UBIFS: add new flash file system

This is a new flash file system. See
http://www.linux-mtd.infradead.org/doc/ubifs.html

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>

1 files changed, 914 insertions, 0 deletions

diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c
new file mode 100644
index 000000000000..3374f91b6709
--- /dev/null
+++ b/fs/ubifs/io.c
@@ -0,0 +1,914 @@
+/*
+ * 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
+ * similarto the mechanism is used by JFFS2.
+ *
+ * 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 all nodes
+ * every time they are read from the flash media.
+ */
+
+#include <linux/crc32.h>
+#include "ubifs.h"
+
+/**
+ * ubifs_check_node - check node.
+ * @c: UBIFS file-system description object
+ * @buf: node to check
+ * @lnum: logical eraseblock number
+ * @offs: offset within the logical eraseblock
+ * @quiet: print no messages
+ *
+ * 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 returns zero in case of success %-EUCLEAN in case of bad CRC
+ * or magic.
+ */
+int ubifs_check_node(const struct ubifs_info *c, const void *buf, int lnum,
+                     int offs, int quiet)
+{
+        int err = -EINVAL, type, node_len;
+        uint32_t crc, node_crc, magic;
+        const struct ubifs_ch *ch = buf;
+
+        ubifs_assert(lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
+        ubifs_assert(!(offs & 7) && offs < c->leb_size);
+
+        magic = le32_to_cpu(ch->magic);
+        if (magic != UBIFS_NODE_MAGIC) {
+                if (!quiet)
+                        ubifs_err("bad magic %#08x, expected %#08x",
+                                  magic, UBIFS_NODE_MAGIC);
+                err = -EUCLEAN;
+                goto out;
+        }
+
+        type = ch->node_type;
+        if (type < 0 || type >= UBIFS_NODE_TYPES_CNT) {
+                if (!quiet)
+                        ubifs_err("bad node type %d", type);
+                goto out;
+        }
+
+        node_len = le32_to_cpu(ch->len);
+        if (node_len + offs > c->leb_size)
+                goto out_len;
+
+        if (c->ranges[type].max_len == 0) {
+                if (node_len != c->ranges[type].len)
+                        goto out_len;
+        } else if (node_len < c->ranges[type].min_len ||
+                   node_len > c->ranges[type].max_len)
+                goto out_len;
+
+        crc = crc32(UBIFS_CRC32_INIT, buf + 8, node_len - 8);
+        node_crc = le32_to_cpu(ch->crc);
+        if (crc != node_crc) {
+                if (!quiet)
+                        ubifs_err("bad CRC: calculated %#08x, read %#08x",
+                                  crc, node_crc);
+                err = -EUCLEAN;
+                goto out;
+        }
+
+        return 0;
+
+out_len:
+        if (!quiet)
+                ubifs_err("bad node length %d", node_len);
+out:
+        if (!quiet) {
+                ubifs_err("bad node at LEB %d:%d", lnum, offs);
+                dbg_dump_node(c, buf);
+                dbg_dump_stack();
+        }
+        return err;
+}
+
+/**
+ * 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)
+{
+        uint32_t crc;
+
+        ubifs_assert(pad >= 0 && !(pad & 7));
+
+        if (pad >= UBIFS_PAD_NODE_SZ) {
+                struct ubifs_ch *ch = buf;
+                struct ubifs_pad_node *pad_node = buf;
+
+                ch->magic = cpu_to_le32(UBIFS_NODE_MAGIC);
+                ch->node_type = UBIFS_PAD_NODE;
+                ch->group_type = UBIFS_NO_NODE_GROUP;
+                ch->padding[0] = ch->padding[1] = 0;
+                ch->sqnum = 0;
+                ch->len = cpu_to_le32(UBIFS_PAD_NODE_SZ);
+                pad -= UBIFS_PAD_NODE_SZ;
+                pad_node->pad_len = cpu_to_le32(pad);
+                crc = crc32(UBIFS_CRC32_INIT, buf + 8, UBIFS_PAD_NODE_SZ - 8);
+                ch->crc = cpu_to_le32(crc);
+                memset(buf + UBIFS_PAD_NODE_SZ, 0, pad);
+        } else if (pad > 0)
+                /* Too little space, padding node won't fit */
+                memset(buf, UBIFS_PADDING_BYTE, pad);
+}
+
+/**
+ * next_sqnum - get next sequence number.
+ * @c: UBIFS file-system description object
+ */
+static unsigned long long next_sqnum(struct ubifs_info *c)
+{
+        unsigned long long sqnum;
+
+        spin_lock(&c->cnt_lock);
+        sqnum = ++c->max_sqnum;
+        spin_unlock(&c->cnt_lock);
+
+        if (unlikely(sqnum >= SQNUM_WARN_WATERMARK)) {
+                if (sqnum >= SQNUM_WATERMARK) {
+                        ubifs_err("sequence number overflow %llu, end of life",
+                                  sqnum);
+                        ubifs_ro_mode(c, -EINVAL);
+                }
+                ubifs_warn("running out of sequence numbers, end of life soon");
+        }
+
+        return sqnum;
+}
+
+/**
+ * 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)
+{
+        uint32_t crc;
+        struct ubifs_ch *ch = node;
+        unsigned long long sqnum = next_sqnum(c);
+
+        ubifs_assert(len >= UBIFS_CH_SZ);
+
+        ch->magic = cpu_to_le32(UBIFS_NODE_MAGIC);
+        ch->len = cpu_to_le32(len);
+        ch->group_type = UBIFS_NO_NODE_GROUP;
+        ch->sqnum = cpu_to_le64(sqnum);
+        ch->padding[0] = ch->padding[1] = 0;
+        crc = crc32(UBIFS_CRC32_INIT, node + 8, len - 8);
+        ch->crc = cpu_to_le32(crc);
+
+        if (pad) {
+                len = ALIGN(len, 8);
+                pad = ALIGN(len, c->min_io_size) - len;
+                ubifs_pad(c, node + len, 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)
+{
+        uint32_t crc;
+        struct ubifs_ch *ch = node;
+        unsigned long long sqnum = next_sqnum(c);
+
+        ubifs_assert(len >= UBIFS_CH_SZ);
+
+        ch->magic = cpu_to_le32(UBIFS_NODE_MAGIC);
+        ch->len = cpu_to_le32(len);
+        if (last)
+                ch->group_type = UBIFS_LAST_OF_NODE_GROUP;
+        else
+                ch->group_type = UBIFS_IN_NODE_GROUP;
+        ch->sqnum = cpu_to_le64(sqnum);
+        ch->padding[0] = ch->padding[1] = 0;
+        crc = crc32(UBIFS_CRC32_INIT, node + 8, len - 8);
+        ch->crc = cpu_to_le32(crc);
+}
+
+/**
+ * wbuf_timer_callback - write-buffer timer callback function.
+ * @data: timer data (write-buffer descriptor)
+ *
+ * This function is called when the write-buffer timer expires.
+ */
+static void wbuf_timer_callback_nolock(unsigned long data)
+{
+        struct ubifs_wbuf *wbuf = (struct ubifs_wbuf *)data;
+
+        wbuf->need_sync = 1;
+        wbuf->c->need_wbuf_sync = 1;
+        ubifs_wake_up_bgt(wbuf->c);
+}
+
+/**
+ * new_wbuf_timer - start new write-buffer timer.
+ * @wbuf: write-buffer descriptor
+ */
+static void new_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
+{
+        ubifs_assert(!timer_pending(&wbuf->timer));
+
+        if (!wbuf->timeout)
+                return;
+
+        wbuf->timer.expires = jiffies + wbuf->timeout;
+        add_timer(&wbuf->timer);
+}
+
+/**
+ * cancel_wbuf_timer - cancel write-buffer timer.
+ * @wbuf: write-buffer descriptor
+ */
+static void cancel_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
+{
+        /*
+         * If the syncer is waiting for the lock (from the background thread's
+         * context) and another task is changing write-buffer then the syncing
+         * should be canceled.
+         */
+        wbuf->need_sync = 0;
+        del_timer(&wbuf->timer);
+}
+
+/**
+ * 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.
+ */
+int ubifs_wbuf_sync_nolock(struct ubifs_wbuf *wbuf)
+{
+        struct ubifs_info *c = wbuf->c;
+        int err, dirt;
+
+        cancel_wbuf_timer_nolock(wbuf);
+        if (!wbuf->used || wbuf->lnum == -1)
+                /* Write-buffer is empty or not seeked */
+                return 0;
+
+        dbg_io("LEB %d:%d, %d bytes",
+               wbuf->lnum, wbuf->offs, wbuf->used);
+        ubifs_assert(!(c->vfs_sb->s_flags & MS_RDONLY));
+        ubifs_assert(!(wbuf->avail & 7));
+        ubifs_assert(wbuf->offs + c->min_io_size <= c->leb_size);
+
+        if (c->ro_media)
+                return -EROFS;
+
+        ubifs_pad(c, wbuf->buf + wbuf->used, wbuf->avail);
+        err = ubi_leb_write(c->ubi, wbuf->lnum, wbuf->buf, wbuf->offs,
+                            c->min_io_size, wbuf->dtype);
+        if (err) {
+                ubifs_err("cannot write %d bytes to LEB %d:%d",
+                          c->min_io_size, wbuf->lnum, wbuf->offs);
+                dbg_dump_stack();
+                return err;
+        }
+
+        dirt = wbuf->avail;
+
+        spin_lock(&wbuf->lock);
+        wbuf->offs += c->min_io_size;
+        wbuf->avail = c->min_io_size;
+        wbuf->used = 0;
+        wbuf->next_ino = 0;
+        spin_unlock(&wbuf->lock);
+
+        if (wbuf->sync_callback)
+                err = wbuf->sync_callback(c, wbuf->lnum,
+                                          c->leb_size - wbuf->offs, dirt);
+        return err;
+}
+
+/**
+ * ubifs_wbuf_seek_nolock - seek write-buffer.
+ * @wbuf: write-buffer
+ * @lnum: logical eraseblock number to seek to
+ * @offs: logical eraseblock offset to seek to
+ * @dtype: data type
+ *
+ * This function targets the write buffer to logical eraseblock @lnum:@offs.
+ * The write-buffer is synchronized if it is not 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,
+                           int dtype)
+{
+        const struct ubifs_info *c = wbuf->c;
+
+        dbg_io("LEB %d:%d", lnum, offs);
+        ubifs_assert(lnum >= 0 && lnum < c->leb_cnt);
+        ubifs_assert(offs >= 0 && offs <= c->leb_size);
+        ubifs_assert(offs % c->min_io_size == 0 && !(offs & 7));
+        ubifs_assert(lnum != wbuf->lnum);
+
+        if (wbuf->used > 0) {
+                int err = ubifs_wbuf_sync_nolock(wbuf);
+
+                if (err)
+                        return err;
+        }
+
+        spin_lock(&wbuf->lock);
+        wbuf->lnum = lnum;
+        wbuf->offs = offs;
+        wbuf->avail = c->min_io_size;
+        wbuf->used = 0;
+        spin_unlock(&wbuf->lock);
+        wbuf->dtype = dtype;
+
+        return 0;
+}
+
+/**
+ * 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)
+{
+        int err, i;
+
+        if (!c->need_wbuf_sync)
+                return 0;
+        c->need_wbuf_sync = 0;
+
+        if (c->ro_media) {
+                err = -EROFS;
+                goto out_timers;
+        }
+
+        dbg_io("synchronize");
+        for (i = 0; i < c->jhead_cnt; i++) {
+                struct ubifs_wbuf *wbuf = &c->jheads[i].wbuf;
+
+                cond_resched();
+
+                /*
+                 * If the mutex is locked then wbuf is being changed, so
+                 * synchronization is not necessary.
+                 */
+                if (mutex_is_locked(&wbuf->io_mutex))
+                        continue;
+
+                mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+                if (!wbuf->need_sync) {
+                        mutex_unlock(&wbuf->io_mutex);
+                        continue;
+                }
+
+                err = ubifs_wbuf_sync_nolock(wbuf);
+                mutex_unlock(&wbuf->io_mutex);
+                if (err) {
+                        ubifs_err("cannot sync write-buffer, error %d", err);
+                        ubifs_ro_mode(c, err);
+                        goto out_timers;
+                }
+        }
+
+        return 0;
+
+out_timers:
+        /* Cancel all timers to prevent repeated errors */
+        for (i = 0; i < c->jhead_cnt; i++) {
+                struct ubifs_wbuf *wbuf = &c->jheads[i].wbuf;
+
+                mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+                cancel_wbuf_timer_nolock(wbuf);
+                mutex_unlock(&wbuf->io_mutex);
+        }
+        return err;
+}
+
+/**
+ * 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 minimal I/O unit. Instead, the node will sit in RAM
+ * until the write-buffer is synchronized (e.g., by timer).
+ *
+ * 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)
+{
+        struct ubifs_info *c = wbuf->c;
+        int err, written, n, aligned_len = ALIGN(len, 8), offs;
+
+        dbg_io("%d bytes (%s) to wbuf at LEB %d:%d", len,
+               dbg_ntype(((struct ubifs_ch *)buf)->node_type), wbuf->lnum,
+               wbuf->offs + wbuf->used);
+        ubifs_assert(len > 0 && wbuf->lnum >= 0 && wbuf->lnum < c->leb_cnt);
+        ubifs_assert(wbuf->offs >= 0 && wbuf->offs % c->min_io_size == 0);
+        ubifs_assert(!(wbuf->offs & 7) && wbuf->offs <= c->leb_size);
+        ubifs_assert(wbuf->avail > 0 && wbuf->avail <= c->min_io_size);
+        ubifs_assert(mutex_is_locked(&wbuf->io_mutex));
+
+        if (c->leb_size - wbuf->offs - wbuf->used < aligned_len) {
+                err = -ENOSPC;
+                goto out;
+        }
+
+        cancel_wbuf_timer_nolock(wbuf);
+
+        if (c->ro_media)
+                return -EROFS;
+
+        if (aligned_len <= wbuf->avail) {
+                /*
+                 * The node is not very large and fits entirely within
+                 * write-buffer.
+                 */
+                memcpy(wbuf->buf + wbuf->used, buf, len);
+
+                if (aligned_len == wbuf->avail) {
+                        dbg_io("flush wbuf to LEB %d:%d", wbuf->lnum,
+                                wbuf->offs);
+                        err = ubi_leb_write(c->ubi, wbuf->lnum, wbuf->buf,
+                                            wbuf->offs, c->min_io_size,
+                                            wbuf->dtype);
+                        if (err)
+                                goto out;
+
+                        spin_lock(&wbuf->lock);
+                        wbuf->offs += c->min_io_size;
+                        wbuf->avail = c->min_io_size;
+                        wbuf->used = 0;
+                        wbuf->next_ino = 0;
+                        spin_unlock(&wbuf->lock);
+                } else {
+                        spin_lock(&wbuf->lock);
+                        wbuf->avail -= aligned_len;
+                        wbuf->used += aligned_len;
+                        spin_unlock(&wbuf->lock);
+                }
+
+                goto exit;
+        }
+
+        /*
+         * The node is large enough and does not fit entirely within current
+         * minimal I/O unit. We have to fill and flush write-buffer and switch
+         * to the next min. I/O unit.
+         */
+        dbg_io("flush wbuf to LEB %d:%d", wbuf->lnum, wbuf->offs);
+        memcpy(wbuf->buf + wbuf->used, buf, wbuf->avail);
+        err = ubi_leb_write(c->ubi, wbuf->lnum, wbuf->buf, wbuf->offs,
+                            c->min_io_size, wbuf->dtype);
+        if (err)
+                goto out;
+
+        offs = wbuf->offs + c->min_io_size;
+        len -= wbuf->avail;
+        aligned_len -= wbuf->avail;
+        written = wbuf->avail;
+
+        /*
+         * The remaining data may take more whole min. I/O units, so write the
+         * remains multiple to min. I/O unit size directly to the flash media.
+         * We align node length to 8-byte boundary because we anyway flash wbuf
+         * if the remaining space is less than 8 bytes.
+         */
+        n = aligned_len >> c->min_io_shift;
+        if (n) {
+                n <<= c->min_io_shift;
+                dbg_io("write %d bytes to LEB %d:%d", n, wbuf->lnum, offs);
+                err = ubi_leb_write(c->ubi, wbuf->lnum, buf + written, offs, n,
+                                    wbuf->dtype);
+                if (err)
+                        goto out;
+                offs += n;
+                aligned_len -= n;
+                len -= n;
+                written += n;
+        }
+
+        spin_lock(&wbuf->lock);
+        if (aligned_len)
+                /*
+                 * And now we have what's left and what does not take whole
+                 * min. I/O unit, so write it to the write-buffer and we are
+                 * done.
+                 */
+                memcpy(wbuf->buf, buf + written, len);
+
+        wbuf->offs = offs;
+        wbuf->used = aligned_len;
+        wbuf->avail = c->min_io_size - aligned_len;
+        wbuf->next_ino = 0;
+        spin_unlock(&wbuf->lock);
+
+exit:
+        if (wbuf->sync_callback) {
+                int free = c->leb_size - wbuf->offs - wbuf->used;
+
+                err = wbuf->sync_callback(c, wbuf->lnum, free, 0);
+                if (err)
+                        goto out;
+        }
+
+        if (wbuf->used)
+                new_wbuf_timer_nolock(wbuf);
+
+        return 0;
+
+out:
+        ubifs_err("cannot write %d bytes to LEB %d:%d, error %d",
+                  len, wbuf->lnum, wbuf->offs, err);
+        dbg_dump_node(c, buf);
+        dbg_dump_stack();
+        dbg_dump_leb(c, wbuf->lnum);
+        return err;
+}
+
+/**
+ * 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
+ * @dtype: node life-time hint (%UBI_LONGTERM, %UBI_SHORTTERM, %UBI_UNKNOWN)
+ *
+ * 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, int dtype)
+{
+        int err, buf_len = ALIGN(len, c->min_io_size);
+
+        dbg_io("LEB %d:%d, %s, length %d (aligned %d)",
+               lnum, offs, dbg_ntype(((struct ubifs_ch *)buf)->node_type), len,
+               buf_len);
+        ubifs_assert(lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
+        ubifs_assert(offs % c->min_io_size == 0 && offs < c->leb_size);
+
+        if (c->ro_media)
+                return -EROFS;
+
+        ubifs_prepare_node(c, buf, len, 1);
+        err = ubi_leb_write(c->ubi, lnum, buf, offs, buf_len, dtype);
+        if (err) {
+                ubifs_err("cannot write %d bytes to LEB %d:%d, error %d",
+                          buf_len, lnum, offs, err);
+                dbg_dump_node(c, buf);
+                dbg_dump_stack();
+        }
+
+        return err;
+}
+
+/**
+ * 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)
+{
+        const struct ubifs_info *c = wbuf->c;
+        int err, rlen, overlap;
+        struct ubifs_ch *ch = buf;
+
+        dbg_io("LEB %d:%d, %s, length %d", lnum, offs, dbg_ntype(type), len);
+        ubifs_assert(wbuf && lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
+        ubifs_assert(!(offs & 7) && offs < c->leb_size);
+        ubifs_assert(type >= 0 && type < UBIFS_NODE_TYPES_CNT);
+
+        spin_lock(&wbuf->lock);
+        overlap = (lnum == wbuf->lnum && offs + len > wbuf->offs);
+        if (!overlap) {
+                /* We may safely unlock the write-buffer and read the data */
+                spin_unlock(&wbuf->lock);
+                return ubifs_read_node(c, buf, type, len, lnum, offs);
+        }
+
+        /* Don't read under wbuf */
+        rlen = wbuf->offs - offs;
+        if (rlen < 0)
+                rlen = 0;
+
+        /* Copy the rest from the write-buffer */
+        memcpy(buf + rlen, wbuf->buf + offs + rlen - wbuf->offs, len - rlen);
+        spin_unlock(&wbuf->lock);
+
+        if (rlen > 0) {
+                /* Read everything that goes before write-buffer */
+                err = ubi_read(c->ubi, lnum, buf, offs, rlen);
+                if (err && err != -EBADMSG) {
+                        ubifs_err("failed to read node %d from LEB %d:%d, "
+                                  "error %d", type, lnum, offs, err);
+                        dbg_dump_stack();
+                        return err;
+                }
+        }
+
+        if (type != ch->node_type) {
+                ubifs_err("bad node type (%d but expected %d)",
+                          ch->node_type, type);
+                goto out;
+        }
+
+        err = ubifs_check_node(c, buf, lnum, offs, 0);
+        if (err) {
+                ubifs_err("expected node type %d", type);
+                return err;
+        }
+
+        rlen = le32_to_cpu(ch->len);
+        if (rlen != len) {
+                ubifs_err("bad node length %d, expected %d", rlen, len);
+                goto out;
+        }
+
+        return 0;
+
+out:
+        ubifs_err("bad node at LEB %d:%d", lnum, offs);
+        dbg_dump_node(c, buf);
+        dbg_dump_stack();
+        return -EINVAL;
+}
+
+/**
+ * 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 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)
+{
+        int err, l;
+        struct ubifs_ch *ch = buf;
+
+        dbg_io("LEB %d:%d, %s, length %d", lnum, offs, dbg_ntype(type), len);
+        ubifs_assert(lnum >= 0 && lnum < c->leb_cnt && offs >= 0);
+        ubifs_assert(len >= UBIFS_CH_SZ && offs + len <= c->leb_size);
+        ubifs_assert(!(offs & 7) && offs < c->leb_size);
+        ubifs_assert(type >= 0 && type < UBIFS_NODE_TYPES_CNT);
+
+        err = ubi_read(c->ubi, lnum, buf, offs, len);
+        if (err && err != -EBADMSG) {
+                ubifs_err("cannot read node %d from LEB %d:%d, error %d",
+                          type, lnum, offs, err);
+                return err;
+        }
+
+        if (type != ch->node_type) {
+                ubifs_err("bad node type (%d but expected %d)",
+                          ch->node_type, type);
+                goto out;
+        }
+
+        err = ubifs_check_node(c, buf, lnum, offs, 0);
+        if (err) {
+                ubifs_err("expected node type %d", type);
+                return err;
+        }
+
+        l = le32_to_cpu(ch->len);
+        if (l != len) {
+                ubifs_err("bad node length %d, expected %d", l, len);
+                goto out;
+        }
+
+        return 0;
+
+out:
+        ubifs_err("bad node at LEB %d:%d", lnum, offs);
+        dbg_dump_node(c, buf);
+        dbg_dump_stack();
+        return -EINVAL;
+}
+
+/**
+ * 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)
+{
+        size_t size;
+
+        wbuf->buf = kmalloc(c->min_io_size, GFP_KERNEL);
+        if (!wbuf->buf)
+                return -ENOMEM;
+
+        size = (c->min_io_size / UBIFS_CH_SZ + 1) * sizeof(ino_t);
+        wbuf->inodes = kmalloc(size, GFP_KERNEL);
+        if (!wbuf->inodes) {
+                kfree(wbuf->buf);
+                wbuf->buf = NULL;
+                return -ENOMEM;
+        }
+
+        wbuf->used = 0;
+        wbuf->lnum = wbuf->offs = -1;
+        wbuf->avail = c->min_io_size;
+        wbuf->dtype = UBI_UNKNOWN;
+        wbuf->sync_callback = NULL;
+        mutex_init(&wbuf->io_mutex);
+        spin_lock_init(&wbuf->lock);
+
+        wbuf->c = c;
+        init_timer(&wbuf->timer);
+        wbuf->timer.function = wbuf_timer_callback_nolock;
+        wbuf->timer.data = (unsigned long)wbuf;
+        wbuf->timeout = DEFAULT_WBUF_TIMEOUT;
+        wbuf->next_ino = 0;
+
+        return 0;
+}
+
+/**
+ * ubifs_wbuf_add_ino_nolock - add an inode number into the wbuf inode array.
+ * @wbuf: the write-buffer whereto 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)
+{
+        if (!wbuf->buf)
+                /* NOR flash or something similar */
+                return;
+
+        spin_lock(&wbuf->lock);
+        if (wbuf->used)
+                wbuf->inodes[wbuf->next_ino++] = inum;
+        spin_unlock(&wbuf->lock);
+}
+
+/**
+ * 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)
+{
+        int i, ret = 0;
+
+        spin_lock(&wbuf->lock);
+        for (i = 0; i < wbuf->next_ino; i++)
+                if (inum == wbuf->inodes[i]) {
+                        ret = 1;
+                        break;
+                }
+        spin_unlock(&wbuf->lock);
+
+        return ret;
+}
+
+/**
+ * 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)
+{
+        int i, err = 0;
+
+        for (i = 0; i < c->jhead_cnt; i++) {
+                struct ubifs_wbuf *wbuf = &c->jheads[i].wbuf;
+
+                if (i == GCHD)
+                        /*
+                         * GC head is special, do not look at it. Even if the
+                         * head contains something related to this inode, it is
+                         * a _copy_ of corresponding on-flash node which sits
+                         * somewhere else.
+                         */
+                        continue;
+
+                if (!wbuf_has_ino(wbuf, inode->i_ino))
+                        continue;
+
+                mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+                if (wbuf_has_ino(wbuf, inode->i_ino))
+                        err = ubifs_wbuf_sync_nolock(wbuf);
+                mutex_unlock(&wbuf->io_mutex);
+
+                if (err) {
+                        ubifs_ro_mode(c, err);
+                        return err;
+                }
+        }
+        return 0;
+}