1/*
 2 * Copyright (c) 2024 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/* Test that kernel thread is reported as such. */
17#undef NDEBUG
18#include <assert.h>
19#include <errno.h>
20#include <fcntl.h>
21#include <string.h>
22#include <unistd.h>
23
24int main(void)
25{
26	/*
27	 * The following solutions don't really work:
28	 *
29	 * 1) jit kernel module which creates kernel thread:
30	 * test becomes arch-specific,
31	 * problems with mandatory module signing,
32	 * problems with lockdown mode,
33	 * doesn't work with CONFIG_MODULES=n at all,
34	 * kthread creation API is formally unstable internal kernel API,
35	 * need a mechanism to report test kernel thread's PID back,
36	 *
37	 * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads,
38	 * but their PIDs are unstable.
39	 *
40	 * Check against kthreadd which always seem to exist under pid 2.
41	 */
42	int fd = open("/proc/2/status", O_RDONLY);
43	assert(fd >= 0);
44
45	char buf[4096];
46	ssize_t rv = read(fd, buf, sizeof(buf));
47	assert(0 <= rv && rv < sizeof(buf));
48	buf[rv] = '\0';
49
50	assert(strstr(buf, "Kthread:\t1\n"));
51
52	return 0;
53}