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From: Jan Kara <jack@suse.cz>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org,
	Richard Weinberger <richard@nod.at>,
	linux-mtd@lists.infradead.org, kernel@pengutronix.de,
	Jan Kara <jack@suse.com>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH 1/8] quota: Allow to pass mount path to quotactl
Date: Wed, 27 Jan 2021 15:46:46 +0100	[thread overview]
Message-ID: <20210127144646.GB13717@quack2.suse.cz> (raw)
In-Reply-To: <20210126104557.GB28722@pengutronix.de>

On Tue 26-01-21 11:45:57, Sascha Hauer wrote:
> On Mon, Jan 25, 2021 at 04:45:07PM +0100, Jan Kara wrote:
> > On Mon 25-01-21 09:38:54, Sascha Hauer wrote:
> > > On Fri, Jan 22, 2021 at 05:16:58PM +0000, Christoph Hellwig wrote:
> > > > On Fri, Jan 22, 2021 at 04:15:29PM +0100, Sascha Hauer wrote:
> > > > > This patch introduces the Q_PATH flag to the quotactl cmd argument.
> > > > > When given, the path given in the special argument to quotactl will
> > > > > be the mount path where the filesystem is mounted, instead of a path
> > > > > to the block device.
> > > > > This is necessary for filesystems which do not have a block device as
> > > > > backing store. Particularly this is done for upcoming UBIFS support.
> > > > > 
> > > > > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > > > 
> > > > I hate overloading quotactl even more.  Why not add a new quotactl_path
> > > > syscall instead?
> > > 
> > > We can probably do that. Honza, what do you think?
> > 
> > Hum, yes, probably it would be cleaner to add a new syscall for this so
> > that we don't overload quotactl(2). I just didn't think of this.
> 
> How should the semantics of that new syscall look like?
> 
> The easiest and most obvious way would be to do it like the quotactl(2)
> and just replace the special argument with a path:
> 
> int quotactl_path(int cmd, const char *path, int id, caddr_t addr);

Yes, that's what I meant.

> If we try adding a new syscall then we could completely redefine the API
> and avoid the shortcomings of the original quotactl(2) if there are any.
> Can you foresee the discussions we end up in? I am afraid I am opening a
> can of worms here.
> OTOH there might be value in keeping the new syscall compatible to the
> existing one, but I don't know how much this argument counts.

That's a good question but also a can of worms as you write :). One obvious
problem with quotactl() is that's it's ioctl-like interface. So we have
several different operations mixed into a single syscall. Currently there
are these operations:

#define Q_SYNC     0x800001     /* sync disk copy of a filesystems quotas */
#define Q_QUOTAON  0x800002     /* turn quotas on */
#define Q_QUOTAOFF 0x800003     /* turn quotas off */
#define Q_GETFMT   0x800004     /* get quota format used on given filesystem */
#define Q_GETINFO  0x800005     /* get information about quota files */
#define Q_SETINFO  0x800006     /* set information about quota files */
#define Q_GETQUOTA 0x800007     /* get user quota structure */
#define Q_SETQUOTA 0x800008     /* set user quota structure */
#define Q_GETNEXTQUOTA 0x800009 /* get disk limits and usage >= ID */
<plus their XFS variants>

In a puristic world they'd be 9 different syscalls ... or somewhat less
because Q_GETNEXTQUOTA is a superset of Q_GETQUOTA, we could drop Q_SYNC
and Q_GETFMT because they have dubious value these days so we'd be left
with 6. I don't have a strong opinion whether 6 syscalls are worth the
cleanliness or whether we should go with just one new quotactl_path()
syscall. I've CCed linux-api in case other people have opinion.

Anyway, even if we go with single quotactl_path() syscall we should remove
the duplication between VFS and XFS quotactls when we are creating a new
syscall. Thoughts?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2021-01-27 14:47 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-22 15:15 [PATCH v5 0/8] Add quota support to UBIFS Sascha Hauer
2021-01-22 15:15 ` [PATCH 1/8] quota: Allow to pass mount path to quotactl Sascha Hauer
2021-01-22 17:16   ` Christoph Hellwig
2021-01-25  8:38     ` Sascha Hauer
2021-01-25 15:45       ` Jan Kara
2021-01-25 20:42         ` Christoph Hellwig
2021-01-26 13:17           ` Jan Kara
2021-01-26 13:34             ` Christoph Hellwig
2021-01-26 16:18               ` Jan Kara
2021-01-27 14:05                 ` Sascha Hauer
2021-01-27 14:19                   ` Jan Kara
2021-01-26 10:45         ` Sascha Hauer
2021-01-27 14:46           ` Jan Kara [this message]
2021-01-27 16:25             ` Christoph Hellwig
2021-01-22 15:15 ` [PATCH 2/8] ubifs: move checks and preparation into setflags() Sascha Hauer
2021-01-22 15:15 ` [PATCH 3/8] ubifs: Add support for FS_IOC_FS[SG]ETXATTR ioctls Sascha Hauer
2021-01-22 17:18   ` Christoph Hellwig
2021-01-22 15:15 ` [PATCH 4/8] ubifs: do not ubifs_inode() on potentially NULL pointer Sascha Hauer
2021-01-22 15:15 ` [PATCH 5/8] ubifs: Factor out ubifs_set_feature_flag() Sascha Hauer
2021-01-22 15:15 ` [PATCH 6/8] ubifs: Add support for project id Sascha Hauer
2021-01-22 15:15 ` [PATCH 7/8] ubifs: export get_znode Sascha Hauer
2021-01-22 17:20   ` Christoph Hellwig
2021-01-22 15:15 ` [PATCH 8/8] ubifs: Add quota support Sascha Hauer
  -- strict thread matches above, loose matches on Subject: below --
2020-01-24 13:13 [PATCH v4 0/8] Add quota support to UBIFS Sascha Hauer
2020-01-24 13:13 ` [PATCH 1/8] quota: Allow to pass mount path to quotactl Sascha Hauer
2020-01-27 10:45   ` Jan Kara
2020-01-28 10:06     ` Sascha Hauer
2020-01-28 11:41       ` Jan Kara
2020-01-29  1:29       ` Al Viro
2020-01-29 16:14         ` Jan Kara
2020-02-04 10:35         ` Sascha Hauer
2020-02-18  9:22           ` Jan Kara

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