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From: Jan Kara <jack@suse.cz>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: 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>
Subject: Re: [PATCH 1/8] quota: Allow to pass mount path to quotactl
Date: Mon, 25 Jan 2021 16:45:07 +0100	[thread overview]
Message-ID: <20210125154507.GH1175@quack2.suse.cz> (raw)
In-Reply-To: <20210125083854.GB31738@pengutronix.de>

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.

> > > +static struct super_block *quotactl_path(const char __user *special, int cmd)
> > > +{
> > > +	struct super_block *sb;
> > > +	struct path path;
> > > +	int error;
> > > +
> > > +	error = user_path_at(AT_FDCWD, special, LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> > > +			   &path);
> > 
> > This adds an overly long line.
> 
> ok, will change.
> 
> > 
> > > +	if (error)
> > > +		return ERR_PTR(error);
> > > +
> > > +	sb = quotactl_sb(path.mnt->mnt_sb->s_dev, cmd);
> > 
> > I think quotactl_sb should take the superblock directly.  This will
> > need a little refactoring of user_get_super, but will lead to much
> > better logic.
> 
> What do you mean by "take"? Take the superblock as an argument to
> quotactl_sb() or take a reference to the superblock?
> Sorry, I don't really get where you aiming at.

I think Christoph was pointing at the fact it is suboptimal to search for
superblock by device number when you already have a pointer to it.  And I
guess he was suggesting we could pass 'sb' pointer to quotactl_sb() when we
already have it. Although to be honest, I'm not sure how Christoph imagines
the refactoring of user_get_super() he mentions - when we have a path
looked up through user_path(), that pins the superblock the path is on so
it cannot be unmounted. So perhaps quotactl_sb() can done like:

	...
retry:
	if (passed_sb) {
		sb = passed_sb;
		sb->s_count++;
		if (excl)
			down_write(&sb->s_umount);
		else
			down_read(&sb->s_umount);
	} else {
		sb = user_get_super(dev, excl);
		if (!sb)
			return ERR_PTR(-ENODEV);
	}
	...


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

  reply	other threads:[~2021-01-25 16:06 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 [this message]
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
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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