From: Eric Sandeen Subject: Re: [PATCH] e2fsck: Let end_blk to be the maximum value of u32. Date: Wed, 16 May 2012 10:31:01 -0500 Message-ID: <4FB3C835.2090509@redhat.com> References: <1337158225-4627-1-git-send-email-tm@tao.ma> <4FB3B404.4080101@redhat.com> <4FB3C2BE.8080502@tao.ma> 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: Tao Ma Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50035 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754686Ab2EPPbF (ORCPT ); Wed, 16 May 2012 11:31:05 -0400 In-Reply-To: <4FB3C2BE.8080502@tao.ma> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 5/16/12 10:07 AM, Tao Ma wrote: > 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? there are regression tests in the e2fsprogs git tree itself. I think a prepared filesytem image may be the way to go for this one. >>> 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. Oh, sorry - this "tried to pick" is what I meant to say :) >>> + 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. Ok. Thanks. -Eric > 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 >