path: root/fs/ubifs/io.c

/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 * Copyright (C) 2006, 2007 University of Szeged, Hungary
 *
 * 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: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 *          Zoltan Sogor
 */

/*
 * This file implements UBIFS I/O subsystem which provides various I/O-related
 * helper functions (reading/writing/checking/validating nodes) and implements
 * write-buffering support. Write buffers help to save space which otherwise
 * would have been wasted for padding to the nearest minimal I/O unit boundary.
 * Instead, data first goes to the write-buffer and is flushed when the
 * buffer is full or when it is not used for some time (by timer). This is
 * similar to the mechanism is used by JFFS2.
 *
 * UBIFS distinguishes between minimum write size (@c->min_io_size) and maximum
 * write size (@c->max_write_size). The latter is the maximum amount of bytes
 * the underlying flash is able to program at a time, and writing in
 * @c->max_write_size units should presumably be faster. Obviously,
 * @c->min_io_size <= @c->max_write_size. Write-buffers are of
 * @c->max_write_size bytes in size for maximum performance. However, when a
 * write-buffer is flushed, only the portion of it (aligned to @c->min_io_size
 * boundary) which contains data is written, not the whole write-buffer,
 * because this is more space-efficient.
 *
 * This optimization adds few complications to the code. Indeed, on the one
 * hand, we want to write in optimal @c->max_write_size bytes chunks, which
 * also means aligning writes at the @c->max_write_size bytes offsets. On the
 * other hand, we do not want to waste space when synchronizing the write
 * buffer, so during synchronization we writes in smaller chunks. And this makes
 * the next write offset to be not aligned to @c->max_write_size bytes. So the
 * have to make sure that the write-buffer offset (@wbuf->offs) becomes aligned
 * to @c->max_write_size bytes again. We do this by temporarily shrinking
 * write-buffer size (@wbuf->size).
 *
 * Write-buffers are defined by 'struct ubifs_wbuf' objects and protected by
 * mutexes defined inside these objects. Since sometimes upper-level code
 * has to lock the write-buffer (e.g. journal space reservation code), many
 * functions related to write-buffers have "nolock" suffix which means that the
 * caller has to lock the write-buffer before calling this function.
 *
 * UBIFS stores nodes at 64 bit-aligned addresses. If the node length is not
 * aligned, UBIFS starts the next node from the aligned address, and the padded
 * bytes may contain any rubbish. In other words, UBIFS does not put padding
 * bytes in those small gaps. Common headers of nodes store real node lengths,
 * not aligned lengths. Indexing nodes also store real lengths in branches.
 *
 * UBIFS uses padding when it pads to the next min. I/O unit. In this case it
 * uses padding nodes or padding bytes, if the padding node does not fit.
 *
 * All UBIFS nodes are protected by CRC checksums and UBIFS checks CRC when
 * they are read from the flash media.
 */

#include <linux/crc32.h>
#include <linux/slab.h>
#include "ubifs.h"

/**
 * ubifs_ro_mode - switch UBIFS to read read-only mode.
 * @c: UBIFS file-system description object
 * @err: error code which is the reason of switching to R/O mode
 */
void ubifs_ro_mode(struct ubifs_info *c, int err)
{
	if (!c->ro_error) {
		c->ro_error = 1;
		c->no_chk_data_crc = 0;
		c->vfs_sb->s_flags |= MS_RDONLY;
		ubifs_warn("switched to read-only mode, error %d", err);
		dump_stack();
	}
}

/*
 * Below are simple wrappers over UBI I/O functions which include some
 * additional checks and UBIFS debugging stuff. See corresponding UBI function
 * for more information.
 */

int ubifs_leb_read(const struct ubifs_info *c, int lnum, void *buf, int offs,
		   int len, int even_ebadmsg)
{
	int err;

	err = ubi_read(c->ubi, lnum, buf, offs, len);
	/*
	 * In case of %-EBADMSG print the error message only if the
	 * @even_ebadmsg is true.
	 */
	if (err && (err != -EBADMSG || even_ebadmsg)) {
		ubifs_err("reading %d bytes from LEB %d:%d failed, error %d",
			  len, lnum, offs, err);
		dump_stack();
	}
	return err;
}

int ubifs_leb_write(struct ubifs_info *c, int lnum, const void *buf, int offs,
		    int len, int dtype)
{
	int err;

	ubifs_assert(!c->ro_media && !c->ro_mount);
	if (c->ro_error)
		return -EROFS;
	if (!dbg_is_tst_rcvry(c))
		err = ubi_leb_write(c->ubi, lnum, buf, offs, len, dtype);
	else
		err = dbg_leb_write(c, lnum, buf, offs, len, dtype);
	if (err) {
		ubifs_err("writing %d bytes to LEB %d:%d failed, error %d",
			  len, lnum, offs, err);
		ubifs_ro_mode(c, err);
		dump_stack();
	}
	return err;
}

int ubifs_leb_change(struct ubifs_info *c, int lnum, const void *buf, int len,
		     int dtype)
{
	int err;

	ubifs_assert(!c->ro_media && !