From: Theodore Ts'o Subject: Re: [PATCH 36/74] libext2fs: detect Date: Thu, 12 Dec 2013 23:39:38 -0500 Message-ID: <20131213043938.GF23888@thunk.org> References: <20131211011813.30655.39624.stgit@birch.djwong.org> <20131211012220.30655.26226.stgit@birch.djwong.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org To: "Darrick J. Wong" Return-path: Received: from imap.thunk.org ([74.207.234.97]:39581 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751774Ab3LMEjk (ORCPT ); Thu, 12 Dec 2013 23:39:40 -0500 Content-Disposition: inline In-Reply-To: <20131211012220.30655.26226.stgit@birch.djwong.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: It looks like the subject line for this commit was truncated --- I could try to make something up, but could you suggest something? Thanks!! - Ted On Tue, Dec 10, 2013 at 05:22:20PM -0800, Darrick J. Wong wrote: > If ext2fs_descriptor_block_loc2() is called with a meta_bg filesystem > and group_block is not the normal value, the function will return the > location of the backup group descriptor block in the next block group. > Unfortunately, it fails to account for the possibility that the backup > group contains a backup superblock but the regular superblock does > not. This is the case with block groups 48-49 on a meta_bg fs with 1k > blocks; in this case, libext2fs will fail to open the filesystem. > > Therefore, teach the function to adjust for superblocks in the backup > group, if necessary. > > Signed-off-by: Darrick J. Wong > --- > lib/ext2fs/openfs.c | 19 +++++++++++++++---- > 1 file changed, 15 insertions(+), 4 deletions(-) > > > diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c > index b2a8abb..92d9e40 100644 > --- a/lib/ext2fs/openfs.c > +++ b/lib/ext2fs/openfs.c > @@ -47,7 +47,7 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block, > bg = EXT2_DESC_PER_BLOCK(fs->super) * i; > if (ext2fs_bg_has_super(fs, bg)) > has_super = 1; > - ret_blk = ext2fs_group_first_block2(fs, bg) + has_super; > + ret_blk = ext2fs_group_first_block2(fs, bg); > /* > * If group_block is not the normal value, we're trying to use > * the backup group descriptors and superblock --- so use the > @@ -57,10 +57,21 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block, > * have the infrastructure in place to do that. > */ > if (group_block != fs->super->s_first_data_block && > - ((ret_blk + fs->super->s_blocks_per_group) < > - ext2fs_blocks_count(fs->super))) > + ((ret_blk + has_super + fs->super->s_blocks_per_group) < > + ext2fs_blocks_count(fs->super))) { > ret_blk += fs->super->s_blocks_per_group; > - return ret_blk; > + > + /* > + * If we're going to jump forward a block group, make sure > + * that we adjust has_super to account for the next group's > + * backup superblock (or lack thereof). > + */ > + if (ext2fs_bg_has_super(fs, bg + 1)) > + has_super = 1; > + else > + has_super = 0; > + } > + return ret_blk + has_super; > } > > blk_t ext2fs_descriptor_block_loc(ext2_filsys fs, blk_t group_block, dgrp_t i) >