Date: Tue, 2 Jul 2002 18:08:43 -0500 (CDT) From: "Matthew D.Fuller" <fullermd@over-yonder.net> To: FreeBSD-gnats-submit@FreeBSD.org Subject: bin/40127: [PATCH] Add functions for PID-file handling Message-ID: <20020702230843.3AA611F02@mortis.over-yonder.net>
next in thread | raw e-mail | index | archive | help
>Number: 40127
>Category: bin
>Synopsis: [PATCH] Add functions for PID-file handling
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Tue Jul 02 16:10:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Matthew D. Fuller
>Release: FreeBSD 5.0-CURRENT i386
>Organization:
>Environment:
System: FreeBSD mortis.sighup.org 5.0-CURRENT FreeBSD 5.0-CURRENT #0: Fri Jun 14 08:09:49 CDT 2002 fullermd@mortis.sighup.org:/usr/obj/usr/src/sys/MORTIS i386
>Description:
There is currently no centralized code to handle PID-files. This
patch provides and documents libutil functions to do so.
These functions have potential use in the large number of programs
which write PID-files, to properly maintain them and use them as a
sort of mutex without deadlocking.
This isn't done in a vacuum; this functionality is desired (by some,
see below) in pw(8) and other password-subsystem altering programs.
Having the functions available, however, is a necessary precursor to
using them, and they have wide use in other areas of the system as
well.
For some notes, see PR bin/38676, and the thread on -stable entitled
"bug in pw, -STABLE [patch]" and its continuation in "Locking the
passwd subsystem (was Re: bug in pw, -STABLE [patch])" on -hackers.
>How-To-Repeat:
>Fix:
Index: lib/libutil/Makefile
===================================================================
RCS file: /usr/cvs/src/lib/libutil/Makefile,v
retrieving revision 1.48
diff -u -r1.48 Makefile
--- lib/libutil/Makefile 26 Jun 2002 13:25:23 -0000 1.48
+++ lib/libutil/Makefile 2 Jul 2002 23:01:14 -0000
@@ -8,7 +8,7 @@
CFLAGS+=-DINET6
SRCS= _secure_path.c auth.c fparseln.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 \
+ login_tty.c logout.c logwtmp.c pid_util.c property.c pty.c \
pw_util.c realhostname.c stub.c \
trimdomain.c uucplock.c
INCS= libutil.h login_cap.h
@@ -16,7 +16,7 @@
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
+ realhostname_sa.3 trimdomain.3 fparseln.3 pid_util.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 +39,6 @@
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+=pid_util.3 pid_begin.3 pid_end.3
.include <bsd.lib.mk>
Index: lib/libutil/libutil.h
===================================================================
RCS file: /usr/cvs/src/lib/libutil/libutil.h,v
retrieving revision 1.37
diff -u -r1.37 libutil.h
--- lib/libutil/libutil.h 8 May 2002 00:50:07 -0000 1.37
+++ lib/libutil/libutil.h 23 Jun 2002 12:35:30 -0000
@@ -82,6 +82,8 @@
struct sockaddr;
int realhostname_sa(char *host, size_t hsize, struct sockaddr *addr,
int addrlen);
+int pid_begin(const char *pidfile, mode_t mode, int flags);
+int pid_end(const char *pidfile);
#ifdef _STDIO_H_ /* avoid adding new includes */
char *fparseln(FILE *, size_t *, size_t *, const char[3], int);
#endif
@@ -128,5 +130,8 @@
/* pw_scan() */
#define PWSCAN_MASTER 0x01
#define PWSCAN_WARN 0x02
+
+/* pid_begin() */
+#define PID_NOBLOCK 0x01
#endif /* !_LIBUTIL_H_ */
Index: lib/libutil/pid_util.c
===================================================================
--- /dev/null Tue Jul 2 18:00:01 2002
+++ lib/libutil/pid_util.c Sun Jun 23 11:50:59 2002
@@ -0,0 +1,178 @@
+/*-
+ * Copyright (c) 2002 Matthew D. Fuller <fullermd@over-yonder.net>
+ * 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.
+ */
+
+#ifndef lint
+static const char rcsid[] =
+ "$FreeBSD$";
+#endif /* not lint */
+
+/*
+ * These functions are for maintenance of locking PID files
+ */
+
+#include <sys/param.h>
+#include <sys/proc.h>
+#include <sys/uio.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <libutil.h>
+
+
+#define PID_LEN 6 /* Currently only need 5 (0-99,999) */
+
+/*
+ * pid_begin: Open a PID file and write PID into it. If one already
+ * exists, try and track down the process which opened it; if it can't be
+ * found, proceed as if the file weren't even there.
+ */
+int
+pid_begin(const char *pidfile, mode_t mode, int flags)
+{
+ int procdead=0;
+ int lockfd;
+ int holding=0;
+ ssize_t readlen;
+ pid_t masterpid;
+ char pidstr[PID_LEN+1];
+
+start:
+ if( (lockfd=open(pidfile, O_RDWR | O_CREAT | O_EXCL | O_EXLOCK,
+ mode)) < 0 )
+ {
+ if(errno!=EEXIST)
+ return(-1); /* Preserve errno */
+
+ /* Open and find PID */
+ if( (lockfd=open(pidfile, O_RDWR | O_EXLOCK, mode)) < 0 )
+ {
+ if(errno==ENOENT || errno==EWOULDBLOCK)
+ {
+ /*
+ * This could use some thought. We're going to
+ * tight-loop if someone else has the file locked
+ * (EWOULDBLOCK). In theory, any locks should be
+ * quite short-lived, so I THINK this will be fine.
+ */
+ goto start;
+ }
+ else
+ return(-1);/* Preserve errno */
+ }
+
+ if( (readlen=read(lockfd, pidstr, PID_LEN)) < 0 )
+ {
+ holding==errno;
+ close(lockfd);
+ errno=holding;
+ return(-1);
+ }
+
+ pidstr[readlen]='\0';
+ masterpid = (pid_t) atoi(pidstr);
+ if(masterpid<1) /* This shouldn't happen */
+ {
+ /* This is really a NFS error, but we'll abuse it */
+ errno=ECANCELED;
+ return(-1);
+ }
+
+ /*
+ * There's a number of ways we could approach this. We could
+ * stat /proc/$PID, but that would fail if /proc wasn't
+ * mounted. We could use libkvm, but that would require
+ * linking libutil with it, as well as being setgid kmem on
+ * the app (which we can't really count on). We could
+ * fork/exec ps(1), but that's a bit ugly.
+ * I'm going to do it in a rather ugly way. SIGWINCH is
+ * fairly harmless in the cases where it's used, and is
+ * ignored by default. These functions are aimed at daemons,
+ * which will generally have no use for it, and thus not
+ * change it from the default discard.
+ * Note that zombie'd processes count as 'nonexistent' to
+ * kill(2).
+ */
+ if( kill(masterpid, SIGWINCH) < 0 )
+ if(errno==ESRCH)
+ procdead=1;
+ else
+ procdead=0;
+ else
+ procdead=0; /* kill(2) succeeded */
+
+ if(procdead==0)
+ {
+ /* Old locker is still alive */
+ close(lockfd);
+ if( (flags & PID_NOBLOCK) )
+ {
+ errno=EWOULDBLOCK;
+ return(-1);
+ }
+ else
+ {
+ sleep(1); /* Arbitrary */
+ goto start;
+ }
+ }
+ /* Old lockholder is dead: fallthru */
+ }
+
+ /*
+ * If we get here, we either ARE the O_EXCL opener, or the process
+ * listed in the file is dead and we're taking it over.
+ */
+ ftruncate(lockfd, 0);
+ lseek(lockfd, 0, SEEK_SET);
+ write( lockfd, pidstr, sprintf(pidstr, "%d", getpid()) );
+
+ close(lockfd);
+ return(0);
+}
+
+
+/*
+ * pid_end: Clean up a lock we hold.
+ */
+int
+pid_end(const char *pidfile)
+{
+ /*
+ * We SHOULDN'T need to aquire a lock on the file, since the only
+ * time anybody else should be writing into it would be if we're
+ * dead, and thus we wouldn't be in this function. If they're just
+ * reading it, unlink()'ing it out from under them won't do any
+ * damage. If we're still alive, pid_begin() should close() the file
+ * and attempt to re-open() for the next attempt, so this should work
+ * nice and cleanly.
+ */
+ return(unlink(pidfile));
+}
Index: lib/libutil/pid_util.3
===================================================================
--- /dev/null Tue Jul 2 18:00:01 2002
+++ lib/libutil/pid_util.3 Sun Jun 23 11:51:39 2002
@@ -0,0 +1,106 @@
+.\" Copyright (c) 2002 Matthew D. Fuller <fullermd@over-yonder.net>
+.\" 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 AUTHOR 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 AUTHOR 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 June 23, 2002
+.Os
+.Dt PID_UTIL 3
+.Sh NAME
+.Nm pid_begin ,
+.Nm pid_end
+.Nd "handle locking and unlocking of PID files"
+.Sh LIBRARY
+.Lb libutil
+.Sh SYNOPSIS
+.In sys/types.h
+.In libutil.h
+.Ft int
+.Fn pid_begin "const char *pidfile" "mode_t mode" "int flags"
+.Ft int
+.Fn pid_end "const char *pidfile"
+.Sh DESCRIPTION
+The function
+.Fn pid_begin
+attempts to open the file referenced by
+.Fa pidfile
+and write the process ID to it.
+If the file already exists,
+.Fn pid_begin
+will determine if the process listed in
+.Fa pidfile
+still exists.
+If the process is still alive,
+.Fn pid_begin
+will block and continue to try aquiring the lock indefinitely, unless
+.Dv PID_NOBLOCK
+is set in the
+.Fa flags ,
+in which case it will return an error.
+If the old process is dead, or the file doesn't exist,
+.Fn pid_begin
+will put its own process ID in the file and continue on its merry way.
+.Pp
+.Fn pid_end
+removes the file referenced by
+.Fa pidfile .
+Note that there is currently no protection afforded here that the process
+calling
+.Fn pid_end
+is actually the process that opened the PID file in the first place.
+.Sh RETURN VALUES
+If successful,
+.Fn pid_begin
+and
+.Fn pid_end
+will return 0.
+They will return -1 on failure, and set
+.Va errno
+to indicate the error.
+.Sh ERRORS
+.Fn pid_begin
+will leave behind a PID file unless:
+.Bl -tag -width Er
+.It Bq Er ECANCELED
+The operation was cancelled due to internal error.
+.It Bq Er EWOULDBLOCK
+The file is already locked by a still-live process and
+.Fa flags
+includes
+.Dv PID_NOBLOCK .
+.El
+.Pp
+The
+.Fn pid_begin
+function may also fail and set errno for any of the errors specified for
+the routines
+.Xr open 2
+or
+.Xr read 2 .
+.Pp
+The
+.Fn pid_end
+function may fail and set errno for any of the errors specified for the
+routine
+.Xr unlink 2 .
>Release-Note:
>Audit-Trail:
>Unformatted:
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-bugs" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20020702230843.3AA611F02>