linux-kernel - Re: [PATCH 28/32] quota: add get_inode_usage callback to transfer multi-inode charges

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Date:   Thu, 22 Jun 2017 11:47:37 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Tahsin Erdogan <tahsin@...gle.com>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 28/32] quota: add get_inode_usage callback to transfer
 multi-inode charges

On Wed, Jun 21, 2017 at 06:49:35PM -0700, Tahsin Erdogan wrote:
> Ext4 ea_inode feature allows storing xattr values in external inodes to
> be able to store values that are bigger than a block in size. Ext4 also
> has deduplication support for these type of inodes. With deduplication,
> the actual storage waste is eliminated but the users of such inodes are
> still charged full quota for the inodes as if there was no sharing
> happening in the background.
> 
> This design requires ext4 to manually charge the users because the
> inodes are shared.
> 
> An implication of this is that, if someone calls chown on a file that
> has such references we need to transfer the quota for the file and xattr
> inodes. Current dquot_transfer() function implicitly transfers one inode
> charge. With ea_inode feature, we would like to transfer multiple inode
> charges.
> 
> Add get_inode_usage callback which can interrogate the total number of
> inodes that were charged for a given inode.
> 
> Signed-off-by: Tahsin Erdogan <tahsin@...gle.com>
> Acked-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted