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 * uid-filter. This program shows how you can use some of the
38 * meta-data provided in the fusd_file_info structure to affect your
39 * driver's behavior.
40 *
41 * In particular, this driver creates a device, /dev/my-pid, that can
42 * not be read by anyone other than the driver owner (not even root!).
43 * When you read from the device, it returns your PID to you.
44 *
45 * $Id: uid-filter.c,v 1.5 2007-12-08 04:05:01 girod Exp $
46 */
47
48 #include <stdio.h>
49 #include <string.h>
50 #include <errno.h>
51 #include <unistd.h>
52
53 #include "fusd.h"
54
55
56 int do_close(struct fusd_file_info *file)
57 {
58 return 0; /* attempts to close the file always succeed */
59 }
60
61 /* EXAMPLE START uid-filter.c */
62 int do_open(struct fusd_file_info *file)
63 {
64 /* If the UID of the process trying to do the read doesn't match the
65 * UID of the owner of the driver, return -EPERM. If you run this
66 * driver as a normal user, even root won't be able to read from the
67 * device file created! */
68 if (file->uid != getuid())
69 return -EPERM;
70
71 return 0;
72 }
73
74 ssize_t do_read(struct fusd_file_info *file, char *user_buffer,
75 size_t user_length, loff_t *offset)
76 {
77 char buf[128];
78 int len;
79
80 /* The first read to the device returns a greeting. The second read
81 * returns EOF. */
82 if (*offset != 0)
83 return 0;
84
85 /* len gets set to the number of characters written to buf */
86 len = sprintf(buf, "Your PID is %d. Have a nice day.\n", file->pid);
87
88 /* NEVER return more data than the user asked for */
89 if (user_length < len)
90 len = user_length;
91
92 memcpy(user_buffer, buf, len);
93 *offset += len;
94 return len;
95 }
96 /* EXAMPLE STOP uid-filter.c */
97
98
99 int main(int argc, char *argv[])
100 {
101 struct fusd_file_operations fops = {
102 open: do_open,
103 read: do_read,
104 close: do_close };
105
106 if (fusd_register("/dev/my-pid", 0666, NULL, &fops) < 0)
107 perror("Unable to register device");
108 else {
109 printf("/dev/my-pid should now exist - calling fusd_run...\n");
110 fusd_run();
111 }
112 return 0;
113 }
114
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