linux-kernel - Re: nommu: handling anonymous mmap clearing in userspace rather than kernel

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Date:	Thu, 03 Apr 2008 13:06:25 +0200
From:	Bernd Schmidt <bernds_cb1@...nline.de>
To:	Mike Frysinger <vapier.adi@...il.com>
CC:	David Howells <dhowells@...hat.com>,
	Greg Ungerer <gerg@...pgear.com>,
	David McCullough <David_Mccullough@...urecomputing.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Bryan Wu <Bryan.Wu@...log.com>,
	Robin Getz <rgetz@...ckfin.uclinux.org>
Subject: Re: nommu: handling anonymous mmap clearing in userspace rather than
 kernel

Mike Frysinger wrote:

> i also expected MAP_UNINITIALIZE to be unacceptable to LKML.  and
> afaik, there doesnt seem to be a way to distinguish in the kernel
> whether the call is coming from userspace or kernel space, so the
> memset() call will still be called for the kernel.  ideally the code
> would read:
> if (!kernel && !(flags & MAP_UNINITIALIZE))
>     memset(base, 0, len);

Have you examined all callers in the kernel whether they can take 
uninitialized memory?  (Your code doesn't match your description btw, so 
I'm only guessing what you actually want to achieve.)

Really, if MAP_UNINITIALIZE is unacceptable, then that's too bad and 
we'll carry it as a local patch, but all the other proposed mechanisms 
are non-solutions because they break an established interface.


Bernd
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