From owner-freebsd-hackers@FreeBSD.ORG  Tue Jul 14 16:32:45 2009
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Date: Tue, 14 Jul 2009 11:32:36 -0500
From: Alan Cox <alc@cs.rice.edu>
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To: John Baldwin <jhb@freebsd.org>
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Cc: Nate Eldredge <neldredge@math.ucsd.edu>, Tijl Coosemans <tijl@ulyssis.org>,
	Alexander Best <alexbestms@math.uni-muenster.de>,
	Alan Cox <alc@freebsd.org>, freebsd-hackers@freebsd.org
Subject: Re: mmap/munmap with zero length
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John Baldwin wrote:
> 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.
>
>   

I have no objections to "uap->len == 0" (without the cast).

Alan