L4 fpages

Adam Lackorzynski adam at os.inf.tu-dresden.de
Fri Jan 14 22:52:46 CET 2011


On Fri Jan 14, 2011 at 09:18:45 -0800, jason philip wrote:
> I new to the L4 microkernel and do not understand how fpages works. What are
> the functions of fpages? Can them be used to extend the address space? Are
> they just for copy a region from one address space to other address space?

A flexpage is a datatype that describes a piece in some space,
compactified in just a single machine word (i.e. 4 or 8 bytes). It
consists of an position in there, a size and some other bits. Yes,
that's abstract.
For example a flexpage for memory describes a memory region. It consists
of an address with the granularity of pages, a size specifying the
number of pages (usually in log2 size) and some rights bits.  Now when
mapping memory around a flexpage describes which memory to map and where
to put it.
Flexpages are also used for capabilities and I/O ports.

Adam                 adam at os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/

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