From: "Darrick J. Wong" Subject: Re: [PATCH 1/2] ext4: Calculate and verify inode checksums Date: Fri, 8 Apr 2011 12:12:48 -0700 Message-ID: <20110408191250.GD24354@tux1.beaverton.ibm.com> References: <20110406224410.GB24354@tux1.beaverton.ibm.com> <20110406224547.GT32706@tux1.beaverton.ibm.com> <86716762-8041-4209-961C-5C0BAB139C5B@dilger.ca> Reply-To: djwong@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Theodore Ts'o" , linux-ext4 , linux-kernel To: Andreas Dilger Return-path: Received: from e34.co.us.ibm.com ([32.97.110.152]:45177 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757516Ab1DHTMx (ORCPT ); Fri, 8 Apr 2011 15:12:53 -0400 Content-Disposition: inline In-Reply-To: <86716762-8041-4209-961C-5C0BAB139C5B@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Apr 08, 2011 at 02:58:27AM -0600, Andreas Dilger wrote: > On 2011-04-06, at 4:45 PM, Darrick J. Wong wrote: > > This patch introduces to ext4 the ability to calculate and verify inode > > checksums. This requires the use of a new ro compatibility flag and some > > accompanying e2fsprogs patches to provide the relevant features in tune2fs and > > e2fsck. > > > > Signed-off-by: Darrick J. Wong > > --- > > > > fs/ext4/ext4.h | 6 ++++-- > > fs/ext4/inode.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++- > > 2 files changed, 55 insertions(+), 3 deletions(-) > > > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > > index 4daaf2b..8815928 100644 > > --- a/fs/ext4/ext4.h > > +++ b/fs/ext4/ext4.h > > @@ -617,7 +617,7 @@ struct ext4_inode { > > } masix2; > > } osd2; /* OS dependent 2 */ > > __le16 i_extra_isize; > > - __le16 i_pad1; > > + __le16 i_checksum; /* crc16(sb_uuid+inodenum+inode) */ > > In previous discussions, we thought about using part/all of the l_i_reserved2 > field to store the inode checksum. The inode checksum is important enough to > warrant a field in the core inode, so that it also works on upgraded > filesystems. Hmm, yes, I better like using that field too, it'll simplify the code. Does anyone know which of the s_creator_os codes map to the Linux format? I'm going to guess 1 and 2 don't... for now I suppose the mount code can check for a Linux creator code if the inode checksum feature is set, and fail the mount if it finds 1 or 2. I'm not sure which version of the osd2 union FreeBSD or "Lites" use. > > +static __le16 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw) > > +{ > > + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); > > + struct ext4_inode_info *ei = EXT4_I(inode); > > + int offset = offsetof(struct ext4_inode, i_checksum); > > + __le32 inum = cpu_to_le32(inode->i_ino); > > + __u16 crc = 0; > > + > > + if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, > > + EXT4_FEATURE_RO_COMPAT_INODE_CSUM) && > > + le16_to_cpu(raw->i_extra_isize) >= 4) { > > If this field remains in the large part of the inode, then this check is > incorrect. i_extra_isize is itself only valid if (s_inode_size is > > EXT4_GOOD_OLD_INODE_SIZE), otherwise it points at the next inode's i_mode. > > Also, instead of hard-coding ">= 4" here, it would be better to use > EXT4_FITS_IN_INODE(raw, EXT4_I(inode), i_checksum). Probably no reason to > put "ei" on the stack at all. As always, thank you for the feedback! --D