linux-ext4 - Re: [PATCH 01/28] ext4: xattr-in-inode support

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Date:   Wed, 31 May 2017 12:59:51 -0700
From:   Tahsin Erdogan <tahsin@...gle.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Jan Kara <jack@...e.com>, "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Dave Kleikamp <shaggy@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Mark Fasheh <mfasheh@...sity.com>,
        Joel Becker <jlbec@...lplan.org>, Jens Axboe <axboe@...com>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Mike Christie <mchristi@...hat.com>,
        Fabian Frederick <fabf@...net.be>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, jfs-discussion@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, ocfs2-devel@....oracle.com,
        reiserfs-devel@...r.kernel.org,
        Andreas Dilger <andreas.dilger@...el.com>,
        Kalpak Shah <kalpak.shah@....com>,
        James Simmons <uja.ornl@...il.com>
Subject: Re: [PATCH 01/28] ext4: xattr-in-inode support

>> allowing the ext4/e2fsck to verify the correct inode is accessed.
>
> Can we store the checksum of the xattr value somewhere?  We already
> checksum the values if they're stored in the ibody or a single external
> block, and I'd hate to lose that protection.
>
> We could probably reuse one of the inode fields (i_version?) for this.
>
The crc32c value of the xattr data is currently stored in the xattr inode:

struct ext4_xattr_ea_info {
__le64 ref_count; /* number of xattr entry references */
__le32 hash; /* crc32c hash of xattr data */
__le32 reserved; /* reserved, must be 0 */
};

We could also save that value in the ext4_xattr_entry->e_value_offs
for stronger binding between parent and xattr inodes. That field is
currently set to 0 for xattr inode references.