dquot.c

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/*
 * Implementation of the diskquota system for the LINUX operating
 * system. QUOTA is implemented using the BSD system call interface as
 * the means of communication with the user level. Currently only the
 * ext2 filesystem has support for disk quotas. Other filesystems may
 * be added in the future. This file contains the generic routines
 * called by the different filesystems on allocation of an inode or
 * block. These routines take care of the administration needed to
 * have a consistent diskquota tracking system. The ideas of both
 * user and group quotas are based on the Melbourne quota system as
 * used on BSD derived systems. The internal implementation is 
 * based on one of the several variants of the LINUX inode-subsystem
 * with added complexity of the diskquota system.
 * 
 * Version: $Id: dquot.c,v 6.3 1996/11/17 18:35:34 mvw Exp mvw $
 * 
 * Author:	Marco van Wieringen <[e-mail]>
 *
 * Fixes:   Dmitry Gorodchanin <[e-mail]>, 11 Feb 96
 *
 *		Revised list management to avoid races
 *		-- Bill Hawes, <[e-mail]>, 9/98
 *
 *		Fixed races in dquot_transfer(), dqget() and dquot_alloc_...().
 *		As the consequence the locking was moved from dquot_decr_...(),
 *		dquot_incr_...() to calling functions.
 *		invalidate_dquots() now writes modified dquots.
 *		Serialized quota_off() and quota_on() for mount point.
 *		Fixed a few bugs in grow_dquots().
 *		Fixed deadlock in write_dquot() - we no longer account quotas on
 *		quota files
 *		remove_dquot_ref() moved to inode.c - it now traverses through inodes
 *		add_dquot_ref() restarts after blocking
 *		Added check for bogus uid and fixed check for group in quotactl.
 *		Jan Kara, <[e-mail]>, sponsored by SuSE CR, 10-11/99
 *
 *		Used struct list_head instead of own list struct
 *		Invalidation of dquots with dq_count > 0 no longer possible
 *		Improved free_dquots list management
 *		Quota and i_blocks are now updated in one place to avoid races
 *		Warnings are now delayed so we won't block in critical section
 *		Write updated not to require dquot lock
 *		Jan Kara, <[e-mail]>, 9/2000
 *
 *		Added dynamic quota structure allocation
 *		Jan Kara <[e-mail]> 12/2000
 *
 * (C) Copyright 1994 - 1997 Marco van Wieringen 
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/fcntl.h>
#include <linux/stat.h>
#include <linux/tty.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/init.h>

#include <asm/uaccess.h>

#define __DQUOT_VERSION__	"dquot_6.4.0"

int nr_dquots, nr_free_dquots;

static char *quotatypes[] = INITQFNAMES;

static inline struct quota_mount_options *sb_dqopt(struct super_block *sb)
{
	return &sb->s_dquot;
}

/*
 * Dquot List Management:
 * The quota code uses three lists for dquot management: the inuse_list,
 * free_dquots, and dquot_hash[] array. A single dquot structure may be
 * on all three lists, depending on its current state.
 *
 * All dquots are placed to the end of inuse_list when first created, and this
 * list is used for the sync and invalidate operations, which must look
 * at every dquot.
 *
 * Unused dquots (dq_count == 0) are added to the free_dquots list when
 * freed, and this list is searched whenever we need an available dquot.
 * Dquots are removed from the list as soon as they are used again, and
 * nr_free_dquots gives the number of dquots on the list. When dquot is
 * invalidated it's completely released from memory.
 *
 * Dquots with a specific identity (device, type and id) are placed on
 * one of the dquot_hash[] hash chains. The provides an efficient search
 * mechanism to locate a specific dquot.
 */

/*
 * Note that any operation which operates on dquot data (ie. dq_dqb) mustn't
 * block while it's updating/reading it. Otherwise races would occur.
 *
 * Locked dquots might not be referenced in inodes - operations like
 * add_dquot_space() does dqduplicate() and would complain. Currently
 * dquot it locked only once in its existence - when it's being read
 * to memory on first dqget() and at that time it can't be referenced
 * from inode. Write operations on dquots don't hold dquot lock as they
 * copy data to internal buffers before writing anyway and copying as well
 * as any data update should be atomic. Also nobody can change used
 * entries in dquot structure as this is done only when quota is destroyed
 * and invalidate_dquots() waits for dquot to have dq_count == 0.
 */

static LIST_HEAD(inuse_list);
static LIST_HEAD(free_dquots);
static struct list_head dquot_hash[NR_DQHASH];

static struct dqstats dqstats;

static void dqput(struct dquot *);
static struct dquot *dqduplicate(struct dquot *);

static inline char is_enabled(struct quota_mount_options *dqopt, short type)
{
	switch (type) {
		case USRQUOTA:
			return((dqopt->flags & DQUOT_USR_ENABLED) != 0);
		case GRPQUOTA:
			return((dqopt->flags & DQUOT_GRP_ENABLED) != 0);
	}
	return(0);
}

static inline char sb_has_quota_enabled(struct super_block *sb, short type)
{
	return is_enabled(sb_dqopt(sb), type);
}

static inline int const hashfn(kdev_t dev, unsigned int id, short type)
{
	return((HASHDEV(dev) ^ id) * (MAXQUOTAS - type)) % NR_DQHASH;
}

static inline void insert_dquot_hash(struct dquot *dquot)
{
	struct list_head *head = dquot_hash + hashfn(dquot->dq_dev, dquot->dq_id, dquot->dq_type);
	list_add(&dquot->dq_hash, head);
}

static inline void remove_dquot_hash(struct dquot *dquot)
{
	list_del(&dquot->dq_hash);
	INIT_LIST_HEAD(&dquot->dq_hash);
}

static inline struct dquot *find_dquot(unsigned int hashent, kdev_t dev, unsigned int id, short type)
{
	struct list_head *head;
	struct dquot *dquot;

	for (head = dquot_hash[hashent].next; head != dquot_hash+hashent; head = head->next) {
		dquot = list_entry(head, struct dquot, dq_hash);
		if (dquot->dq_dev == dev && dquot->dq_id == id && dquot->dq_type == type)
			return dquot;
	}
	return NODQUOT;
}

/* Add a dquot to the head of the free list */
static inline void put_dquot_head(struct dquot *dquot)
{
	list_add(&dquot->dq_free, &free_dquots);
	nr_free_dquots++;
}

/* Add a dquot to the tail of the free list */
static inline void put_dquot_last(struct dquot *dquot)
{
	list_add(&dquot->dq_free, free_dquots.prev);
	nr_free_dquots++;
}

/* Move dquot to the head of free list (it must be already on it) */
static inline void move_dquot_head(struct dquot *dquot)
{
	list_del(&dquot->dq_free);
	list_add(&dquot->dq_free, &free_dquots);
}

static inline void remove_free_dquot(struct dquot *dquot)
{
	if (list_empty(&dquot->dq_free))
		return;
	list_del(&dquot->dq_free);
	INIT_LIST_HEAD(&dquot->dq_free);
	nr_free_dquots--;
}

static inline void put_inuse(struct dquot *dquot)
{
	/* We add to the back of inuse list so we don't have to restart
	 * when traversing this list and we block */
	list_add(&dquot->dq_inuse, inuse_list.prev);
	nr_dquots++;
}

static inline void remove_inuse(struct dquot *dquot)
{
	nr_dquots--;
	list_del(&dquot->dq_inuse);
}

static void __wait_on_dquot(struct dquot *dquot)
{
	DECLARE_WAITQUEUE(wait, current);

	add_wait_queue(&dquot->dq_wait_lock, &wait);
repeat:
	set_current_state(TASK_UNINTERRUPTIBLE);
	if (dquot->dq_flags & DQ_LOCKED) {
		schedule();
		goto repeat;
	}
	remove_wait_queue(&dquot->dq_wait_lock, &wait);
	current->state = TASK_RUNNING;
}

static inline void wait_on_dquot(struct dquot *dquot)
{
	if (dquot->dq_flags & DQ_LOCKED)
		__wait_on_dquot(dquot);
}

static inline void lock_dquot(struct dquot *dquot)
{
	wait_on_dquot(dquot);
	dquot->dq_flags |= DQ_LOCKED;
}

static inline void unlock_dquot(struct dquot *dquot)
{
	dquot->dq_flags &= ~DQ_LOCKED;
	wake_up(&dquot->dq_wait_lock);
}

static void __wait_dquot_unused(struct dquot *dquot)
{
	DECLARE_WAITQUEUE(wait, current);

	add_wait_queue(&dquot->dq_wait_free, &wait);
repeat:
	set_current_state(TASK_UNINTERRUPTIBLE);
	if (dquot->dq_count) {
		schedule();
		goto repeat;
	}
	remove_wait_queue(&dquot->dq_wait_free, &wait);
	current->state = TASK_RUNNING;
}

/*
 *	We don't have to be afraid of deadlocks as we never have quotas on quota files...
 */
static void write_dquot(struct dquot *dquot)
{
	short type = dquot->dq_type;
	struct file *filp;
	mm_segment_t fs;
	loff_t offset;
	ssize_t ret;
	struct semaphore *sem = &dquot->dq_sb->s_dquot.dqio_sem;
	struct dqblk dqbuf;

	down(sem);
	filp = dquot->dq_sb->s_dquot.files[type];
	offset = dqoff(dquot->dq_id);
	fs = get_fs();
	set_fs(KERNEL_DS);

	/*
	 * Note: clear the DQ_MOD flag unconditionally,
	 * so we don't loop forever on failure.
	 */
	memcpy(&dqbuf, &dquot->dq_dqb, sizeof(struct dqblk));
	dquot->dq_flags &= ~DQ_MOD;
	ret = 0;
	if (filp)
		ret = filp->f_op->write(filp, (char *)&dqbuf, 
					sizeof(struct dqblk), &offset);
	if (ret != sizeof(struct dqblk))
		printk(KERN_WARNING "VFS: dquota write failed on dev %s\n",
			kdevname(dquot->dq_dev));

	set_fs(fs);
	up(sem);
	dqstats.writes++;
}

static void read_dquot(struct dquot *dquot)
{
	short type = dquot->dq_type;
	struct file *filp;
	mm_segment_t fs;
	loff_t offset;

	filp = dquot->dq_sb->s_dquot.files[type];
	if (filp == (struct file *)NULL)
		return;

	lock_dquot(dquot);
	if (!dquot->dq_sb)	/* Invalidated quota? */
		goto out_lock;
	/* Now we are sure filp is valid - the dquot isn't invalidated */
	down(&dquot->dq_sb->s_dquot.dqio_sem);
	offset = dqoff(dquot->dq_id);
	fs = get_fs();
	set_fs(KERNEL_DS);
	filp->f_op->read(filp, (char *)&dquot->dq_dqb, sizeof(struct dqblk), &offset);
	up(&dquot->dq_sb->s_dquot.dqio_sem);
	set_fs(fs);

	if (dquot->dq_bhardlimit == 0 && dquot->dq_bsoftlimit == 0 &&
	    dquot->dq_ihardlimit == 0 && dquot->dq_isoftlimit == 0)
		dquot->dq_flags |= DQ_FAKE;
	dqstats.reads++;
out_lock:
	unlock_dquot(dquot);
}

/* Invalidate all dquots on the list, wait for all users. Note that this function is called
 * after quota is disabled so no new quota might be created. As we only insert to the end of
 * inuse list, we don't have to restart searching... */
static void invalidate_dquots(struct super_block *sb, short type)
{
	struct dquot *dquot;
	struct list_head *head;

restart:
	for (head = inuse_list.next; head != &inuse_list; head = head->next) {
		dquot = list_entry(head, struct dquot, dq_inuse);
		if (dquot->dq_sb != sb)
			continue;
		if (dquot->dq_type != type)
			continue;
		dquot->dq_flags |= DQ_INVAL;
		if (dquot->dq_count)
			/*
			 *  Wait for any users of quota. As we have already cleared the flags in
			 *  superblock and cleared all pointers from inodes we are assured
			 *  that there will be no new users of this quota.
			 */
			__wait_dquot_unused(dquot);
		/* Quota now have no users and it has been written on last dqput() */
		remove_dquot_hash(dquot);
		remove_free_dquot(dquot);
		remove_inuse(dquot);
		kmem_cache_free(dquot_cachep, dquot);
		goto restart;
	}
}

int sync_dquots(kdev_t dev, short type)
{
	struct list_head *head;
	struct dquot *dquot;

	lock_kernel();
restart:
	for (head = inuse_list.next; head != &inuse_list; head = head->next) {
		dquot = list_entry(head, struct dquot, dq_inuse);
		if (dev && dquot->dq_dev != dev)
			continue;
                if (type != -1 && dquot->dq_type != type)
			continue;
		if (!dquot->dq_sb)	/* Invalidated? */
			continue;
		if (!(dquot->dq_flags & (DQ_MOD | DQ_LOCKED)))
			continue;
		/* Raise use count so quota won't be invalidated. We can't use dqduplicate() as it does too many tests */
		dquot->dq_count++;
		if (dquot->dq_flags & DQ_LOCKED)
			wait_on_dquot(dquot);
		if (dquot->dq_flags & DQ_MOD)
			write_dquot(dquot);
		dqput(dquot);
		goto restart;
	}
	dqstats.syncs++;
	unlock_kernel();
	return 0;
}

/* Free unused dquots from cache */
static void prune_dqcache(int count)
{
	struct list_head *head;
	struct dquot *dquot;

	head = free_dquots.prev;
	while (head != &free_dquots && count) {
		dquot = list_entry(head, struct dquot, dq_free);
		remove_dquot_hash(dquot);
		remove_free_dquot(dquot);
		remove_inuse(dquot);
		kmem_cache_free(dquot_cachep, dquot);
		count--;
		head = free_dquots.prev;
	}
}

int shrink_dqcache_memory(int priority, unsigned int gfp_mask)
{
	lock_kernel();
	prune_dqcache(nr_free_dquots / (priority + 1));
	unlock_kernel();
	kmem_cache_shrink(dquot_cachep);
	return 0;
}

/* NOTE: If you change this function please check whether dqput_blocks() works right... */
static void dqput(struct dquot *dquot)
{
	if (!dquot)
		return;
	if (!dquot->dq_count) {
		printk("VFS: dqput: trying to free free dquot\n");
		printk("VFS: device %s, dquot of %s %d\n",
			kdevname(dquot->dq_dev), quotatypes[dquot->dq_type],
			dquot->dq_id);
		return;
	}

	dqstats.drops++;
we_slept:
	if (dquot->dq_count > 1) {
		/* We have more than one user... We can simply decrement use count */
		dquot->dq_count--;
		return;
	}
	if (dquot->dq_flags & DQ_MOD) {
		write_dquot(dquot);
		goto we_slept;
	}

	/* sanity check */
	if (!list_empty(&dquot->dq_free)) {
		printk(KERN_ERR "dqput: dquot already on free list??\n");
		dquot->dq_count--;	/* J.K. Just decrementing use count seems safer... */
		return;
	}
	dquot->dq_count--;
	/* If dquot is going to be invalidated invalidate_dquots() is going to free it so */
	if (!(dquot->dq_flags & DQ_INVAL))
		put_dquot_last(dquot);	/* Place at end of LRU free queue */
	wake_up(&dquot->dq_wait_free);
}

static struct dquot *get_empty_dquot(void)
{
	struct dquot *dquot;

	dquot = kmem_cache_alloc(dquot_cachep, SLAB_KERNEL);
	if(!dquot)
		return NODQUOT;

	memset((caddr_t)dquot, 0, sizeof(struct dquot));
	init_waitqueue_head(&dquot->dq_wait_free);
	init_waitqueue_head(&dquot->dq_wait_lock);
	INIT_LIST_HEAD(&dquot->dq_free);
	INIT_LIST_HEAD(&dquot->dq_inuse);
	INIT_LIST_HEAD(&dquot->dq_hash);
	dquot->dq_count = 1;
	/* all dquots go on the inuse_list */
	put_inuse(dquot);

	return dquot;
}

static struct dquot *dqget(struct super_block *sb, unsigned int id, short type)
{
	unsigned int hashent = hashfn(sb->s_dev, id, type);
	struct dquot *dquot, *empty = NODQUOT;
	struct quota_mount_options *dqopt = sb_dqopt(sb);

we_slept:
        if (!is_enabled(dqopt, type)) {
		if (empty)
			dqput(empty);
                return NODQUOT;
	}

	if ((dquot = find_dquot(hashent, sb->s_dev, id, type)) == NODQUOT) {
		if (empty == NODQUOT) {
			if ((empty = get_empty_dquot()) == NODQUOT)