[PATCH 2.6] fix mmap() return value to conform POSIX

[Gordon Jin <gordon.jin@intel.com>]

This patch fixes 2 return values in mmap() to conform POSIX spec:

[EINVAL]
        The value of len is zero.
        
[ENOMEM]
        MAP_FIXED was specified, and the range [addr,addr+len) exceeds
        that allowed for the address space of a process; or, if
        MAP_FIXED was not specified and there is insufficient room in
        the address space to effect the mapping.

--- linux-2.6.11.3/mm/mmap.c.orig	2005-03-14 13:20:11.000000000 -0800
+++ linux-2.6.11.3/mm/mmap.c	2005-03-14 17:24:37.000000000 -0800
@@ -897,12 +897,12 @@ unsigned long do_mmap_pgoff(struct file 
 			prot |= PROT_EXEC;
 
 	if (!len)
-		return addr;
+		return -EINVAL;
 
 	/* Careful about overflows.. */
 	len = PAGE_ALIGN(len);
 	if (!len || len > TASK_SIZE)
-		return -EINVAL;
+		return -ENOMEM;
 
 	/* offset overflow? */
 	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)