/**
* slibc — Yet another C library
* Copyright © 2015, 2016 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <unistd.h>
#include <fcntl.h>
/**
* Detach the process from the controlling terminal
* and run in the background.
*
* The function shall change the working directory
* to '/' to avoid block a mountpoint from being
* unmounted. It shall also change direct stdin,
* stdout, and stderr to '/dev/null'. It shall
* then double-fork, and between the fork, become
* a session leader, temporarily, so that the
* it no longer has a controlling terminal.
*
* Note well, this function does not implement a
* reliable or particularly correct mechanism for
* daemonising a process. It shall not be used!
* Note, the GNU implementation is slightly
* different because of a bug.
*
* @etymology (Daemon)ise!
*
* @param nochdir The not change working directory to '/'.
* @param noclose The not redirect stdin, stdout, and stderr to '/dev/null'.
* @return Zero on success, -1 on error.
*
* @throws EACCES If `nochdir` is zero, and the user is denied access to '/'.
* @throws Any error specified for open(3).
* @throws Any error specified for dup2(3).
* @throws Any error specified for fork(3).
* @throws Any error specified for setsid(3).
*
* @since Always.
*/
int daemon(int nochdir, int noclose)
{
int fd = -1;
int saved_errno;
if (nochdir ? 0 : chdir("/"))
return -1;
if (noclose == 0)
{
if (fd = open("/dev/null", O_RDWR), fd < 0)
return -1;
if (dup2(fd, 0) < 0) goto fail;
if (dup2(fd, 1) < 0) goto fail;
if (dup2(fd, 2) < 0) goto fail;
if (fd > 2)
close(fd);
}
switch (fork())
{
case 0: break;
case -1: return -1;
default: _exit(0);
}
if (setsid() < 0)
return -1;
switch (fork())
{
case 0: break;
case -1: return -1;
default: _exit(0);
}
return 0;
fail:
saved_errno = errno;
if (fd > 2)
close (fd);
errno = saved_errno;
return -1;
}
