Re: Problem trying to address custom hardware

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.

quoted

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.

-Matt

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