libxltypes IDL
--------------

Each type in the libxl interface is represented by an object of type
libxltypes.Type (or a subclass thereof). Every local variable defined
by the .idl file must be an instance of libxltypes.Type (e.g. you may
not define Python functions or any other construct other than defining
variables)

The name of the type must be passed as the first argument to the
constructor when defining a new type. The name given should not
contain the initial namespace element (e.g. "libxl_"). See below for
how to specify a namespace.

The Type.typename contains the C name of the type _including_ the
namespace element.

The libxltypes.Type base class has several other properties which
apply to all types. The properties are set by passing a named
parameter to the constructor.

Type.comment:

  A free text comment which describes the type.

Type.namespace: (default: "libxl_")

 The namespace in which the type resides. Usually this is "libxl_" but
 system defined and builtin types may differ.

 If the typename is not None then the namespace is prepended to the
 type.
 
Type.passby: (default: libxltypes.PASS_BY_VALUE)

 Defines the manner in which a type should be passed to C
 functions. Valid values for this fields are:
   libxltypes.PASS_BY_VALUE
   libxltypes.PASS_BY_REFERENCE

Type.destructor_fn: (default: typename + "_destroy" or None if type == None)

 The name of the C function which will free all dynamically allocated
 memory contained within this type (but not the type itself).

Type.autogenerate_destructor: (default: True)

 Indicates if the above named Type.destructor_fn should be
 autogenerated.

Other simple type-Classes
-------------------------

libxltype.Builtin

 Instances of this class represent types which are predefined within
 the system.

libxltype.UInt

 Instances of this class represent the standard uint<N>_t types.

 The <N> for a given instance must be passed to the constructor and is
 then available in UInt.width

libxltype.BitField

 Instances of this class represent bitfield type classes.

 The base type and desired width for a given instance must be passed
 to the contructor. The base type becomes the type of the instance and
 width is contained in BitField.width

libxltype.Reference

 Instances of this type represent a reference to another type

 The referant type must be passed to the constructor and is then
 available in Reference.ref_type

Complex type-Classes
--------------------

libxltype.Aggregate

 Base class for type-Classes which contain a number of other types
 (e.g. structs and unions).

 The contained types are available in the list Aggregate.fields. Each
 element in the list is of type libxltype.Field representing a member
 of the aggregate.

 Each field has the following properties:

  Field.type	The type of the member (a libxltypes.Type).
  Field.name    The name of the member (can be None for anonymous
		fields).
  Field.const	Boolean, true if the member is const.
  Field.comment	A free text comment which describes the member.

libxltype.Struct

 A subclass of libxltype.Aggregate representing the C struct type.

 Struct.kind == "struct"

libxltype.Union

 A subclass of libxltype.Aggregate representing the C union type.

 Union.kind == "union"

libxltype.KeyedUnion

 A subclass of libxltype.Aggregate which represents the C union type
 where the currently valid member of the union can be determined based
 upon another member in the containing type.

 The KeyedUnion.keyvar_name must contain the name of the member of the
 containing type which determines the valid member of the union

 The fields in a KeyedUnion have an extra Field.keyvar_expr
 property. This must be a string containing a single "%s" format
 specifier such that when "%s" is substited by an instance of
 KeyedUnion.keyvar_name it becomes a C expression which evaluates to
 True IFF this field currently contains valid data.

Standard Types
--------------

Several standard types a predefined. They are

void			(void pointer type)
bool
size_t
integer			(C int type)
unsigned_integer	(C unsigned int type) 
unsigned		(C unsigned int type) 
unsigned_long		(C unsigned long type)

uint{8,16,32,64}	uint{8,16,32,64}_t

domid			Domain ID

string			NULL terminated string

inaddr_ip		struct in_addr