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.ds RH "Adding New Devices
ADDING NEW SYSTEM SOFTWARE

This section is not for the novice, it describes some of the inner workings of the configuration process as well as the pertinent 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:

general guidelines to be followed in modifying system code, how to add non-standard system facilities to 4.4BSD, how to add a device driver to 4.4BSD, and Modifying system code

If you wish to make site-specific modifications to the system it is best to bracket them with #ifdef SITENAME ... #endif to allow your source to be easily distributed to others, and also to simplify diff\|(1) listings. If you choose not to use a source code control system (e.g. SCCS, RCS), and perhaps even if you do, it is recommended that you save the old code with something of the form: #ifndef SITENAME ... #endif We try to isolate our site-dependent code in individual files which may be configured with pseudo-device specifications.

Indicate machine-specific code with ``#ifdef vax'' (or other machine, as appropriate). 4.4BSD underwent extensive work to make it extremely portable to machines with similar architectures- you may someday find yourself trying to use a single copy of the source code on multiple machines. Adding non-standard system facilities

This section considers the work needed to augment config 's data base files for non-standard system facilities. Config uses a set of files that list the source modules that may be required when building a system. The data bases are taken from the directory in which config is run, normally /sys/conf. Three such files may be used: files , files .machine, and files .ident. The first is common to all systems, the second contains files unique to a single machine type, and the third is an optional list of modules for use on a specific machine. This last file may override specifications in the first two. The format of the files file has grown somewhat complex over time. Entries are normally of the form

dir/source.c type option-list modifiers

for example,

vaxuba/foo.c optional foo device-driver

The
 type is one of
 standard or
 optional . Files marked as standard 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 configuration file,
or the names of system options that may be defined.
An optional file may be listed multiple times with different options;
if all of the options for any of the entries are satisfied,
the module is included.

If a file is specified as a
 device-driver , any special compilation options for device drivers will be invoked.
On the VAX this results in the use of the
 -i option for the C optimizer. This is required when pointer references
are made to memory locations in the VAX I/O address space.

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

sys/subr_mcount.c optional profiling-routine


The 
 profiling-routine keyword forces
 config not to compile the source file with the 
 -pg option.

The second keyword which can be of use is the
 config-dependent keyword. This causes
 config to compile the indicated module with the global configuration
parameters. This allows certain modules, such as
 machdep.c to size system data structures based on the maximum number
of users configured for the system.

Adding device drivers to 4.4BSD

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


/sys/h machine independent include files
/sys/sys machine-independent system source files
/sys/conf site configuration files and basic templates
/sys/net network-protocol-independent, but network-related code
/sys/netinet DARPA Internet code
/sys/netimp IMP support code
/sys/netns Xerox NS code
/sys/vax VAX-specific mainline code
/sys/vaxif VAX network interface code
/sys/vaxmba VAX MASSBUS device drivers and related code
/sys/vaxuba VAX UNIBUS device drivers and related code



Existing block and character device drivers for the VAX 
reside in ``/sys/vax'', ``/sys/vaxmba'', and ``/sys/vaxuba''. Network
interface drivers reside in ``/sys/vaxif''. 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 ``dh''
device driver is named ``dh.c'' and its associated include file is
named ``dhreg.h''.

Once the source for the device driver has been placed in a directory,
the file ``/sys/conf/files.machine'', and possibly
``/sys/conf/devices.machine'' should be modified. The 
 files 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 ``/sys/conf/files,'' while machine specific files
are in ``/sys/conf/files.machine.'' The ``devices.machine'' 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
 files 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 number.
The block major number is needed in the ``devices.machine'' file
if the device is a disk.