Added <errno.h> and made kernel use it

kernel/include/errno.h

@@ -0,0 +1,35 @@
+#ifndef _ERRNO_H
+#define _ERRNO_H
+
+#include <kernel.h>
+
+#define ERRNO_MAX 4095
+
+#define IS_ERR(_ptr) ((uintptr_t)(_ptr) >= (uintptr_t)(-ERRNO_MAX))
+
+#define ERR_PTR(_err) ((void*)(_err))
+#define PTR_ERR(_ptr) ((int)(intptr_t)(_ptr))
+
+// TODO: Add correct errno.h numbers
+enum {
+	SUCCESS = 0,
+	ENOMEM,		// Cannot allocate memory
+	EPERM,		// Operation not permitted
+	ENOENT,		// No entry (no such file or directory)
+	EIO,		// Input/Output error
+	ENXIO,		// No such device or address
+	EAGAIN,		// Resource temporarly busy
+	EACCES,		// Permission denied
+	EFAULT,		// Bad address
+	ENODEV,		// No such device
+	EINVAL,		// Invalid argument
+	EDOM,		// Numerical argument out of domain
+	ERANGE,		// Numerical result out of range
+	ENOSYS,		// Function not implemented
+	ENOTSUP,	// Not supported
+	EILLSEQ,	// Illegal byte sequence
+	EOVERFLOW,	// 
+	EALIGN,		// Not aligned
+};
+
+#endif