Re: [PATCH 7/7] ubifs: Add quota support

[Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>]

On Mon, Nov 11, 2019 at 05:34:46PM +0100, Jan Kara wrote:
> Hi Sascha!
> 
> On Mon 11-11-19 09:57:45, Sascha Hauer wrote:
> > On Wed, Nov 06, 2019 at 11:14:28AM +0100, Jan Kara wrote:
> > > > +/**
> > > > + * ubifs_dqblk_find_next - find the next qid
> > > > + * @c: UBIFS file-system description object
> > > > + * @qid: The qid to look for
> > > > + *
> > > > + * Find the next dqblk entry with a qid that is bigger or equally big than the
> > > > + * given qid. Returns the next dqblk entry if found or NULL if no dqblk exists
> > > > + * with a qid that is at least equally big.
> > > > + */
> > > > +static struct ubifs_dqblk *ubifs_dqblk_find_next(struct ubifs_info *c,
> > > > +						 struct kqid qid)
> > > > +{
> > > > +	struct rb_node *node = c->dqblk_tree[qid.type].rb_node;
> > > > +	struct ubifs_dqblk *next = NULL;
> > > > +
> > > > +	while (node) {
> > > > +		struct ubifs_dqblk *ud = rb_entry(node, struct ubifs_dqblk, rb);
> > > > +
> > > > +		if (qid_eq(qid, ud->kqid))
> > > > +			return ud;
> > > > +
> > > > +		if (qid_lt(qid, ud->kqid)) {
> > > > +			if (!next || qid_lt(ud->kqid, next->kqid))
> 			^^^
> This condition looks superfluous as it should be always true. The last node
> where you went left should be the least greater node if you didn't find the
> exact match...

You are right. I can't say why I thought this is necessary when I wrote
this.

> 
> > > > +				next = ud;
> > > > +
> > > > +			node = node->rb_left;
> > > > +		} else {
> > > > +			node = node->rb_right;
> > > > +		}
> > > > +	}
> > > > +
> > > > +	return next;
> > > > +}
> > > 
> > > Why not use rb_next() here? It should do what you need, shouldn't it?
> > 
> > I could use rb_next(), but it defeats the purpose of a tree to iterate
> > over the whole tree to find an entry. If I wanted that I would have used
> > a list.
> 
> I wasn't quite clear in my suggestion and now that I look at it it was
> actually misleading. I'm sorry for that. So a second try :):
> 
> You have ubifs_dqblk_find() and ubifs_dqblk_find_next() doing very similar
> rbtree traversal. I think you could remove that duplication by using
> ubifs_dqblk_find_next() from ubifs_dqblk_find()?

Ok, with this the two functions can be simplified to:

/**
 * ubifs_dqblk_find_next - find the next qid
 * @c: UBIFS file-system description object
 * @qid: The qid to look for
 *
 * Find the next dqblk entry with a qid that is bigger or equally big than the
 * given qid. Returns the next dqblk entry if found or NULL if no dqblk exists
 * with a qid that is at least equally big.
 */
static struct ubifs_dqblk *ubifs_dqblk_find_next(struct ubifs_info *c,
						 struct kqid qid)
{
	struct rb_node *node = c->dqblk_tree[qid.type].rb_node;
	struct ubifs_dqblk *next = NULL;

	while (node) {
		struct ubifs_dqblk *ud = rb_entry(node, struct ubifs_dqblk, rb);

		if (qid_eq(qid, ud->kqid))
			return ud;

		if (qid_lt(qid, ud->kqid)) {
			next = ud;
			node = node->rb_left;
		} else {
			node = node->rb_right;
		}
	}

	return next;
}

/**
 * ubifs_dqblk_find - find qid in tree
 * @c: UBIFS file-system description object
 * @qid: The qid to look for
 *
 * This walks the dqblk tree and searches a given qid. Returns the dqblk entry
 * when found or NULL otherwise.
 */
static struct ubifs_dqblk *ubifs_dqblk_find(struct ubifs_info *c,
					    struct kqid qid)
{
	struct ubifs_dqblk *next = NULL;

	next = ubifs_dqblk_find_next(c, qid);

	if (next && qid_eq(qid, next->kqid))
		return next;

	return NULL;
}

If this looks good now I'll integrate it for the next round. I'll delay
sending a new version until Richard has had a look into this series.

Sascha

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