headers: Add err.h header

Instead of bloating util.h lets move ERR_
helpers to own err.h header. This allow
to reuse it where needed without util.h
inclusion.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/err.h

@@ -0,0 +1,53 @@
+/*
+ * Adopted from linux kernel
+ */
+#ifndef __CR_ERR_H__
+#define __CR_ERR_H__
+
+#include "compiler.h"
+
+/*
+ * The address of a block returned by malloc or realloc in GNU
+ * systems is always a multiple of eight (or sixteen on 64-bit systems).
+ *
+ * Thus we may encode error number in low bits.
+ */
+#define MAX_ERRNO	4095
+
+#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
+
+static inline void *ERR_PTR(long error)
+{
+	return (void *)error;
+}
+
+static inline long PTR_ERR(const void *ptr)
+{
+	return (long)ptr;
+}
+
+static inline long IS_ERR(const void *ptr)
+{
+	return IS_ERR_VALUE((unsigned long)ptr);
+}
+
+static inline long IS_ERR_OR_NULL(const void *ptr)
+{
+	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
+}
+
+static inline void *ERR_CAST(const void *ptr)
+{
+	/* cast away the const */
+	return (void *)ptr;
+}
+
+static inline int PTR_RET(const void *ptr)
+{
+	if (IS_ERR(ptr))
+		return PTR_ERR(ptr);
+	else
+		return 0;
+}
+
+#endif /* __CR_ERR_H__ */