[linux-2.6-omap-h63xx.git] / fs / ocfs2 / aops.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
 *
 * 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 021110-1307, USA.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <asm/byteorder.h>
#include <linux/swap.h>
#include <linux/pipe_fs_i.h>
#include <linux/mpage.h>

#define MLOG_MASK_PREFIX ML_FILE_IO
#include <cluster/masklog.h>

#include "ocfs2.h"

#include "alloc.h"
#include "aops.h"
#include "dlmglue.h"
#include "extent_map.h"
#include "file.h"
#include "inode.h"
#include "journal.h"
#include "suballoc.h"
#include "super.h"
#include "symlink.h"

#include "buffer_head_io.h"

static int ocfs2_symlink_get_block(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create)
{
        int err = -EIO;
        int status;
        struct ocfs2_dinode *fe = NULL;
        struct buffer_head *bh = NULL;
        struct buffer_head *buffer_cache_bh = NULL;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        void *kaddr;

        mlog_entry("(0x%p, %llu, 0x%p, %d)\n", inode,
                   (unsigned long long)iblock, bh_result, create);

        BUG_ON(ocfs2_inode_is_fast_symlink(inode));

        if ((iblock << inode->i_sb->s_blocksize_bits) > PATH_MAX + 1) {
                mlog(ML_ERROR, "block offset > PATH_MAX: %llu",
                     (unsigned long long)iblock);
                goto bail;
        }

        status = ocfs2_read_block(OCFS2_SB(inode->i_sb),
                                  OCFS2_I(inode)->ip_blkno,
                                  &bh, OCFS2_BH_CACHED, inode);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }
        fe = (struct ocfs2_dinode *) bh->b_data;

        if (!OCFS2_IS_VALID_DINODE(fe)) {
                mlog(ML_ERROR, "Invalid dinode #%llu: signature = %.*s\n",
                     (unsigned long long)le64_to_cpu(fe->i_blkno), 7,
                     fe->i_signature);
                goto bail;
        }

        if ((u64)iblock >= ocfs2_clusters_to_blocks(inode->i_sb,
                                                    le32_to_cpu(fe->i_clusters))) {
                mlog(ML_ERROR, "block offset is outside the allocated size: "
                     "%llu\n", (unsigned long long)iblock);
                goto bail;
        }

        /* We don't use the page cache to create symlink data, so if
         * need be, copy it over from the buffer cache. */
        if (!buffer_uptodate(bh_result) && ocfs2_inode_is_new(inode)) {
                u64 blkno = le64_to_cpu(fe->id2.i_list.l_recs[0].e_blkno) +
                            iblock;
                buffer_cache_bh = sb_getblk(osb->sb, blkno);
                if (!buffer_cache_bh) {
                        mlog(ML_ERROR, "couldn't getblock for symlink!\n");
                        goto bail;
                }

                /* we haven't locked out transactions, so a commit
                 * could've happened. Since we've got a reference on
                 * the bh, even if it commits while we're doing the
                 * copy, the data is still good. */
                if (buffer_jbd(buffer_cache_bh)
                    && ocfs2_inode_is_new(inode)) {
                        kaddr = kmap_atomic(bh_result->b_page, KM_USER0);
                        if (!kaddr) {
                                mlog(ML_ERROR, "couldn't kmap!\n");
                                goto bail;
                        }
                        memcpy(kaddr + (bh_result->b_size * iblock),
                               buffer_cache_bh->b_data,
                               bh_result->b_size);
                        kunmap_atomic(kaddr, KM_USER0);
                        set_buffer_uptodate(bh_result);
                }
                brelse(buffer_cache_bh);
        }

        map_bh(bh_result, inode->i_sb,
               le64_to_cpu(fe->id2.i_list.l_recs[0].e_blkno) + iblock);

        err = 0;

bail:
        if (bh)
                brelse(bh);

        mlog_exit(err);
        return err;
}

static int ocfs2_get_block(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh_result, int create)
{
        int err = 0;
        unsigned int ext_flags;
        u64 max_blocks = bh_result->b_size >> inode->i_blkbits;
        u64 p_blkno, count, past_eof;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

        mlog_entry("(0x%p, %llu, 0x%p, %d)\n", inode,
                   (unsigned long long)iblock, bh_result, create);

        if (OCFS2_I(inode)->ip_flags & OCFS2_INODE_SYSTEM_FILE)
                mlog(ML_NOTICE, "get_block on system inode 0x%p (%lu)\n",
                     inode, inode->i_ino);

        if (S_ISLNK(inode->i_mode)) {
                /* this always does I/O for some reason. */
                err = ocfs2_symlink_get_block(inode, iblock, bh_result, create);
                goto bail;
        }

        err = ocfs2_extent_map_get_blocks(inode, iblock, &p_blkno, &count,
                                          &ext_flags);
        if (err) {
                mlog(ML_ERROR, "Error %d from get_blocks(0x%p, %llu, 1, "
                     "%llu, NULL)\n", err, inode, (unsigned long long)iblock,
                     (unsigned long long)p_blkno);
                goto bail;
        }

        if (max_blocks < count)
                count = max_blocks;

        /*
         * ocfs2 never allocates in this function - the only time we
         * need to use BH_New is when we're extending i_size on a file
         * system which doesn't support holes, in which case BH_New
         * allows block_prepare_write() to zero.
         *
         * If we see this on a sparse file system, then a truncate has
         * raced us and removed the cluster. In this case, we clear
         * the buffers dirty and uptodate bits and let the buffer code
         * ignore it as a hole.
         */
        if (create && p_blkno == 0 && ocfs2_sparse_alloc(osb)) {
                clear_buffer_dirty(bh_result);
                clear_buffer_uptodate(bh_result);
                goto bail;
        }

        /* Treat the unwritten extent as a hole for zeroing purposes. */
        if (p_blkno && !(ext_flags & OCFS2_EXT_UNWRITTEN))
                map_bh(bh_result, inode->i_sb, p_blkno);

        bh_result->b_size = count << inode->i_blkbits;

        if (!ocfs2_sparse_alloc(osb)) {
                if (p_blkno == 0) {
                        err = -EIO;
                        mlog(ML_ERROR,
                             "iblock = %llu p_blkno = %llu blkno=(%llu)\n",
                             (unsigned long long)iblock,
                             (unsigned long long)p_blkno,
                             (unsigned long long)OCFS2_I(inode)->ip_blkno);
                        mlog(ML_ERROR, "Size %llu, clusters %u\n", (unsigned long long)i_size_read(inode), OCFS2_I(inode)->ip_clusters);
                        dump_stack();
                }

                past_eof = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
                mlog(0, "Inode %lu, past_eof = %llu\n", inode->i_ino,
                     (unsigned long long)past_eof);

                if (create && (iblock >= past_eof))
                        set_buffer_new(bh_result);
        }

bail:
        if (err < 0)
                err = -EIO;

        mlog_exit(err);
        return err;
}

int ocfs2_read_inline_data(struct inode *inode, struct page *page,
                           struct buffer_head *di_bh)
{
        void *kaddr;
        loff_t size;
        struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;

        if (!(le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL)) {
                ocfs2_error(inode->i_sb, "Inode %llu lost inline data flag",
                            (unsigned long long)OCFS2_I(inode)->ip_blkno);
                return -EROFS;
        }

        size = i_size_read(inode);

        if (size > PAGE_CACHE_SIZE ||
            size > ocfs2_max_inline_data(inode->i_sb)) {
                ocfs2_error(inode->i_sb,
                            "Inode %llu has with inline data has bad size: %Lu",
                            (unsigned long long)OCFS2_I(inode)->ip_blkno,
                            (unsigned long long)size);
                return -EROFS;
        }

        kaddr = kmap_atomic(page, KM_USER0);
        if (size)
                memcpy(kaddr, di->id2.i_data.id_data, size);
        /* Clear the remaining part of the page */
        memset(kaddr + size, 0, PAGE_CACHE_SIZE - size);
        flush_dcache_page(page);
        kunmap_atomic(kaddr, KM_USER0);

        SetPageUptodate(page);

        return 0;
}

static int ocfs2_readpage_inline(struct inode *inode, struct page *page)
{
        int ret;
        struct buffer_head *di_bh = NULL;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

        BUG_ON(!PageLocked(page));
        BUG_ON(!(OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL));

        ret = ocfs2_read_block(osb, OCFS2_I(inode)->ip_blkno, &di_bh,
                               OCFS2_BH_CACHED, inode);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        ret = ocfs2_read_inline_data(inode, page, di_bh);
out:
        unlock_page(page);

        brelse(di_bh);
        return ret;
}

static int ocfs2_readpage(struct file *file, struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct ocfs2_inode_info *oi = OCFS2_I(inode);
        loff_t start = (loff_t)page->index << PAGE_CACHE_SHIFT;
        int ret, unlock = 1;

        mlog_entry("(0x%p, %lu)\n", file, (page ? page->index : 0));

        ret = ocfs2_inode_lock_with_page(inode, NULL, 0, page);
        if (ret != 0) {
                if (ret == AOP_TRUNCATED_PAGE)
                        unlock = 0;
                mlog_errno(ret);
                goto out;
        }

        if (down_read_trylock(&oi->ip_alloc_sem) == 0) {
                ret = AOP_TRUNCATED_PAGE;
                goto out_inode_unlock;
        }

        /*
         * i_size might have just been updated as we grabed the meta lock.  We
         * might now be discovering a truncate that hit on another node.
         * block_read_full_page->get_block freaks out if it is asked to read
         * beyond the end of a file, so we check here.  Callers
         * (generic_file_read, vm_ops->fault) are clever enough to check i_size
         * and notice that the page they just read isn't needed.
         *
         * XXX sys_readahead() seems to get that wrong?
         */
        if (start >= i_size_read(inode)) {
                zero_user(page, 0, PAGE_SIZE);
                SetPageUptodate(page);
                ret = 0;
                goto out_alloc;
        }

        if (oi->ip_dyn_features & OCFS2_INLINE_DATA_FL)
                ret = ocfs2_readpage_inline(inode, page);
        else
                ret = block_read_full_page(page, ocfs2_get_block);
        unlock = 0;

out_alloc:
        up_read(&OCFS2_I(inode)->ip_alloc_sem);
out_inode_unlock:
        ocfs2_inode_unlock(inode, 0);
out:
        if (unlock)
                unlock_page(page);
        mlog_exit(ret);
        return ret;
}

/*
 * This is used only for read-ahead. Failures or difficult to handle
 * situations are safe to ignore.
 *
 * Right now, we don't bother with BH_Boundary - in-inode extent lists
 * are quite large (243 extents on 4k blocks), so most inodes don't
 * grow out to a tree. If need be, detecting boundary extents could
 * trivially be added in a future version of ocfs2_get_block().
 */
static int ocfs2_readpages(struct file *filp, struct address_space *mapping,
                           struct list_head *pages, unsigned nr_pages)
{
        int ret, err = -EIO;
        struct inode *inode = mapping->host;
        struct ocfs2_inode_info *oi = OCFS2_I(inode);
        loff_t start;
        struct page *last;

        /*
         * Use the nonblocking flag for the dlm code to avoid page
         * lock inversion, but don't bother with retrying.
         */
        ret = ocfs2_inode_lock_full(inode, NULL, 0, OCFS2_LOCK_NONBLOCK);
        if (ret)
                return err;

        if (down_read_trylock(&oi->ip_alloc_sem) == 0) {
                ocfs2_inode_unlock(inode, 0);
                return err;
        }

        /*
         * Don't bother with inline-data. There isn't anything
         * to read-ahead in that case anyway...
         */
        if (oi->ip_dyn_features & OCFS2_INLINE_DATA_FL)
                goto out_unlock;

        /*
         * Check whether a remote node truncated this file - we just
         * drop out in that case as it's not worth handling here.
         */
        last = list_entry(pages->prev, struct page, lru);
        start = (loff_t)last->index << PAGE_CACHE_SHIFT;
        if (start >= i_size_read(inode))
                goto out_unlock;

        err = mpage_readpages(mapping, pages, nr_pages, ocfs2_get_block);

out_unlock:
        up_read(&oi->ip_alloc_sem);
        ocfs2_inode_unlock(inode, 0);

        return err;
}

/* Note: Because we don't support holes, our allocation has
 * already happened (allocation writes zeros to the file data)
 * so we don't have to worry about ordered writes in
 * ocfs2_writepage.
 *
 * ->writepage is called during the process of invalidating the page cache
 * during blocked lock processing.  It can't block on any cluster locks
 * to during block mapping.  It's relying on the fact that the block
 * mapping can't have disappeared under the dirty pages that it is
 * being asked to write back.
 */
static int ocfs2_writepage(struct page *page, struct writeback_control *wbc)
{
        int ret;

        mlog_entry("(0x%p)\n", page);

        ret = block_write_full_page(page, ocfs2_get_block, wbc);

        mlog_exit(ret);

        return ret;
}

/*
 * This is called from ocfs2_write_zero_page() which has handled it's
 * own cluster locking and has ensured allocation exists for those
 * blocks to be written.
 */
int ocfs2_prepare_write_nolock(struct inode *inode, struct page *page,
                               unsigned from, unsigned to)
{
        int ret;

        ret = block_prepare_write(page, from, to, ocfs2_get_block);

        return ret;
}

/* Taken from ext3. We don't necessarily need the full blown
 * functionality yet, but IMHO it's better to cut and paste the whole
 * thing so we can avoid introducing our own bugs (and easily pick up
 * their fixes when they happen) --Mark */
int walk_page_buffers(  handle_t *handle,
                        struct buffer_head *head,
                        unsigned from,
                        unsigned to,
                        int *partial,
                        int (*fn)(      handle_t *handle,
                                        struct buffer_head *bh))
{
        struct buffer_head *bh;
        unsigned block_start, block_end;
        unsigned blocksize = head->b_size;
        int err, ret = 0;
        struct buffer_head *next;

        for (   bh = head, block_start = 0;
                ret == 0 && (bh != head || !block_start);
                block_start = block_end, bh = next)
        {
                next = bh->b_this_page;
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (partial && !buffer_uptodate(bh))
                                *partial = 1;
                        continue;
                }
                err = (*fn)(handle, bh);
                if (!ret)
                        ret = err;
        }
        return ret;
}

handle_t *ocfs2_start_walk_page_trans(struct inode *inode,
                                                         struct page *page,
                                                         unsigned from,
                                                         unsigned to)
{
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        handle_t *handle;
        int ret = 0;

        handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);
        if (IS_ERR(handle)) {
                ret = -ENOMEM;
                mlog_errno(ret);
                goto out;
        }

        if (ocfs2_should_order_data(inode)) {
                ret = ocfs2_jbd2_file_inode(handle, inode);
#ifdef CONFIG_OCFS2_COMPAT_JBD
                ret = walk_page_buffers(handle,
                                        page_buffers(page),
                                        from, to, NULL,
                                        ocfs2_journal_dirty_data);
#endif
                if (ret < 0)
                        mlog_errno(ret);
        }
out:
        if (ret) {
                if (!IS_ERR(handle))
                        ocfs2_commit_trans(osb, handle);
                handle = ERR_PTR(ret);
        }
        return handle;
}

static sector_t ocfs2_bmap(struct address_space *mapping, sector_t block)
{
        sector_t status;
        u64 p_blkno = 0;
        int err = 0;
        struct inode *inode = mapping->host;

        mlog_entry("(block = %llu)\n", (unsigned long long)block);

        /* We don't need to lock journal system files, since they aren't
         * accessed concurrently from multiple nodes.
         */
        if (!INODE_JOURNAL(inode)) {
                err = ocfs2_inode_lock(inode, NULL, 0);
                if (err) {
                        if (err != -ENOENT)
                                mlog_errno(err);
                        goto bail;
                }
                down_read(&OCFS2_I(inode)->ip_alloc_sem);
        }

        if (!(OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL))
                err = ocfs2_extent_map_get_blocks(inode, block, &p_blkno, NULL,
                                                  NULL);

        if (!INODE_JOURNAL(inode)) {
                up_read(&OCFS2_I(inode)->ip_alloc_sem);
                ocfs2_inode_unlock(inode, 0);
        }

        if (err) {
                mlog(ML_ERROR, "get_blocks() failed, block = %llu\n",
                     (unsigned long long)block);
                mlog_errno(err);
                goto bail;
        }

bail:
        status = err ? 0 : p_blkno;

        mlog_exit((int)status);

        return status;
}

/*
 * TODO: Make this into a generic get_blocks function.
 *
 * From do_direct_io in direct-io.c:
 *  "So what we do is to permit the ->get_blocks function to populate
 *   bh.b_size with the size of IO which is permitted at this offset and
 *   this i_blkbits."
 *
 * This function is called directly from get_more_blocks in direct-io.c.
 *
 * called like this: dio->get_blocks(dio->inode, fs_startblk,
 *                                      fs_count, map_bh, dio->rw == WRITE);
 */
static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
                                     struct buffer_head *bh_result, int create)
{
        int ret;
        u64 p_blkno, inode_blocks, contig_blocks;
        unsigned int ext_flags;
        unsigned char blocksize_bits = inode->i_sb->s_blocksize_bits;
        unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;

        /* This function won't even be called if the request isn't all
         * nicely aligned and of the right size, so there's no need
         * for us to check any of that. */

        inode_blocks = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));

        /*
         * Any write past EOF is not allowed because we'd be extending.
         */
        if (create && (iblock + max_blocks) > inode_blocks) {
                ret = -EIO;
                goto bail;
        }

        /* This figures out the size of the next contiguous block, and
         * our logical offset */
        ret = ocfs2_extent_map_get_blocks(inode, iblock, &p_blkno,
                                          &contig_blocks, &ext_flags);
        if (ret) {
                mlog(ML_ERROR, "get_blocks() failed iblock=%llu\n",
                     (unsigned long long)iblock);
                ret = -EIO;
                goto bail;
        }

        if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)) && !p_blkno && create) {
                ocfs2_error(inode->i_sb,
                            "Inode %llu has a hole at block %llu\n",
                            (unsigned long long)OCFS2_I(inode)->ip_blkno,
                            (unsigned long long)iblock);
                ret = -EROFS;
                goto bail;
        }

        /*
         * get_more_blocks() expects us to describe a hole by clearing
         * the mapped bit on bh_result().
         *
         * Consider an unwritten extent as a hole.
         */
        if (p_blkno && !(ext_flags & OCFS2_EXT_UNWRITTEN))
                map_bh(bh_result, inode->i_sb, p_blkno);
        else {
                /*
                 * ocfs2_prepare_inode_for_write() should have caught
                 * the case where we'd be filling a hole and triggered
                 * a buffered write instead.
                 */
                if (create) {
                        ret = -EIO;
                        mlog_errno(ret);
                        goto bail;
                }

                clear_buffer_mapped(bh_result);
        }

        /* make sure we don't map more than max_blocks blocks here as
           that's all the kernel will handle at this point. */
        if (max_blocks < contig_blocks)
                contig_blocks = max_blocks;
        bh_result->b_size = contig_blocks << blocksize_bits;
bail:
        return ret;
}

/* 
 * ocfs2_dio_end_io is called by the dio core when a dio is finished.  We're
 * particularly interested in the aio/dio case.  Like the core uses
 * i_alloc_sem, we use the rw_lock DLM lock to protect io on one node from
 * truncation on another.
 */
static void ocfs2_dio_end_io(struct kiocb *iocb,
                             loff_t offset,
                             ssize_t bytes,
                             void *private)
{
        struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
        int level;

        /* this io's submitter should not have unlocked this before we could */
        BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));

        ocfs2_iocb_clear_rw_locked(iocb);

        level = ocfs2_iocb_rw_locked_level(iocb);
        if (!level)
                up_read(&inode->i_alloc_sem);
        ocfs2_rw_unlock(inode, level);
}

/*
 * ocfs2_invalidatepage() and ocfs2_releasepage() are shamelessly stolen
 * from ext3.  PageChecked() bits have been removed as OCFS2 does not
 * do journalled data.
 */
static void ocfs2_invalidatepage(struct page *page, unsigned long offset)
{
        journal_t *journal = OCFS2_SB(page->mapping->host->i_sb)->journal->j_journal;

        jbd2_journal_invalidatepage(journal, page, offset);
}

static int ocfs2_releasepage(struct page *page, gfp_t wait)
{
        journal_t *journal = OCFS2_SB(page->mapping->host->i_sb)->journal->j_journal;

        if (!page_has_buffers(page))
                return 0;
        return jbd2_journal_try_to_free_buffers(journal, page, wait);
}

static ssize_t ocfs2_direct_IO(int rw,
                               struct kiocb *iocb,
                               const struct iovec *iov,
                               loff_t offset,
                               unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_path.dentry->d_inode->i_mapping->host;
        int ret;

        mlog_entry_void();

        /*
         * Fallback to buffered I/O if we see an inode without
         * extents.
         */
        if (OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL)
                return 0;

        ret = blockdev_direct_IO_no_locking(rw, iocb, inode,
                                            inode->i_sb->s_bdev, iov, offset,
                                            nr_segs, 
                                            ocfs2_direct_IO_get_blocks,
                                            ocfs2_dio_end_io);

        mlog_exit(ret);
        return ret;
}

static void ocfs2_figure_cluster_boundaries(struct ocfs2_super *osb,
                                            u32 cpos,
                                            unsigned int *start,
                                            unsigned int *end)
{
        unsigned int cluster_start = 0, cluster_end = PAGE_CACHE_SIZE;

        if (unlikely(PAGE_CACHE_SHIFT > osb->s_clustersize_bits)) {
                unsigned int cpp;

                cpp = 1 << (PAGE_CACHE_SHIFT - osb->s_clustersize_bits);

                cluster_start = cpos % cpp;
                cluster_start = cluster_start << osb->s_clustersize_bits;

                cluster_end = cluster_start + osb->s_clustersize;
        }

        BUG_ON(cluster_start > PAGE_SIZE);
        BUG_ON(cluster_end > PAGE_SIZE);

        if (start)
                *start = cluster_start;
        if (end)
                *end = cluster_end;
}

/*
 * 'from' and 'to' are the region in the page to avoid zeroing.
 *
 * If pagesize > clustersize, this function will avoid zeroing outside
 * of the cluster boundary.
 *
 * from == to == 0 is code for "zero the entire cluster region"
 */
static void ocfs2_clear_page_regions(struct page *page,
                                     struct ocfs2_super *osb, u32 cpos,
                                     unsigned from, unsigned to)
{
        void *kaddr;
        unsigned int cluster_start, cluster_end;

        ocfs2_figure_cluster_boundaries(osb, cpos, &cluster_start, &cluster_end);

        kaddr = kmap_atomic(page, KM_USER0);

        if (from || to) {
                if (from > cluster_start)
                        memset(kaddr + cluster_start, 0, from - cluster_start);
                if (to < cluster_end)
                        memset(kaddr + to, 0, cluster_end - to);
        } else {
                memset(kaddr + cluster_start, 0, cluster_end - cluster_start);
        }

        kunmap_atomic(kaddr, KM_USER0);
}

/*
 * Nonsparse file systems fully allocate before we get to the write
 * code. This prevents ocfs2_write() from tagging the write as an
 * allocating one, which means ocfs2_map_page_blocks() might try to
 * read-in the blocks at the tail of our file. Avoid reading them by
 * testing i_size against each block offset.
 */
static int ocfs2_should_read_blk(struct inode *inode, struct page *page,
                                 unsigned int block_start)
{
        u64 offset = page_offset(page) + block_start;

        if (ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)))
                return 1;

        if (i_size_read(inode) > offset)
                return 1;

        return 0;
}

/*
 * Some of this taken from block_prepare_write(). We already have our
 * mapping by now though, and the entire write will be allocating or
 * it won't, so not much need to use BH_New.
 *
 * This will also skip zeroing, which is handled externally.
 */
int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
                          struct inode *inode, unsigned int from,
                          unsigned int to, int new)
{
        int ret = 0;
        struct buffer_head *head, *bh, *wait[2], **wait_bh = wait;
        unsigned int block_end, block_start;
        unsigned int bsize = 1 << inode->i_blkbits;

        if (!page_has_buffers(page))
                create_empty_buffers(page, bsize, 0);

        head = page_buffers(page);
        for (bh = head, block_start = 0; bh != head || !block_start;
             bh = bh->b_this_page, block_start += bsize) {
                block_end = block_start + bsize;

                clear_buffer_new(bh);

                /*
                 * Ignore blocks outside of our i/o range -
                 * they may belong to unallocated clusters.
                 */
                if (block_start >= to || block_end <= from) {
                        if (PageUptodate(page))
                                set_buffer_uptodate(bh);
                        continue;
                }

                /*
                 * For an allocating write with cluster size >= page
                 * size, we always write the entire page.
                 */
                if (new)
                        set_buffer_new(bh);

                if (!buffer_mapped(bh)) {
                        map_bh(bh, inode->i_sb, *p_blkno);
                        unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
                }

                if (PageUptodate(page)) {
                        if (!buffer_uptodate(bh))
                                set_buffer_uptodate(bh);
                } else if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
                           !buffer_new(bh) &&
                           ocfs2_should_read_blk(inode, page, block_start) &&
                           (block_start < from || block_end > to)) {
                        ll_rw_block(READ, 1, &bh);
                        *wait_bh++=bh;
                }

                *p_blkno = *p_blkno + 1;
        }

        /*
         * If we issued read requests - let them complete.
         */
        while(wait_bh > wait) {
                wait_on_buffer(*--wait_bh);
                if (!buffer_uptodate(*wait_bh))
                        ret = -EIO;
        }

        if (ret == 0 || !new)
                return ret;

        /*
         * If we get -EIO above, zero out any newly allocated blocks
         * to avoid exposing stale data.
         */
        bh = head;
        block_start = 0;
        do {
                block_end = block_start + bsize;
                if (block_end <= from)
                        goto next_bh;
                if (block_start >= to)
                        break;

                zero_user(page, block_start, bh->b_size);
                set_buffer_uptodate(bh);
                mark_buffer_dirty(bh);

next_bh:
                block_start = block_end;
                bh = bh->b_this_page;
        } while (bh != head);

        return ret;
}

#if (PAGE_CACHE_SIZE >= OCFS2_MAX_CLUSTERSIZE)
#define OCFS2_MAX_CTXT_PAGES    1
#else
#define OCFS2_MAX_CTXT_PAGES    (OCFS2_MAX_CLUSTERSIZE / PAGE_CACHE_SIZE)
#endif

#define OCFS2_MAX_CLUSTERS_PER_PAGE     (PAGE_CACHE_SIZE / OCFS2_MIN_CLUSTERSIZE)

/*
 * Describe the state of a single cluster to be written to.
 */
struct ocfs2_write_cluster_desc {
        u32             c_cpos;
        u32             c_phys;
        /*
         * Give this a unique field because c_phys eventually gets
         * filled.
         */
        unsigned        c_new;
        unsigned        c_unwritten;
};

static inline int ocfs2_should_zero_cluster(struct ocfs2_write_cluster_desc *d)
{
        return d->c_new || d->c_unwritten;
}

struct ocfs2_write_ctxt {
        /* Logical cluster position / len of write */
        u32                             w_cpos;
        u32                             w_clen;

        struct ocfs2_write_cluster_desc w_desc[OCFS2_MAX_CLUSTERS_PER_PAGE];

        /*
         * This is true if page_size > cluster_size.
         *
         * It triggers a set of special cases during write which might
         * have to deal with allocating writes to partial pages.
         */
        unsigned int                    w_large_pages;

        /*
         * Pages involved in this write.
         *
         * w_target_page is the page being written to by the user.
         *
         * w_pages is an array of pages which always contains
         * w_target_page, and in the case of an allocating write with
         * page_size < cluster size, it will contain zero'd and mapped
         * pages adjacent to w_target_page which need to be written
         * out in so that future reads from that region will get
         * zero's.
         */
        struct page                     *w_pages[OCFS2_MAX_CTXT_PAGES];
        unsigned int                    w_num_pages;
        struct page                     *w_target_page;

        /*
         * ocfs2_write_end() uses this to know what the real range to
         * write in the target should be.
         */
        unsigned int                    w_target_from;
        unsigned int                    w_target_to;

        /*
         * We could use journal_current_handle() but this is cleaner,
         * IMHO -Mark
         */
        handle_t                        *w_handle;

        struct buffer_head              *w_di_bh;

        struct ocfs2_cached_dealloc_ctxt w_dealloc;
};

void ocfs2_unlock_and_free_pages(struct page **pages, int num_pages)
{
        int i;

        for(i = 0; i < num_pages; i++) {
                if (pages[i]) {
                        unlock_page(pages[i]);
                        mark_page_accessed(pages[i]);
                        page_cache_release(pages[i]);
                }
        }
}

static void ocfs2_free_write_ctxt(struct ocfs2_write_ctxt *wc)
{
        ocfs2_unlock_and_free_pages(wc->w_pages, wc->w_num_pages);

        brelse(wc->w_di_bh);
        kfree(wc);
}

static int ocfs2_alloc_write_ctxt(struct ocfs2_write_ctxt **wcp,
                                  struct ocfs2_super *osb, loff_t pos,
                                  unsigned len, struct buffer_head *di_bh)
{
        u32 cend;
        struct ocfs2_write_ctxt *wc;

        wc = kzalloc(sizeof(struct ocfs2_write_ctxt), GFP_NOFS);
        if (!wc)
                return -ENOMEM;

        wc->w_cpos = pos >> osb->s_clustersize_bits;
        cend = (pos + len - 1) >> osb->s_clustersize_bits;
        wc->w_clen = cend - wc->w_cpos + 1;
        get_bh(di_bh);
        wc->w_di_bh = di_bh;

        if (unlikely(PAGE_CACHE_SHIFT > osb->s_clustersize_bits))
                wc->w_large_pages = 1;
        else
                wc->w_large_pages = 0;

        ocfs2_init_dealloc_ctxt(&wc->w_dealloc);

        *wcp = wc;

        return 0;
}

/*
 * If a page has any new buffers, zero them out here, and mark them uptodate
 * and dirty so they'll be written out (in order to prevent uninitialised
 * block data from leaking). And clear the new bit.
 */
static void ocfs2_zero_new_buffers(struct page *page, unsigned from, unsigned to)
{
        unsigned int block_start, block_end;
        struct buffer_head *head, *bh;

        BUG_ON(!PageLocked(page));
        if (!page_has_buffers(page))
                return;

        bh = head = page_buffers(page);
        block_start = 0;
        do {
                block_end = block_start + bh->b_size;

                if (buffer_new(bh)) {
                        if (block_end > from && block_start < to) {
                                if (!PageUptodate(page)) {
                                        unsigned start, end;

                                        start = max(from, block_start);
                                        end = min(to, block_end);

                                        zero_user_segment(page, start, end);
                                        set_buffer_uptodate(bh);
                                }

                                clear_buffer_new(bh);
                                mark_buffer_dirty(bh);
                        }
                }

                block_start = block_end;
                bh = bh->b_this_page;
        } while (bh != head);
}

/*
 * Only called when we have a failure during allocating write to write
 * zero's to the newly allocated region.
 */
static void ocfs2_write_failure(struct inode *inode,
                                struct ocfs2_write_ctxt *wc,
                                loff_t user_pos, unsigned user_len)
{
        int i;
        unsigned from = user_pos & (PAGE_CACHE_SIZE - 1),
                to = user_pos + user_len;
        struct page *tmppage;

        ocfs2_zero_new_buffers(wc->w_target_page, from, to);

        for(i = 0; i < wc->w_num_pages; i++) {
                tmppage = wc->w_pages[i];

                if (page_has_buffers(tmppage)) {
                        if (ocfs2_should_order_data(inode)) {
                                ocfs2_jbd2_file_inode(wc->w_handle, inode);
#ifdef CONFIG_OCFS2_COMPAT_JBD
                                walk_page_buffers(wc->w_handle,
                                                  page_buffers(tmppage),
                                                  from, to, NULL,
                                                  ocfs2_journal_dirty_data);
#endif
                        }

                        block_commit_write(tmppage, from, to);
                }
        }
}

static int ocfs2_prepare_page_for_write(struct inode *inode, u64 *p_blkno,
                                        struct ocfs2_write_ctxt *wc,
                                        struct page *page, u32 cpos,
                                        loff_t user_pos, unsigned user_len,
                                        int new)
{
        int ret;
        unsigned int map_from = 0, map_to = 0;
        unsigned int cluster_start, cluster_end;
        unsigned int user_data_from = 0, user_data_to = 0;

        ocfs2_figure_cluster_boundaries(OCFS2_SB(inode->i_sb), cpos,
                                        &cluster_start, &cluster_end);

        if (page == wc->w_target_page) {
                map_from = user_pos & (PAGE_CACHE_SIZE - 1);
                map_to = map_from + user_len;

                if (new)
                        ret = ocfs2_map_page_blocks(page, p_blkno, inode,
                                                    cluster_start, cluster_end,
                                                    new);
                else
                        ret = ocfs2_map_page_blocks(page, p_blkno, inode,
                                                    map_from, map_to, new);
                if (ret) {
                        mlog_errno(ret);
                        goto out;
                }

                user_data_from = map_from;
                user_data_to = map_to;
                if (new) {
                        map_from = cluster_start;
                        map_to = cluster_end;
                }
        } else {
                /*
                 * If we haven't allocated the new page yet, we
                 * shouldn't be writing it out without copying user
                 * data. This is likely a math error from the caller.
                 */
                BUG_ON(!new);

                map_from = cluster_start;
                map_to = cluster_end;

                ret = ocfs2_map_page_blocks(page, p_blkno, inode,
                                            cluster_start, cluster_end, new);
                if (ret) {
                        mlog_errno(ret);
                        goto out;
                }
        }

        /*
         * Parts of newly allocated pages need to be zero'd.
         *
         * Above, we have also rewritten 'to' and 'from' - as far as
         * the rest of the function is concerned, the entire cluster
         * range inside of a page needs to be written.
         *
         * We can skip this if the page is up to date - it's already
         * been zero'd from being read in as a hole.
         */
        if (new && !PageUptodate(page))
                ocfs2_clear_page_regions(page, OCFS2_SB(inode->i_sb),
                                         cpos, user_data_from, user_data_to);

        flush_dcache_page(page);

out:
        return ret;
}

/*
 * This function will only grab one clusters worth of pages.
 */
static int ocfs2_grab_pages_for_write(struct address_space *mapping,
                                      struct ocfs2_write_ctxt *wc,
                                      u32 cpos, loff_t user_pos, int new,
                                      struct page *mmap_page)
{
        int ret = 0, i;
        unsigned long start, target_index, index;
        struct inode *inode = mapping->host;

        target_index = user_pos >> PAGE_CACHE_SHIFT;

        /*
         * Figure out how many pages we'll be manipulating here. For
         * non allocating write, we just change the one
         * page. Otherwise, we'll need a whole clusters worth.
         */
        if (new) {
                wc->w_num_pages = ocfs2_pages_per_cluster(inode->i_sb);
                start = ocfs2_align_clusters_to_page_index(inode->i_sb, cpos);
        } else {
                wc->w_num_pages = 1;
                start = target_index;
        }

        for(i = 0; i < wc->w_num_pages; i++) {
                index = start + i;

                if (index == target_index && mmap_page) {
                        /*
                         * ocfs2_pagemkwrite() is a little different
                         * and wants us to directly use the page
                         * passed in.
                         */
                        lock_page(mmap_page);

                        if (mmap_page->mapping != mapping) {
                                unlock_page(mmap_page);
                                /*
                                 * Sanity check - the locking in
                                 * ocfs2_pagemkwrite() should ensure
                                 * that this code doesn't trigger.
                                 */
                                ret = -EINVAL;
                                mlog_errno(ret);
                                goto out;
                        }

                        page_cache_get(mmap_page);
                        wc->w_pages[i] = mmap_page;
                } else {
                        wc->w_pages[i] = find_or_create_page(mapping, index,
                                                             GFP_NOFS);
                        if (!wc->w_pages[i]) {
                                ret = -ENOMEM;
                                mlog_errno(ret);
                                goto out;
                        }
                }

                if (index == target_index)
                        wc->w_target_page = wc->w_pages[i];
        }
out:
        return ret;
}

/*
 * Prepare a single cluster for write one cluster into the file.
 */
static int ocfs2_write_cluster(struct address_space *mapping,
                               u32 phys, unsigned int unwritten,
                               struct ocfs2_alloc_context *data_ac,
                               struct ocfs2_alloc_context *meta_ac,
                               struct ocfs2_write_ctxt *wc, u32 cpos,
                               loff_t user_pos, unsigned user_len)
{
        int ret, i, new, should_zero = 0;
        u64 v_blkno, p_blkno;
        struct inode *inode = mapping->host;
        struct ocfs2_extent_tree et;

        new = phys == 0 ? 1 : 0;
        if (new || unwritten)
                should_zero = 1;

        if (new) {
                u32 tmp_pos;

                /*
                 * This is safe to call with the page locks - it won't take
                 * any additional semaphores or cluster locks.
                 */
                tmp_pos = cpos;
                ret = ocfs2_add_inode_data(OCFS2_SB(inode->i_sb), inode,
                                           &tmp_pos, 1, 0, wc->w_di_bh,
                                           wc->w_handle, data_ac,
                                           meta_ac, NULL);
                /*
                 * This shouldn't happen because we must have already
                 * calculated the correct meta data allocation required. The
                 * internal tree allocation code should know how to increase
                 * transaction credits itself.
                 *
                 * If need be, we could handle -EAGAIN for a
                 * RESTART_TRANS here.
                 */
                mlog_bug_on_msg(ret == -EAGAIN,
                                "Inode %llu: EAGAIN return during allocation.\n",
                                (unsigned long long)OCFS2_I(inode)->ip_blkno);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }
        } else if (unwritten) {
                ocfs2_init_dinode_extent_tree(&et, inode, wc->w_di_bh);
                ret = ocfs2_mark_extent_written(inode, &et,
                                                wc->w_handle, cpos, 1, phys,
                                                meta_ac, &wc->w_dealloc);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }
        }

        if (should_zero)
                v_blkno = ocfs2_clusters_to_blocks(inode->i_sb, cpos);
        else
                v_blkno = user_pos >> inode->i_sb->s_blocksize_bits;

        /*
         * The only reason this should fail is due to an inability to
         * find the extent added.
         */
        ret = ocfs2_extent_map_get_blocks(inode, v_blkno, &p_blkno, NULL,
                                          NULL);
        if (ret < 0) {
                ocfs2_error(inode->i_sb, "Corrupting extend for inode %llu, "
                            "at logical block %llu",
                            (unsigned long long)OCFS2_I(inode)->ip_blkno,
                            (unsigned long long)v_blkno);
                goto out;
        }

        BUG_ON(p_blkno == 0);

        for(i = 0; i < wc->w_num_pages; i++) {
                int tmpret;

                tmpret = ocfs2_prepare_page_for_write(inode, &p_blkno, wc,
                                                      wc->w_pages[i], cpos,
                                                      user_pos, user_len,
                                                      should_zero);
                if (tmpret) {
                        mlog_errno(tmpret);
                        if (ret == 0)
                                tmpret = ret;
                }
        }

        /*
         * We only have cleanup to do in case of allocating write.
         */
        if (ret && new)
                ocfs2_write_failure(inode, wc, user_pos, user_len);

out:

        return ret;
}

static int ocfs2_write_cluster_by_desc(struct address_space *mapping,
                                       struct ocfs2_alloc_context *data_ac,
                                       struct ocfs2_alloc_context *meta_ac,
                                       struct ocfs2_write_ctxt *wc,
                                       loff_t pos, unsigned len)
{
        int ret, i;
        loff_t cluster_off;
        unsigned int local_len = len;
        struct ocfs2_write_cluster_desc *desc;
        struct ocfs2_super *osb = OCFS2_SB(mapping->host->i_sb);

        for (i = 0; i < wc->w_clen; i++) {
                desc = &wc->w_desc[i];

                /*
                 * We have to make sure that the total write passed in
                 * doesn't extend past a single cluster.
                 */
                local_len = len;
                cluster_off = pos & (osb->s_clustersize - 1);
                if ((cluster_off + local_len) > osb->s_clustersize)
                        local_len = osb->s_clustersize - cluster_off;

                ret = ocfs2_write_cluster(mapping, desc->c_phys,
                                          desc->c_unwritten, data_ac, meta_ac,
                                          wc, desc->c_cpos, pos, local_len);
                if (ret) {
                        mlog_errno(ret);
                        goto out;
                }

                len -= local_len;
                pos += local_len;
        }

        ret = 0;
out:
        return ret;
}

/*
 * ocfs2_write_end() wants to know which parts of the target page it
 * should complete the write on. It's easiest to compute them ahead of
 * time when a more complete view of the write is available.
 */
static void ocfs2_set_target_boundaries(struct ocfs2_super *osb,
                                        struct ocfs2_write_ctxt *wc,
                                        loff_t pos, unsigned len, int alloc)
{
        struct ocfs2_write_cluster_desc *desc;

        wc->w_target_from = pos & (PAGE_CACHE_SIZE - 1);
        wc->w_target_to = wc->w_target_from + len;

        if (alloc == 0)
                return;

        /*
         * Allocating write - we may have different boundaries based
         * on page size and cluster size.
         *
         * NOTE: We can no longer compute one value from the other as
         * the actual write length and user provided length may be
         * different.
         */

        if (wc->w_large_pages) {
                /*
                 * We only care about the 1st and last cluster within
                 * our range and whether they should be zero'd or not. Either
                 * value may be extended out to the start/end of a
                 * newly allocated cluster.
                 */
                desc = &wc->w_desc[0];
                if (ocfs2_should_zero_cluster(desc))
                        ocfs2_figure_cluster_boundaries(osb,
                                                        desc->c_cpos,
                                                        &wc->w_target_from,
                                                        NULL);

                desc = &wc->w_desc[wc->w_clen - 1];
                if (ocfs2_should_zero_cluster(desc))
                        ocfs2_figure_cluster_boundaries(osb,
                                                        desc->c_cpos,
                                                        NULL,
                                                        &wc->w_target_to);
        } else {
                wc->w_target_from = 0;
                wc->w_target_to = PAGE_CACHE_SIZE;
        }
}

/*
 * Populate each single-cluster write descriptor in the write context
 * with information about the i/o to be done.
 *
 * Returns the number of clusters that will have to be allocated, as
 * well as a worst case estimate of the number of extent records that
 * would have to be created during a write to an unwritten region.
 */
static int ocfs2_populate_write_desc(struct inode *inode,
                                     struct ocfs2_write_ctxt *wc,
                                     unsigned int *clusters_to_alloc,
                                     unsigned int *extents_to_split)
{
        int ret;
        struct ocfs2_write_cluster_desc *desc;
        unsigned int num_clusters = 0;
        unsigned int ext_flags = 0;
        u32 phys = 0;
        int i;

        *clusters_to_alloc = 0;
        *extents_to_split = 0;

        for (i = 0; i < wc->w_clen; i++) {
                desc = &wc->w_desc[i];
                desc->c_cpos = wc->w_cpos + i;

                if (num_clusters == 0) {
                        /*
                         * Need to look up the next extent record.
                         */
                        ret = ocfs2_get_clusters(inode, desc->c_cpos, &phys,
                                                 &num_clusters, &ext_flags);
                        if (ret) {
                                mlog_errno(ret);
                                goto out;
                        }

                        /*
                         * Assume worst case - that we're writing in
                         * the middle of the extent.
                         *
                         * We can assume that the write proceeds from
                         * left to right, in which case the extent
                         * insert code is smart enough to coalesce the
                         * next splits into the previous records created.
                         */
                        if (ext_flags & OCFS2_EXT_UNWRITTEN)
                                *extents_to_split = *extents_to_split + 2;
                } else if (phys) {
                        /*
                         * Only increment phys if it doesn't describe
                         * a hole.
                         */
                        phys++;
                }

                desc->c_phys = phys;
                if (phys == 0) {
                        desc->c_new = 1;
                        *clusters_to_alloc = *clusters_to_alloc + 1;
                }
                if (ext_flags & OCFS2_EXT_UNWRITTEN)
                        desc->c_unwritten = 1;

                num_clusters--;
        }

        ret = 0;
out:
        return ret;
}

static int ocfs2_write_begin_inline(struct address_space *mapping,
                                    struct inode *inode,
                                    struct ocfs2_write_ctxt *wc)
{
        int ret;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        struct page *page;
        handle_t *handle;
        struct ocfs2_dinode *di = (struct ocfs2_dinode *)wc->w_di_bh->b_data;

        page = find_or_create_page(mapping, 0, GFP_NOFS);
        if (!page) {
                ret = -ENOMEM;
                mlog_errno(ret);
                goto out;
        }
        /*
         * If we don't set w_num_pages then this page won't get unlocked
         * and freed on cleanup of the write context.
         */
        wc->w_pages[0] = wc->w_target_page = page;
        wc->w_num_pages = 1;

        handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                mlog_errno(ret);
                goto out;
        }

        ret = ocfs2_journal_access(handle, inode, wc->w_di_bh,
                                   OCFS2_JOURNAL_ACCESS_WRITE);
        if (ret) {
                ocfs2_commit_trans(osb, handle);

                mlog_errno(ret);
                goto out;
        }

        if (!(OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL))
                ocfs2_set_inode_data_inline(inode, di);

        if (!PageUptodate(page)) {
                ret = ocfs2_read_inline_data(inode, page, wc->w_di_bh);
                if (ret) {
                        ocfs2_commit_trans(osb, handle);

                        goto out;
                }
        }

        wc->w_handle = handle;
out:
        return ret;
}

int ocfs2_size_fits_inline_data(struct buffer_head *di_bh, u64 new_size)
{
        struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;

        if (new_size <= le16_to_cpu(di->id2.i_data.id_count))
                return 1;
        return 0;
}

static int ocfs2_try_to_write_inline_data(struct address_space *mapping,
                                          struct inode *inode, loff_t pos,
                                          unsigned len, struct page *mmap_page,
                                          struct ocfs2_write_ctxt *wc)
{
        int ret, written = 0;
        loff_t end = pos + len;
        struct ocfs2_inode_info *oi = OCFS2_I(inode);

        mlog(0, "Inode %llu, write of %u bytes at off %llu. features: 0x%x\n",
             (unsigned long long)oi->ip_blkno, len, (unsigned long long)pos,
             oi->ip_dyn_features);

        /*
         * Handle inodes which already have inline data 1st.
         */
        if (oi->ip_dyn_features & OCFS2_INLINE_DATA_FL) {
                if (mmap_page == NULL &&
                    ocfs2_size_fits_inline_data(wc->w_di_bh, end))
                        goto do_inline_write;

                /*
                 * The write won't fit - we have to give this inode an
                 * inline extent list now.
                 */
                ret = ocfs2_convert_inline_data_to_extents(inode, wc->w_di_bh);
                if (ret)
                        mlog_errno(ret);
                goto out;
        }

        /*
         * Check whether the inode can accept inline data.
         */
        if (oi->ip_clusters != 0 || i_size_read(inode) != 0)
                return 0;

        /*
         * Check whether the write can fit.
         */
        if (mmap_page || end > ocfs2_max_inline_data(inode->i_sb))
                return 0;

do_inline_write:
        ret = ocfs2_write_begin_inline(mapping, inode, wc);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        /*
         * This signals to the caller that the data can be written
         * inline.
         */
        written = 1;
out:
        return written ? written : ret;
}

/*
 * This function only does anything for file systems which can't
 * handle sparse files.
 *
 * What we want to do here is fill in any hole between the current end
 * of allocation and the end of our write. That way the rest of the
 * write path can treat it as an non-allocating write, which has no
 * special case code for sparse/nonsparse files.
 */
static int ocfs2_expand_nonsparse_inode(struct inode *inode, loff_t pos,
                                        unsigned len,
                                        struct ocfs2_write_ctxt *wc)
{
        int ret;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        loff_t newsize = pos + len;

        if (ocfs2_sparse_alloc(osb))
                return 0;

        if (newsize <= i_size_read(inode))
                return 0;

        ret = ocfs2_extend_no_holes(inode, newsize, newsize - len);
        if (ret)
                mlog_errno(ret);

        return ret;
}

int ocfs2_write_begin_nolock(struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned flags,
                             struct page **pagep, void **fsdata,
                             struct buffer_head *di_bh, struct page *mmap_page)
{
        int ret, credits = OCFS2_INODE_UPDATE_CREDITS;
        unsigned int clusters_to_alloc, extents_to_split;
        struct ocfs2_write_ctxt *wc;
        struct inode *inode = mapping->host;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        struct ocfs2_dinode *di;
        struct ocfs2_alloc_context *data_ac = NULL;
        struct ocfs2_alloc_context *meta_ac = NULL;
        handle_t *handle;
        struct ocfs2_extent_tree et;

        ret = ocfs2_alloc_write_ctxt(&wc, osb, pos, len, di_bh);
        if (ret) {
                mlog_errno(ret);
                return ret;
        }

        if (ocfs2_supports_inline_data(osb)) {
                ret = ocfs2_try_to_write_inline_data(mapping, inode, pos, len,
                                                     mmap_page, wc);
                if (ret == 1) {
                        ret = 0;
                        goto success;
                }
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }
        }

        ret = ocfs2_expand_nonsparse_inode(inode, pos, len, wc);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        ret = ocfs2_populate_write_desc(inode, wc, &clusters_to_alloc,
                                        &extents_to_split);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        di = (struct ocfs2_dinode *)wc->w_di_bh->b_data;

        /*
         * We set w_target_from, w_target_to here so that
         * ocfs2_write_end() knows which range in the target page to
         * write out. An allocation requires that we write the entire
         * cluster range.
         */
        if (clusters_to_alloc || extents_to_split) {
                /*
                 * XXX: We are stretching the limits of
                 * ocfs2_lock_allocators(). It greatly over-estimates
                 * the work to be done.
                 */
                mlog(0, "extend inode %llu, i_size = %lld, di->i_clusters = %u,"
                     " clusters_to_add = %u, extents_to_split = %u\n",
                     (unsigned long long)OCFS2_I(inode)->ip_blkno,
                     (long long)i_size_read(inode), le32_to_cpu(di->i_clusters),
                     clusters_to_alloc, extents_to_split);

                ocfs2_init_dinode_extent_tree(&et, inode, wc->w_di_bh);
                ret = ocfs2_lock_allocators(inode, &et,
                                            clusters_to_alloc, extents_to_split,
                                            &data_ac, &meta_ac);
                if (ret) {
                        mlog_errno(ret);
                        goto out;
                }

                credits = ocfs2_calc_extend_credits(inode->i_sb,
                                                    &di->id2.i_list,
                                                    clusters_to_alloc);

        }

        ocfs2_set_target_boundaries(osb, wc, pos, len,
                                    clusters_to_alloc + extents_to_split);

        handle = ocfs2_start_trans(osb, credits);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                mlog_errno(ret);
                goto out;
        }

        wc->w_handle = handle;

        /*
         * We don't want this to fail in ocfs2_write_end(), so do it
         * here.
         */
        ret = ocfs2_journal_access(handle, inode, wc->w_di_bh,
                                   OCFS2_JOURNAL_ACCESS_WRITE);
        if (ret) {
                mlog_errno(ret);
                goto out_commit;
        }

        /*
         * Fill our page array first. That way we've grabbed enough so
         * that we can zero and flush if we error after adding the
         * extent.
         */
        ret = ocfs2_grab_pages_for_write(mapping, wc, wc->w_cpos, pos,
                                         clusters_to_alloc + extents_to_split,
                                         mmap_page);
        if (ret) {
                mlog_errno(ret);
                goto out_commit;
        }

        ret = ocfs2_write_cluster_by_desc(mapping, data_ac, meta_ac, wc, pos,
                                          len);
        if (ret) {
                mlog_errno(ret);
                goto out_commit;
        }

        if (data_ac)
                ocfs2_free_alloc_context(data_ac);
        if (meta_ac)
                ocfs2_free_alloc_context(meta_ac);

success:
        *pagep = wc->w_target_page;
        *fsdata = wc;
        return 0;
out_commit:
        ocfs2_commit_trans(osb, handle);

out:
        ocfs2_free_write_ctxt(wc);

        if (data_ac)
                ocfs2_free_alloc_context(data_ac);
        if (meta_ac)
                ocfs2_free_alloc_context(meta_ac);
        return ret;
}

static int ocfs2_write_begin(struct file *file, struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned flags,
                             struct page **pagep, void **fsdata)
{
        int ret;
        struct buffer_head *di_bh = NULL;
        struct inode *inode = mapping->host;

        ret = ocfs2_inode_lock(inode, &di_bh, 1);
        if (ret) {
                mlog_errno(ret);
                return ret;
        }

        /*
         * Take alloc sem here to prevent concurrent lookups. That way
         * the mapping, zeroing and tree manipulation within
         * ocfs2_write() will be safe against ->readpage(). This
         * should also serve to lock out allocation from a shared
         * writeable region.
         */
        down_write(&OCFS2_I(inode)->ip_alloc_sem);

        ret = ocfs2_write_begin_nolock(mapping, pos, len, flags, pagep,
                                       fsdata, di_bh, NULL);
        if (ret) {
                mlog_errno(ret);
                goto out_fail;
        }

        brelse(di_bh);

        return 0;

out_fail:
        up_write(&OCFS2_I(inode)->ip_alloc_sem);

        brelse(di_bh);
        ocfs2_inode_unlock(inode, 1);

        return ret;
}

static void ocfs2_write_end_inline(struct inode *inode, loff_t pos,
                                   unsigned len, unsigned *copied,
                                   struct ocfs2_dinode *di,
                                   struct ocfs2_write_ctxt *wc)
{
        void *kaddr;

        if (unlikely(*copied < len)) {
                if (!PageUptodate(wc->w_target_page)) {
                        *copied = 0;
                        return;
                }
        }

        kaddr = kmap_atomic(wc->w_target_page, KM_USER0);
        memcpy(di->id2.i_data.id_data + pos, kaddr + pos, *copied);
        kunmap_atomic(kaddr, KM_USER0);

        mlog(0, "Data written to inode at offset %llu. "
             "id_count = %u, copied = %u, i_dyn_features = 0x%x\n",
             (unsigned long long)pos, *copied,
             le16_to_cpu(di->id2.i_data.id_count),
             le16_to_cpu(di->i_dyn_features));
}

int ocfs2_write_end_nolock(struct address_space *mapping,
                           loff_t pos, unsigned len, unsigned copied,
                           struct page *page, void *fsdata)
{
        int i;
        unsigned from, to, start = pos & (PAGE_CACHE_SIZE - 1);
        struct inode *inode = mapping->host;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        struct ocfs2_write_ctxt *wc = fsdata;
        struct ocfs2_dinode *di = (struct ocfs2_dinode *)wc->w_di_bh->b_data;
        handle_t *handle = wc->w_handle;
        struct page *tmppage;

        if (OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) {
                ocfs2_write_end_inline(inode, pos, len, &copied, di, wc);
                goto out_write_size;
        }

        if (unlikely(copied < len)) {
                if (!PageUptodate(wc->w_target_page))
                        copied = 0;

                ocfs2_zero_new_buffers(wc->w_target_page, start+copied,
                                       start+len);
        }
        flush_dcache_page(wc->w_target_page);

        for(i = 0; i < wc->w_num_pages; i++) {
                tmppage = wc->w_pages[i];

                if (tmppage == wc->w_target_page) {
                        from = wc->w_target_from;
                        to = wc->w_target_to;

                        BUG_ON(from > PAGE_CACHE_SIZE ||
                               to > PAGE_CACHE_SIZE ||
                               to < from);
                } else {
                        /*
                         * Pages adjacent to the target (if any) imply
                         * a hole-filling write in which case we want
                         * to flush their entire range.
                         */
                        from = 0;
                        to = PAGE_CACHE_SIZE;
                }

                if (page_has_buffers(tmppage)) {
                        if (ocfs2_should_order_data(inode)) {
                                ocfs2_jbd2_file_inode(wc->w_handle, inode);
#ifdef CONFIG_OCFS2_COMPAT_JBD
                                walk_page_buffers(wc->w_handle,
                                                  page_buffers(tmppage),
                                                  from, to, NULL,
                                                  ocfs2_journal_dirty_data);
#endif
                        }
                        block_commit_write(tmppage, from, to);
                }
        }

out_write_size:
        pos += copied;
        if (pos > inode->i_size) {
                i_size_write(inode, pos);
                mark_inode_dirty(inode);
        }
        inode->i_blocks = ocfs2_inode_sector_count(inode);
        di->i_size = cpu_to_le64((u64)i_size_read(inode));
        inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        di->i_mtime = di->i_ctime = cpu_to_le64(inode->i_mtime.tv_sec);
        di->i_mtime_nsec = di->i_ctime_nsec = cpu_to_le32(inode->i_mtime.tv_nsec);
        ocfs2_journal_dirty(handle, wc->w_di_bh);

        ocfs2_commit_trans(osb, handle);

        ocfs2_run_deallocs(osb, &wc->w_dealloc);

        ocfs2_free_write_ctxt(wc);

        return copied;
}

static int ocfs2_write_end(struct file *file, struct address_space *mapping,
                           loff_t pos, unsigned len, unsigned copied,
                           struct page *page, void *fsdata)
{
        int ret;
        struct inode *inode = mapping->host;

        ret = ocfs2_write_end_nolock(mapping, pos, len, copied, page, fsdata);

        up_write(&OCFS2_I(inode)->ip_alloc_sem);
        ocfs2_inode_unlock(inode, 1);

        return ret;
}

const struct address_space_operations ocfs2_aops = {
        .readpage       = ocfs2_readpage,
        .readpages      = ocfs2_readpages,
        .writepage      = ocfs2_writepage,
        .write_begin    = ocfs2_write_begin,
        .write_end      = ocfs2_write_end,
        .bmap           = ocfs2_bmap,
        .sync_page      = block_sync_page,
        .direct_IO      = ocfs2_direct_IO,
        .invalidatepage = ocfs2_invalidatepage,
        .releasepage    = ocfs2_releasepage,
        .migratepage    = buffer_migrate_page,
};