Date: Fri, 27 Oct 1995 14:18:02 -0700 From: John Polstra <jdp@polstra.com> To: freebsd-hackers@freebsd.org Subject: What does MAP_COPY do? Message-ID: <199510272118.OAA07337@freebie.polstra.com>
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Could somebody please explain to me what mmap(2) does when the flag MAP_COPY
is passed to it? The only documentation I can find is a comment in
/usr/include/sys/mman.h:
#define MAP_COPY 0x0004 /* "copy" region at mmap time */
It sounds like this means that a private copy is immediately made of the
region. I.e., if two processes map the same file, each with MAP_COPY, they
will get completely separate copies of the data. Is that right?
Is the actual data copied, or just the page table entries?
The only reason I can think of that this behavior would be desired would be as
a work-around for a non-working copy-on-write implementation. Is that what
it's for?
Thanks -- enquiring minds gotta know.
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Self-knowledge is always bad news." -- John Barth
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