/*
 * Copyright (c) 2024 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.
 */
/* Test that kernel thread is reported as such. */
#undef NDEBUG
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

int main(void)
{
        /*
         * The following solutions don't really work:
         *
         * 1) jit kernel module which creates kernel thread:
         * test becomes arch-specific,
         * problems with mandatory module signing,
         * problems with lockdown mode,
         * doesn't work with CONFIG_MODULES=n at all,
         * kthread creation API is formally unstable internal kernel API,
         * need a mechanism to report test kernel thread's PID back,
         *
         * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads,
         * but their PIDs are unstable.
         *
         * Check against kthreadd which always seem to exist under pid 2.
         */
        int fd = open("/proc/2/status", O_RDONLY);
        assert(fd >= 0);

        char buf[4096];
        ssize_t rv = read(fd, buf, sizeof(buf));
        assert(0 <= rv && rv < sizeof(buf));
        buf[rv] = '\0';

        assert(strstr(buf, "Kthread:\t1\n"));

        return 0;
}