linux/mm/shmem_quota.c

// 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 <[email protected]>
 *		Carlos Maiolino <[email protected]>
 *
 * 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>

#ifdef CONFIG_TMPFS_QUOTA

/*
 * 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 …
#define SHMEM_MAX_DQ_TIME …

struct quota_id { … };

static int shmem_check_quota_file(struct super_block *sb, int type)
{ … }

/*
 * 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)
{ … }

static int shmem_write_file_info(struct super_block *sb, int type)
{ … }

/*
 * 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)
{ … }

static int shmem_get_next_id(struct super_block *sb, struct kqid *qid)
{ … }

/*
 * 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)
{ … }

static bool shmem_is_empty_dquot(struct dquot *dquot)
{ … }
/*
 * 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)
{ … }

static int shmem_mark_dquot_dirty(struct dquot *dquot)
{ … }

static int shmem_dquot_write_info(struct super_block *sb, int type)
{ … }

static const struct quota_format_ops shmem_format_ops = …;

struct quota_format_type shmem_quota_format = …;

const struct dquot_operations shmem_quota_operations = …;
#endif /* CONFIG_TMPFS_QUOTA */