From: "Darrick J. Wong" <djwong@us.ibm.com>
To: "Ted Ts'o" <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org
Subject: Re: [PATCH 06/22] ext4: Calculate and verify inode checksums
Date: Mon, 5 Dec 2011 11:45:39 -0800 [thread overview]
Message-ID: <20111205194539.GD7137@tux1.beaverton.ibm.com> (raw)
In-Reply-To: <20111205162406.GB32031@thunk.org>
On Mon, Dec 05, 2011 at 11:24:06AM -0500, Ted Ts'o wrote:
> On Mon, Nov 28, 2011 at 03:26:56PM -0800, Darrick J. Wong wrote:
> > + /* Precompute second piece of csum */
> > + if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
> > + __u32 csum;
> > + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> > + __le32 inum = cpu_to_le32(inode->i_ino);
> > + __le32 gen = cpu_to_le32(inode->i_generation);
> > + csum = ext4_chksum(sbi, sbi->s_uuid_csum, (__u8 *)&inum,
> > + sizeof(inum));
> > + ei->i_uuid_inum_csum = ext4_chksum(sbi, csum, (__u8 *)&gen,
> > + sizeof(gen));
> > + }
>
> Why do we include a copy of i_generation in the precomputed initial
> part of the checksum? Since i_generation is in the raw, on-disk
> version of the inode, what's the rationale for including it here? It
> shouldn't *hurt*, but it a few extra CPU cycles, and I'm not seeing
> how it helps.
i_uuid_inum_csum seeds crc32c for all the metadata objects that are attached to
an inode (extents, dir blocks, xattrs), not just the inode itself. That way
you can ensure that a piece of metadata corresponds to a specific incarnation
of an inode, not just any of the inode's incarnations since mkfs time.
--D
>
> - Ted
> --
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next prev parent reply other threads:[~2011-12-05 19:50 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-28 23:26 [PATCH v2.1 00/22] ext4: Add metadata checksumming Darrick J. Wong
2011-11-28 23:26 ` [PATCH 01/22] ext4: Create a new BH_Verified flag to avoid unnecessary metadata validation Darrick J. Wong
2011-11-28 23:26 ` [PATCH 02/22] ext4: Create a rocompat flag for extended metadata checksumming Darrick J. Wong
2011-12-05 15:41 ` Ted Ts'o
2011-12-05 19:24 ` Darrick J. Wong
2011-11-28 23:26 ` [PATCH 03/22] ext4: Record the checksum algorithm in use in the superblock Darrick J. Wong
2011-12-05 15:46 ` Ted Ts'o
2011-12-05 19:32 ` Darrick J. Wong
[not found] ` <E0964BB6-793D-49AF-A2B0-20748C6DAE2B@dilger.ca>
2011-12-07 7:42 ` Darrick J. Wong
2011-12-07 8:40 ` Andreas Dilger
2011-11-28 23:26 ` [PATCH 04/22] ext4: Only call out to crc32c if necessary Darrick J. Wong
2011-12-05 15:52 ` Ted Ts'o
2011-12-05 19:38 ` Darrick J. Wong
2011-11-28 23:26 ` [PATCH 05/22] ext4: Calculate and verify superblock checksum Darrick J. Wong
2011-11-28 23:26 ` [PATCH 06/22] ext4: Calculate and verify inode checksums Darrick J. Wong
2011-12-05 16:24 ` Ted Ts'o
2011-12-05 19:45 ` Darrick J. Wong [this message]
2011-11-28 23:27 ` [PATCH 07/22] ext4: Create bitmap checksum helper functions Darrick J. Wong
2011-12-05 16:33 ` Ted Ts'o
2011-12-05 20:31 ` Darrick J. Wong
2011-12-05 23:54 ` Darrick J. Wong
2011-12-06 17:19 ` Andreas Dilger
2011-12-06 20:59 ` Darrick J. Wong
2011-11-28 23:27 ` [PATCH 08/22] ext4: Calculate and verify checksums for inode bitmaps Darrick J. Wong
2011-11-28 23:27 ` [PATCH 09/22] ext4: Calculate and verify block bitmap checksum Darrick J. Wong
2011-11-28 23:27 ` [PATCH 10/22] ext4: Verify and calculate checksums for extent tree blocks Darrick J. Wong
2011-12-05 16:40 ` Ted Ts'o
2011-12-05 19:50 ` Darrick J. Wong
2011-11-28 23:27 ` [PATCH 11/22] ext4: Calculate and verify checksums for htree nodes Darrick J. Wong
2011-11-28 23:27 ` [PATCH 12/22] ext4: Calculate and verify checksums of directory leaf blocks Darrick J. Wong
2011-11-28 23:27 ` [PATCH 13/22] ext4: Calculate and verify checksums of extended attribute blocks Darrick J. Wong
2011-11-28 23:27 ` [PATCH 14/22] ext4: Add new feature to make block group checksums use metadata_csum algorithm Darrick J. Wong
2011-11-28 23:28 ` [PATCH 15/22] ext4: Add checksums to the MMP block Darrick J. Wong
2011-11-28 23:28 ` [PATCH 16/22] jbd2: Update structure definitions and flags to support extended checksumming Darrick J. Wong
2011-11-28 23:28 ` [PATCH 17/22] jbd2: Grab a reference to the crc32c driver only when necessary Darrick J. Wong
2011-11-28 23:28 ` [PATCH 18/22] jbd2: Update structure definitions and flags to support extended checksumming Darrick J. Wong
2011-11-28 23:28 ` [PATCH 19/22] jbd2: Checksum revocation blocks Darrick J. Wong
2011-12-12 15:39 ` Ted Ts'o
2011-11-28 23:28 ` [PATCH 20/22] jbd2: Checksum descriptor blocks Darrick J. Wong
2011-11-28 23:28 ` [PATCH 21/22] jbd2: Checksum commit blocks Darrick J. Wong
2011-11-28 23:28 ` [PATCH 22/22] jbd2: Checksum data blocks that are stored in the journal Darrick J. Wong
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