From: Andreas Dilger <adilger.kernel@dilger.ca>
To: djwong@us.ibm.com
Cc: Theodore Tso <tytso@mit.edu>,
Sunil Mushran <sunil.mushran@oracle.com>,
Martin K Petersen <martin.petersen@oracle.com>,
Greg Freemyer <greg.freemyer@gmail.com>,
Amir Goldstein <amir73il@gmail.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andi Kleen <andi@firstfloor.org>, Mingming Cao <cmm@us.ibm.com>,
Joel Becker <jlbec@evilplan.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-ext4@vger.kernel.org, Coly Li <colyli@gmail.com>
Subject: Re: [PATCH 11/28] ext4: Calculate and verify inode checksums
Date: Wed, 12 Oct 2011 18:02:21 -0600 [thread overview]
Message-ID: <ADB8AAAD-4422-4FD1-99BF-3E2A15C80BBB@dilger.ca> (raw)
In-Reply-To: <20111012210342.GO12447@tux1.beaverton.ibm.com>
On 2011-10-12, at 3:03 PM, Darrick J. Wong wrote:
> On Wed, Oct 12, 2011 at 12:45:01PM -0700, Andreas Dilger wrote:
>>> +static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
>>> + struct ext4_inode_info *ei)
>>> +{
>>> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>> + __u16 crc_lo;
>>> + __u16 crc_hi = 0;
>>> + __u32 crc;
>>> +
>>> + crc_lo = raw->i_checksum_lo;
>>> + raw->i_checksum_lo = 0;
>>> + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
>>> + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
>>> + crc_hi = raw->i_checksum_hi;
>>> + raw->i_checksum_hi = 0;
>>> + }
>>> +
>>> + crc = ext4_chksum(sbi, ei->i_uuid_inum_crc, (__u8 *)raw,
>>> + EXT4_INODE_SIZE(inode->i_sb));
>>> +
>>> + raw->i_checksum_lo = crc_lo;
>>> + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
>>> + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
>>> + raw->i_checksum_hi = crc_hi;
>>> +
>>> + return crc;
>>> +}
>>
>> This computes both the _lo and _hi parts of the checksum and overwrites
>> what is in the inode...
>
> I don't follow your logic ... for the _lo component, first I save the old
> i_checksum_lo contents in crc_lo. Then I stuff zero into i_checksum_lo.
> Next I perform the checksum computation (with the checksum field
> effectively "zero") and put the results into crc. Then I copy whatever
> I saved in crc_lo back into i_checksum_lo.
>
> crc_lo, crc_hi, and crc are three separate variables, and neither crc_lo
> nor crc_hi are ever assigned any part of crc. Therefore crc_lo and
> crc_hi should always contain the old checksum contents.
>
> Did I miss something? Afaict the contents of raw should be the same
> before and after the call to ext4_inode_csum(), but maybe I've been
> looking at this too long. :)
No, you are right. I misread the code and thought that crc_lo and crc_hi
were derived from the computed value.
Cheers, Andreas
next prev parent reply other threads:[~2011-10-13 0:01 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-08 7:53 [PATCH v2 00/28] ext4: Add metadata checksumming Darrick J. Wong
2011-10-08 7:53 ` [PATCH 01/28] ext4: ext4_dx_add_entry should dirty directory metadata with the directory inode Darrick J. Wong
2011-10-08 7:53 ` [PATCH 02/28] ext4: ext4_rename should dirty dir_bh with the correct directory Darrick J. Wong
2011-10-08 7:54 ` [PATCH 03/28] ext4: ext4_mkdir should dirty dir_block with the parent inode Darrick J. Wong
2011-10-08 7:54 ` [PATCH 04/28] ext4: Prevent stack overrun in ext4_file_open when recording last known mountpoint Darrick J. Wong
2011-10-08 7:54 ` [PATCH 05/28] ext4: Fix endian problem in MMP initialization Darrick J. Wong
2011-10-08 7:54 ` [PATCH 06/28] ext4: Create a new BH_Verified flag to avoid unnecessary metadata validation Darrick J. Wong
2011-10-08 7:54 ` [PATCH 07/28] ext4: Create a rocompat flag for extended metadata checksumming Darrick J. Wong
2011-10-08 7:54 ` [PATCH 08/28] ext4: Record the checksum algorithm in use in the superblock Darrick J. Wong
2011-10-08 7:54 ` [PATCH 09/28] ext4: Only call out to crc32c if necessary Darrick J. Wong
2011-10-08 7:54 ` [PATCH 10/28] ext4: Calculate and verify superblock checksum Darrick J. Wong
2011-10-08 7:54 ` [PATCH 11/28] ext4: Calculate and verify inode checksums Darrick J. Wong
2011-10-12 19:45 ` Andreas Dilger
2011-10-12 21:03 ` Darrick J. Wong
2011-10-13 0:02 ` Andreas Dilger [this message]
2011-10-08 7:55 ` [PATCH 12/28] ext4: Use i_generation in inode-related metadata checksums Darrick J. Wong
2011-10-12 19:52 ` Andreas Dilger
2011-10-12 21:28 ` Darrick J. Wong
2011-10-13 0:06 ` Andreas Dilger
2011-10-08 7:55 ` [PATCH 13/28] ext4: Create bitmap checksum helper functions Darrick J. Wong
2011-10-08 7:55 ` [PATCH 14/28] ext4: Calculate and verify checksums for inode bitmaps Darrick J. Wong
2011-10-08 7:55 ` [PATCH 15/28] ext4: Calculate and verify block bitmap checksum Darrick J. Wong
[not found] ` <AE869D1A-2A06-4849-8752-74924B0C05BD@dilger.ca>
2011-10-13 7:16 ` Darrick J. Wong
2011-11-07 20:00 ` Darrick J. Wong
2011-11-07 21:44 ` Andreas Dilger
2011-11-10 0:57 ` Darrick J. Wong
2011-11-10 2:34 ` Andreas Dilger
2011-10-08 7:55 ` [PATCH 16/28] ext4: Verify and calculate checksums for extent tree blocks Darrick J. Wong
2011-10-08 7:55 ` [PATCH 17/28] ext4: Calculate and verify checksums for htree nodes Darrick J. Wong
[not found] ` <F6453844-06CC-4245-BB39-EBA4327D4C92@dilger.ca>
2011-10-13 7:21 ` Darrick J. Wong
2011-10-08 7:55 ` [PATCH 18/28] ext4: Calculate and verify checksums of directory leaf blocks Darrick J. Wong
2011-10-08 7:55 ` [PATCH 19/28] ext4: Calculate and verify checksums of extended attribute blocks Darrick J. Wong
2011-10-08 7:55 ` [PATCH 20/28] ext4: Add new feature to make block group checksums use metadata_csum algorithm Darrick J. Wong
2011-10-08 7:56 ` [PATCH 21/28] ext4: Add checksums to the MMP block Darrick J. Wong
2011-10-08 7:56 ` [PATCH 22/28] jbd2: Update structure definitions and flags to support extended checksumming Darrick J. Wong
2011-10-08 7:56 ` [PATCH 23/28] jbd2: Grab a reference to the crc32c driver only when necessary Darrick J. Wong
2011-10-08 7:56 ` [PATCH 24/28] jbd2: Update structure definitions and flags to support extended checksumming Darrick J. Wong
2011-10-08 7:56 ` [PATCH 25/28] jbd2: Checksum revocation blocks Darrick J. Wong
2011-10-08 7:56 ` [PATCH 26/28] jbd2: Checksum descriptor blocks Darrick J. Wong
2011-10-08 7:56 ` [PATCH 27/28] jbd2: Checksum commit blocks Darrick J. Wong
2011-10-08 7:56 ` [PATCH 28/28] jbd2: Checksum data blocks that are stored in the journal Darrick J. Wong
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