/*
* This file is part of UBIFS.
*
* Copyright (C) 2006-2008 Nokia Corporation
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*
* 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., 51
* Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* Authors: Adrian Hunter
* Artem Bityutskiy (Битюцкий Артём)
*/
/*
* This file implements functions needed to recover from unclean un-mounts.
* When UBIFS is mounted, it checks a flag on the master node to determine if
* an un-mount was completed successfully. If not, the process of mounting
* incorporates additional checking and fixing of on-flash data structures.
* UBIFS always cleans away all remnants of an unclean un-mount, so that
* errors do not accumulate. However UBIFS defers recovery if it is mounted
* read-only, and the flash is not modified in that case.
*
* The general UBIFS approach to the recovery is that it recovers from
* corruptions which could be caused by power cuts, but it refuses to recover
* from corruption caused by other reasons. And UBIFS tries to distinguish
* between these 2 reasons of corruptions and silently recover in the former
* case and loudly complain in the latter case.
*
* UBIFS writes only to erased LEBs, so it writes only to the flash space
* containing only 0xFFs. UBIFS also always writes strictly from the beginning
* of the LEB to the end. And UBIFS assumes that the underlying flash media
* writes in @c->max_write_size bytes at a time.
*
* Hence, if UBIFS finds a corrupted node at offset X, it expects only the min.
* I/O unit corresponding to offset X to contain corrupted data, all the
* following min. I/O units have to contain empty space (all 0xFFs). If this is
* not true, the corruption cannot be the result of a power cut, and UBIFS
* refuses to mount.
*/
#include <linux/crc32.h>
#include <linux/slab.h>
#include "ubifs.h"
/**
* is_empty - determine whether a buffer is empty (contains all 0xff).
* @buf: buffer to clean
* @len: length of buffer
*
* This function returns %1 if the buffer is empty (contains all 0xff) otherwise
* %0 is returned.
*/
static
