io.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0-only
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 * Copyright (C) 2006, 2007 University of Szeged, Hungary
 *
 * 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)
{ … }

/*
 * 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 ubifs_leb_write(struct ubifs_info *c, int lnum, const void *buf, int offs,
		    int len)
{ … }

int ubifs_leb_change(struct ubifs_info *c, int lnum, const void *buf, int len)
{ … }

int ubifs_leb_unmap(struct ubifs_info *c, int lnum)
{ … }

int ubifs_leb_map(struct ubifs_info *c, int lnum)
{ … }

int ubifs_is_mapped(const struct ubifs_info *c, int lnum)
{ … }

static void record_magic_error(struct ubifs_stats_info *stats)
{ … }

static void record_node_error(struct ubifs_stats_info *stats)
{ … }

static void record_crc_error(struct ubifs_stats_info *stats)
{ … }

/**
 * ubifs_check_node - check node.
 * @c: UBIFS file-system description object
 * @buf: node to check
 * @len: node length
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 * @quiet: print no messages
 * @must_chk_crc: indicates whether to always check the CRC
 *
 * This function checks node magic number and CRC checksum. This function also
 * validates node length to prevent UBIFS from becoming crazy when an attacker
 * feeds it a file-system image with incorrect nodes. For example, too large
 * node length in the common header could cause UBIFS to read memory outside of
 * allocated buffer when checking the CRC checksum.
 *
 * This function may skip data nodes CRC checking if @c->no_chk_data_crc is
 * true, which is controlled by corresponding UBIFS mount option. However, if
 * @must_chk_crc is true, then @c->no_chk_data_crc is ignored and CRC is
 * checked. Similarly, if @c->mounting or @c->remounting_rw is true (we are
 * mounting or re-mounting to R/W mode), @c->no_chk_data_crc is ignored and CRC
 * is checked. This is because during mounting or re-mounting from R/O mode to
 * R/W mode we may read journal nodes (when replying the journal or doing the
 * recovery) and the journal nodes may potentially be corrupted, so checking is
 * required.
 *
 * This function returns zero in case of success and %-EUCLEAN in case of bad
 * CRC or magic.
 */
int ubifs_check_node(const struct ubifs_info *c, const void *buf, int len,
		     int lnum, int offs, int quiet, int must_chk_crc)
{ … }

/**
 * ubifs_pad - pad flash space.
 * @c: UBIFS file-system description object
 * @buf: buffer to put padding to
 * @pad: how many bytes to pad
 *
 * The flash media obliges us to write only in chunks of %c->min_io_size and
 * when we have to write less data we add padding node to the write-buffer and
 * pad it to the next minimal I/O unit's boundary. Padding nodes help when the
 * media is being scanned. If the amount of wasted space is not enough to fit a
 * padding node which takes %UBIFS_PAD_NODE_SZ bytes, we write padding bytes
 * pattern (%UBIFS_PADDING_BYTE).
 *
 * Padding nodes are also used to fill gaps when the "commit-in-gaps" method is
 * used.
 */
void ubifs_pad(const struct ubifs_info *c, void *buf, int pad)
{ … }

/**
 * next_sqnum - get next sequence number.
 * @c: UBIFS file-system description object
 */
static unsigned long long next_sqnum(struct ubifs_info *c)
{ … }

void ubifs_init_node(struct ubifs_info *c, void *node, int len, int pad)
{ … }

void ubifs_crc_node(struct ubifs_info *c, void *node, int len)
{ … }

/**
 * ubifs_prepare_node_hmac - prepare node to be written to flash.
 * @c: UBIFS file-system description object
 * @node: the node to pad
 * @len: node length
 * @hmac_offs: offset of the HMAC in the node
 * @pad: if the buffer has to be padded
 *
 * This function prepares node at @node to be written to the media - it
 * calculates node CRC, fills the common header, and adds proper padding up to
 * the next minimum I/O unit if @pad is not zero. if @hmac_offs is positive then
 * a HMAC is inserted into the node at the given offset.
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int ubifs_prepare_node_hmac(struct ubifs_info *c, void *node, int len,
			    int hmac_offs, int pad)
{ … }

/**
 * ubifs_prepare_node - prepare node to be written to flash.
 * @c: UBIFS file-system description object
 * @node: the node to pad
 * @len: node length
 * @pad: if the buffer has to be padded
 *
 * This function prepares node at @node to be written to the media - it
 * calculates node CRC, fills the common header, and adds proper padding up to
 * the next minimum I/O unit if @pad is not zero.
 */
void ubifs_prepare_node(struct ubifs_info *c, void *node, int len, int pad)
{ … }

/**
 * ubifs_prep_grp_node - prepare node of a group to be written to flash.
 * @c: UBIFS file-system description object
 * @node: the node to pad
 * @len: node length
 * @last: indicates the last node of the group
 *
 * This function prepares node at @node to be written to the media - it
 * calculates node CRC and fills the common header.
 */
void ubifs_prep_grp_node(struct ubifs_info *c, void *node, int len, int last)
{ … }

/**
 * wbuf_timer_callback_nolock - write-buffer timer callback function.
 * @timer: timer data (write-buffer descriptor)
 *
 * This function is called when the write-buffer timer expires.
 */
static enum hrtimer_restart wbuf_timer_callback_nolock(struct hrtimer *timer)
{ … }

/**
 * new_wbuf_timer_nolock - start new write-buffer timer.
 * @c: UBIFS file-system description object
 * @wbuf: write-buffer descriptor
 */
static void new_wbuf_timer_nolock(struct ubifs_info *c, struct ubifs_wbuf *wbuf)
{ … }

/**
 * cancel_wbuf_timer_nolock - cancel write-buffer timer.
 * @wbuf: write-buffer descriptor
 */
static void cancel_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
{ … }

/**
 * ubifs_wbuf_sync_nolock - synchronize write-buffer.
 * @wbuf: write-buffer to synchronize
 *
 * This function synchronizes write-buffer @buf and returns zero in case of
 * success or a negative error code in case of failure.
 *
 * Note, although write-buffers are of @c->max_write_size, this function does
 * not necessarily writes all @c->max_write_size bytes to the flash. Instead,
 * if the write-buffer is only partially filled with data, only the used part
 * of the write-buffer (aligned on @c->min_io_size boundary) is synchronized.
 * This way we waste less space.
 */
int ubifs_wbuf_sync_nolock(struct ubifs_wbuf *wbuf)
{ … }

/**
 * ubifs_wbuf_seek_nolock - seek write-buffer.
 * @wbuf: write-buffer
 * @lnum: logical eraseblock number to seek to
 * @offs: logical eraseblock offset to seek to
 *
 * This function targets the write-buffer to logical eraseblock @lnum:@offs.
 * The write-buffer has to be empty. Returns zero in case of success and a
 * negative error code in case of failure.
 */
int ubifs_wbuf_seek_nolock(struct ubifs_wbuf *wbuf, int lnum, int offs)
{ … }

/**
 * ubifs_bg_wbufs_sync - synchronize write-buffers.
 * @c: UBIFS file-system description object
 *
 * This function is called by background thread to synchronize write-buffers.
 * Returns zero in case of success and a negative error code in case of
 * failure.
 */
int ubifs_bg_wbufs_sync(struct ubifs_info *c)
{ … }

/**
 * ubifs_wbuf_write_nolock - write data to flash via write-buffer.
 * @wbuf: write-buffer
 * @buf: node to write
 * @len: node length
 *
 * This function writes data to flash via write-buffer @wbuf. This means that
 * the last piece of the node won't reach the flash media immediately if it
 * does not take whole max. write unit (@c->max_write_size). Instead, the node
 * will sit in RAM until the write-buffer is synchronized (e.g., by timer, or
 * because more data are appended to the write-buffer).
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure. If the node cannot be written because there is no more
 * space in this logical eraseblock, %-ENOSPC is returned.
 */
int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
{ … }

/**
 * ubifs_write_node_hmac - write node to the media.
 * @c: UBIFS file-system description object
 * @buf: the node to write
 * @len: node length
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 * @hmac_offs: offset of the HMAC within the node
 *
 * This function automatically fills node magic number, assigns sequence
 * number, and calculates node CRC checksum. The length of the @buf buffer has
 * to be aligned to the minimal I/O unit size. This function automatically
 * appends padding node and padding bytes if needed. Returns zero in case of
 * success and a negative error code in case of failure.
 */
int ubifs_write_node_hmac(struct ubifs_info *c, void *buf, int len, int lnum,
			  int offs, int hmac_offs)
{ … }

/**
 * ubifs_write_node - write node to the media.
 * @c: UBIFS file-system description object
 * @buf: the node to write
 * @len: node length
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 *
 * This function automatically fills node magic number, assigns sequence
 * number, and calculates node CRC checksum. The length of the @buf buffer has
 * to be aligned to the minimal I/O unit size. This function automatically
 * appends padding node and padding bytes if needed. Returns zero in case of
 * success and a negative error code in case of failure.
 */
int ubifs_write_node(struct ubifs_info *c, void *buf, int len, int lnum,
		     int offs)
{ … }

/**
 * ubifs_read_node_wbuf - read node from the media or write-buffer.
 * @wbuf: wbuf to check for un-written data
 * @buf: buffer to read to
 * @type: node type
 * @len: node length
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 *
 * This function reads a node of known type and length, checks it and stores
 * in @buf. If the node partially or fully sits in the write-buffer, this
 * function takes data from the buffer, otherwise it reads the flash media.
 * Returns zero in case of success, %-EUCLEAN if CRC mismatched and a negative
 * error code in case of failure.
 */
int ubifs_read_node_wbuf(struct ubifs_wbuf *wbuf, void *buf, int type, int len,
			 int lnum, int offs)
{ … }

/**
 * ubifs_read_node - read node.
 * @c: UBIFS file-system description object
 * @buf: buffer to read to
 * @type: node type
 * @len: node length (not aligned)
 * @lnum: logical eraseblock number
 * @offs: offset within the logical eraseblock
 *
 * This function reads a node of known type and length, checks it and
 * stores in @buf. Returns zero in case of success, %-EUCLEAN if CRC mismatched
 * and a negative error code in case of failure.
 */
int ubifs_read_node(const struct ubifs_info *c, void *buf, int type, int len,
		    int lnum, int offs)
{ … }

/**
 * ubifs_wbuf_init - initialize write-buffer.
 * @c: UBIFS file-system description object
 * @wbuf: write-buffer to initialize
 *
 * This function initializes write-buffer. Returns zero in case of success
 * %-ENOMEM in case of failure.
 */
int ubifs_wbuf_init(struct ubifs_info *c, struct ubifs_wbuf *wbuf)
{ … }

/**
 * ubifs_wbuf_add_ino_nolock - add an inode number into the wbuf inode array.
 * @wbuf: the write-buffer where to add
 * @inum: the inode number
 *
 * This function adds an inode number to the inode array of the write-buffer.
 */
void ubifs_wbuf_add_ino_nolock(struct ubifs_wbuf *wbuf, ino_t inum)
{ … }

/**
 * wbuf_has_ino - returns if the wbuf contains data from the inode.
 * @wbuf: the write-buffer
 * @inum: the inode number
 *
 * This function returns with %1 if the write-buffer contains some data from the
 * given inode otherwise it returns with %0.
 */
static int wbuf_has_ino(struct ubifs_wbuf *wbuf, ino_t inum)
{ … }

/**
 * ubifs_sync_wbufs_by_inode - synchronize write-buffers for an inode.
 * @c: UBIFS file-system description object
 * @inode: inode to synchronize
 *
 * This function synchronizes write-buffers which contain nodes belonging to
 * @inode. Returns zero in case of success and a negative error code in case of
 * failure.
 */
int ubifs_sync_wbufs_by_inode(struct ubifs_info *c, struct inode *inode)
{ … }
linux/fs/ubifs/io.c
