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CONFIG(5) File Formats Manual CONFIG(5)
NAME
config - kernel configuration file syntax
DESCRIPTION
The kernel configuration file specifies the way the kernel should be
compiled by the rest of the toolchain. It is processed by config(1) to
produce a number of files that will allow the user to compile a possibly
customised kernel. One compilation can issue several kernel binaries,
with different root and dump devices configurations, or with full
debugging information.
This manual page is intended to serve as a complete reference of all
aspects of the syntax used in the many files processed by config(1). The
novice user will prefer looking at the examples given in
config.samples(5) in order to understand better how the default
configuration can be changed, and how all of its elements interact with
each other.
The kernel configuration file actually contains the description of all
the options, drivers and source files involved in the kernel compilation,
and the logic that binds them. The machine statement, usually found in
the std.${MACHINE} file, hides this from the user by automatically
including all the descriptive files spread all around the kernel source
tree, the main one being conf/files.
Thus, the kernel configuration file contains two parts: the description
of the compilation options, and the selection of those options. However,
it begins with a small preamble that controls a couple of options of
config(1), and a few statements belong to any of the two sections.
The user controls the options selection part, which is located in a file
commonly referenced as the main configuration file or simply the kernel
configuration file. The developer is responsible for describing the
options in the relevant files from the kernel source tree.
Statements are separated by new-line characters. However, new-line
characters can appear in the middle of a given statement, with the value
of a space character.
OBJECTS AND NAMES
config(1) is a rather complicated piece of software that tries to comply
with any configuration the user might think of. Quite a few different
objects are manipulated through the kernel configuration file, therefore
some definitions are needed.
Options and attributes
The basic objects driving the kernel compilation are options, and are
called attributes in some contexts. An attribute usually refers to a
feature a given piece of hardware might have. However, the scope of an
attribute is rather wide and can just be a place holder to group some
source files together.
There is a special class of attribute, named interface attribute, which
represents a hook that allows a device to attach to (i.e., be a child of)
another device. An interface attribute has a (possibly empty) list of
locators to match the actual location of a device. For example, on a PCI
bus, devices are located by a device number that is fixed by the wiring
of the motherboard. Additionally, each of those devices can appear
through several interfaces named functions. A single PCI device entity
is a unique function number of a given device from the considered PCI
bus. Therefore, the locators for a pci(4) device are `dev' (for device),
and `function'.
A locator can either be a single integer value, or an array of integer
values. It can have a default value, in which case it can be wildcarded
with a `?' in the options selection section of the configuration file. A
single locator definition can take one of the following forms:
⊕ locator
⊕ locator=value
⊕ [locator=value]
⊕ locator[length]
⊕ locator[length]={value, ...}
⊕ [locator[length]={value, ...}]
The variants that specify a default value can be enclosed into square
brackets, in which case the locator will not have to be specified later
in the options selection section of the configuration file.
In the options selection section, the locators are specified when
declaring an instance as a space-separated list of "<locator> <value>"
where value can be the `?' wildcard if the locator allows it.
Devices, instances and attachments
The main benefit of the kernel configuration file is to allow the user to
avoid compiling some drivers, and wire down the configuration of some
others. We have already seen that devices attach to each other through
interface attributes, but not everything can attach to anything.
Furthermore, the user has the ability to define precise instances for the
devices. An instance is simply the reality of a device when it is probed
and attached by the kernel.
Each driver has a name for its devices. It is called the base device
name and is found as "base" in this documentation. An instance is the
concatenation of a base device name and a number. In the kernel
configuration file, instances can sometimes be wildcarded (i.e., the
number is replaced by a `*' or a `?') in order to match all the possible
instances of a device.
The usual `*' becomes a `?' when the instance name is used as an
attachment name. In the options selection part of the kernel
configuration files, an attachment is an interface attribute concatenated
with a number or the wildcard `?'.
Pseudo-devices
Some components of the kernel behave like a device although they don't
have any actual reality in the hardware. For example, this is the case
for special network devices, such as tun(4) and tap(4). They are
integrated in the kernel as pseudo-devices, and can have several
instances and even children, just like normal devices.
Dependencies
The options description part of the kernel configuration file contains
all the logic that ties the source files together, and it is done first
through writing down dependencies between config(1) objects.
In this documentation, the syntax for dependencies is a comma-separated
list of options and attributes .
For example, the use of an Ethernet network card requires the source
files that handle the specificities of that protocol. Therefore, all
Ethernet network card drivers depend on the `ether' attribute.
Conditions
Finally, source file selection is possible through the help of
conditionals, referred to as "condition" later in this documentation.
The syntax for those conditions uses well-known operators (`&', `|', and
`!') to combine options and attributes .
CONTEXT NEUTRAL STATEMENTS
version yyyymmdd
Indicates the syntax version used by the rest of the file, or
until the next version statement. The argument is an ISO
date. A given config(1) binary might only be compatible with
a limited range of version numbers.
include path
Includes a file. The path is relative to the top of the
kernel source tree, or the inner-most defined prefix.
cinclude path
Conditionally includes a file. Contrary to include, it will
not produce an error if the file does not exist. The
argument obeys the same rules as for include.
prefix [path]
If path is given, it pushes a new prefix for file, include
and cinclude. prefix statements act like a stack, and an
empty path argument has the latest prefix popped out. The
path argument is either absolute or relative to the current
defined prefix, which defaults to the top of the kernel
source tree.
buildprefix [path]
If path is given, it pushes a new build prefix for file.
buildprefix statements act like a stack, and an empty path
argument has the latest prefix popped out. The path argument
is relative to the current defined buildprefix, which
defaults to the top of the kernel build directory. When
prefix is either absolute or relative out of the kernel
source tree (../), buildprefix must be defined.
ifdef attribute
ifndef attribute
elifdef attribute
elifndef attribute
else
endif Conditionally interprets portions of the current file. Those
statements depend on whether or not the given attribute has
been previously defined, through define or any other
statement that implicitly defines attributes such as device.
PREAMBLE
In addition to include, cinclude, and prefix, the preamble may contain
the following optional statements:
build path Defines the build directory for the compilation of the
kernel. It replaces the default of ../compile/<config-file>
and is superseded by the -b parameter of config(1).
source path
Defines the directory in which the source of the kernel
lives. It replaces the default of ../../../.. and is
superseded by the -s parameter of config(1).
OPTIONS DESCRIPTION
The user will not usually have to use descriptive statements, as they are
meant for the developer to tie a given piece of code to the rest of the
kernel. However, third parties may provide sources to add to the kernel
compilation, and the logic that binds them to the NetBSD kernel will have
to be added to the user-edited configuration file.
devclass class
Defines a special attribute, named device class. A given
device cannot belong to more than one device class.
config(1) translates that property by the rule that a device
cannot depend on more than one device class, and will
properly fill the configuration information file it generates
according to that value.
defflag [file] option [option [...]] [: dependencies]
Defines a boolean option, that can either be selected or be
un-selected by the user with the options statement. The
optional file argument names a header file that will contain
the C pre-processor definition for the option. If no file
name is given, it will default to opt_<option>.h. config(1)
will always create the header file, but if the user choose
not to select the option, it will be empty. Several options
can be combined in one header file, for convenience. The
header file is created in the compilation directory, making
them directly accessible by source files.
defparam [file] option[=value] [:=lint-value] [option [...]]
[: dependencies]
Behaves like defflag, except the defined option must have a
value. Such options are not typed: they can have either a
numeric or a string value. If a value is specified, it is
treated as a default, and the option is always defined in the
corresponding header file. If a lint-value is specified,
config(1) will use it as a value when generating a lint
configuration with -L, and ignore it in all other cases.
deffs name ...
Defines a file-system name. It is no more than a regular
option, as defined by defflag, but it allows the user to
select the file-systems to be compiled in the kernel with the
file-system statement instead of the options statement.
obsolete defflag [file] option ...
obsolete defparam [file] option ...
Those two statements are identical and mark the listed option
names as obsolete. If the user selects one of the listed
options in the kernel configuration file, config(1) will emit
a warning and ignore the option. The optional file argument
should match the original definition of the option.
define attribute [{ locators }] [: dependencies]
Defines an attribute. The locators list is optional, and can
be empty. If the pair of braces are present, the locator
list is defined and the declared attribute becomes an
interface attribute, on which devices can attach.
maxpartitions number
Defines the maximum number of partitions the disklabels for
the considered architecture can hold. This statement cannot
be repeated and should only appear in the std.${ARCH} file.
maxusers min default max
Indicates the range of values that will later be accepted by
config(1) for the maxusers statement in the options selection
part of the configuration file. In case the user doesn't
include a maxusers statement in the configuration file, the
value default is used instead.
device base [{ locators }] [: dependencies]
Declares a device of name base. The optional list of
locators, which can also be empty, indicates the device can
have children attached directly to it. Internally, that
means base becomes an interface attribute. For every device
the user selects, config(1) will add the matching
CFDRIVER_DECL() statement to ioconf.c. However, it is the
responsibility of the developer to add the relevant
CFATTACH_DECL_NEW() line to the source of the device's
driver.
attach base at attr[, attr[, ...]] [with name] [: dependencies]
All devices must have at least one declared attachment.
Otherwise, they will never be found in the autoconf(9)
process. The attributes on which an instance of device base
can attach must be interface attributes, or root in case the
device is at the top-level, which is usually the case of
e.g., mainbus(4). The instances of device base will later
attach to one interface attribute from the specified list.
Different attach definitions must use different names using
the with option. It is then possible to use the associated
name as a conditional element in a file statement.
defpseudo base [: dependencies]
Declares a pseudo-device. Those devices don't need an
attachment to be declared, they will always be attached if
they were selected by the user.
defpseudodev base [{ locators }] [: dependencies]
Declares a pseudo-device. Those devices don't need an
attachment to be declared, they will always be attached if
they were selected by the user. This declaration should be
used if the pseudodevice uses autoconf(9) functions to manage
its instances or attach children. As for normal devices, an
optional list of locators can be defined, which implies an
interface attribute named base, allowing the pseudo-device to
have children. Interface attributes can also be defined in
the dependencies list.
file path [condition] [needs-count] [needs-flag] [compile with rule]
Adds a source file to the list of files to be compiled into
the kernel, if the condition is met. The needs-count option
indicates that the source file requires the number of all the
countable objects it depends on (through the condition) to be
defined. It is usually used for pseudo-devices whose number
can be specified by the user in the pseudo-device statement.
Countable objects are devices and pseudo-devices. For the
former, the count is the number of declared instances. For
the latter, it is the number specified by the user,
defaulting to 1. The needs-flag options requires that a flag
indicating the selection of an attribute to be created, but
the precise number isn't needed. This is useful for source
files that only partly depend on the attribute, and thus need
to add pre-processor statements for it.
Both needs-count and needs-flag produce a header file for
each of the considered attributes. The name of that file is
<attribute>.h. It contains one pre-processor definition of
NATTRIBUTE set to 0 if the attribute was not selected by the
user, or to the number of instances of the device in the
needs-count case, or to 1 in all the other cases.
The rule argument specifies the make(1) rule that will be
used to compile the source file. If it is not given, the
default rule for the type of the file will be used. For a
given file, there can be more than one file statement, but
not from the same configuration source file, and all later
statements can only specify a rule argument, and no condition
or flags. This is useful when a file needs special
consideration from one particular architecture.
The path is relative to the top of the kernel source tree, or
the inner-most defined prefix.
object path [condition]
Adds an object file to the list of objects to be linked into
the kernel, if the conditions are met. This is most useful
for third parties providing binary-only components.
The path is relative to the top of the kernel source tree, or
the inner-most defined prefix.
device-major base [char number] [block number] [condition]
Associates a major device number with the device base. A
device can be a character device, a block device, or both,
and can have different numbers for each. The condition
indicates when the relevant line should be added to ioconf.c,
and works just like the file statement.
makeoptions condition name+=value[, condition name+=value[, ...]]
Appends to a definition in the generated Makefile.
This variant of makeoptions belongs to the options
description section. The condition is mandatory and only +=
can be used. Not to be confused with the confusingly similar
variant of makeoptions used in the selections section.
OPTIONS SELECTION
machine machine [arch [subarch [...]]]
The machine statement should appear first in the kernel
configuration file, with the exception of context-neutral
statements. It makes config(1) include, in that order, the
following files:
1. conf/files
2. arch/${ARCH}/conf/files.${ARCH} if defined
3. arch/${SUBARCH}/conf/files.${SUBARCH} for each defined
sub-architecture
4. arch/${MACHINE}/conf/files.${MACHINE}
It also defines an attribute for the machine, the arch and
each of the subarch.
package path
Simpler version of:
prefix DIR
include FILE
prefix
ident string
Defines the identification string of the kernel. This
statement is optional, and the name of the main configuration
file will be used as a default value.
no ident Deletes any pre-existing identification string of the kernel.
maxusers number
Despite its name, this statement does not limit the maximum
number of users on the system. There is no such limit,
actually. However, some kernel structures need to be
adjusted to accommodate with more users, and the maxusers
parameter is used for example to compute the maximum number
of opened files, and the maximum number of processes, which
itself is used to adjust a few other parameters.
options name[=value][, name[=value][, ...]]
Selects the option name, affecting it a value if the options
requires it (see the defflag and defparam statements).
If the option has not been declared in the options
description part of the kernel configuration machinery, it
will be added as a pre-processor definition when source files
are compiled. If the option has previously been selected,
the statement produces a warning, and the new options
statement replaces the original.
no options name[, name[, ...]]
Un-selects the option name. If option name has not
previously been selected, the statement produces a warning.
file-system name[, name[, ...]]
Adds support for all the listed file-systems.
no file-system name[, name[, ...]]
Removes support for all the listed file-systems.
config name root on device [type fs] [dumps on device]
Adds name to the list of kernel binaries to compile from the
configuration file, using the specified root and dump devices
information.
Any of the device and fs parameters can be wildcarded with
`?' to let the kernel automatically discover those values.
The device can also be specified as a quoted specification
string. The kernel interprets this string like the console
input when prompting for a root device. E.g., "wedge:NAME"
specifies a named disk wedge.
At least one config statement must appear in the
configuration file.
no config name
Removes name from the list of kernel binaries to compile from
the configuration file.
instance at attachment [locator-specifications ...]
Configures an instance of a device attaching at a specific
location in the device tree. All parameters can be
wildcarded, with a `*' for instance, and a `?' for attachment
and the locators.
no instance [at attachment]
Removes the previously configured instances of a device that
exactly match the given specification. If two instances
differ only by their locators, both are removed. If no
attachment is specified, all matching instances are removed.
If instance is a bare device name, all the previously defined
instances of that device, regardless of the numbers or
wildcard, are removed.
no device at attachment
Removes all previously configured instances that attach to
the specified attachment. If attachment ends with a `*', all
instances attaching to all the variants of attachment are
removed.
pseudo-device device [number]
Adds support for the specified pseudo-device. The parameter
number is passed to the initialisation function of the
pseudo-device, usually to indicate how many instances should
be created. It defaults to 1, and some pseudo-devices ignore
that parameter.
no pseudo-device name
Removes support for the specified pseudo-device.
makeoptions name=value[, name+=value[, ...]]
Adds or appends to a definition in the generated Makefile. A
definition cannot be overridden, it must be removed before it
can be added again. Optionally, if an option
makeoptions_<name> is defined with defparam, the value is
defined as an option too.
This variant of makeoptions belongs to the options selection
section. Both = and += can be used. Not to be confused with
the confusingly similar variant of makeoptions used in the
descriptions section.
no makeoptions name[, name[, ...]]
Removes one or more definitions from the generated Makefile.
select name
Adds the specified attribute and its dependencies.
no select name
Removes the specified attribute and all the attributes which
depend on it.
FILES
The files are relative to the kernel source top directory (e.g.,
/usr/src/sys).
arch/${MACHINE}/conf/std.${MACHINE}
Standard configuration for the given architecture. This
file should always be included.
arch/${MACHINE}/conf/GENERIC
Standard options selection file for the given
architecture. Users should always start changing their
main kernel configuration file by editing a copy of this
file.
conf/files Main options description file.
EXAMPLES
config.samples(5) uses several examples to cover all the practical
aspects of writing or modifying a kernel configuration file.
SEE ALSO
config(1), options(4), config.samples(5), config(9)
NetBSD 10.99 July 19, 2016 NetBSD 10.99