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From: Dave Chinner <david@fromorbit.com>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
	fsdevel <linux-fsdevel@vger.kernel.org>,
	xfs@oss.sgi.com, Eric Sandeen <sandeen@sandeen.net>,
	Eric Sandeen <sandeen@redhat.com>
Subject: Re: [PATCH 0/4] quota: add new quotactl Q_XGETQUOTA2
Date: Sat, 16 Jan 2016 09:50:22 +1100	[thread overview]
Message-ID: <20160115225022.GO6033@dastard> (raw)
In-Reply-To: <20160115093507.GA15950@quack.suse.cz>

On Fri, Jan 15, 2016 at 10:35:07AM +0100, Jan Kara wrote:
> On Wed 13-01-16 16:40:58, Eric Sandeen wrote:
> > Actually, that's exactly what I thought would *need* to happen ... we already
> > have this weird 15-year-old split-brain quota interface, so if xfs and ext4
> > both need the same functionality, then we'd probably add both GETQUOTA2 and
> > XGETQUOTA2.  If we were doing this all from scratch, sure, but adding a new
> > handles-both-quota-types interface when every other operation is already split
> > between the two almost seems to make matters worse.
> 
> Well, currently GETQUOTA and XGETQUOTA (and all the other quotactls) are
> actually translated so they work regardless of the underlying filesystem.
> So the only difference between XFS and VFS quotactls is in the formatting
> of input/output structures. So from kernel POV it seems somewhat pointless
> to add two calls doing the same thing and differing just in the formatting
> of output - especially when we want the call to be extensible.
> 
> I agree that having a unified call means having a new structure for passing
> dquot info between kernel and userspace. So just for adding that one small
> feature you want it seems like an overkill. But when thinking about new
> extensible getquota quotactl it IMHO makes sense to unify the VFS/XFS split
> brain. Thoughts?

A new unified userspace quota API would be nice, but it's a
completely separate piece of work. We'd also need to do userspace
work to support it, so I think this is a valid medium term goal,
but not somethign that should gate the work Eric is doing.

i.e. it might be best to introduce a quotactl2 syscall for a
unified interface, such that the syscall itself has a flags
argument rather than having to jump through hoops to embed flags
in argument structures.....

FWIW, converting xfs_quota to use a new kernel API is trivial (half
an hour's work) as it already has a kernel API abstraction layer for
cross platform support. Hence we can quickly get userspace support
in place to test such a new kernel API...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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WARNING: multiple messages have this Message-ID (diff)
From: Dave Chinner <david@fromorbit.com>
To: Jan Kara <jack@suse.cz>
Cc: Eric Sandeen <sandeen@sandeen.net>,
	Christoph Hellwig <hch@infradead.org>,
	fsdevel <linux-fsdevel@vger.kernel.org>,
	Eric Sandeen <sandeen@redhat.com>,
	xfs@oss.sgi.com
Subject: Re: [PATCH 0/4] quota: add new quotactl Q_XGETQUOTA2
Date: Sat, 16 Jan 2016 09:50:22 +1100	[thread overview]
Message-ID: <20160115225022.GO6033@dastard> (raw)
In-Reply-To: <20160115093507.GA15950@quack.suse.cz>

On Fri, Jan 15, 2016 at 10:35:07AM +0100, Jan Kara wrote:
> On Wed 13-01-16 16:40:58, Eric Sandeen wrote:
> > Actually, that's exactly what I thought would *need* to happen ... we already
> > have this weird 15-year-old split-brain quota interface, so if xfs and ext4
> > both need the same functionality, then we'd probably add both GETQUOTA2 and
> > XGETQUOTA2.  If we were doing this all from scratch, sure, but adding a new
> > handles-both-quota-types interface when every other operation is already split
> > between the two almost seems to make matters worse.
> 
> Well, currently GETQUOTA and XGETQUOTA (and all the other quotactls) are
> actually translated so they work regardless of the underlying filesystem.
> So the only difference between XFS and VFS quotactls is in the formatting
> of input/output structures. So from kernel POV it seems somewhat pointless
> to add two calls doing the same thing and differing just in the formatting
> of output - especially when we want the call to be extensible.
> 
> I agree that having a unified call means having a new structure for passing
> dquot info between kernel and userspace. So just for adding that one small
> feature you want it seems like an overkill. But when thinking about new
> extensible getquota quotactl it IMHO makes sense to unify the VFS/XFS split
> brain. Thoughts?

A new unified userspace quota API would be nice, but it's a
completely separate piece of work. We'd also need to do userspace
work to support it, so I think this is a valid medium term goal,
but not somethign that should gate the work Eric is doing.

i.e. it might be best to introduce a quotactl2 syscall for a
unified interface, such that the syscall itself has a flags
argument rather than having to jump through hoops to embed flags
in argument structures.....

FWIW, converting xfs_quota to use a new kernel API is trivial (half
an hour's work) as it already has a kernel API abstraction layer for
cross platform support. Hence we can quickly get userspace support
in place to test such a new kernel API...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  parent reply	other threads:[~2016-01-15 22:50 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-08 16:56 [PATCH 0/4] quota: add new quotactl Q_XGETQUOTA2 Eric Sandeen
2016-01-08 16:56 ` Eric Sandeen
2016-01-08 16:57 ` [PATCH 1/4] " Eric Sandeen
2016-01-08 16:57   ` Eric Sandeen
2016-01-08 16:57 ` [PATCH 2/4] xfs: get quota inode from mp & flags rather than dqp Eric Sandeen
2016-01-08 16:57   ` Eric Sandeen
2016-01-08 16:58 ` [PATCH 3/4] xfs: Factor xfs_seek_hole_data into helper Eric Sandeen
2016-01-08 16:58   ` Eric Sandeen
2016-01-08 17:07   ` [PATCH 3/4 V2] " Eric Sandeen
2016-01-11 15:57   ` [PATCH 3/4] " Jan Kara
2016-01-11 15:57     ` Jan Kara
2016-01-11 16:01   ` [PATCH 3/4 V3] " Eric Sandeen
2016-01-11 16:01     ` Eric Sandeen
2016-01-08 16:59 ` [PATCH 4/4] xfs: wire up Q_XGETQUOTA2 / get_dqblk2 Eric Sandeen
2016-01-08 16:59   ` Eric Sandeen
2016-01-08 18:36 ` [PATCH] linux-quota: wire Q_XGETQUOTA2 into generic repquota Eric Sandeen
2016-01-08 18:36   ` Eric Sandeen
2016-01-09  7:26 ` [PATCH 0/4] quota: add new quotactl Q_XGETQUOTA2 Christoph Hellwig
2016-01-09  7:26   ` Christoph Hellwig
2016-01-11 13:26   ` Jan Kara
2016-01-11 13:26     ` Jan Kara
2016-01-11 16:07     ` Eric Sandeen
2016-01-11 16:07       ` Eric Sandeen
2016-01-11 16:28       ` Jan Kara
2016-01-11 16:28         ` Jan Kara
2016-01-13 22:40         ` Eric Sandeen
2016-01-13 22:40         ` Eric Sandeen
2016-01-13 22:40           ` Eric Sandeen
2016-01-15  9:35           ` Jan Kara
2016-01-15  9:35             ` Jan Kara
2016-01-15 17:31             ` Eric Sandeen
2016-01-15 17:31               ` Eric Sandeen
2016-01-15 19:38               ` Eric Sandeen
2016-01-15 19:38                 ` Eric Sandeen
2016-01-18 10:33               ` Jan Kara
2016-01-18 10:33                 ` Jan Kara
2016-01-18 11:00                 ` Christoph Hellwig
2016-01-18 11:00                   ` Christoph Hellwig
2016-01-18 15:18                 ` Eric Sandeen
2016-01-18 15:18                   ` Eric Sandeen
2016-01-18 15:40                   ` Jan Kara
2016-01-18 15:40                     ` Jan Kara
2016-01-19  0:31                     ` Eric Sandeen
2016-01-15 22:50             ` Dave Chinner [this message]
2016-01-15 22:50               ` Dave Chinner

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