Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.arch
Subject: Re: fork() vs vfork() and COW
Message-ID: <3733@auspex.auspex.com>
Date: 24 Jul 90 02:05:15 GMT
References: <58053@bbn.BBN.COM> <476@exodus.Eng.Sun.COM> <58086@bbn.BBN.COM>
Organization: Auspex Systems, Santa Clara
Lines: 31

>Does SunOS 4.1 really have COW?

Yes; so did 4.0.  Was this really not generally known?

>Where is it documented?

*Virtual Memory Architecture in SunOS*, Summer 1987 USENIX Proceedings.

*SunOS Virtual Memory Implementation*, some recent EUUG procedings (it
even uses the phrase "copy-on-write", unlike some of the other
references).

SunOS 4.0 MMAP(2) manual page:

     MAP_SHARED and MAP_PRIVATE describe the disposition of write
     references  to  the  memory object.  If MAP_SHARED is speci-
     fied, write references will change the  memory  object.   If
     MAP_PRIVATE  is  specified, the initial write reference will
     create a private copy of the memory object page and redirect
     the  mapping  to  the  copy.   The  mapping type is retained
     across a fork(2).

etc..

(BTW, for those who insist on making some stupid BSD vs. S5 debate out
of this, note that S5R4 has "vfork()", and that the S5R4 "vfork()" man
page includes a warning from which one could possibly infer that it
operates similarly to the 4.xBSD and SunOS 4.x "vfork()".  This may have
been done for the benefit of code written by people incapable of
reading, or incapable of comprehending, the "don't depend on this
sharing!" stuff in the BSD manual page....)