1 /*
2 *
3 * Copyright (c) 2003 The Regents of the University of California. All
4 * rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * - Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 *
13 * - Neither the name of the University nor the names of its
14 * contributors may be used to endorse or promote products derived
15 * from this software without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS''
18 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
19 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
20 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR
21 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
22 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
23 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
24 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
25 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 *
29 */
30
31
32 /*
33 * FUSD - The Framework for UserSpace Devices - Example program
34 *
35 * Jeremy Elson <jelson@circlemud.org>
36 *
37 * echo.c: Example of how to use both the 'read' and 'write' callbacks.
38 *
39 * This example creates a single device, /dev/echo. If you write
40 * something to /dev/echo (e.g., "echo HI THERE > /dev/echo"), it gets
41 * stored. Then, when you read (e.g. "cat /dev/echo"), you get back
42 * whatever you wrote most recently.
43 *
44 * $Id: echo.c,v 1.7 2007-12-08 04:05:01 girod Exp $
45 */
46
47 #include <stdio.h>
48 #include <stdlib.h>
49 #include <string.h>
50 #include <errno.h>
51 #include <unistd.h>
52
53 #include "fusd.h"
54
55 #define MIN(x, y) ((x) < (y) ? (x) : (y))
56
57 /* EXAMPLE START echo.c */
58 char *data = NULL;
59 int data_length = 0;
60
61 ssize_t echo_read(struct fusd_file_info *file, char *user_buffer,
62 size_t user_length, loff_t *offset)
63 {
64 /* if the user has read past the end of the data, return EOF */
65 if (*offset >= data_length)
66 return 0;
67
68 /* only return as much data as we have */
69 user_length = MIN(user_length, data_length - *offset);
70
71 /* copy data to user starting from the first byte they haven't seen */
72 memcpy(user_buffer, data + *offset, user_length);
73 *offset += user_length;
74
75 /* tell them how much data they got */
76 return user_length;
77 }
78
79 ssize_t echo_write(struct fusd_file_info *file, const char *user_buffer,
80 size_t user_length, loff_t *offset)
81 {
82 /* free the old data, if any */
83 if (data != NULL) {
84 free(data);
85 data = NULL;
86 data_length = 0;
87 }
88
89 /* allocate space for new data; return error if that fails */
90 if ((data = malloc(user_length)) == NULL)
91 return -ENOMEM;
92
93 /* make a copy of user's data; tell the user we copied everything */
94 memcpy(data, user_buffer, user_length);
95 data_length = user_length;
96 return user_length;
97 }
98 /* EXAMPLE STOP */
99
100 int do_open_or_close(struct fusd_file_info *file)
101 {
102 return 0; /* opens and closes always succeed */
103 }
104
105
106 struct fusd_file_operations echo_fops = {
107 open: do_open_or_close,
108 read: echo_read,
109 write: echo_write,
110 close: do_open_or_close
111 };
112
113
114 int main(int argc, char *argv[])
115 {
116 if (fusd_register("/dev/echo", 0666, NULL, &echo_fops) < 0) {
117 perror("register of /dev/echo failed");
118 exit(1);
119 }
120
121 fprintf(stderr, "calling fusd_run...\n");
122 fusd_run();
123 return 0;
124 }
125
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