1 /*
2 * Copyright (c) 2025 Alexey Dobriyan <adobriyan@gmail.com>
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16 #undef _GNU_SOURCE
17 #define _GNU_SOURCE
18 #undef NDEBUG
19 #include <assert.h>
20 #include <errno.h>
21 #include <fcntl.h>
22 #include <string.h>
23 #include <unistd.h>
24 #include <sched.h>
25 /*
26 * Test that lseek("/proc/net/dev/", 0, SEEK_SET)
27 * a) works,
28 * b) does what you think it does.
29 */
main(void)30 int main(void)
31 {
32 /* /proc/net/dev output is deterministic in fresh netns only. */
33 if (unshare(CLONE_NEWNET) == -1) {
34 if (errno == ENOSYS || errno == EPERM) {
35 return 4;
36 }
37 return 1;
38 }
39
40 const int fd = open("/proc/net/dev", O_RDONLY);
41 assert(fd >= 0);
42
43 char buf1[4096];
44 const ssize_t rv1 = read(fd, buf1, sizeof(buf1));
45 /*
46 * Not "<=", this file can't be empty:
47 * there is header, "lo" interface with some zeroes.
48 */
49 assert(0 < rv1);
50 assert(rv1 <= sizeof(buf1));
51
52 /* Believe it or not, this line broke one day. */
53 assert(lseek(fd, 0, SEEK_SET) == 0);
54
55 char buf2[4096];
56 const ssize_t rv2 = read(fd, buf2, sizeof(buf2));
57 /* Not "<=", see above. */
58 assert(0 < rv2);
59 assert(rv2 <= sizeof(buf2));
60
61 /* Test that lseek rewinds to the beginning of the file. */
62 assert(rv1 == rv2);
63 assert(memcmp(buf1, buf2, rv1) == 0);
64
65 /* Contents of the file is not validated: this test is about lseek(). */
66
67 return 0;
68 }
69