// Copyright(c) 2017-2020, Intel Corporation
//
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// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
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//   and/or other materials provided with the distribution.
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//   may be used to  endorse or promote  products derived  from this  software
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/*
 * daemonize.c : routine to become a system daemon process.
 */

#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>

int daemonize(void (*hndlr)(int, siginfo_t *, void *), mode_t mask, const char *dir)
{
	pid_t pid;
	pid_t sid;
	int res;
	int fd;
	struct sigaction sa;

	pid = fork();
	if (pid < 0) // fork() failed.
		return errno;

	// 1) Orphan the child process so that it runs in the background.
	if (pid > 0)
		exit(0);

	// 2) Become leader of a new session and process group leader of new process
	// group. The process is now detached from its controlling terminal.
	sid = setsid();
	if (sid < 0)
		return errno;

	// 3) Establish signal handler.
	memset(&sa, 0, sizeof(sa));
	sa.sa_flags     = SA_SIGINFO | SA_RESETHAND;
	sa.sa_sigaction = hndlr;

	res = sigaction(SIGINT, &sa, NULL);
	if (res < 0)
		return errno;

	res = sigaction(SIGTERM, &sa, NULL);
	if (res < 0)
		return errno;

	// 4) Orphan the child again - the session leading process terminates.
	// (only session leaders can request TTY).
	pid = fork();
	if (pid < 0) // fork() failed.
		return errno;

	if (pid > 0)
		exit(0);

	// 5) Set new file mode mask.
	umask(mask);

	// 6) change directory
	res = chdir(dir);
	if (res < 0)
		return errno;

	// 7) Close all open file descriptors
	fd = sysconf(_SC_OPEN_MAX);
	while (fd >= 0)
		close(fd--);

	return 0;
}