check ATTR_SIZE contraints in inode_change_ok

Make sure we check the truncate constraints early on in ->setattr by adding
those checks to inode_change_ok.  Also clean up and document inode_change_ok
to make this obvious.

As a fallout we don't have to call inode_newsize_ok from simple_setsize and
simplify it down to a truncate_setsize which doesn't return an error.  This
simplifies a lot of setattr implementations and means we use truncate_setsize
almost everywhere.  Get rid of fat_setsize now that it's trivial and mark
ext2_setsize static to make the calling convention obvious.

Keep the inode_newsize_ok in vmtruncate for now as all callers need an
audit for its removal anyway.

Note: setattr code in ecryptfs doesn't call inode_change_ok at all and
needs a deeper audit, but that is left for later.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 703000d..54fe087 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -702,12 +702,12 @@
 	page_cache_release(page);
 
 	/*
-	 * XXX(hch): the call below should probably be replaced with
+	 * XXX(truncate): the call below should probably be replaced with
 	 * a call to the gfs2-specific truncate blocks helper to actually
 	 * release disk blocks..
 	 */
 	if (pos + len > ip->i_inode.i_size)
-		simple_setsize(&ip->i_inode, ip->i_inode.i_size);
+		truncate_setsize(&ip->i_inode, ip->i_inode.i_size);
 out_endtrans:
 	gfs2_trans_end(sdp);
 out_trans_fail: