linux-ext4 - Re: [PATCH v2] xfstests, generic: add project quota attribute tests

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Message-ID: <20160711171242.GA21285@thunk.org>
Date:	Mon, 11 Jul 2016 13:12:42 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Eric Sandeen <sandeen@...deen.net>,
	Dave Chinner <david@...morbit.com>,
	Wang Shilong <wangshilong1991@...il.com>,
	fstests@...r.kernel.org, linux-ext4@...r.kernel.org,
	sihara@....com, lixi@....com, Wang Shilong <wshilong@....com>
Subject: Re: [PATCH v2] xfstests, generic: add project quota attribute tests

On Mon, Jul 11, 2016 at 06:15:56PM +0200, Jan Kara wrote:
> 
> What would you like to achieve with this? There is 'QF_META' format which
> is different from 'QF_XFS' format basically only in the set of quotactls
> used. As I said above it might be nice to separate kernel-api from the
> underlying-quota-format but in reality these two were bound together in
> older kernels so they are not really independent.

The main reason why I noticed is with the new (err, "latest") ext4
quota (enabled via mke2fs -t ext4 -O quota) implementation, we enable
quota tracking at mount time.  (This may be true with journalled quota
as well, actually).  But we don't actually enable quota *enforcement*
until quotaon is given.

The problem is that quotaon -p prints the status of whether or not
quota *tracking* is enabled, and with the new ext4 quota, quota
tracking is *always* enabled.  So quota -p doesn't report anything
useful for new ext4 quota systems, and when I started to look at how
to change things, that's when I noticed that we weren't using the new
quotactl commands with ext4 even though they worked, and that the new
quotactl implementation had more functionality than the older ones.

BTW, I've seriously been thinking about changing the default so that
if you use mke2fs -O quota, quota enforcement is also enabled by
default at mount time, and we use a mount option to disable quota
enforcement.  If we then added a way of selectively enabling and
disabling quota enforcement via quota-tools, then we would be bringing
behaivour of how ext4 quota works to like how xfs treats quota.  The
question I have is how to do this in a way that isn't surprising for
people who are used to the old behaviour --- but mke2fs -O quota is
still relatively new, so maybe we could get away with it without
having to add more superblock flags.

							- Ted
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