// 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_obj(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_obj(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,
};