Problem trying to address custom hardware

Matt Porter mporter at
Thu Aug 26 09:05:25 EST 2004

On Wed, Aug 25, 2004 at 03:29:20PM -0700, Oliver King-Smith wrote:
> Things are working much better.  Both the driver and the main code work
> without crashing now.
> > Others addressed your core problem, but you should know that this
> > mmap request won't produce the desired result. You need MAP_SHARED
> > since MAP_PRIVATE will result in a COW when you attempt to modify
> > your register.
> I am not sure I understand why this needs to be MAP_SHARED (it sure does
> though).  Is there a good resource I can read to understand this a bit
> better?

The mmap(2) manpage explains the difference pretty well.  MAP_PRIVATE
indicates that any modification are local to the process. So, as
soon as you write to it, it makes a copy of the page for your process
to modify. MAP_SHARED indicates that any modifications are seen by
any processes that also map the region.

googling will probably yield many threads on lkml on this topic.


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