MMap "access" keyword, choice of exception class

[Jay Todd Miller]

Hi,

I have written (and submitted) a patch which adds a  new keyword
parameter to mmap: "access".  One dubious kind
of access which I added for the sake of completeness is "readonly".  A
readonly mmap maps true
OS protected readonly memory and does not update the underlying file.
When python detects and attempt
to write a readonly mmap, an exception is raised;  Is there an obvious
choice for what the exception class should be?

I need to re-submit the patch for a few stylistic issues anyway, and
would like to fix this while I'm at it.  Right now, the
patch raises ValueError.  SystemError and RuntimeError also come to
mind.

Thanks,
Todd