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Initial import of the lockf utility. It executes an arbitrary command

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while holding an exclusive lock on a file.
This commit is contained in:
John Polstra 1997-01-08 20:12:59 +00:00
parent 62ce633d36
commit c8929a4926
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/cvs2svn/branches/JDP/; revision=21439
3 changed files with 314 additions and 0 deletions
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6
usr.bin/lockf/Makefile Normal file
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# $Id$
PROG= lockf
CFLAGS+=-Wall
.include <bsd.prog.mk>

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usr.bin/lockf/lockf.1 Normal file
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.\"
.\" Copyright (C) 1997 John D. Polstra. 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 JOHN D. POLSTRA 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 JOHN D. POLSTRA 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.
.\"
.\" $Id$
.\"
.Dd January 8, 1997
.Os FreeBSD
.Dt LOCKF 1
.Sh NAME
.Nm lockf
.Nd execute a command while holding a file lock
.Sh SYNOPSIS
.Nm
.Op Fl s
.Op Fl t Ar seconds
.Ar file
.Ar command
.Op Ar arguments
.Sh DESCRIPTION
The
.Nm
utility acquires an exclusive lock on a
.Ar file ,
creating it if necessary.
While holding the lock, it executes a
.Ar command
with optional
.Ar arguments .
After the
.Ar command
completes,
.Nm
releases the lock and removes the
.Ar file .
BSD-style locking is used, as described in
.Xr flock 2 ;
the mere existence of the
.Ar file
is not considered to constitute a lock.
.Pp
The following options are supported:
.Bl -tag -width Fl
.It Fl s
Causes
.Nm
to operate silently.
Failure to acquire the lock is indicated only in the exit status.
.It Fl t Ar seconds
Specifies a timeout for waiting for the lock. By default,
.Nm
waits indefinitely to acquire the lock.
If a timeout is specified with this option,
.Nm
will wait at most the given number of
.Ar seconds
before giving up. A timeout of 0 may be given, in which case
.Nm
will fail unless it can acquire the lock immediately.
.El
.Pp
In no event will
.Nm
break a lock that is held by another process.
.Sh DIAGNOSTICS
If
.Nm
is unable to acquire the lock, it returns an exit status of 1.
Otherwise, it returns the exit status produced by
.Ar command .
.Sh SEE ALSO
.Xr flock 2 .
.Sh AUTHORS
John Polstra,
.Aq jdp@polstra.com .

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usr.bin/lockf/lockf.c Normal file
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/*
* Copyright (C) 1997 John D. Polstra. 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 JOHN D. POLSTRA 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 JOHN D. POLSTRA 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.
*
* $Id$
*/
#include <sys/types.h>
#include <sys/wait.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static int acquire_lock(const char *name);
static void cleanup(void);
static void killed(int sig);
static void timeout(int sig);
static void usage(void);
static void wait_for_lock(const char *name);
static const char *lockname;
static volatile sig_atomic_t timed_out;
/*
* Execute an arbitrary command while holding a file lock.
*/
int
main(int argc, char **argv)
{
int ch;
int lockfd;
int silent;
int status;
int waitsec;
pid_t child;
silent = 0;
waitsec = -1; /* Infinite. */
while ((ch = getopt(argc, argv, "st:")) != EOF) {
switch (ch) {
case 's':
silent = 1;
break;
case 't':
{
char *endptr;
waitsec = strtol(optarg, &endptr, 0);
if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
errx(1, "invalid timeout \"%s\"", optarg);
}
break;
default:
usage();
}
}
if (argc - optind < 2)
usage();
lockname = argv[optind++];
argc -= optind;
argv += optind;
if (waitsec > 0) { /* Set up a timeout. */
struct sigaction act;
act.sa_handler = timeout;
sigemptyset(&act.sa_mask);
act.sa_flags = 0; /* Note that we do not set SA_RESTART. */
sigaction(SIGALRM, &act, NULL);
alarm(waitsec);
}
lockfd = acquire_lock(lockname);
while (lockfd == -1 && !timed_out && waitsec != 0) {
wait_for_lock(lockname);
lockfd = acquire_lock(lockname);
}
if (waitsec > 0)
alarm(0);
if (lockfd == -1) { /* We failed to acquire the lock. */
if (silent)
exit(1);
errx(1, "%s: already locked", lockname);
}
/* At this point, we own the lock. */
if (atexit(cleanup) == -1)
err(1, "atexit failed");
if ((child = fork()) == -1)
err(1, "cannot fork");
if (child == 0) { /* The child process. */
close(lockfd);
execvp(argv[0], argv);
perror(argv[0]);
_exit(1);
}
/* This is the parent process. */
signal(SIGINT, SIG_IGN);
signal(SIGQUIT, SIG_IGN);
signal(SIGTERM, killed);
if (waitpid(child, &status, 0) == -1)
err(1, "waitpid failed");
return WIFEXITED(status) ? WEXITSTATUS(status) : 1;
}
/*
* Try to acquire a lock on the given file, but don't wait for it. Returns
* an open file descriptor on success, or -1 on failure.
*/
static int
acquire_lock(const char *name)
{
int fd;
if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|O_NONBLOCK, 0666)) == -1) {
if (errno == EAGAIN || errno == EINTR)
return -1;
err(1, "cannot open %s", name);
}
return fd;
}
/*
* Remove the lock file.
*/
static void
cleanup(void)
{
if (unlink(lockname) == -1 && errno != ENOENT)
err(1, "cannot unlink %s", lockname);
}
/*
* Signal handler for SIGTERM. Cleans up the lock file, then re-raises
* the signal.
*/
static void
killed(int sig)
{
cleanup();
signal(sig, SIG_DFL);
if (kill(getpid(), sig) == -1)
err(1, "kill failed");
}
/*
* Signal handler for SIGALRM.
*/
static void
timeout(int sig)
{
timed_out = 1;
}
static void
usage(void)
{
errx(1, "usage: lockf [-s] [-t seconds] file command [arguments]");
}
/*
* Wait until it might be possible to acquire a lock on the given file.
*/
static void
wait_for_lock(const char *name)
{
int fd;
if ((fd = open(name, O_RDONLY|O_EXLOCK)) == -1) {
if (errno == ENOENT || errno == EINTR)
return;
err(1, "cannot open %s", name);
}
close(fd);
return;
}