Add a family of functions for reliable pidfiles handling.

Idea from:	jmg
Discussed on:	arch@

1 files changed, 227 insertions, 0 deletions

diff --git a/lib/libutil/pidfile.3 b/lib/libutil/pidfile.3
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+.\" Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd August 22, 2005
+.Dt PIDFILE 3
+.Os
+.Sh NAME
+.Nm pidfile_open ,
+.Nm pidfile_write ,
+.Nm pidfile_close ,
+.Nm pidfile_remove
+.Nd library for PID files handling
+.Sh LIBRARY
+.Lb libutil
+.Sh SYNOPSIS
+.In sys/param.h
+.In libutil.h
+.Ft struct pidfh *
+.Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr"
+.Ft int
+.Fn pidfile_write "struct pidfh *pfh"
+.Ft int
+.Fn pidfile_close "struct pidfh *pfh"
+.Ft int
+.Fn pidfile_remove "struct pidfh *pfh"
+.Sh DESCRIPTION
+The
+.Nm libpidfile
+library provides functions for daemons to handle file with PID.
+It uses
+.Xr flock 2
+to lock pidfile and detect already running daemons.
+.Pp
+The
+.Fn pidfile_open
+function opens (or creates) a file specified by
+.Fa path
+argument and locks it with
+.Xr flock 2
+syscall.
+If file can not be locked, PID of already running daemon is returned in
+.Fa pidptr
+argument (if it is not NULL).
+The function doesn't write process' PID into the file here, so it can be
+used before fork()ing and exit with proper error message when needed.
+If
+.Fa path
+argument is NULL,
+.Pa /var/run/<progname>.pid
+file will be used.
+.Pp
+The
+.Fn pidfile_write
+function write process' PID into previously opened file.
+.Pp
+The
+.Fn pidfile_close
+function closes pidfile.
+It should be used after daemon fork()s to start a child process.
+.Pp
+The
+.Fn pidfile_remove
+function closes and removes pidfile.
+.Sh RETURN VALUES
+The
+.Fn pidfile_open
+function return a valid pointer to a pidfh structure on success or
+.Dv NULL
+if an error occurs.
+If an error does occur,
+.Va errno
+will be set.
+.Rv -std pidfile_write pidfile_close pidfile_remove
+.Sh EXAMPLES
+The following example shows in which order those functions should be used.
+.Bd -literal
+struct pidfh *pfh;
+pid_t otherpid, childpid;
+
+pfh = pidfile_open("/var/run/daemon.pid", 0644, &otherpid);
+if (pfh == NULL) {
+	if (errno == EEXIST)
+		errx(EXIT_FAILURE, "Daemon already running, pid: %d.", otherpid);
+	/* If we cannot create pidfile from other reasons, only warn. */
+	warn("Cannot open or create pidfile");
+}
+
+if (daemon(0, 0) == -1) {
+	warn("Cannot daemonize");
+	pidfile_remove(pfh);
+	exit(EXIT_FAILURE);
+}
+
+pidfile_write(pfh);
+
+for (;;) {
+	/* Do work. */
+	childpid = fork();
+	switch (childpid) {
+	case -1:
+		syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno));
+		break;
+	case 0:
+		pidfile_close(pfh);
+		/* Do child work. */
+		break;
+	default:
+		syslog(LOG_INFO, "Child %d started.", childpid);
+		break;
+	}
+}
+
+pidfile_remove(pfh);
+exit(EXIT_SUCCESS);
+.Ed
+.Sh ERRORS
+The
+.Fn pidfile_open
+function will fail if:
+.Bl -tag -width Er
+.It Bq Er EEXIST
+Some process already holds the lock on the given pidfile, which means,
+daemon is already running.
+.It Bq Er ENAMETOOLONG
+Specified pidfile's name is too long.
+.It Bq Er EINVAL
+Some process already holds the lock on the given pidfile, but PID read
+from there is invalid.
+.El
+.Pp
+The
+.Fn pidfile_open
+function may also fail and set
+.Va errno
+for any errors specified for the
+.Xr fstat 2 ,
+.Xr open 2 ,
+.Xr read 2
+routines.
+.Pp
+The
+.Fn pidfile_write
+function will fail if:
+.Bl -tag -width Er
+.It Bq Er EDOOFUS
+Inproper function use.
+Probably called before
+.Fn pidfile_open .
+.El
+.Pp
+The
+.Fn pidfile_write
+function may also fail and set
+.Va errno
+for any errors specified for the
+.Xr fstat 2 ,
+.Xr ftruncate 2 ,
+.Xr write 2
+routines.
+.Pp
+The
+.Fn pidfile_close
+function may fail and set
+.Va errno
+for any errors specified for the
+.Xr close 2 ,
+.Xr fstat 2
+routines.
+.Pp
+The
+.Fn pidfile_remove
+function will fail if:
+.Bl -tag -width Er
+.It Bq Er EDOOFUS
+Inproper function use.
+Probably called not from the process which made
+.Fn pidfile_write .
+.El
+.Pp
+The
+.Fn pidfile_remove
+function may also fail and set
+.Va errno
+for any errors specified for the
+.Xr close 2 ,
+.Xr flock 2 ,
+.Xr fstat 2 ,
+.Xr write 2 ,
+.Xr unlink 2
+routines.
+.Pp
+.Sh SEE ALSO
+.Xr flock 2 ,
+.Xr open 2 ,
+.Xr daemon 3
+.Sh AUTHORS
+.An -nosplit
+The
+.Xr pidfile 3
+functionality is based on ideas from
+.An John-Mark Gurney Aq jmg@FreeBSD.org .
+.Pp
+The code and manual page was written by
+.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .