linux-ext4 - Re: [PATCH 28/28] quota: add extra inode count to dquot transfer functions

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Date:   Fri, 16 Jun 2017 18:50:58 -0700
From:   Tahsin Erdogan <tahsin@...gle.com>
To:     Jan Kara <jack@...e.cz>
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
Subject: Re: [PATCH 28/28] quota: add extra inode count to dquot transfer functions

On Thu, Jun 15, 2017 at 12:57 AM, Jan Kara <jack@...e.cz> wrote:
> Hum, rather handle this similarly to how we handle delalloc reserved space.
> Add a callback to dq_ops to get "inode usage" of an inode and then use it
> in dquot_transfer(), dquot_free_inode(), dquot_alloc_inode().

I tried that approach by adding a "int get_inode_usage(struct inode
*inode, qsize_t *usage)" callback to dquot_operations. Unfortunately,
ext4 code that calculates the number of internal inodes
(ext4_xattr_inode_count()) is subject to failures so the callback has
to be able to report errors. And, that itself is problematic because
we can't afford to have errors in dquot_free_inode(). If you have
thoughts about how to address this please let me know.

Alternatively, I could try to make this patch less intrusive by
keeping the existing dquot_transfer() signature and add a new
dquot_transfer_usage() that accepts inode_usage as a parameter. What
do you think?