linking the kernel,
in an order that satisfies any dependencies amongst them.
Each item
.I x
corresponds to
.BI /$objtype/lib x .a ,
a target-specific library
produced by compiling the C source code in
.BI /sys/src/lib item,
where
.B objtype
is set in the platform's
.B mkfile
to the target system's object type
(eg,
.BR 386 ,
.BR power ,
etc).
.PP
An item in the
.B bootdir
section
has one of the forms:
.IP
.EX
.I name
.I "source name"
.EE
.PP
where
.I name
and
.I source
are path names (often absolute path names).
The kernel's initial root file system (see
.IR root (3))
will contain a file or directory with the given
.IR name .
The contents will come from the file
.I name
(which must exist) unless an explicit
.I source
file is given.
.PP
The
.B port
section usually contains initialisations for kernel-specific values.
The most common one is
.IP
.EX
	int cpuserver = \fIn\fP;
.EE
.PP
where
.I n
is non-zero for cpu servers and file servers, and zero otherwise.
.SH FILES
.B /sys/src/9/port/mkdevc
.br
.B /sys/src/9/port/mkdevlist
.br
.B /sys/src/9/port/mkroot
.SH SEE ALSO
.IR mk (1)