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daemon.c

/*
 * daemon.c -- turn a process into a daemon under POSIX, SYSV, BSD.
 *
 * For license terms, see the file COPYING in this directory.
 */

#include "config.h"

#include <stdio.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <sys/types.h>
#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#else /* !HAVE_FCNTL_H */
#ifdef HAVE_SYS_FCNTL_H
#include <sys/fcntl.h>
#endif /* HAVE_SYS_FCNTL_H */
#endif /* !HAVE_FCNTL_H */
#include <sys/stat.h>   /* get umask(2) prototyped */

#if defined(HAVE_UNISTD_H)
#include <unistd.h>
#endif

#if defined(STDC_HEADERS)
#include <stdlib.h>
#endif

#if defined(QNX)
#include <unix.h>
#endif

#if !defined(HAVE_SETSID) && defined(SIGTSTP)
#if defined(HAVE_TERMIOS_H)
#  include <termios.h>        /* for TIOCNOTTY under Linux */
#endif

#if !defined(TIOCNOTTY) && defined(HAVE_SGTTY_H)
#  include <sgtty.h>          /* for TIOCNOTTY under NEXTSTEP */
#endif
#endif /* !defined(HAVE_SETSID) && defined(SIGTSTP) */

/* BSD portability hack */
#if !defined(SIGCHLD) && defined(SIGCLD)
#define SIGCHLD   SIGCLD
#endif

#include "fetchmail.h"
#include "tunable.h"

RETSIGTYPE
sigchld_handler (int sig)
/* process SIGCHLD to obtain the exit code of the terminating process */
{
    extern volatile int lastsig;          /* last signal received */
    pid_t pid;

#if   defined(HAVE_WAITPID)                     /* the POSIX way */
    int status;

    while ((pid = waitpid(-1, &status, WNOHANG)) > 0)
      continue; /* swallow 'em up. */
#elif       defined(HAVE_WAIT3)                       /* the BSD way */
#if defined(HAVE_UNION_WAIT) && !defined(__FreeBSD__)
    union wait status;
#else
    int status;
#endif

    while ((pid = wait3(&status, WNOHANG, 0)) > 0)
      continue; /* swallow 'em up. */
#else /* Zooks! Nothing to do but wait(), and hope we don't block... */
    int status;

    wait(&status);
#endif
    lastsig = SIGCHLD;
}

RETSIGTYPE null_signal_handler(int sig) { }

SIGHANDLERTYPE set_signal_handler(int sig, SIGHANDLERTYPE handler)
/* 
 * This function is called by other parts of the program to
 * setup the signal handler after a change to the signal context.
 * This is done to improve robustness of the signal handling code.
 * It has the same prototype as signal(2).
 */
{
  SIGHANDLERTYPE rethandler;
#ifdef HAVE_SIGACTION
  struct sigaction sa_new, sa_old;

  memset (&sa_new, 0, sizeof sa_new);
  sigemptyset (&sa_new.sa_mask);
  sa_new.sa_handler = handler;
  sa_new.sa_flags = 0;
#ifdef SA_RESTART /* SunOS 4.1 portability hack */
  /* system call should restart on all signals except SIGALRM */
  if (sig != SIGALRM)
      sa_new.sa_flags |= SA_RESTART;
#endif
#ifdef SA_NOCLDSTOP     /* SunOS 4.1 portability hack */
  if (sig == SIGCHLD)
      sa_new.sa_flags |= SA_NOCLDSTOP;
#endif
  sigaction(sig, &sa_new, &sa_old);
  rethandler = sa_old.sa_handler;
#if defined(SIGPWR)
  if (sig == SIGCHLD)
     sigaction(SIGPWR, &sa_new, NULL);
#endif
#else /* HAVE_SIGACTION */
  rethandler = signal(sig, handler);
#if defined(SIGPWR)
  if (sig == SIGCHLD)
      signal(SIGPWR, handler);
#endif
  /* system call should restart on all signals except SIGALRM */
  siginterrupt(sig, sig == SIGALRM);
#endif /* HAVE_SIGACTION */
  return rethandler;
}

void deal_with_sigchld(void)
{
  set_signal_handler(SIGCHLD, sigchld_handler);
}

int
daemonize (const char *logfile, void (*termhook)(int))
/* detach from control TTY, become process group leader, catch SIGCHLD */
{
  int fd;
  pid_t childpid;

  /* if we are started by init (process 1) via /etc/inittab we needn't 
     bother to detach from our process group context */

  if (getppid() == 1) 
    goto nottyDetach;

  /* Ignore BSD terminal stop signals */
#ifdef      SIGTTOU
  set_signal_handler(SIGTTOU, SIG_IGN);
#endif
#ifdef      SIGTTIN
  set_signal_handler(SIGTTIN, SIG_IGN);
#endif
#ifdef      SIGTSTP
  set_signal_handler(SIGTSTP, SIG_IGN);
#endif

  /* In case we were not started in the background, fork and let
     the parent exit.  Guarantees that the child is not a process
     group leader */

  if ((childpid = fork()) < 0) {
    report(stderr, "fork (%s)\n", strerror(errno));
    return(PS_IOERR);
  }
  else if (childpid > 0) 
    exit(0);  /* parent */

  
  /* Make ourselves the leader of a new process group with no
     controlling terminal */

#if   defined(HAVE_SETSID)          /* POSIX */
  /* POSIX makes this soooo easy to do */
  if (setsid() < 0) {
    report(stderr, "setsid (%s)\n", strerror(errno));
    return(PS_IOERR);
  }
#elif defined(SIGTSTP)        /* BSD */
  /* change process group */
#ifndef __EMX__
  setpgrp(0, getpid());
#endif
  /* lose controlling tty */
  if ((fd = open("/dev/tty", O_RDWR)) >= 0) {
    ioctl(fd, TIOCNOTTY, (char *) 0);
    close(fd);    /* not checking should be safe, there were no writes */
  }
#else                         /* SVR3 and older */
  /* change process group */
#ifndef __EMX__
  setpgrp();
#endif
  
  /* lose controlling tty */
  set_signal_handler(SIGHUP, SIG_IGN);
  if ((childpid = fork()) < 0) {
    report(stderr, "fork (%s)\n", strerror(errno));
    return(PS_IOERR);
  }
  else if (childpid > 0) {
    exit(0);      /* parent */
  }
#endif

nottyDetach:

  /* Close any/all open file descriptors */
#if   defined(HAVE_GETDTABLESIZE)
  for (fd = getdtablesize()-1;  fd >= 0;  fd--)
#elif defined(NOFILE)
  for (fd = NOFILE-1;  fd >= 0;  fd--)
#else       /* make an educated guess */
  for (fd = 19;  fd >= 0;  fd--)
#endif
  {
    close(fd);    /* not checking this should be safe, no writes */
  }

  /* Reopen stdin descriptor on /dev/null */
  if ((fd = open("/dev/null", O_RDWR)) < 0) {   /* stdin */
    report(stderr, "open: /dev/null (%s)\n", strerror(errno));
    return(PS_IOERR);
  }

  if (logfile)
  {
    if ((fd = open(logfile, O_CREAT|O_WRONLY|O_APPEND, 0666)) < 0) {    /* stdout */
      report(stderr, "open %s (%s)\n", logfile, strerror(errno));
      return(PS_IOERR);
    }
  }
  else
  {
    if (dup(fd) < 0) {                    /* stdout */
      report(stderr, "dup (%s)\n", strerror(errno));
      return(PS_IOERR);
    }
  }
  if (dup(fd) < 0) {                      /* stderr */
    report(stderr, "dup (%s)\n", strerror(errno));
    return(PS_IOERR);
  }

#ifdef HAVE_GETCWD
  /* move to root directory, so we don't prevent filesystem unmounts */
  chdir("/");
#endif

  /* set our umask to something reasonable (we hope) */
#if defined(DEF_UMASK)
  umask(DEF_UMASK);
#else
  umask(022);
#endif

  deal_with_sigchld();

  return(0);
}

flag isafile(int fd)
/* is the given fd attached to a file? (used to control logging) */
{
    struct stat stbuf;

    /*
     * We'd like just to return 1 on (S_IFREG | S_IFBLK),
     * but weirdly enough, Linux ptys seem to have S_IFBLK
     * so this test would fail when run on an xterm.
     */
    if (isatty(fd) || fstat(fd, &stbuf))
      return(0);
    else if (stbuf.st_mode & (S_IFREG))
      return(1);
    return(0);
}

/* daemon.c ends here */

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