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DEFINITIONS
This source file includes following definitions.
- nullopen
- nullclose
- nullio
- nullioctl
- devnull_create
1 /*
2 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
3 * The President and Fellows of Harvard College.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 /*
31 * Implementation of the null device, "null:", which generates an
32 * immediate EOF on read and throws away anything written to it.
33 */
34 #include <types.h>
35 #include <kern/errno.h>
36 #include <lib.h>
37 #include <uio.h>
38 #include <vfs.h>
39 #include <device.h>
40
41 /* For open() */
42 static
43 int
44 nullopen(struct device *dev, int openflags)
45 {
46 (void)dev;
47 (void)openflags;
48
49 return 0;
50 }
51
52 /* For close() */
53 static
54 int
55 nullclose(struct device *dev)
56 {
57 (void)dev;
58 return 0;
59 }
60
61 /* For d_io() */
62 static
63 int
64 nullio(struct device *dev, struct uio *uio)
65 {
66 /*
67 * On write, discard everything without looking at it.
68 * On read, do nothing, generating an immediate EOF.
69 */
70
71 (void)dev; // unused
72
73 if (uio->uio_rw == UIO_WRITE) {
74 uio->uio_resid = 0;
75 }
76
77 return 0;
78 }
79
80 /* For ioctl() */
81 static
82 int
83 nullioctl(struct device *dev, int op, userptr_t data)
84 {
85 /*
86 * No ioctls.
87 */
88
89 (void)dev;
90 (void)op;
91 (void)data;
92
93 return EINVAL;
94 }
95
96 /*
97 * Function to create and attach null:
98 */
99 void
100 devnull_create(void)
101 {
102 int result;
103 struct device *dev;
104
105 dev = kmalloc(sizeof(*dev));
106 if (dev==NULL) {
107 panic("Could not add null device: out of memory\n");
108 }
109
110
111 dev->d_open = nullopen;
112 dev->d_close = nullclose;
113 dev->d_io = nullio;
114 dev->d_ioctl = nullioctl;
115
116 dev->d_blocks = 0;
117 dev->d_blocksize = 1;
118
119 dev->d_devnumber = 0; /* assigned by vfs_adddev */
120
121 dev->d_data = NULL;
122
123 result = vfs_adddev("null", dev, 0);
124 if (result) {
125 panic("Could not add null device: %s\n", strerror(result));
126 }
127 }