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

fusl/src/fcntl/fcntl.c

Index: fusl/src/fcntl/fcntl.c
diff --git a/fusl/src/fcntl/fcntl.c b/fusl/src/fcntl/fcntl.c
new file mode 100644
index 0000000000000000000000000000000000000000..ce615d0e5dcce990992bd99d65b52f1ec0a3d53c
--- /dev/null
+++ b/fusl/src/fcntl/fcntl.c
@@ -0,0 +1,49 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdarg.h>
+#include <errno.h>
+#include "syscall.h"
+#include "libc.h"
+
+int fcntl(int fd, int cmd, ...)
+{
+	unsigned long arg;
+	va_list ap;
+	va_start(ap, cmd);
+	arg = va_arg(ap, unsigned long);
+	va_end(ap);
+	if (cmd == F_SETFL) arg |= O_LARGEFILE;
+	if (cmd == F_SETLKW) return syscall_cp(SYS_fcntl, fd, cmd, (void *)arg);
+	if (cmd == F_GETOWN) {
+		struct f_owner_ex ex;
+		int ret = __syscall(SYS_fcntl, fd, F_GETOWN_EX, &ex);
+		if (ret == -EINVAL) return __syscall(SYS_fcntl, fd, cmd, (void *)arg);
+		if (ret) return __syscall_ret(ret);
+		return ex.type == F_OWNER_PGRP ? -ex.pid : ex.pid;
+	}
+	if (cmd == F_DUPFD_CLOEXEC) {
+		int ret = __syscall(SYS_fcntl, fd, F_DUPFD_CLOEXEC, arg);
+		if (ret != -EINVAL) {
+			if (ret >= 0)
+				__syscall(SYS_fcntl, ret, F_SETFD, FD_CLOEXEC);
+			return __syscall_ret(ret);
+		}
+		ret = __syscall(SYS_fcntl, fd, F_DUPFD_CLOEXEC, 0);
+		if (ret != -EINVAL) {
+			if (ret >= 0) __syscall(SYS_close, ret);
+			return __syscall_ret(-EINVAL);
+		}
+		ret = __syscall(SYS_fcntl, fd, F_DUPFD, arg);
+		if (ret >= 0) __syscall(SYS_fcntl, ret, F_SETFD, FD_CLOEXEC);
+		return __syscall_ret(ret);
+	}
+	switch (cmd) {
+	case F_SETLK:
+	case F_GETLK:
+	case F_GETOWN_EX:
+	case F_SETOWN_EX:
+		return syscall(SYS_fcntl, fd, cmd, (void *)arg);
+	default:
+		return syscall(SYS_fcntl, fd, cmd, arg);
+	}
+}