1 files changed, 118 insertions, 0 deletions
diff --git a/flock_mmap/flock_mmap.c b/flock_mmap/flock_mmap.c
new file mode 100644
index 0000000..7954a40
--- /dev/null
+++ b/flock_mmap/flock_mmap.c
@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <unistd.h>
+#include <getopt.h>
+#include <fcntl.h>
+#include <sys/file.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+
+static const size_t M_SIZE = 1;
+static bool use_fcntl = false;
+static bool close_fd = true;
+static bool should_wait = false;
+static bool verbose = false;
+static const char *path;
+
+static bool parse_args (const int argc, const char **argv) {
+	int opt;
+
+	while ((opt = getopt(argc, (char *const*)argv, "fnwV")) != -1) {
+		switch (opt) {
+		case 'f': use_fcntl = true; break;
+		case 'n': close_fd = false; break;
+		case 'w': should_wait = true; break;
+		case 'V': verbose = true; break;
+		default: return false;
+		}
+	}
+
+	if (optind >= argc) {
+		return false;
+	}
+	else {
+		path = argv[optind];
+	}
+
+	return true;
+}
+
+int main (const int argc, const char **argv) {
+	int ec = 0;
+	int fd = -1;
+	int f_ret;
+	void *m = MAP_FAILED;
+
+	if (!parse_args(argc, argv)) {
+		ec = 2;
+		fprintf(stderr, "Usage: %s -fnw <lock file path>\n", argv[0]);
+		goto END;
+	}
+
+	if (!verbose) {
+		close(STDOUT_FILENO);
+	}
+
+	fd = open(path, O_CREAT | O_TRUNC | O_RDWR, 0755);
+	if (fd < 0) {
+		ec = 1;
+		perror(path);
+		goto END;
+	}
+
+	if (use_fcntl) {
+		struct flock fl;
+
+		memset(&fl, 0, sizeof(fl));
+		fl.l_type = F_WRLCK;
+		fl.l_whence = SEEK_SET;
+		fl.l_len = M_SIZE;
+
+		f_ret = fcntl(fd, F_SETLK, &fl);
+	}
+	else {
+		f_ret = flock(fd, LOCK_EX | LOCK_NB);
+	}
+
+	if (f_ret != 0) {
+		ec = 1;
+		perror(path);
+		goto END;
+	}
+
+	f_ret = ftruncate(fd, M_SIZE);
+	if (f_ret != 0) {
+		ec = 1;
+		perror(path);
+		goto END;
+	}
+
+	m = mmap(NULL, M_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (m == MAP_FAILED) {
+		ec = 1;
+		perror(path);
+		goto END;
+	}
+
+	// This block
+	if (close_fd) {
+		close(fd);
+		fd = -1;
+	}
+
+	printf("Lock holding\n");
+	if (should_wait) {
+		pause();
+	}
+
+END:
+	if (fd >= 0) {
+		close(fd);
+	}
+	if (m != MAP_FAILED) {
+		munmap(m, M_SIZE);
+	}
+	return ec;
+}