NetBSD/sys/lkm/syscall/example

#
# Copyright (c) 1993 Terrence R. Lambert.
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#	$NetBSD: README,v 1.1 2000/12/11 13:48:12 jdolecek Exp $
#

1.0	Overview

	This is the README file for the sample loaded system call.


2.0	Directions

	To test the module, do the following:

		make load

	A load message (the copyright) will be printed on the console.

		cd test
		make load

	The system call prints a message on the console when called.
	This message will be printed when running "make load" in
	the "test" subdirectory.


3.0	Recovering resources

	The system call consumes 8 pages of memory when loaded; it
	can be freed up by unloading it.  To unload it, type the
	following from the directory this file is in:

		cd module
		make unload

	The system call will be unloaded by name.

4.0	System call modules

        System calls as loadable modules use one of two approaches.

        If the system call slot is unspecified (-1), it will attempt
        to locate (and allocate) the next free call slot that points
        to the address of the "lkmnosys" function (an alias for the
        "nosys" function).  It replaces this with the user's call;
        the user can tell which slot was allocated using the "modstat"
        command (the call slot is indicated by the value of "Off").

        If the system call slot is specified, it will replace that
        specific call (assuming it is in range of the entries in the
        sysent[] table).  Care should be taken when replacing system
        calls.  Good candiates are calls which the user is attempting
        to repair or make POSIX compliant.  It is possible to replace
        all calls, although care should be taken with the "ioctl()"
        call, as it is the interface for the lkm loader.

        When unloaded, the system call module replaces the previous
        contents of the call slot it was loaded in.  If this was an
        allocable slot, it is now reallocable; if it was a particular
        call slot, the previous function is restored.

        The directory ./sample/syscall contains a sample implementation
        of a loadable system call.


5.0	END OF DOCUMENT