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>
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>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
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