--- /dev/null
+/*
+ * File locker
+ *
+ * Usage: with-lock-ex -<mode> <lockfile> <command> <args>...
+ *
+ * modes are
+ * w wait for the lock
+ * f fail if the lock cannot be acquired
+ * q silently do nothing if the lock cannot be acquired
+ *
+ * with-lock-ex will open and lock the lockfile for writing and
+ * then feed the remainder of its arguments to exec(2); when
+ * that process terminates the fd will be closed and the file
+ * unlocked automatically by the kernel.
+ *
+ * If invoked as with-lock, behaves like with-lock-ex -f (for backward
+ * compatibility with an earlier version).
+ *
+ * This file written by me, Ian Jackson, in 1993, 1994, 1995, 1996,
+ * 1998, 1999. I hereby place it in the public domain.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/stat.h>
+
+static const char *cmd;
+
+static void fail(const char *why) __attribute__((noreturn));
+
+static void fail(const char *why) {
+ fprintf(stderr,"with-lock-ex %s: %s: %s\n",cmd,why,strerror(errno));
+ exit(255);
+}
+
+int main(int argc, char **argv) {
+ int fd, mode, um;
+ struct stat stab, fstab;
+ long cloexec;
+ struct flock fl;
+ const char *p;
+
+ if (argc >= 3 && !strcmp((p= strrchr(argv[0],'/')) ? ++p : argv[0], "with-lock")) {
+ mode= 'f';
+ } else if (argc < 4 || argv[1][0] != '-' || argv[1][2] ||
+ ((mode= argv[1][1]) != 'w' && mode != 'q' && mode != 'f')) {
+ fputs("usage: with-lock-ex -w|-q|-f <lockfile> <command> <args>...\n"
+ " with-lock <lockfile> <command> <args>...\n",
+ stderr);
+ exit(255);
+ } else {
+ argv++; argc--;
+ }
+ cmd= argv[2];
+ um= umask(0777); if (um==-1) fail("find umask");
+ if (umask(um)==-1) fail("reset umask");
+
+ for (;;) {
+
+ fd= open(argv[1],O_RDWR|O_CREAT,0666&~(um|((um&0222)<<1)));
+ if (fd<0) fail(argv[1]);
+
+ for (;;) {
+ fl.l_type= F_WRLCK;
+ fl.l_whence= SEEK_SET;
+ fl.l_start= 0;
+ fl.l_len= 1;
+ if (fcntl(fd, mode=='w' ? F_SETLKW : F_SETLK, &fl) != -1) break;
+ if (mode=='q' &&
+ (errno == EAGAIN || errno == EWOULDBLOCK || errno == EBUSY))
+ exit(0);
+ if (errno != EINTR) fail("could not acquire lock");
+ }
+
+ if (fstat(fd, &fstab)) fail("could not fstat lock fd");
+ if (stat(argv[1], &stab)) {
+ if (errno != ENOENT) fail("could not stat lockfile");
+ } else {
+ if (stab.st_dev == fstab.st_dev &&
+ stab.st_ino == fstab.st_ino) break;
+ }
+ close(fd);
+ }
+
+ cloexec= fcntl(fd, F_GETFD); if (cloexec==-1) fail("fcntl F_GETFD");
+ cloexec &= ~1;
+ if (fcntl(fd, F_SETFD, cloexec)==-1) fail("fcntl F_SETFD");
+
+ execvp(cmd,argv+2);
+ fail("unable to execute command");
+}