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Add a family of functions for reliable pidfiles handling.

Browse Source 
Idea from:	jmg
Discussed on:	arch@
This commit is contained in:
pjd 2005-08-24 17:21:38 +00:00
parent 473f777e4d
commit a5fe3401b9
4 changed files with 498 additions and 3 deletions
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11
lib/libutil/Makefile
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@ -8,15 +8,16 @@ CFLAGS+=-DLIBC_SCCS -I${.CURDIR} -I${.CURDIR}/../libc/gen/
CFLAGS+=-DINET6
SRCS= _secure_path.c auth.c fparseln.c humanize_number.c login.c \
login_auth.c login_cap.c login_class.c login_crypt.c login_ok.c \
login_times.c login_tty.c logout.c logwtmp.c property.c pty.c \
pw_util.c realhostname.c stub.c \
login_times.c login_tty.c logout.c logwtmp.c \
pidfile.c property.c pty.c pw_util.c realhostname.c stub.c \
trimdomain.c uucplock.c
INCS= libutil.h login_cap.h
MAN+= login.3 login_auth.3 login_tty.3 logout.3 logwtmp.3 pty.3 \
login_cap.3 login_class.3 login_times.3 login_ok.3 \
_secure_path.3 uucplock.3 property.3 auth.3 realhostname.3 \
realhostname_sa.3 trimdomain.3 fparseln.3 humanize_number.3
realhostname_sa.3 trimdomain.3 fparseln.3 humanize_number.3 \
pidfile.3
MAN+= login.conf.5 auth.conf.5
MLINKS+= property.3 properties_read.3 property.3 properties_free.3
MLINKS+= property.3 property_find.3
@ -39,5 +40,9 @@ MLINKS+=login_ok.3 auth_ttyok.3 login_ok.3 auth_hostok.3 \
MLINKS+=login_auth.3 auth_checknologin.3 login_auth.3 auth_cat.3
MLINKS+=uucplock.3 uu_lock.3 uucplock.3 uu_lock_txfr.3 \
uucplock.3 uu_unlock.3 uucplock.3 uu_lockerr.3
MLINKS+=pidfile.3 pidfile_open.3 \
pidfile.3 pidfile_write.3 \
pidfile.3 pidfile_close.3 \
pidfile.3 pidfile_remove.3
.include <bsd.lib.mk>

17
lib/libutil/libutil.h
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@ -49,6 +49,16 @@ typedef struct _property {
char *value;
} *properties;
#ifdef _SYS_PARAM_H_
/* for pidfile.c */
struct pidfh {
int pf_fd;
char pf_path[MAXPATHLEN + 1];
__dev_t pf_dev;
ino_t pf_ino;
};
#endif
/* Avoid pulling in all the include files for no need */
struct termios;
struct winsize;
@ -102,6 +112,13 @@ struct passwd *pw_scan(const char *_line, int _flags);
const char *pw_tempname(void);
int pw_tmp(int _mfd);
#endif
#ifdef _SYS_PARAM_H_
struct pidfh *pidfile_open(const char *path, mode_t mode, pid_t *pidptr);
int pidfile_write(struct pidfh *pfh);
int pidfile_close(struct pidfh *pfh);
int pidfile_remove(struct pidfh *pfh);
#endif
__END_DECLS
#define UU_LOCK_INUSE (1)

227
lib/libutil/pidfile.3 Normal file
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@ -0,0 +1,227 @@
.\" 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 .

246
lib/libutil/pidfile.c Normal file
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@ -0,0 +1,246 @@
/*-
* 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.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <err.h>
#include <errno.h>
#include <libutil.h>
static int _pidfile_remove(struct pidfh *pfh, int freeit);
static int
pidfile_verify(struct pidfh *pfh)
{
struct stat sb;
int fd;
if (pfh == NULL || pfh->pf_fd == -1)
return (EDOOFUS);
/*
* Check remembered descriptor.
*/
if (fstat(pfh->pf_fd, &sb) == -1)
return (errno);
if (sb.st_dev != pfh->pf_dev || sb.st_ino != pfh->pf_ino)
return (EDOOFUS);
return (0);
}
static int
pidfile_read(const char *path, pid_t *pidptr)
{
char buf[16], *endptr;
int error, fd, i;
fd = open(path, O_RDONLY);
if (fd == -1)
return (errno);
i = read(fd, buf, sizeof(buf) - 1);
error = errno; /* Remember errno in case close() wants to change it. */
close(fd);
if (i == -1)
return (error);
buf[i] = '\0';
*pidptr = strtol(buf, &endptr, 10);
if (endptr != &buf[i])
return (EINVAL);
return (0);
}
struct pidfh *
pidfile_open(const char *path, mode_t mode, pid_t *pidptr)
{
struct pidfh *pfh;
struct stat sb;
int error, fd;
pfh = malloc(sizeof(*pfh));
if (pfh == NULL)
return (NULL);
if (path == NULL) {
snprintf(pfh->pf_path, sizeof(pfh->pf_path), "/var/run/%s.pid",
getprogname());
} else {
strlcpy(pfh->pf_path, path, sizeof(pfh->pf_path));
}
if (strlen(pfh->pf_path) == sizeof(pfh->pf_path) - 1) {
free(pfh);
errno = ENAMETOOLONG;
return (NULL);
}
/*
* Open the PID file and obtain exclusive lock.
* We truncate PID file here only to remove old PID immediatelly,
* PID file will be truncated again in pidfile_write(), so
* pidfile_write() can be called multiple times.
*/
fd = open(pfh->pf_path,
O_WRONLY | O_CREAT | O_EXLOCK | O_TRUNC | O_NONBLOCK, mode);
if (fd == -1) {
if (errno == EWOULDBLOCK && pidptr != NULL) {
errno = pidfile_read(pfh->pf_path, pidptr);
if (errno == 0)
errno = EEXIST;
}
free(pfh);
return (NULL);
}
/*
* Remember file information, so in pidfile_write() we are sure we write
* to the proper descriptor.
*/
if (fstat(fd, &sb) == -1) {
error = errno;
unlink(pfh->pf_path);
close(fd);
free(pfh);
errno = error;
return (NULL);
}
pfh->pf_fd = fd;
pfh->pf_dev = sb.st_dev;
pfh->pf_ino = sb.st_ino;
return (pfh);
}
int
pidfile_write(struct pidfh *pfh)
{
struct stat sb;
char pidstr[16];
int error, fd;
/*
* Check remembered descriptor, so we don't overwrite some other
* file if pidfile was closed and descriptor reused.
*/
errno = pidfile_verify(pfh);
if (errno != 0) {
/*
* Don't close descriptor, because we are not sure if it's ours.
*/
return (-1);
}
fd = pfh->pf_fd;
/*
* Truncate PID file, so multiple calls of pidfile_write() are allowed.
*/
if (ftruncate(fd, 0) == -1) {
error = errno;
_pidfile_remove(pfh, 0);
errno = error;
return (-1);
}
snprintf(pidstr, sizeof(pidstr), "%u", getpid());
if (write(fd, pidstr, strlen(pidstr)) != (ssize_t)strlen(pidstr)) {
error = errno;
_pidfile_remove(pfh, 0);
errno = error;
return (-1);
}
return (0);
}
int
pidfile_close(struct pidfh *pfh)
{
int error;
error = pidfile_verify(pfh);
if (error != 0) {
errno = error;
return (-1);
}
if (close(pfh->pf_fd) == -1)
error = errno;
free(pfh);
if (error != 0) {
errno = error;
return (-1);
}
return (0);
}
static int
_pidfile_remove(struct pidfh *pfh, int freeit)
{
int error;
error = pidfile_verify(pfh);
if (error != 0) {
errno = error;
return (-1);
}
if (unlink(pfh->pf_path) == -1)
error = errno;
if (flock(pfh->pf_fd, LOCK_UN) == -1) {
if (error == 0)
error = errno;
}
if (close(pfh->pf_fd) == -1) {
if (error == 0)
error = errno;
}
if (freeit)
free(pfh);
else
pfh->pf_fd = -1;
if (error != 0) {
errno = error;
return (-1);
}
return (0);
}
int
pidfile_remove(struct pidfh *pfh)
{
return (_pidfile_remove(pfh, 1));
}