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

fusl/src/stdio/freopen.c

Index: fusl/src/stdio/freopen.c
diff --git a/fusl/src/stdio/freopen.c b/fusl/src/stdio/freopen.c
new file mode 100644
index 0000000000000000000000000000000000000000..6c1b575f527963566a7b457f29c18dea45b2505a
--- /dev/null
+++ b/fusl/src/stdio/freopen.c
@@ -0,0 +1,54 @@
+#include "stdio_impl.h"
+#include <fcntl.h>
+
+/* The basic idea of this implementation is to open a new FILE,
+ * hack the necessary parts of the new FILE into the old one, then
+ * close the new FILE. */
+
+/* Locking IS necessary because another thread may provably hold the
+ * lock, via flockfile or otherwise, when freopen is called, and in that
+ * case, freopen cannot act until the lock is released. */
+
+int __dup3(int, int, int);
+
+FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict f)
+{
+	int fl = __fmodeflags(mode);
+	FILE *f2;
+
+	FLOCK(f);
+
+	fflush(f);
+
+	if (!filename) {
+		if (fl&O_CLOEXEC)
+			__syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
+		fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
+		if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
+			goto fail;
+	} else {
+		f2 = fopen(filename, mode);
+		if (!f2) goto fail;
+		if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
+		else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
+
+		f->flags = (f->flags & F_PERM) | f2->flags;
+		f->read = f2->read;
+		f->write = f2->write;
+		f->seek = f2->seek;
+		f->close = f2->close;
+
+		fclose(f2);
+	}
+
+	FUNLOCK(f);
+	return f;
+
+fail2:
+	fclose(f2);
+fail:
+	fclose(f);
+	return NULL;
+}
+
+LFS64(freopen);