From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from terminus.zytor.com ([198.137.202.10]:57006 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750755AbaETXjY (ORCPT ); Tue, 20 May 2014 19:39:24 -0400 Message-ID: <537BE7A4.5060508@zytor.com> Date: Tue, 20 May 2014 16:39:16 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 To: Chris Mason , "linux-btrfs@vger.kernel.org" Subject: Re: Formalizing the use of Boot Area B References: <537403E3.6090902@zytor.com> <537BE54B.3060603@zytor.com> <537BE73F.7040307@fb.com> In-Reply-To: <537BE73F.7040307@fb.com> Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 05/20/2014 04:37 PM, Chris Mason wrote: > On 05/20/2014 07:29 PM, H. Peter Anvin wrote: >> On 05/14/2014 05:01 PM, H. Peter Anvin wrote: >>> 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 >>> >> >> Ping on this? If I don't hear back on this I will probably just go >> ahead and use 128K-1024K. > > Hi Peter, > > We do leave the first 1MB of each device alone. Can we do 256K-1024K > for the boot loader? We don't have an immediate need for the extra > space, but I'd like to reserve a little more than the extra 64KB. > Works for me. So 64-256K (192K) is reserved for the file system, and Boot Area B is 256-1024K (768K). -hpa