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/* lckdo.c: run a program with a lock held,
* to prevent multiple processes running in parallel.
* Use just like `nice' or `nohup'.
* Written by Michael Tokarev <mjt@tls.msk.ru>
* Public domain.
*/
#define _GNU_SOURCE
#define _BSD_SOURCE
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <stdarg.h>
#include <sysexits.h>
#include <sys/file.h>
#include <sys/wait.h>
#include <signal.h>
/* compile with -DUSE_FLOCK to use flock() instead of fcntl() */
#if !defined(USE_FLOCK) && !defined(F_SETLKW)
# define USE_FLOCK
#endif
#ifndef __GNUC__
# ifndef __attribute__
# define __attribute__(x)
# endif
#endif
static char *progname;
static void
__attribute__((format(printf,3,4)))
__attribute__((noreturn))
error(int errnum, int exitcode, const char *fmt, ...) {
va_list ap;
fprintf(stderr, "%s: ", progname);
va_start(ap, fmt); vfprintf(stderr, fmt, ap); va_end(ap);
if (errnum)
fprintf(stderr, ": %s\n", strerror(errnum));
else
fputs("\n", stderr);
exit(exitcode);
}
static const char *lckfile;
static int quiet;
static void sigalarm(int sig) {
if (quiet)
_exit(EX_TEMPFAIL);
error(0, EX_TEMPFAIL,
"lock file `%s' is already locked (timeout waiting)", lckfile);
}
int main(int argc, char **argv) {
int fd;
int c;
int create = O_CREAT;
int dofork = 1;
int waittime = 0;
int shared = 0;
int test = 0;
int fdn = -1;
#ifndef USE_FLOCK
struct flock fl;
#endif
if ((progname = strrchr(argv[0], '/')) == NULL)
progname = argv[0];
else
argv[0] = ++progname;
if (argc == 1) {
printf(
"%s: execute a program with a lock set.\n"
"Usage: %s [options] lockfile program [arguments]\n"
"where options are:\n"
" -w - if the lock is already held by another process,\n"
" wait for it to complete instead of failing immediately\n"
" -W sec - the same as -w but wait not more than sec seconds\n"
" -e - execute the program directly, no fork/wait\n"
" (keeps extra open file descriptor)\n"
" -E nnn - set the fd# to keep open in -e case (implies -e)\n"
" -n - do not create the lock file if it does not exist\n"
" -q - produce no output if lock is already held\n"
" -s - lock in shared (read) mode\n"
" -x - lock in exclusive (write) mode (default)\n"
" -t - test for lock existence"
#ifndef USE_FLOCK
" (just prints pid if any with -q)\n"
#endif
" (implies -n)\n"
, progname, progname);
return 0;
}
while ((c = getopt(argc, argv, "+wW:neE:sxtq")) != EOF) {
switch(c) {
case 'w':
if (!waittime)
waittime = -1;
break;
case 'W':
if ((waittime = atoi(optarg)) < 1)
error(0, EX_USAGE, "invalid wait time `%s'", optarg);
break;
case 't':
test = 1;
/* fall thru */
case 'n':
create = 0;
break;
case 'E':
if ((fdn = atoi(optarg)) < 0 || fdn == 2)
error(0, EX_USAGE, "invalid fd# `%s'", optarg);
/* fall thru */
case 'e':
dofork = 0;
break;
case 's':
shared = 1;
break;
case 'x':
shared = 0;
break;
case 'q':
quiet = 1;
break;
default:
return EX_USAGE;
}
}
argc -= optind; argv += optind;
if (!argc || (!test && argc < 2))
error(0, EX_USAGE, "too few arguments given");
lckfile = *argv++;
#ifdef USE_FLOCK
create |= O_RDONLY;
#else
if (!test)
create |= shared ? O_RDONLY : O_WRONLY;
#endif
fd = open(lckfile, create, 0666);
if (fd < 0) {
if (test && errno == ENOENT) {
if (!quiet)
printf("lockfile `%s' is not locked\n", lckfile);
return 0;
}
error(errno, EX_CANTCREAT, "unable to open `%s'", lckfile);
}
if (!test && fdn >= 0) {
/* dup it early to comply with stupid POSIX fcntl locking
* semantics */
if (dup2(fd, fdn) < 0)
error(errno, EX_OSERR, "dup2(%d,%d) failed", fd, fdn);
close(fd);
fd = fdn;
}
if (test)
waittime = 0;
else if (waittime > 0) {
alarm(waittime);
signal(SIGALRM, sigalarm);
}
#ifdef USE_FLOCK
c = flock(fd, (shared ? LOCK_SH : LOCK_EX) | (waittime ? 0 : LOCK_NB));
if (test && c < 0 &&
(errno == EWOULDBLOCK || errno == EAGAIN || errno == EACCES)) {
if (!quiet)
printf("lockfile `%s' is locked\n", lckfile);
else
printf("locked\n");
return EX_TEMPFAIL;
}
#else
memset(&fl, 0, sizeof(fl));
fl.l_type = shared ? F_RDLCK : F_WRLCK;
c = fcntl(fd, test ? F_GETLK : waittime ? F_SETLKW : F_SETLK, &fl);
if (test && c == 0) {
if (fl.l_type == F_UNLCK) {
if (!quiet)
printf("lockfile `%s' is not locked\n", lckfile);
return 0;
}
if (!quiet)
printf("lockfile `%s' is locked by process %d\n", lckfile, fl.l_pid);
else
printf("%d\n", fl.l_pid);
return EX_TEMPFAIL;
}
#endif
if (waittime > 0)
alarm(0);
if (c < 0) {
if (errno != EWOULDBLOCK && errno != EAGAIN && errno != EACCES)
error(errno, EX_OSERR, "unable to lock `%s'", lckfile);
else if (quiet)
return EX_TEMPFAIL;
else
error(0, EX_TEMPFAIL, "lockfile `%s' is already locked", lckfile);
}
if (dofork) {
pid_t pid;
int flags = fcntl(fd, F_GETFD, 0);
if (flags < 0)
error(errno, EX_OSERR, "fcntl() failed");
fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
pid = fork();
if (pid < 0)
error(errno, EX_OSERR, "unable to fork");
else if (pid) {
if (wait(&c) < 0)
error(errno, EX_OSERR, "wait() failed");
if (WIFSIGNALED(c))
error(0, EX_SOFTWARE, "%s: %s", *argv,
strsignal(WTERMSIG(c)));
return WEXITSTATUS(c);
}
}
execvp(*argv, argv);
error(errno, EX_OSERR, "unable to execute %s", *argv);
}
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