From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from terminus.zytor.com ([198.137.202.10]:34489 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751252AbaEOABq (ORCPT ); Wed, 14 May 2014 20:01:46 -0400 Message-ID: <537403E3.6090902@zytor.com> Date: Wed, 14 May 2014 17:01:39 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 To: "linux-btrfs@vger.kernel.org" Subject: Formalizing the use of Boot Area B Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: It turns out that the primary 64K "Boot Area A" is too small for some applications and/or some architectures. When I discussed this with Chris Mason, he pointed out that the area beyond the superblock is also unused, up until at least the megabyte point (from my reading of the mkfs code, it is actually slightly more than a megabyte.) This is present in all versions of mkfs.btrfs that has the superblock at 64K (some very early ones had the superblock at 16K, but that format is no longer supported), so all that is needed is formalizing the specs as to the use of this area. My suggestion is that 64-128K is reserved for extension of the superblock and/or any other filesystem uses, and 128-1024K is defined as Boot Area B. However, if there may be reason to reserve more, then we should do that. Hence requesting a formal decision as to the extent and ownership of this area. -hpa