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Lionel Sambuc
2013-09-26 17:14:40 +02:00
commit 785076ae39
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15
pkgtools/shlock/DESCR Normal file
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The shlock command can create or verify a lock file on behalf of a
shell or other script program. When it attempts to create a lock
file, if one already exists, shlock verifies that it is or is not
valid. If valid, shlock will exit with a non-zero exit code. If
invalid, shlock will re- move the lock file, and create a new one.
shlock uses the rename(2) system call to make the final target lock
file, which is an atomic operation (i.e. "dot locking", so named for
this mech- anism's original use for locking system mailboxes). It
puts the process ID ("PID") from the command line into the requested
lock file.
shlock verifies that an extant lock file is still valid by using
kill(2) with a zero signal to check for the existence of the process
that holds the lock.

21
pkgtools/shlock/Makefile Normal file
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# $NetBSD: Makefile,v 1.25 2012/09/11 23:19:40 asau Exp $
#
DISTNAME= shlock-20080529
CATEGORIES= pkgtools sysutils
MASTER_SITES= # empty
DISTFILES= # empty
MAINTAINER= pkgsrc-users@NetBSD.org
#HOMEPAGE=
COMMENT= Shell utility to perform dot-locking
USE_BSD_MAKEFILE= yes
INSTALLATION_DIRS+= bin ${PKGMANDIR}/man1 ${PKGMANDIR}/cat1
PKGSRC_LOCKTYPE= none # avoid "bootstrapping problem"
do-extract:
${CP} -R ${FILESDIR} ${WRKSRC}
.include "../../mk/bsd.pkg.mk"

4
pkgtools/shlock/PLIST Normal file
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@comment $NetBSD: PLIST,v 1.3 2012/04/22 15:17:29 mspo Exp $
bin/shlock
man/cat1/shlock.0
man/man1/shlock.1

5
pkgtools/shlock/files/Makefile Normal file
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# $NetBSD: Makefile,v 1.6 2008/05/30 10:02:38 tnn Exp $
PROG= shlock
.include <bsd.prog.mk>

121
pkgtools/shlock/files/shlock.1 Normal file
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.\" $NetBSD: shlock.1,v 1.1.1.1 2002/01/15 13:20:28 agc Exp $
.\"
.Dd June 29, 1997
.Dt SHLOCK 1
.Os
.Sh NAME
.Nm shlock
.Nd create or verify a lock file for shell scripts
.Sh SYNOPSIS
.Nm
.Fl f
.Ar lockfile
.Op Fl p Ar PID
.Op Fl u
.Op Fl d
.Sh DESCRIPTION
The
.Nm
command can create or verify a lock file on behalf of a shell or
other script program.
When it attempts to create a lock file, if one already exists,
.Nm
verifies that it is or is not valid.
If valid,
.Nm
will exit with a non-zero exit code.
If invalid,
.Nm
will remove the lock file, and
create a new one.
.Pp
.Nm
uses the
.Xr rename 2
system call to make the final target lock file, which is an atomic
operation (i.e. "dot locking", so named for this mechanism's original
use for locking system mailboxes).
It puts the process ID ("PID") from the command line into the
requested lock file.
.Pp
.Nm
verifies that an extant lock file is still valid by
using
.Xr kill 2
with a zero signal to check for the existence of the process that
holds the lock.
.Pp
The
.Fl f
argument with
.Ar lockfile
is always required.
.Pp
The
.Fl p
option with
.Ar PID
is given when the program is to create a lock file; when absent,
.Nm
will simply check for the validity of the lock file.
.Pp
The
.Fl u
option causes
.Nm
to read and write the PID as a binary pid_t, instead of as ASCII,
to be compatible with the locks created by UUCP.
.Pp
The
.Fl d
option causes
.Nm
to be verbose about what it is doing.
.Sh EXIT STATUS
A zero exit code indicates a valid lock file.
.Sh EXAMPLES
.Ss BOURNE SHELL
.Bd -literal
#!/bin/sh
lckfile=/tmp/foo.lock
if shlock -f ${lckfile} -p $$
then
# do what required the lock
rm ${lckfile}
else
echo Lock ${lckfile} already held by `cat ${lckfile}`
fi
.Ed
.Ss C SHELL
.Bd -literal
#!/bin/csh -f
set lckfile=/tmp/foo.lock
shlock -f ${lckfile} -p $$
if ($status == 0) then
# do what required the lock
rm ${lckfile}
else
echo Lock ${lckfile} already held by `cat ${lckfile}`
endif
.Ed
.Pp
The examples assume that the filesystem where the lock file is to
be created is writeable by the user, and has space available.
.Sh HISTORY
.Nm
was written for the first Network News Transfer Protocol (NNTP)
software distribution, released in March 1986.
The algorithm was suggested by Peter Honeyman,
from work he did on HoneyDanBer UUCP.
.Sh AUTHORS
.An Erik E. Fair Aq fair@clock.org
.Sh BUGS
Does not work on NFS or other network filesystem on different
systems because the disparate systems have disjoint PID spaces.
.Pp
Cannot handle the case where a lock file was not deleted, the
process that created it has exited, and the system has created a
new process with the same PID as in the dead lock file.
The lock file will appear to be valid even though the process is
unrelated to the one that created the lock in the first place.
Always remove your lock files after you're done.

345
pkgtools/shlock/files/shlock.c Normal file
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/* $NetBSD: shlock.c,v 1.1.1.1 2002/01/15 13:20:28 agc Exp $ */
/*
** Program to produce reliable locks for shell scripts.
** Algorithm suggested by Peter Honeyman, January 1984,
** in connection with HoneyDanBer UUCP.
**
** I tried extending this to handle shared locks in November 1987,
** and ran into to some fundamental problems:
**
** Neither 4.3 BSD nor System V have an open(2) with locking,
** so that you can open a file and have it locked as soon as
** it's real; you have to make two system calls, and there's
** a race...
**
** When removing dead process id's from a list in a file,
** you need to truncate the file (you don't want to create a
** new one; see above); unfortunately for the portability of
** this program, only 4.3 BSD has ftruncate(2).
**
** Erik E. Fair <fair@ucbarpa.berkeley.edu>, November 8, 1987
**
** Extensions for UUCP style locks (i.e. pid is an int in the file,
** rather than an ASCII string). Also fix long standing bug with
** full file systems and temporary files.
**
** Erik E. Fair <fair@apple.com>, November 12, 1989
**
** ANSIfy the code somewhat to make gcc -Wall happy with the code.
** Submit to NetBSD
**
** Erik E. Fair <fair@clock.org>, May 20, 1997
*/
#include <sys/types.h>
#include <sys/file.h>
#include <fcntl.h> /* Needed on hpux */
#include <stdio.h>
#include <signal.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#define LOCK_SET 0
#define LOCK_FAIL 1
#define LOCK_GOOD 0
#define LOCK_BAD 1
#define FAIL (-1)
#define TRUE 1
#define FALSE 0
int Debug = FALSE;
char *Pname;
const char USAGE[] = "%s: USAGE: shlock -f file -p pid [-d][-u]\n";
const char E_unlk[] = "%s: unlink(%s): %s\n";
const char E_open[] = "%s: open(%s): %s\n";
#define dprintf if (Debug) printf
/*
** Prototypes to make the ANSI compilers happy
** Didn't lint used to do type and argument checking?
** (and wasn't that sufficient?)
*/
#ifdef __STDC__
/* the following is in case you need to make the prototypes go away. */
#define _P(x) x
char *xtmpfile _P((char *, pid_t, int));
int p_exists _P((pid_t));
int cklock _P((char *, int));
int mklock _P((char *, pid_t, int));
void bad_usage _P((void));
int main _P((int, char **));
#endif /* __STDC__ */
/*
** Create a temporary file, all ready to lock with.
** The file arg is so we get the filename right, if he
** gave us a full path, instead of using the current directory
** which might not be in the same filesystem.
*/
char *
xtmpfile(file, pid, uucpstyle)
char *file;
pid_t pid;
int uucpstyle;
{
int fd;
int len;
char *cp, buf[BUFSIZ];
static char tempname[BUFSIZ];
sprintf(buf, "shlock%ld", (u_long)getpid());
if ((cp = strrchr(strcpy(tempname, file), '/')) != (char *)NULL) {
*++cp = '\0';
(void) strcat(tempname, buf);
} else
(void) strcpy(tempname, buf);
dprintf("%s: temporary filename: %s\n", Pname, tempname);
sprintf(buf, "%ld\n", (u_long)pid);
len = strlen(buf);
openloop:
if ((fd = open(tempname, O_RDWR|O_CREAT|O_EXCL, 0644)) < 0) {
switch(errno) {
case EEXIST:
dprintf("%s: file %s exists already.\n",
Pname, tempname);
if (unlink(tempname) < 0) {
fprintf(stderr, E_unlk,
Pname, tempname, strerror(errno));
return((char *)NULL);
}
/*
** Further profanity
*/
goto openloop;
default:
fprintf(stderr, E_open,
Pname, tempname, strerror(errno));
return((char *)NULL);
}
}
/*
** Write the PID into the temporary file before attempting to link
** to the actual lock file. That way we have a valid lock the instant
** the link succeeds.
*/
if (uucpstyle ?
(write(fd, &pid, sizeof(pid)) != sizeof(pid)) :
(write(fd, buf, len) < 0))
{
fprintf(stderr, "%s: write(%s,%ld): %s\n",
Pname, tempname, (u_long)pid, strerror(errno));
(void) close(fd);
if (unlink(tempname) < 0) {
fprintf(stderr, E_unlk,
Pname, tempname, strerror(errno));
}
return((char *)NULL);
}
(void) close(fd);
return(tempname);
}
/*
** Does the PID exist?
** Send null signal to find out.
*/
int
p_exists(pid)
pid_t pid;
{
dprintf("%s: process %ld is ", Pname, (u_long)pid);
if (pid <= 0) {
dprintf("invalid\n");
return(FALSE);
}
if (kill(pid, 0) < 0) {
switch(errno) {
case ESRCH:
dprintf("dead\n");
return(FALSE); /* pid does not exist */
case EPERM:
dprintf("alive\n");
return(TRUE); /* pid exists */
default:
dprintf("state unknown: %s\n", strerror(errno));
return(TRUE); /* be conservative */
}
}
dprintf("alive\n");
return(TRUE); /* pid exists */
}
/*
** Check the validity of an existing lock file.
**
** Read the PID out of the lock
** Send a null signal to determine whether that PID still exists
** Existence (or not) determines the validity of the lock.
**
** Two bigs wins to this algorithm:
**
** o Locks do not survive crashes of either the system or the
** application by any appreciable period of time.
**
** o No clean up to do if the system or application crashes.
**
*/
int
cklock(file, uucpstyle)
char *file;
int uucpstyle;
{
int fd = open(file, O_RDONLY);
ssize_t len;
pid_t pid;
char buf[BUFSIZ];
dprintf("%s: checking extant lock <%s>\n", Pname, file);
if (fd < 0) {
if (errno != ENOENT)
fprintf(stderr, E_open, Pname, file, strerror(errno));
return(TRUE); /* might or might not; conservatism */
}
if (uucpstyle ?
((len = read(fd, &pid, sizeof(pid))) != sizeof(pid)) :
((len = read(fd, buf, sizeof(buf))) <= 0))
{
close(fd);
dprintf("%s: lock file format error\n", Pname);
return(FALSE);
}
close(fd);
buf[len + 1] = '\0';
return(p_exists(uucpstyle ? pid : atoi(buf)));
}
int
mklock(file, pid, uucpstyle)
char *file;
pid_t pid;
int uucpstyle;
{
char *tmp;
int retcode = FALSE;
dprintf("%s: trying lock <%s> for process %ld\n", Pname, file,
(u_long)pid);
if ((tmp = xtmpfile(file, pid, uucpstyle)) == (char *)NULL)
return(FALSE);
linkloop:
if (link(tmp, file) < 0) {
switch(errno) {
case EEXIST:
dprintf("%s: lock <%s> already exists\n", Pname, file);
if (cklock(file, uucpstyle)) {
dprintf("%s: extant lock is valid\n", Pname);
break;
} else {
dprintf("%s: lock is invalid, removing\n",
Pname);
if (unlink(file) < 0) {
fprintf(stderr, E_unlk,
Pname, file, strerror(errno));
break;
}
}
/*
** I hereby profane the god of structured programming,
** Edsgar Dijkstra
*/
goto linkloop;
default:
fprintf(stderr, "%s: link(%s, %s): %s\n",
Pname, tmp, file, strerror(errno));
break;
}
} else {
dprintf("%s: got lock <%s>\n", Pname, file);
retcode = TRUE;
}
if (unlink(tmp) < 0) {
fprintf(stderr, E_unlk, Pname, tmp, strerror(errno));
}
return(retcode);
}
void
bad_usage()
{
fprintf(stderr, USAGE, Pname);
exit(LOCK_FAIL);
}
int
main(ac, av)
int ac;
char *av[];
{
int x;
char *file = (char *)NULL;
pid_t pid = 0;
int uucpstyle = FALSE; /* indicating UUCP style locks */
int only_check = TRUE; /* don't make a lock */
Pname = ((Pname = strrchr(av[0], '/')) ? Pname + 1 : av[0]);
for(x = 1; x < ac; x++) {
if (av[x][0] == '-') {
switch(av[x][1]) {
case 'u':
uucpstyle = TRUE;
break;
case 'd':
Debug = TRUE;
break;
case 'p':
if (strlen(av[x]) > 2) {
pid = atoi(&av[x][2]);
} else {
if (++x >= ac) {
bad_usage();
}
pid = atoi(av[x]);
}
only_check = FALSE; /* wants one */
break;
case 'f':
if (strlen(av[x]) > 2) {
file = &av[x][2];
} else {
if (++x >= ac) {
bad_usage();
}
file = av[x];
}
break;
default:
fprintf(stderr, USAGE, Pname);
exit(LOCK_FAIL);
}
}
}
if (file == (char *)NULL || (!only_check && pid <= 0)) {
bad_usage();
}
if (only_check) {
exit(cklock(file, uucpstyle) ? LOCK_GOOD : LOCK_BAD);
}
exit(mklock(file, pid, uucpstyle) ? LOCK_SET : LOCK_FAIL);
}