Thread

Re: [HACKERS] mmap and MAP_ANON

Goran Thyni <goran@bildbasen.se> — 1998-05-11T14:08:58Z

Bruce Momjian wrote:
> 
> Would people tell me what platforms do NOT support the MAP_ANON flag to
> the mmap() system call?  You should find it in the mmap() manual page.
> 
> *BSD has it, but I am not sure of the others.  I am researching cache
> size issues and the use of mmap vs. SYSV shared memory.

SVR4 (at least older ones) does not support MMAP_ANON,
but the recommended in W. Richards Stevens' 
"Advanced programming in the Unix environment" (aka the Bible part 2)
is to use /dev/zero.

This should be configurable with autoconf:

<PSEUDO CODE>

if (exists MAP_ANON) use it; else use /dev/zero

------------

flags = MAP_SHARED;
#ifdef HAS_MMAP_ANON
fd = -1;
flags |= MAP_ANON;
#else
fd = open('/dev/zero, O_RDWR);
#endif
area = mmap(0, size, PROT_READ|PROT_WRITE, flags, fd, 0);

</PSEUDO CODE>


	regards,
-- 
---------------------------------------------
Göran Thyni, sysadm, JMS Bildbasen, Kiruna