mk 'CONF=conf'

where conf is a text file that specifies drivers, protocols and other parameters for that particular kernel: a parts list. The result of a successful mk is an executable or bootable file with a name determined by the platform's mkfile, typically iconf for all native platforms, $O.conf for Plan 9, Unix and clones, and iconf.exe for Windows.

A kernel configuration file has several sections of the form

label
	item [ subitem ... ]
	...

Each section begins with a label at the start of a line, which names a configuration category, followed by a list of each item to select from that category, one line per item, with white space (ie, blank or tab) at the start of the line. An item line can optionally list one or more subitems that must be included in the kernel to support it. A line that starts with a # is a comment. Empty lines are ignored.

Labels are chosen from the following set, listed in the order in which they conventionally appear in a configuration file:

dev

Device drivers

ip

IP protocols (native kernels only) taken from ../ip

link

Hardware-specific parts of device drivers.

misc

Architecture-specific files; specific VGA and SCSI interfaces

lib

Libraries to link with the kernel

mod

Builtin Dis modules

port

Portable components (other than drivers) from ../port

code

C code and declarations to include as-is in the generated configuration file

init

Dis init program

root

List of files and directories to put in the root(3) file system

When an item is listed under a given label it causes a corresponding component to be included in the kernel. The details depend on the label, as discussed below. Each subitem represents a kernel subcomponent required by the corresponding 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 ../port and ../ip, under control of the platform's mkfile and ../port/portmkfile (which is included by mkfile). Resulting object files are left in the platform directory.

Outside the dev section, each item and subitem x causes the kernel image to include the code compiled from x.c, (or x.s or x.S for assembly-language support), or portdir/x.c, where portdir is one of the portable directories mentioned above. In the dev section, an item x corresponds instead to the driver source file devx.c in the current (platform-specific) directory or a portable driver portdir/devx.c. Subitems are handled as in any other section. Typically they are auxiliary files that are needed by the associated driver.

For instance, in a native kernel the portable driver for the draw device uses platform-specific code from screen.c. That can be represented as follows:

dev
	draw	screen

Each item x in the ip section corresponds to a protocol implementation compiled from ../ip/x.c. Any subitems are dealt with in the same way as in the dev section.

The 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 x, the kernel will call the function xlink 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, ethersmc is an interface-specific component:

link
	...
	ethersmc

and its source file ethersmc.c provides a function ethersmclink that calls addethercard in the interface-invariant part of the driver, devether.c:

void
ethersmclink(void)
{
	addethercard("smc91cXX", reset);
}

Similarly, during kernel initialisation, for each item x in the mod section, the kernel calls the function xinit, to initialise the corresponding built-in Limbo module.

The init section selects the first Dis program run by the system. For native kernels, a given item x refers to ../init/x.dis, which is automatically built from ../init/x.b. For hosted kernels, emuinit is normally used, referring to /dis/emuinit.dis.

The lib section lists the libraries to include when linking the kernel, in an order that satisfies any dependencies amongst them. Each item x corresponds to /$SYSTARG/$OBJTYPE/libx.a, a target-specific library produced by compiling the C source code in /libitem, where SYSTARG and OBJTYPE are set in mkfile to the target system and object types.

An item in the root section has one of the forms:

name

name source

where name and source are both absolute path names rooted at the Inferno source tree. The kernel's initial root file system (see root(3)) will contain a file or directory with the given name. Name must exist in the Inferno root, or an existing source file must be named. In either case, if the existing name refers to a file, the file in the root file system will have that file's current contents. If it is a directory, the root file file system will have a directory with that name, but the directory will contain only those names listed in the configuration file as belonging to that directory. Source is often / to force a target name to be a directory.