Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!wb1.cs.cmu.edu!avie
From: avie@wb1.cs.cmu.edu (Avadis Tevanian)
Newsgroups: comp.os.mach
Subject: Re: bug in Mach 2.5 in copy-on-write?
Message-ID: <10107@pt.cs.cmu.edu>
Date: 4 Aug 90 06:39:37 GMT
References: <10871@spool.cs.wisc.edu>
Organization: NeXT, Inc.
Lines: 21

In article <10871@spool.cs.wisc.edu> shekita@provolone.cs.wisc.edu (E Shekita) writes:
>
>for (i = 0; i < 100; i++) {
....
>    source_page[0] = 'a'; 
....
>    vm_read(task_self(), (vm_address_t) source_page, vm_page_size, 
>	   (vm_address_t*) &destination_page, &readCount);
....
>    destination_page[0] = 'b';

No bug here... if you remember that both the source and destination pages
are set to copy-on-write then you realize that each time you touch the 
source page after the vm_read you generate another COW fault.  The result
you get of 199 is exactly as expected.

-- 
Avadis Tevanian, Jr.    (Avie)
Manager, System Software
NeXT, Inc.
avie@NeXT.COM