The attached patch changes mm/nommu.c to better support mmap() when MMU
support is disabled (as it is in uClinux).

This was discussed on the uclibc mailing list in a thread revolving around the
following message:

	Date: Thu, 1 Apr 2004 12:05:50 +1000
	From: David McCullough <davidm@snapgear.com>
	To: David Howells <dhowells@redhat.com>
	Cc: Alexandre Oliva <aoliva@redhat.com>, uclibc@uclibc.org
	Subject: Re: [uClibc] mmaps for malloc should be private
	Message-ID: <20040401020550.GG3150@beast>

The revised rules are:

 (1) Anonymous mappings can be shared or private, read or write.

 (2) Chardevs can be mapped shared, provided they supply a get_unmapped_area()
     file operation and use that to set the address of the mapping (as a frame
     buffer driver might do, for instance).

 (3) Files (and blockdevs) cannot be mapped shared since it is not really
     possible to honour this by writing any changes back to the backing device.

 (4) Files (or sections thereof) can be mapped read-only private, in which case
     the mapped bit will be read into memory and shared, and its address will
     be returned. Any excess beyond EOF will be cleared.

 (5) Files (or sections thereof) can be mapped writable private, in which case
     a private copy of the mapped bit will be read into a new bit memory, and
     its address will be returned. Any excess beyond EOF will be cleared.

Mappings are per MM structure still. You can only unmap what you've mapped.

Fork semantics are irrelevant, since there's no fork.

A global list of VMA's is maintained to keep track of the bits of memory
currently mapped on the system.

The new binfmt makes use of (4) to implement shared libraries.
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>