path: root/drivers/mtd/ubi/scan.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)
 */

/*
 * UBI scanning sub-system.
 *
 * This sub-system is responsible for scanning the flash media, checking UBI
 * headers and providing complete information about the UBI flash image.
 *
 * The scanning information is represented by a &struct ubi_scan_info' object.
 * Information about found volumes is represented by &struct ubi_scan_volume
 * objects which are kept in volume RB-tree with root at the @volumes field.
 * The RB-tree is indexed by the volume ID.
 *
 * Scanned logical eraseblocks are represented by &struct ubi_scan_leb objects.
 * These objects are kept in per-volume RB-trees with the root at the
 * corresponding &struct ubi_scan_volume object. To put it differently, we keep
 * an RB-tree of per-volume objects and each of these objects is the root of
 * RB-tree of per-eraseblock objects.
 *
 * Corrupted physical eraseblocks are put to the @corr list, free physical
 * eraseblocks are put to the @free list and the physical eraseblock to be
 * erased are put to the @erase list.
 *
 * UBI tries to distinguish between 2 types of corruptions.
 * 1. Corruptions caused by power cuts. These are harmless and expected
 *    corruptions and UBI tries to handle them gracefully, without printing too
 *    many warnings and error messages. The idea is that we do not lose
 *    important data in these case - we may lose only the data which was being
 *    written to the media just before the power cut happened, and the upper
 *    layers (e.g., UBIFS) are supposed to handle these situations. UBI puts
 *    these PEBs to the head of the @erase list and they are scheduled for
 *    erasure.
 *
 * 2. Unexpected corruptions which are not caused by power cuts. During
 *    scanning, such PEBs are put to the @corr list and UBI preserves them.
 *    Obviously, this lessens the amount of available PEBs, and if at some
 *    point UBI runs out of free PEBs, it switches to R/O mode. UBI also loudly
 *    informs about such PEBs every time the MTD device is attached.
 *
 * However, it is difficult to reliably distinguish between these types of
 * corruptions and UBI's strategy is as follows. UBI assumes (2.) if the VID
 * header is corrupted and the data area does not contain all 0xFFs, and there
 * were not bit-flips or integrity errors while reading the data area. Otherwise
 * UBI assumes (1.). The assumptions are:
 *   o if the data area contains only 0xFFs, there is no data, and it is safe
 *     to just erase this PEB.
 *   o if the data area has bit-flips and data integrity errors (ECC errors on
 *     NAND), it is probably a PEB which was being erased when power cut
 *     happened.
 */

#include <linux/err.h>
#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/math64.h>
#include <linux/random.h>
#include "ubi.h"

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
static int paranoid_check_si(struct ubi_device *ubi, struct ubi_scan_info *si);
#else
#define paranoid_check_si(ubi, si) 0
#endif

/* Temporary variables used during scanning */
static struct ubi_ec_hdr *ech;
static struct ubi_vid_hdr *vidh;

/**
 * add_to_list - add physical eraseblock to a list.
 * @si: scanning information
 * @pnum: physical eraseblock number to add
 * @ec: erase counter of the physical eraseblock
 * @to_head: if not zero, add to the head of the list
 * @list: the list to add to
 *
 * This function adds physical eraseblock @pnum to free, erase, or alien lists.
 * If @to_head is not zero, PEB will be added to the head of the list, which
 * basically means it will be processed first later. E.g., we add corrupted
 * PEBs (corrupted due to power cuts) to the head of the erase list to make
 * sure we erase them first and get rid of corruptions ASAP. This function
 * returns zero in case of success and a negative error code in case of
 * failure.
 */
static int add_to_list(struct ubi_scan_info *si, int pnum, int ec, int to_head,
		       struct list_head *list)
{
	struct ubi_scan_leb *seb;

	if (list == &si->free) {
		dbg_bld("add to free: PEB %d, EC %d", pnum, ec);
	} else if (list == &si->erase) {
		dbg_bld("add to erase: PEB %d, EC %d", pnum, ec);
	} else if (list == &si->alien) {
		dbg_bld("add to alien: PEB %d, EC %d", pnum, ec);
		si->alien_peb_count += 1;
	} else
		BUG();

	seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_KERNEL);
	if (!seb)
		return -ENOMEM;

	seb->pnum = pnum;
	seb->ec = ec;
	if (to_head)
		list_add(&seb->u.list, list);
	else
		list_add_tail(&seb->u.list, list);
	return 0;
}

/**
 * add_corrupted - add a corrupted physical eraseblock.
 * @si: scanning information
 * @pnum: physical eraseblock number to add
 * @ec: erase counter of the physical eraseblock
 *
 * This function adds corrupted physical eraseblock @pnum to the 'corr' list.
 * The corruption was presumably not caused by a power cut. Returns zero in
 * case of success and a negative error code in case of failure.
 */
static int add_corrupted(struct ubi_scan_info *si, int pnum, int ec)
{
	struct ubi_scan_leb *seb;

	dbg_bld("add to corrupted: PEB %d, EC %d", pnum, ec);

	seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_