+#ifndef F_TLOCK
+#define F_TLOCK 2
+
+#include <sys/file.h>
+
+static int lockf(int fd, int cmd, off_t len)
+{
+ if (cmd != F_TLOCK || len != 0)
+ return -1;
+
+ return flock(fd, LOCK_EX | LOCK_NB);
+}
+#endif // F_TLOCK
+
+/*
+ * Each daemon tries to create and lock BASE/lock file,
+ * if it's successful we are sure we're the only daemon
+ * running over the BASE.
+ *
+ * Once daemon is finished, file descriptor to lock file
+ * is closed and lock is released.
+ */
+static int check_lock(struct daemon *daemon)
+{
+ char path[PATH_MAX];
+ char buf[20];
+ int fd, pid;
+ ssize_t len;
+
+ scnprintf(path, sizeof(path), "%s/lock", daemon->base);
+
+ fd = open(path, O_RDWR|O_CREAT|O_CLOEXEC, 0640);
+ if (fd < 0)
+ return -1;
+
+ if (lockf(fd, F_TLOCK, 0) < 0) {
+ filename__read_int(path, &pid);
+ fprintf(stderr, "failed: another perf daemon (pid %d) owns %s\n",
+ pid, daemon->base);
+ close(fd);
+ return -1;
+ }
+
+ scnprintf(buf, sizeof(buf), "%d", getpid());
+ len = strlen(buf);
+
+ if (write(fd, buf, len) != len) {
+ perror("failed: write");
+ close(fd);
+ return -1;
+ }
+
+ if (ftruncate(fd, len)) {
+ perror("failed: ftruncate");
+ close(fd);
+ return -1;
+ }
+
+ return 0;
+}
+