Date: Sun, 05 Jul 2009 09:32:25 +0200 (CEST) From: Alexander Best <alexbestms@math.uni-muenster.de> To: Nate Eldredge <neldredge@math.ucsd.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: mmap/munmap with zero length Message-ID: <permail-200907050732251e86ffa8000022a8-a_best01@message-id.uni-muenster.de> In-Reply-To: <Pine.GSO.4.64.0907041735580.4747@zeno.ucsd.edu>
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so mmap differs from the POSIX recommendation right. the malloc.conf option seems more like a workaround/hack. imo it's confusing to have mmap und munmap deal differently with len=0. being able to succesfully alocate memory which cannot be removed doesn't seem logical to me. alex Nate Eldredge schrieb am 2009-07-05: > 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
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