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From: John Baldwin <jhb@freebsd.org>
To: Tijl Coosemans <tijl@ulyssis.org>
Date: Mon, 13 Jul 2009 16:39:09 -0400
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Cc: Nate Eldredge <neldredge@math.ucsd.edu>, freebsd-hackers@freebsd.org,
	Alexander Best <alexbestms@math.uni-muenster.de>,
	Alan Cox <alc@freebsd.org>
Subject: Re: mmap/munmap with zero length
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On Monday 13 July 2009 3:33:51 pm Tijl Coosemans wrote:
> On Monday 13 July 2009 20:28:08 John Baldwin wrote:
> > On Sunday 05 July 2009 3:32:25 am Alexander Best wrote:
> >> 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.
> > 
> > This should fix it:
> > 
> > --- //depot/user/jhb/acpipci/vm/vm_mmap.c
> > +++ /home/jhb/work/p4/acpipci/vm/vm_mmap.c
> > @@ -229,7 +229,7 @@
> > 
> >         fp = NULL;
> >         /* make sure mapping fits into numeric range etc */
> > -       if ((ssize_t) uap->len < 0 ||
> > +       if ((ssize_t) uap->len <= 0 ||
> >             ((flags & MAP_ANON) && uap->fd != -1))
> >                 return (EINVAL);
> 
> Why not "uap->len == 0"? Sizes of 2GiB and more (32bit) shouldn't cause
> an error.

I don't actually disagree and know of locally modified versions of FreeBSD 
that remove this check for precisely that reason.

-- 
John Baldwin