Re: detecting mmap?

[Bruce Korb]

Donn Terry wrote:

> (You do make a good point, however.  Maybe we need to consider adding a
> "MAP_ALL" flag
> to mmap() that says "validly map size, even if it's bigger than the
> object" (and zero fill)).
> That could be prototyped now, and proposed for the next POSIX if it
> works out to be useful.
> (Yeah, I know, it doesn't solve the immediate problem, but in the long
> run....))

That is a fix POSIX should make to mmap spec so it can do the
oversize mapping.  If you try to mmap a PAGESIZE file into
a 2*PAGESIZE chunk of memory, the second page won't be mapped.
strlen() still faults.  It's the spec.  It's dumb.  It's too early
for a "MAP_ALL".  Anyway, back to the real argument: it is pretty
clear that either multiple tests are required, or you have to
parameterize the features and either select what you want or
have a feature test that emits multiple results:

  #define MMAP_CAN_MAP_HEAP
  #define MMAP_CAN_MAP_FIXED
  #define HAVE_MMAP /* to some minimal degree */
  ... etc