path: root/drivers/mtd/ubi/eba.c

/*
 * Copyright (c) International Business Machines Corp., 2006
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
 * the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Author: Artem Bityutskiy (Битюцкий Артём)
 */

/*
 * The UBI Eraseblock Association (EBA) unit.
 *
 * This unit is responsible for I/O to/from logical eraseblock.
 *
 * Although in this implementation the EBA table is fully kept and managed in
 * RAM, which assumes poor scalability, it might be (partially) maintained on
 * flash in future implementations.
 *
 * The EBA unit implements per-logical eraseblock locking. Before accessing a
 * logical eraseblock it is locked for reading or writing. The per-logical
 * eraseblock locking is implemented by means of the lock tree. The lock tree
 * is an RB-tree which refers all the currently locked logical eraseblocks. The
 * lock tree elements are &struct ltree_entry objects. They are indexed by
 * (@vol_id, @lnum) pairs.
 *
 * EBA also maintains the global sequence counter which is incremented each
 * time a logical eraseblock is mapped to a physical eraseblock and it is
 * stored in the volume identifier header. This means that each VID header has
 * a unique sequence number. The sequence number is only increased an we assume
 * 64 bits is enough to never overflow.
 */

#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/err.h>
#include "ubi.h"

/**
 * struct ltree_entry - an entry in the lock tree.
 * @rb: links RB-tree nodes
 * @vol_id: volume ID of the locked logical eraseblock
 * @lnum: locked logical eraseblock number
 * @users: how many tasks are using this logical eraseblock or wait for it
 * @mutex: read/write mutex to implement read/write access serialization to
 * the (@vol_id, @lnum) logical eraseblock
 *
 * When a logical eraseblock is being locked - corresponding &struct ltree_entry
 * object is inserted to the lock tree (@ubi->ltree).
 */
struct ltree_entry {
	struct rb_node rb;
	int vol_id;
	int lnum;
	int users;
	struct rw_semaphore mutex;
};

/* Slab cache for lock-tree entries */
static struct kmem_cache *ltree_slab;

/**
 * next_sqnum - get next sequence number.
 * @ubi: UBI device description object
 *
 * This function returns next sequence number to use, which is just the current
 * global sequence counter value. It also increases the global sequence
 * counter.
 */
static unsigned long long next_sqnum(struct ubi_device *ubi)
{
	unsigned long long sqnum;

	spin_lock(&ubi->ltree_lock);
	sqnum = ubi->global_sqnum++;
	spin_unlock(&ubi->ltree_lock);

	return sqnum;
}

/**
 * ubi_get_compat - get compatibility flags of a volume.
 * @ubi: UBI device description object
 * @vol_id: volume ID
 *
 * This function returns compatibility flags for an internal volume. User
 * volumes have no compatibility flags, so %0 is returned.
 */
static int ubi_get_compat(const struct ubi_device *ubi, int vol_id)
{
	if (vol_id == UBI_LAYOUT_VOL_ID)
		return UBI_LAYOUT_VOLUME_COMPAT;
	return 0;
}

/**
 * ltree_lookup - look up the lock tree.
 * @ubi: UBI device description object
 * @vol_id: volume ID
 * @lnum: logical eraseblock number
 *
 * This function returns a pointer to the corresponding &struct ltree_entry
 * object if the logical eraseblock is locked and %NULL if it is not.
 * @ubi->ltree_lock has to be locked.
 */
static struct ltree_entry *ltree_lookup(struct ubi_device *ubi, int vol_id,
					int lnum)
{
	struct rb_node *p;

	p = ubi->ltree.rb_node;
	while (p) {
		struct ltree_entry *le;

		le = rb_entry(p, struct ltree_entry, rb);

		if (vol_id < le->vol_id)
			p = p->rb_left;
		else if (vol_id > le->vol_id)
			p = p->rb_right;
		else {
			if (lnum < le->lnum)
				p = p->rb_left;
			else if (lnum > le->lnum)
				p = p->rb_right;
			else
				return le;
		}
	}