Index: abi/include/_bits/errno.h
===================================================================
--- abi/include/_bits/errno.h	(revision 549bef19d0cb4650592539cc4d784cbcf34926ea)
+++ abi/include/_bits/errno.h	(revision 549bef19d0cb4650592539cc4d784cbcf34926ea)
@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2017 CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/* Authors:
+ *	Jiří Zárevúcky (jzr) <zarevucky.jiri@gmail.com>
+ */
+
+/** @addtogroup bits
+ * @{
+ */
+/** @file
+ */
+
+#ifndef _BITS_ERRNO_H_
+#define _BITS_ERRNO_H_
+
+#ifdef __OPAQUE_ERRNO__
+#include <_bits/opaque_handle.h>
+
+opaque_handle(errno_t);
+typedef errno_t sys_errno_t;
+#define __errno_t(val) ((errno_t) val)
+
+#else
+
+#include <_bits/native.h>
+
+/**
+ * The type of <errno.h> constants. Normally, this is an alias for `int`,
+ * but we support an alternative definition that allows us to verify
+ * integrity of error handling without using external tools.
+ */
+typedef int errno_t;
+
+/**
+ * Same as `errno_t`, except represented as `sysarg_t`. Used in kernel in
+ * places where error number is always passed, but the type must be `sysarg_t`.
+ */
+typedef sysarg_t sys_errno_t;
+
+/**
+ * A C++-style "cast" to `errno_t`.
+ * Used in <abi/errno.h> to define error constants. Normally, it doesn't do
+ * anything at all.
+ */
+#define __errno_t(val) val
+
+#endif
+
+#endif
Index: abi/include/_bits/opaque_handle.h
===================================================================
--- abi/include/_bits/opaque_handle.h	(revision 549bef19d0cb4650592539cc4d784cbcf34926ea)
+++ abi/include/_bits/opaque_handle.h	(revision 549bef19d0cb4650592539cc4d784cbcf34926ea)
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2017 CZ.NIC, z.s.p.o.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/* Authors:
+ *	Jiří Zárevúcky (jzr) <zarevucky.jiri@gmail.com>
+ */
+
+/** @addtogroup bits
+ * @{
+ */
+
+#ifndef _BITS_OPAQUE_HANDLE_H_
+#define _BITS_OPAQUE_HANDLE_H_
+
+#define opaque_handle(__name) typedef struct __opaque_##__name *__name
+
+#endif
+
+/** @}
+ */