Re: [Monotone-devel] daemon support

[Ben Walton]

Thanks for this Ralf.  I'll look at it shortly.  I realize that I
relied on the daemon call...I'm not sure as to the portability of this
call, but it is common to Linux systems and (as cygwin relies heavily
on linux libs/tools/etc) cygwin [I haven't built against cygwin though
and don't know the details of the implementation underneath].  I'd be
happy to make this better and will use your code below if that's the
best path.

Thanks!
-Ben

On 9/11/07, Ralf S. Engelschall <address@hidden> wrote:
> On Mon, Sep 10, 2007, Ben Walton wrote:
>
> > I just synced a branch called nvm.daemon-support.  All tests are
> > passing on my tree, but I've only got Ubuntu Feisty to test on right
> > now.  I hope that someone can build/test it on more platforms (windows
> > would be especially helpful).
> >
> > Let me know if you can help out.
>
> I've not built the sources on your branch, but in the commit notify
> mails I see you are just calling the 4.4BSD function daemon(3).
> Unfortunaely, IMHO this function is not portable enough for Monotone.
>
> You at least need some Autoconf glue for checking its availability
> and provide --daemon only if daemon(3) is available or (my personal
> preference) provide at least an own Unix fallback implementation of
> daemon(3).
>
> I append you a possible fallback implementation of daemon(3) which I've
> created some years ago based on STEVENS and related resources. Feel free
> to take it over into Monotone's code base under the GPL if you wish.
>
> Also, for Windows I guess daemon(3) also doesn't exist, but I'm a
> Unix-only hacker and have no clue about the Windows APIs and how it can
> be emulated under Windows...
>
>                                        Ralf S. Engelschall
>                                        address@hidden
>                                        www.engelschall.com
>
> /*
> **  my_daemon.c -- daemonize current process, fallback for daemon(3)
> **  Copyright (c) 1999-2005 Ralf S. Engelschall <address@hidden>
> */
>
> #include <fcntl.h>
> #include <unistd.h>
> #include <signal.h>
> #include <sys/stat.h>
> #include <sys/ioctl.h>
>
> int my_daemon(int nochdir, int noclose)
> {
>     int fd;
>     int rc;
>
>     /* ignore tty related signals */
> #ifdef  SIGTTOU
>     signal(SIGTTOU, SIG_IGN);
> #endif
> #ifdef  SIGTTIN
>     signal(SIGTTIN, SIG_IGN);
> #endif
> #ifdef  SIGTSTP
>     signal(SIGTSTP, SIG_IGN);
> #endif
>
>     /* fork so the parent can exit, this returns control to the command line
>        or shell invoking your program. This step is required so that the new
>        process is guaranteed not to be a process group leader (The next step,
>        setsid, would fail if you're a process group leader). */
>     rc = fork();
>     switch (rc) {
>         case -1: return -1;
>         case  0: break;
>         default: _exit(0); /* exit original process */
>     }
>
>     /* setsid to become a process group and session group leader. Since a
>        controlling terminal is associated with a session, and this new session
>        has not yet acquired a controlling terminal our process now has no
>        controlling terminal, which is a Good Thing for daemons. */
> #ifdef HAVE_SETSID
>     if (setsid() == -1)
>         return -1;
> #else
>     if (setpgid(0, getpid()) == -1)
>         return -1;
> #ifndef _PATH_TTY
> #define _PATH_TTY "/dev/tty"
> #endif
>     if ((fd = open(_PATH_TTY, O_RDWR)) == -1)
>         return -1;
>     ioctl(fd, TIOCNOTTY, NULL);
>     close(fd);
> #endif
>
>     /* fork again so the parent (the session group leader) can exit. This
>        means that we, as a non-session group leader, can never regain a
>        controlling terminal. */
>     rc = fork();
>     switch (rc) {
>         case -1: return -1;
>         case  0: break;
>         default: _exit(0); /* exit original process */
>     }
>
>     /* change to root directory ensure that our process doesn't keep
>        any directory in use. Failure to do this could make it so that
>        an administrator couldn't unmount a filesystem, because it was
>        our current directory. [Equivalently, we could change to any
>        directory containing files important to the daemon's operation.] */
>     if (!nochdir)
>         chdir("/");
>
>     /* give us complete control over the permissions of anything we
>        write. We don't know what umask we may have inherited.
>        [This step is optional] */
>     umask(0);
>
>     /* close fds 0, 1, and 2. This releases the standard in, out, and
>        error we inherited from our parent process. We have no way of
>        knowing where these fds might have been redirected to. */
>     if (!noclose && (fd = open("/dev/null", O_RDWR, 0)) != -1) {
>         dup2(fd, STDIN_FILENO);
>         dup2(fd, STDOUT_FILENO);
>         dup2(fd, STDERR_FILENO);
>         if (fd > 2)
>             close(fd);
>     }
>
>     return 0;
> }
>
>


-- 
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Ben Walton <address@hidden>

When one person suffers from a delusion, it is called insanity. When
many people suffer from a delusion it is called Religion.
Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

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