1# Copyright (c) 1998 Rajesh Vaidheeswarran
2# All rights reserved.
3#
4# Redistribution and use in source and binary forms, with or without
5# modification, are permitted provided that the following conditions
6# are met:
7# 1. Redistributions of source code must retain the above copyright
8# notice, this list of conditions and the following disclaimer.
9# 2. Redistributions in binary form must reproduce the above copyright
10# notice, this list of conditions and the following disclaimer in the
11# documentation and/or other materials provided with the distribution.
12# 3. All advertising materials mentioning features or use of this software
13# must display the following acknowledgement:
14# This product includes software developed by Rajesh Vaidheeswarran
15# 4. The name Rajesh Vaidheeswarran may not be used to endorse or promote
16# products derived from this software without specific prior written
17# permission.
18#
19# THIS SOFTWARE IS PROVIDED BY RAJESH VAIDHEESWARRAN ``AS IS'' AND ANY
20# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22# ARE DISCLAIMED. IN NO EVENT SHALL THE RAJESH VAIDHEESWARRAN BE LIABLE
23# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29# SUCH DAMAGE.
30#
31# Copyright (c) 1993 Terrence R. Lambert.
32# All rights reserved.
33#
34# Redistribution and use in source and binary forms, with or without
35# modification, are permitted provided that the following conditions
36# are met:
37# 1. Redistributions of source code must retain the above copyright
38# notice, this list of conditions and the following disclaimer.
39# 2. Redistributions in binary form must reproduce the above copyright
40# notice, this list of conditions and the following disclaimer in the
41# documentation and/or other materials provided with the distribution.
42# 3. All advertising materials mentioning features or use of this software
43# must display the following acknowledgement:
44# This product includes software developed by Terrence R. Lambert.
45# 4. The name Terrence R. Lambert may not be used to endorse or promote
46# products derived from this software without specific prior written
47# permission.
48#
49# THIS SOFTWARE IS PROVIDED BY TERRENCE R. LAMBERT ``AS IS'' AND ANY
50# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
51# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
52# ARE DISCLAIMED. IN NO EVENT SHALL THE TERRENCE R. LAMBERT BE LIABLE
53# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
54# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
55# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
56# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
57# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
58# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
59# SUCH DAMAGE.
60#
61# $FreeBSD: releng/10.3/share/examples/kld/cdev/README 66549 2000-10-02 14:14:07Z sobomax $
62#
63
641.0 Overview
65
66 This is the README file for the sample kld module
67 that mimics a character device driver.
68
69 A kld module may be used to load any data or
70 program into the kernel that can be made available by
71 modifying a table, pointer, or other kernel data to inform
72 the kernel that the module should be used instead of the
73 previous code/data path.
74
75 Generally, it is assumed that a loadable module is one of
76 a set of similar modules (such as a file system or console
77 terminal emulation), and that the reference is through a
78 table (such as vfssw[]), and that a "special" value is
79 assigned to the slots which are allowed to be replaced.
80 This is not enforced, so you may use the kld module
81 any way you see fit.
82
83 As with the loadable system calls, it may be desirable to
84 allow the module loader to replace an *existing* entry to
85 try out changes to kernel code without rebuilding and
86 booting from the new kernel.
87
88 The idea behind this example is to show some interaction
89 with the device driver. Therefore the flow of the code that
90 this driver is aimed at is as follows:
91
92 open(2) -> ioctl(2) -> write(2) -> read(2) -> close(2).
93
94 We will first open the device in the /dev/ directory; then
95 we will send an ioctl message to it using ioctl(2) call;
96 then write a small string via the write(2) call. This string
97 we write to the device will be stored in a static buffer,
98 and later will be accessible via the read(2) call. Finally,
99 we will close(2) our open()'d device so that we may no
100 longer make read or write calls on it.
101
1022.0 Directions
103
104 To test the module, do the following:
105
106 cd module
107 make load
108
109 A load message (the copyright) will be printed on the console.
110
111 cd ../test
112 make load
113
114 The system call prints a message on the console when called.
115 This message will be printed when running "make load" in
116 the "test" subdirectory.
117
118
1193.0 Recovering resources
120
121 The module consumes memory when loaded; it can be freed up by
122 unloading it. To unload it, type the following from the directory
123 this file is in:
124
125 cd module
126 make unload
127
128 The miscellaneous module will be unloaded by name.
129
130
1314.0 END OF DOCUMENT
132