From: Tao Ma Subject: Re: [PATCH] e2fsck: Let end_blk to be the maximum value of u32. Date: Wed, 16 May 2012 23:07:42 +0800 Message-ID: <4FB3C2BE.8080502@tao.ma> References: <1337158225-4627-1-git-send-email-tm@tao.ma> <4FB3B404.4080101@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, Theodore Ts'o To: Eric Sandeen Return-path: Received: from oproxy9.bluehost.com ([69.89.24.6]:56310 "HELO oproxy9.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753231Ab2EPPIJ (ORCPT ); Wed, 16 May 2012 11:08:09 -0400 In-Reply-To: <4FB3B404.4080101@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 05/16/2012 10:04 PM, Eric Sandeen wrote: > On 5/16/12 3:50 AM, Tao Ma wrote: >> From: Tao Ma >> >> Now we can use fallocate to create a large file while keep the size >> to be small. It will cause the e2fsck complain about it. The test >> script is simple and I have pasted it here. >> >> DEVICE=/dev/sdb1 >> mount -t ext4 $DEVICE /mnt/ext4 >> for((i=0;i<10;i++))do fallocate -n -o $[$i*8192] -l 4096 /mnt/ext4/a;done >> umount $DEVICE >> e2fsck -fn $DEVICE > > Should this be put into an e2fsprogs regression test? sure, but could you please tell me where I can find the repo? > >> The error message will be like this: >> e2fsck 1.42.3 (14-May-2012) >> Pass 1: Checking inodes, blocks, and sizes >> Inode 12 has zero length extent >> (invalid logical block 0, physical block 32775) >> Clear? no >> >> Inode 12, i_blocks is 88, should be 0. Fix? no >> >> Pass 2: Checking directory structure >> Pass 3: Checking directory connectivity >> Pass 4: Checking reference counts >> Pass 5: Checking group summary information >> Block bitmap differences: -(8231--8232) -(32770--32778) >> Fix? no >> >> Now actually the end_blk can be any value which is less than >> u32, so make end_blk be the maximum value of u32. >> >> Cc: Theodore Ts'o >> Signed-off-by: Tao Ma >> --- >> lib/ext2fs/extent.c | 4 +--- >> 1 files changed, 1 insertions(+), 3 deletions(-) >> >> diff --git a/lib/ext2fs/extent.c b/lib/ext2fs/extent.c >> index eb096d6..e2815c2 100644 >> --- a/lib/ext2fs/extent.c >> +++ b/lib/ext2fs/extent.c >> @@ -253,9 +253,7 @@ extern errcode_t ext2fs_extent_open2(ext2_filsys fs, ext2_ino_t ino, >> ext2fs_le16_to_cpu(eh->eh_entries); >> handle->path[0].max_entries = ext2fs_le16_to_cpu(eh->eh_max); >> handle->path[0].curr = 0; >> - handle->path[0].end_blk = >> - (EXT2_I_SIZE(handle->inode) + fs->blocksize - 1) >> >> - EXT2_BLOCK_SIZE_BITS(fs->super); > > Hm, so this picked the actual last block of the file, whereas No, it doesn't. With fallocate(FALLOC_FL_KEEP_SIZE), we have no idea of what is the last block until we iterate the last leaf ext4_extent. > >> + handle->path[0].end_blk = ((((unsigned long long) 1) << 32) - 1); > > this gives it an upper bound... why is that ok? It's been a long time since > I looked at this code, but some explanation in the commit and in code > comments would be helpful. > > If end_blk can be any value less than u32, what is its purpose? As I have mentioned above, now there is no way for us to tell the end block of a file at the very beginning of ext2fs_extent_open2, so actually any value less than u32 could be OK if we have a sparse file while the last block is fallocated near the end of u32 logical block offset. Actually path[0]->end_blk is only used when we have no idea of the length of the last ext4_extent_idx. See ext2fs_extent_get. if (path->left > 0) { ix++; newpath->end_blk = ext2fs_le32_to_cpu(ix->ei_block); } else newpath->end_blk = path->end_blk; Having said that, I have to admit that I didn't think of the case of ext3 and I am not sure whether this change will affect it or not. Thanks Tao > > -Eric > >> handle->path[0].visit_num = 1; >> handle->level = 0; >> handle->magic = EXT2_ET_MAGIC_EXTENT_HANDLE; > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html