// SPDX-License-Identifier: GPL-2.0-only
/*
 * In memory quota format relies on quota infrastructure to store dquot
 * information for us. While conventional quota formats for file systems
 * with persistent storage can load quota information into dquot from the
 * storage on-demand and hence quota dquot shrinker can free any dquot
 * that is not currently being used, it must be avoided here. Otherwise we
 * can lose valuable information, user provided limits, because there is
 * no persistent storage to load the information from afterwards.
 *
 * One information that in-memory quota format needs to keep track of is
 * a sorted list of ids for each quota type. This is done by utilizing
 * an rb tree which root is stored in mem_dqinfo->dqi_priv for each quota
 * type.
 *
 * This format can be used to support quota on file system without persistent
 * storage such as tmpfs.
 *
 * Author:	Lukas Czerner <lczerner@redhat.com>
 *		Carlos Maiolino <cmaiolino@redhat.com>
 *
 * Copyright (C) 2023 Red Hat, Inc.
 */
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include <linux/shmem_fs.h>

#include <linux/quotaops.h>
#include <linux/quota.h>

/*
 * The following constants define the amount of time given a user
 * before the soft limits are treated as hard limits (usually resulting
 * in an allocation failure). The timer is started when the user crosses
 * their soft limit, it is reset when they go below their soft limit.
 */
#define SHMEM_MAX_IQ_TIME 604800	/* (7*24*60*60) 1 week */
#define SHMEM_MAX_DQ_TIME 604800	/* (7*24*60*60) 1 week */

struct quota_id {
	struct rb_node	node;
	qid_t		id;
	qsize_t		bhardlimit;
	qsize_t		bsoftlimit;
	qsize_t		ihardlimit;
	qsize_t		isoftlimit;
};

static int shmem_check_quota_file(struct super_block *sb, int type)
{
	/* There is no real quota file, nothing to do */
	return 1;
}

/*
 * There is no real quota file. Just allocate rb_root for quota ids and
 * set limits
 */
static int shmem_read_file_info(struct super_block *sb, int type)
{
	struct quota_info *dqopt = sb_dqopt(sb);
	struct mem_dqinfo *info = &dqopt->info[type];

	info->dqi_priv = kzalloc(sizeof(struct rb_root), GFP_NOFS);
	if (!info->dqi_priv)
		return -ENOMEM;

	info->dqi_max_spc_limit = SHMEM_QUOTA_MAX_SPC_LIMIT;
	info->dqi_max_ino_limit = SHMEM_QUOTA_MAX_INO_LIMIT;

	info->dqi_bgrace = SHMEM_MAX_DQ_TIME;
	info->dqi_igrace = SHMEM_MAX_IQ_TIME;
	info->dqi_flags = 0;

	return 0;
}

static int shmem_write_file_info(struct super_block *sb, int type)
{
	/* There is no real quota file, nothing to do */
	return 0;
}

/*
 * Free all the quota_id entries in the rb tree and rb_root.
 */
static int shmem_free_file_info(struct super_block *sb, int type)
{
	struct mem_dqinfo *info = &sb_dqopt(sb)->info[type];
	struct rb_root *root = info->dqi_priv;
	struct quota_id *entry;
	struct rb_node *node;

	info->dqi_priv = NULL;
	node = rb_first(root);
	while (node) {
		entry = rb_entry(node, struct quota_id, node);
		node = rb_next(&entry->node);

		rb_erase(&entry->node, root);
		kfree(entry);
	}

	kfree(root);
	return 0;
}

static int shmem_get_next_id(struct super_block *sb, struct kqid *qid)
{
	struct mem_dqinfo *info = sb_dqinfo(sb, qid->type);
	struct rb_node *node;
	qid_t id = from_kqid(&init_user_ns, *qid);
	struct quota_info *dqopt = sb_dqopt(sb);
	struct quota_id *entry = NULL;
	int ret = 0;

	if (!sb_has_quota_active(sb, qid->type))
		return -ESRCH;

	down_read(&dqopt->dqio_sem);
	node = ((struct rb_root *)info->dqi_priv)->rb_node;
	while (node) {
		entry = rb_entry(node, struct quota_id, node);

		if (id < entry->id)
			node = node->rb_left;
		else if (id > entry->id)
			node = node->rb_right;
		else
			goto got_next_id;
	}

	if (!entry) {
		ret = -ENOENT;
		goto out_unlock;
	}

	if (id > entry->id) {
		node = rb_next(&entry->node);
		if (!node) {
			ret = -ENOENT;
			goto out_unlock;
		}
		entry = rb_entry(node, struct quota_id, node);
	}

got_next_id:
	*qid = make_kqid(&init_user_ns, qid->type, entry->id);
out_unlock:
	up_read(&dqopt->dqio_sem);
	return ret;
}

/*
 * Load dquot with limits from existing entry, or create the new entry if
 * it does not exist.
 */
static int shmem_acquire_dquot(struct dquot *dquot)
{
	struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
	struct rb_node **n;
	struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info;
	struct rb_node *parent = NULL, *new_node = NULL;
	struct quota_id *new_entry, *entry;
	qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
	int ret = 0;

	mutex_lock(&dquot->dq_lock);

	down_write(&dqopt->dqio_sem);
	n = &((struct rb_root *)info->dqi_priv)->rb_node;

	while (*n) {
		parent = *n;
		entry = rb_entry(parent, struct quota_id, node);

		if (id < entry->id)
			n = &(*n)->rb_left;
		else if (id > entry->id)
			n = &(*n)->rb_right;
		else
			goto found;
	}

	/* We don't have entry for this id yet, create it */
	new_entry = kzalloc(sizeof(struct quota_id), GFP_NOFS);
	if (!new_entry) {
		ret = -ENOMEM;
		goto out_unlock;
	}

	new_entry->id = id;
	if (dquot->dq_id.type == USRQUOTA) {
		new_entry->bhardlimit = sbinfo->qlimits.usrquota_bhardlimit;
		new_entry->ihardlimit = sbinfo->qlimits.usrquota_ihardlimit;
	} else if (dquot->dq_id.type == GRPQUOTA) {
		new_entry->bhardlimit = sbinfo->qlimits.grpquota_bhardlimit;
		new_entry->ihardlimit = sbinfo->qlimits.grpquota_ihardlimit;
	}

	new_node = &new_entry->node;
	rb_link_node(new_node, parent, n);
	rb_insert_color(new_node, (struct rb_root *)info->dqi_priv);
	entry = new_entry;

found:
	/* Load the stored limits from the tree */
	spin_lock(&dquot->dq_dqb_lock);
	dquot->dq_dqb.dqb_bhardlimit = entry->bhardlimit;
	dquot->dq_dqb.dqb_bsoftlimit = entry->bsoftlimit;
	dquot->dq_dqb.dqb_ihardlimit = entry->ihardlimit;
	dquot->dq_dqb.dqb_isoftlimit = entry->isoftlimit;

	if (!dquot->dq_dqb.dqb_bhardlimit &&
	    !dquot->dq_dqb.dqb_bsoftlimit &&
	    !dquot->dq_dqb.dqb_ihardlimit &&
	    !dquot->dq_dqb.dqb_isoftlimit)
		set_bit(DQ_FAKE_B, &dquot->dq_flags);
	spin_unlock(&dquot->dq_dqb_lock);

	/* Make sure flags update is visible after dquot has been filled */
	smp_mb__before_atomic();
	set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
out_unlock:
	up_write(&dqopt->dqio_sem);
	mutex_unlock(&dquot->dq_lock);
	return ret;
}

static bool shmem_is_empty_dquot(struct dquot *dquot)
{
	struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info;
	qsize_t bhardlimit;
	qsize_t ihardlimit;

	if (dquot->dq_id.type == USRQUOTA) {
		bhardlimit = sbinfo->qlimits.usrquota_bhardlimit;
		ihardlimit = sbinfo->qlimits.usrquota_ihardlimit;
	} else if (dquot->dq_id.type == GRPQUOTA) {
		bhardlimit = sbinfo->qlimits.grpquota_bhardlimit;
		ihardlimit = sbinfo->qlimits.grpquota_ihardlimit;
	}

	if (test_bit(DQ_FAKE_B, &dquot->dq_flags) ||
		(dquot->dq_dqb.dqb_curspace == 0 &&
		 dquot->dq_dqb.dqb_curinodes == 0 &&
		 dquot->dq_dqb.dqb_bhardlimit == bhardlimit &&
		 dquot->dq_dqb.dqb_ihardlimit == ihardlimit))
		return true;

	return false;
}
/*
 * Store limits from dquot in the tree unless it's fake. If it is fake
 * remove the id from the tree since there is no useful information in
 * there.
 */
static int shmem_release_dquot(struct dquot *dquot)
{
	struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
	struct rb_node *node;
	qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
	struct quota_id *entry = NULL;

	mutex_lock(&dquot->dq_lock);
	/* Check whether we are not racing with some other dqget() */
	if (dquot_is_busy(dquot))
		goto out_dqlock;

	down_write(&dqopt->dqio_sem);
	node = ((struct rb_root *)info->dqi_priv)->rb_node;
	while (node) {
		entry = rb_entry(node, struct quota_id, node);

		if (id < entry->id)
			node = node->rb_left;
		else if (id > entry->id)
			node = node->rb_right;
		else
			goto found;
	}

	/* We should always find the entry in the rb tree */
	WARN_ONCE(1, "quota id %u from dquot %p, not in rb tree!\n", id, dquot);
	up_write(&dqopt->dqio_sem);
	mutex_unlock(&dquot->dq_lock);
	return -ENOENT;

found:
	if (shmem_is_empty_dquot(dquot)) {
		/* Remove entry from the tree */
		rb_erase(&entry->node, info->dqi_priv);
		kfree(entry);
	} else {
		/* Store the limits in the tree */
		spin_lock(&dquot->dq_dqb_lock);
		entry->bhardlimit = dquot->dq_dqb.dqb_bhardlimit;
		entry->bsoftlimit = dquot->dq_dqb.dqb_bsoftlimit;
		entry->ihardlimit = dquot->dq_dqb.dqb_ihardlimit;
		entry->isoftlimit = dquot->dq_dqb.dqb_isoftlimit;
		spin_unlock(&dquot->dq_dqb_lock);
	}

	clear_bit(DQ_ACTIVE_B, &dquot->dq_flags);
	up_write(&dqopt->dqio_sem);

out_dqlock:
	mutex_unlock(&dquot->dq_lock);
	return 0;
}

static int shmem_mark_dquot_dirty(struct dquot *dquot)
{
	return 0;
}

static int shmem_dquot_write_info(struct super_block *sb, int type)
{
	return 0;
}

static const struct quota_format_ops shmem_format_ops = {
	.check_quota_file	= shmem_check_quota_file,
	.read_file_info		= shmem_read_file_info,
	.write_file_info	= shmem_write_file_info,
	.free_file_info		= shmem_free_file_info,
};

struct quota_format_type shmem_quota_format = {
	.qf_fmt_id = QFMT_SHMEM,
	.qf_ops = &shmem_format_ops,
	.qf_owner = THIS_MODULE
};

const struct dquot_operations shmem_quota_operations = {
	.acquire_dquot		= shmem_acquire_dquot,
	.release_dquot		= shmem_release_dquot,
	.alloc_dquot		= dquot_alloc,
	.destroy_dquot		= dquot_destroy,
	.write_info		= shmem_dquot_write_info,
	.mark_dirty		= shmem_mark_dquot_dirty,
	.get_next_id		= shmem_get_next_id,
};