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Date: Sat, 4 Jul 2009 17:40:19 -0700 (PDT)
From: Nate Eldredge <neldredge@math.ucsd.edu>
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To: Alexander Best <alexbestms@math.uni-muenster.de>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: mmap/munmap with zero length
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On Sun, 5 Jul 2009, Alexander Best wrote:

> i'm wondering why mmap and munmap behave differently when it comes to a length
> argument of zero. allocating memory with mmap for a zero length file returns a
> valid pointer to the mapped region.
>
> munmap however isn't able to remove a mapping with no length.
>
> wouldn't it be better to either forbid this in mmap or to allow it in munmap?

POSIX has an opinion:

http://www.opengroup.org/onlinepubs/9699919799/functions/mmap.html

"If len is zero, mmap() shall fail and no mapping shall be established."

http://www.opengroup.org/onlinepubs/9699919799/functions/munmap.html

"The munmap() function shall fail if:
...
[EINVAL]
     The len argument is 0."


-- 

Nate Eldredge
neldredge@math.ucsd.edu