Broken autoconf mmap test

[Christopher Faylor]

On Thu, Mar 24, 2011 at 10:23:57AM -0600, Eric Blake wrote:
>On 03/24/2011 10:21 AM, Christopher Faylor wrote:
>>> - In all three possible solutions above: What if the original file
>>>  handle used in the mmap call has been closed and the file permissions
>>>  have been changed in the meantime so that the process does not have
>>>  write permissions anymore?
>> 
>> - Isn't it going to be really slow?  I guess if it only happens once
>> per page it won't be that bad but still: ouch.
>
>And if I'm understanding correctly, it only needs to happen for the one
>page at the end of the file; all earlier 64k chunks of the file can be
>mapped normally, if you can guarantee that the normal mappings are
>adjacent with the one special mapping.

Ah.  So that would make it like a stack guard page then.

cgf