Hi there,
I've ported lockf(1) from Freebsd, made some style changes to conform
to style(9) and added an option to write the lock holder pid in the
lockfile (-p) option.
It's a single file with 246 lines.
I'll port/write the manpage if you think the port may be
accepted. This is the first port I'm proposing, so please tell me if
I'm doing something wrong.
What to do with the header copyright ? Do I change it ?
Here is the diff from the freebsd code, below is code itself.
--- lockf.orig.c Thu Apr 16 20:20:20 2009
+++ lockf.c Thu Apr 16 21:27:28 2009
@@ -34,15 +34,16 @@
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
+#include <string.h>
#include <sysexits.h>
#include <unistd.h>
-static int acquire_lock(const char *name, int flags);
+static int acquire_lock(const char *, int);
static void cleanup(void);
-static void killed(int sig);
-static void timeout(int sig);
+static void killed(int);
+static void timeout(int);
static void usage(void);
-static void wait_for_lock(const char *name);
+static void wait_for_lock(const char *);
static const char *lockname;
static int lockfd = -1;
@@ -55,13 +56,17 @@ static volatile sig_atomic_t timed_out;
int
main(int argc, char **argv)
{
- int ch, silent, status, waitsec;
+ char pidbuf[32];
+ int ch, silent, status, waitsec, storepid;
pid_t child;
-
- silent = keep = 0;
+
+ silent = keep = storepid = 0;
waitsec = -1; /* Infinite. */
- while ((ch = getopt(argc, argv, "skt:")) != -1) {
+ while ((ch = getopt(argc, argv, "pskt:")) != -1) {
switch (ch) {
+ case 'p':
+ storepid = 1;
+ break;
case 'k':
keep = 1;
break;
@@ -134,6 +139,13 @@ main(int argc, char **argv)
errx(EX_TEMPFAIL, "%s: already locked", lockname);
}
/* At this point, we own the lock. */
+ if (storepid) {
+ if (ftruncate(lockfd, 0) == -1) /* Make sure file is empty */
+ err(EX_IOERR, "ftruncate error");
+ snprintf(pidbuf, sizeof(pidbuf), "%ld", (unsigned long)
getpid());
+ if (write(lockfd, pidbuf, strlen(pidbuf)) < 0)
+ err(EX_IOERR, "write error");
+ }
if (atexit(cleanup) == -1)
err(EX_OSERR, "atexit failed");
if ((child = fork()) == -1)
@@ -164,7 +176,7 @@ acquire_lock(const char *name, int flags)
{
int fd;
- if ((fd = open(name, O_RDONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
+ if ((fd = open(name, O_WRONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
if (errno == EAGAIN || errno == EINTR)
return (-1);
err(EX_CANTCREAT, "cannot open %s", name);
@@ -192,7 +204,6 @@ cleanup(void)
static void
killed(int sig)
{
-
cleanup();
signal(sig, SIG_DFL);
if (kill(getpid(), sig) == -1)
@@ -208,13 +219,13 @@ timeout(int sig)
timed_out = 1;
}
-static void
+__dead void
usage(void)
{
-
- fprintf(stderr,
- "usage: lockf [-ks] [-t seconds] file command [arguments]\n");
- exit(EX_USAGE);
+ extern char *__progname;
+
+ err(EX_USAGE,
+ "usage: %s [-pks] [-t seconds] file command [arguments]\n",
__progname);
}
/*
Follows the complete source file.
/*
* 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.
*/
#include <sys/cdefs.h>
#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 <string.h>
#include <sysexits.h>
#include <unistd.h>
static int acquire_lock(const char *, int);
static void cleanup(void);
static void killed(int);
static void timeout(int);
static void usage(void);
static void wait_for_lock(const char *);
static const char *lockname;
static int lockfd = -1;
static int keep;
static volatile sig_atomic_t timed_out;
/*
* Execute an arbitrary command while holding a file lock.
*/
int
main(int argc, char **argv)
{
char pidbuf[32];
int ch, silent, status, waitsec, storepid;
pid_t child;
silent = keep = storepid = 0;
waitsec = -1; /* Infinite. */
while ((ch = getopt(argc, argv, "pskt:")) != -1) {
switch (ch) {
case 'p':
storepid = 1;
break;
case 'k':
keep = 1;
break;
case 's':
silent = 1;
break;
case 't':
{
char *endptr;
waitsec = strtol(optarg, &endptr, 0);
if (*optarg == '\0' || *endptr != '\0' || waitsec < 0)
errx(EX_USAGE,
"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);
}
/*
* If the "-k" option is not given, then we must not block when
* acquiring the lock. If we did, then the lock holder would
* unlink the file upon releasing the lock, and we would acquire
* a lock on a file with no directory entry. Then another
* process could come along and acquire the same lock. To avoid
* this problem, we separate out the actions of waiting for the
* lock to be available and of actually acquiring the lock.
*
* That approach produces behavior that is technically correct;
* however, it causes some performance & ordering problems for
* locks that have a lot of contention. First, it is unfair in
* the sense that a released lock isn't necessarily granted to
* the process that has been waiting the longest. A waiter may
* be starved out indefinitely. Second, it creates a thundering
* herd situation each time the lock is released.
*
* When the "-k" option is used, the unlink race no longer
* exists. In that case we can block while acquiring the lock,
* avoiding the separate step of waiting for the lock. This
* yields fairness and improved performance.
*/
lockfd = acquire_lock(lockname, O_NONBLOCK);
while (lockfd == -1 && !timed_out && waitsec != 0) {
if (keep)
lockfd = acquire_lock(lockname, 0);
else {
wait_for_lock(lockname);
lockfd = acquire_lock(lockname, O_NONBLOCK);
}
}
if (waitsec > 0)
alarm(0);
if (lockfd == -1) { /* We failed to acquire the lock. */
if (silent)
exit(EX_TEMPFAIL);
errx(EX_TEMPFAIL, "%s: already locked", lockname);
}
/* At this point, we own the lock. */
if (storepid) {
if (ftruncate(lockfd, 0) == -1) /* Make sure file is empty */
err(EX_IOERR, "ftruncate error");
snprintf(pidbuf, sizeof(pidbuf), "%ld", (unsigned long)
getpid());
if (write(lockfd, pidbuf, strlen(pidbuf)) < 0)
err(EX_IOERR, "write error");
}
if (atexit(cleanup) == -1)
err(EX_OSERR, "atexit failed");
if ((child = fork()) == -1)
err(EX_OSERR, "cannot fork");
if (child == 0) { /* The child process. */
close(lockfd);
execvp(argv[0], argv);
warn("%s", 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(EX_OSERR, "waitpid failed");
return (WIFEXITED(status) ? WEXITSTATUS(status) : EX_SOFTWARE);
}
/*
* Try to acquire a lock on the given file, creating the file if
* necessary. The flags argument is O_NONBLOCK or 0, depending on
* whether we should wait for the lock. Returns an open file descriptor
* on success, or -1 on failure.
*/
static int
acquire_lock(const char *name, int flags)
{
int fd;
if ((fd = open(name, O_WRONLY|O_CREAT|O_EXLOCK|flags, 0666)) == -1) {
if (errno == EAGAIN || errno == EINTR)
return (-1);
err(EX_CANTCREAT, "cannot open %s", name);
}
return (fd);
}
/*
* Remove the lock file.
*/
static void
cleanup(void)
{
if (keep)
flock(lockfd, LOCK_UN);
else
unlink(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(EX_OSERR, "kill failed");
}
/*
* Signal handler for SIGALRM.
*/
static void
timeout(int sig)
{
timed_out = 1;
}
__dead void
usage(void)
{
extern char *__progname;
err(EX_USAGE,
"usage: %s [-pks] [-t seconds] file command [arguments]\n",
__progname);
}
/*
* Wait until it might be possible to acquire a lock on the given file.
* If the file does not exist, return immediately without creating it.
*/
static void
wait_for_lock(const char *name)
{
int fd;
if ((fd = open(name, O_RDONLY|O_EXLOCK, 0666)) == -1) {
if (errno == ENOENT || errno == EINTR)
return;
err(EX_CANTCREAT, "cannot open %s", name);
}
close(fd);
}
