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/*
* Copyright (c) 2025 Alexey Dobriyan <adobriyan@gmail.com>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#undef _GNU_SOURCE
#define _GNU_SOURCE
#undef NDEBUG
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sched.h>
/*
* Test that lseek("/proc/net/dev/", 0, SEEK_SET)
* a) works,
* b) does what you think it does.
*/
int main(void)
{
/* /proc/net/dev output is deterministic in fresh netns only. */
if (unshare(CLONE_NEWNET) == -1) {
if (errno == ENOSYS || errno == EPERM) {
return 4;
}
return 1;
}
const int fd = open("/proc/net/dev", O_RDONLY);
assert(fd >= 0);
char buf1[4096];
const ssize_t rv1 = read(fd, buf1, sizeof(buf1));
/*
* Not "<=", this file can't be empty:
* there is header, "lo" interface with some zeroes.
*/
assert(0 < rv1);
assert(rv1 <= sizeof(buf1));
/* Believe it or not, this line broke one day. */
assert(lseek(fd, 0, SEEK_SET) == 0);
char buf2[4096];
const ssize_t rv2 = read(fd, buf2, sizeof(buf2));
/* Not "<=", see above. */
assert(0 < rv2);
assert(rv2 <= sizeof(buf2));
/* Test that lseek rewinds to the beginning of the file. */
assert(rv1 == rv2);
assert(memcmp(buf1, buf2, rv1) == 0);
/* Contents of the file is not validated: this test is about lseek(). */
return 0;
}
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