Add a "fork" of musl as //fusl.

fusl/src/misc/lockf.c

Index: fusl/src/misc/lockf.c
diff --git a/fusl/src/misc/lockf.c b/fusl/src/misc/lockf.c
new file mode 100644
index 0000000000000000000000000000000000000000..d8f82efd3b1d2395bfdd6ef9464e2bc0b28feb0f
--- /dev/null
+++ b/fusl/src/misc/lockf.c
@@ -0,0 +1,33 @@
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "libc.h"
+
+int lockf(int fd, int op, off_t size)
+{
+	struct flock l = {
+		.l_type = F_WRLCK,
+		.l_whence = SEEK_CUR,
+		.l_len = size,
+	};
+	switch (op) {
+	case F_TEST:
+		l.l_type = F_RDLCK;
+		if (fcntl(fd, F_GETLK, &l) < 0)
+			return -1;
+		if (l.l_type == F_UNLCK || l.l_pid == getpid())
+			return 0;
+		errno = EACCES;
+		return -1;
+	case F_ULOCK:
+		l.l_type = F_UNLCK;
+	case F_TLOCK:
+		return fcntl(fd, F_SETLK, &l);
+	case F_LOCK:
+		return fcntl(fd, F_SETLKW, &l);
+	}
+	errno = EINVAL;
+	return -1;
+}
+
+LFS64(lockf);