ocfs2: zero tail of sparse files on truncate

[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>

#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)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;
        u64 p_blkno, 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, NULL);
        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;
        }

        /*
         * 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.
         */
        mlog_bug_on_msg(create && p_blkno == 0 && ocfs2_sparse_alloc(osb),
                        "ino %lu, iblock %llu\n", inode->i_ino,
                        (unsigned long long)iblock);

        if (p_blkno)
                map_bh(bh_result, inode->i_sb, p_blkno);

        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;
}

static int ocfs2_readpage(struct file *file, struct page *page)
{
        struct inode *inode = page->mapping->host;
        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_meta_lock_with_page(inode, NULL, 0, page);
        if (ret != 0) {
                if (ret == AOP_TRUNCATED_PAGE)
                        unlock = 0;
                mlog_errno(ret);
                goto out;
        }

        down_read(&OCFS2_I(inode)->ip_alloc_sem);

        /*
         * 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, fault->nopage) 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)) {
                char *addr = kmap(page);
                memset(addr, 0, PAGE_SIZE);
                flush_dcache_page(page);
                kunmap(page);
                SetPageUptodate(page);
                ret = 0;
                goto out_alloc;
        }

        ret = ocfs2_data_lock_with_page(inode, 0, page);
        if (ret != 0) {
                if (ret == AOP_TRUNCATED_PAGE)
                        unlock = 0;
                mlog_errno(ret);
                goto out_alloc;
        }

        ret = block_read_full_page(page, ocfs2_get_block);
        unlock = 0;

        ocfs2_data_unlock(inode, 0);
out_alloc:
        up_read(&OCFS2_I(inode)->ip_alloc_sem);
        ocfs2_meta_unlock(inode, 0);
out:
        if (unlock)
                unlock_page(page);
        mlog_exit(ret);
        return ret;
}

/* 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;

        down_read(&OCFS2_I(inode)->ip_alloc_sem);

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

        up_read(&OCFS2_I(inode)->ip_alloc_sem);

        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 = NULL;
        int ret = 0;

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

        if (ocfs2_should_order_data(inode)) {
                ret = walk_page_buffers(handle,
                                        page_buffers(page),
                                        from, to, NULL,
                                        ocfs2_journal_dirty_data);
                if (ret < 0) 
                        mlog_errno(ret);
        }
out:
        if (ret) {
                if (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_meta_lock(inode, NULL, 0);
                if (err) {
                        if (err != -ENOENT)
                                mlog_errno(err);
                        goto bail;
                }
                down_read(&OCFS2_I(inode)->ip_alloc_sem);
        }

        err = ocfs2_extent_map_get_blocks(inode, block, &p_blkno, NULL);

        if (!INODE_JOURNAL(inode)) {
                up_read(&OCFS2_I(inode)->ip_alloc_sem);
                ocfs2_meta_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;
        int contig_blocks;
        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);
        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) {
                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().
         */
        if (p_blkno)
                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;

        /* 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);
        up_read(&inode->i_alloc_sem);
        ocfs2_rw_unlock(inode, 0);
}

/*
 * 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;

        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 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();

        if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb))) {
                /*
                 * We get PR data locks even for O_DIRECT.  This
                 * allows concurrent O_DIRECT I/O but doesn't let
                 * O_DIRECT with extending and buffered zeroing writes
                 * race.  If they did race then the buffered zeroing
                 * could be written back after the O_DIRECT I/O.  It's
                 * one thing to tell people not to mix buffered and
                 * O_DIRECT writes, but expecting them to understand
                 * that file extension is also an implicit buffered
                 * write is too much.  By getting the PR we force
                 * writeback of the buffered zeroing before
                 * proceeding.
                 */
                ret = ocfs2_data_lock(inode, 0);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }
                ocfs2_data_unlock(inode, 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);
out:
        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);
}

/*
 * 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;

                /*
                 * 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 (buffer_new(bh))
                        clear_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) &&
                     (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 {
                void *kaddr;

                block_end = block_start + bsize;
                if (block_end <= from)
                        goto next_bh;
                if (block_start >= to)
                        break;

                kaddr = kmap_atomic(page, KM_USER0);
                memset(kaddr+block_start, 0, bh->b_size);
                flush_dcache_page(page);
                kunmap_atomic(kaddr, KM_USER0);
                set_buffer_uptodate(bh);
                mark_buffer_dirty(bh);

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

        return ret;
}

/*
 * This will copy user data from the iovec in the buffered write
 * context.
 */
int ocfs2_map_and_write_user_data(struct inode *inode,
                                  struct ocfs2_write_ctxt *wc, u64 *p_blkno,
                                  unsigned int *ret_from, unsigned int *ret_to)
{
        int ret;
        unsigned int to, from, cluster_start, cluster_end;
        unsigned long bytes, src_from;
        char *dst;
        struct ocfs2_buffered_write_priv *bp = wc->w_private;
        const struct iovec *cur_iov = bp->b_cur_iov;
        char __user *buf;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

        ocfs2_figure_cluster_boundaries(osb, wc->w_cpos, &cluster_start,
                                        &cluster_end);

        buf = cur_iov->iov_base + bp->b_cur_off;
        src_from = (unsigned long)buf & ~PAGE_CACHE_MASK;

        from = wc->w_pos & (PAGE_CACHE_SIZE - 1);

        /*
         * This is a lot of comparisons, but it reads quite
         * easily, which is important here.
         */
        /* Stay within the src page */
        bytes = PAGE_SIZE - src_from;
        /* Stay within the vector */
        bytes = min(bytes,
                    (unsigned long)(cur_iov->iov_len - bp->b_cur_off));
        /* Stay within count */
        bytes = min(bytes, (unsigned long)wc->w_count);
        /*
         * For clustersize > page size, just stay within
         * target page, otherwise we have to calculate pos
         * within the cluster and obey the rightmost
         * boundary.
         */
        if (wc->w_large_pages) {
                /*
                 * For cluster size < page size, we have to
                 * calculate pos within the cluster and obey
                 * the rightmost boundary.
                 */
                bytes = min(bytes, (unsigned long)(osb->s_clustersize
                                   - (wc->w_pos & (osb->s_clustersize - 1))));
        } else {
                /*
                 * cluster size > page size is the most common
                 * case - we just stay within the target page
                 * boundary.
                 */
                bytes = min(bytes, PAGE_CACHE_SIZE - from);
        }

        to = from + bytes;

        if (wc->w_this_page_new)
                ret = ocfs2_map_page_blocks(wc->w_this_page, p_blkno, inode,
                                            cluster_start, cluster_end, 1);
        else
                ret = ocfs2_map_page_blocks(wc->w_this_page, p_blkno, inode,
                                            from, to, 0);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        BUG_ON(from > PAGE_CACHE_SIZE);
        BUG_ON(to > PAGE_CACHE_SIZE);
        BUG_ON(from > osb->s_clustersize);
        BUG_ON(to > osb->s_clustersize);

        dst = kmap(wc->w_this_page);
        memcpy(dst + from, bp->b_src_buf + src_from, bytes);
        kunmap(wc->w_this_page);

        /*
         * XXX: This is slow, but simple. The caller of
         * ocfs2_buffered_write_cluster() is responsible for
         * passing through the iovecs, so it's difficult to
         * predict what our next step is in here after our
         * initial write. A future version should be pushing
         * that iovec manipulation further down.
         *
         * By setting this, we indicate that a copy from user
         * data was done, and subsequent calls for this
         * cluster will skip copying more data.
         */
        wc->w_finished_copy = 1;

        *ret_from = from;
        *ret_to = to;
out:

        return bytes ? (unsigned int)bytes : ret;
}

/*
 * Map, fill and write a page to disk.
 *
 * The work of copying data is done via callback.  Newly allocated
 * pages which don't take user data will be zero'd (set 'new' to
 * indicate an allocating write)
 *
 * Returns a negative error code or the number of bytes copied into
 * the page.
 */
int ocfs2_write_data_page(struct inode *inode, handle_t *handle,
                          u64 *p_blkno, struct page *page,
                          struct ocfs2_write_ctxt *wc, int new)
{
        int ret, copied = 0;
        unsigned int from = 0, to = 0;
        unsigned int cluster_start, cluster_end;
        unsigned int zero_from = 0, zero_to = 0;

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

        if ((wc->w_pos >> PAGE_CACHE_SHIFT) == page->index
            && !wc->w_finished_copy) {

                wc->w_this_page = page;
                wc->w_this_page_new = new;
                ret = wc->w_write_data_page(inode, wc, p_blkno, &from, &to);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }

                copied = ret;

                zero_from = from;
                zero_to = to;
                if (new) {
                        from = cluster_start;
                        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);

                from = cluster_start;
                to = cluster_end;

                ret = ocfs2_map_page_blocks(page, p_blkno, inode,
                                            cluster_start, cluster_end, 1);
                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),
                                         wc->w_cpos, zero_from, zero_to);

        flush_dcache_page(page);

        if (ocfs2_should_order_data(inode)) {
                ret = walk_page_buffers(handle,
                                        page_buffers(page),
                                        from, to, NULL,
                                        ocfs2_journal_dirty_data);
                if (ret < 0)
                        mlog_errno(ret);
        }

        /*
         * We don't use generic_commit_write() because we need to
         * handle our own i_size update.
         */
        ret = block_commit_write(page, from, to);
        if (ret)
                mlog_errno(ret);
out:

        return copied ? copied : ret;
}

/*
 * Do the actual write of some data into an inode. Optionally allocate
 * in order to fulfill the write.
 *
 * cpos is the logical cluster offset within the file to write at
 *
 * 'phys' is the physical mapping of that offset. a 'phys' value of
 * zero indicates that allocation is required. In this case, data_ac
 * and meta_ac should be valid (meta_ac can be null if metadata
 * allocation isn't required).
 */
static ssize_t ocfs2_write(struct file *file, u32 phys, handle_t *handle,
                           struct buffer_head *di_bh,
                           struct ocfs2_alloc_context *data_ac,
                           struct ocfs2_alloc_context *meta_ac,
                           struct ocfs2_write_ctxt *wc)
{
        int ret, i, numpages = 1, new;
        unsigned int copied = 0;
        u32 tmp_pos;
        u64 v_blkno, p_blkno;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        unsigned long index, start;
        struct page **cpages;

        new = phys == 0 ? 1 : 0;

        /*
         * 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)
                numpages = ocfs2_pages_per_cluster(inode->i_sb);

        cpages = kzalloc(sizeof(*cpages) * numpages, GFP_NOFS);
        if (!cpages) {
                ret = -ENOMEM;
                mlog_errno(ret);
                return ret;
        }

        /*
         * 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.
         */
        if (new) {
                start = ocfs2_align_clusters_to_page_index(inode->i_sb,
                                                           wc->w_cpos);
                v_blkno = ocfs2_clusters_to_blocks(inode->i_sb, wc->w_cpos);
        } else {
                start = wc->w_pos >> PAGE_CACHE_SHIFT;
                v_blkno = wc->w_pos >> inode->i_sb->s_blocksize_bits;
        }

        for(i = 0; i < numpages; i++) {
                index = start + i;

                cpages[i] = grab_cache_page(mapping, index);
                if (!cpages[i]) {
                        ret = -ENOMEM;
                        mlog_errno(ret);
                        goto out;
                }
        }

        if (new) {
                /*
                 * This is safe to call with the page locks - it won't take
                 * any additional semaphores or cluster locks.
                 */
                tmp_pos = wc->w_cpos;
                ret = ocfs2_do_extend_allocation(OCFS2_SB(inode->i_sb), inode,
                                                 &tmp_pos, 1, di_bh, 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;
                }
        }

        ret = ocfs2_extent_map_get_blocks(inode, v_blkno, &p_blkno, NULL);
        if (ret < 0) {

                /*
                 * XXX: Should we go readonly here?
                 */

                mlog_errno(ret);
                goto out;
        }

        BUG_ON(p_blkno == 0);

        for(i = 0; i < numpages; i++) {
                ret = ocfs2_write_data_page(inode, handle, &p_blkno, cpages[i],
                                            wc, new);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto out;
                }

                copied += ret;
        }

out:
        for(i = 0; i < numpages; i++) {
                unlock_page(cpages[i]);
                mark_page_accessed(cpages[i]);
                page_cache_release(cpages[i]);
        }
        kfree(cpages);

        return copied ? copied : ret;
}

static void ocfs2_write_ctxt_init(struct ocfs2_write_ctxt *wc,
                                  struct ocfs2_super *osb, loff_t pos,
                                  size_t count, ocfs2_page_writer *cb,
                                  void *cb_priv)
{
        wc->w_count = count;
        wc->w_pos = pos;
        wc->w_cpos = wc->w_pos >> osb->s_clustersize_bits;
        wc->w_finished_copy = 0;

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

        wc->w_write_data_page = cb;
        wc->w_private = cb_priv;
}

/*
 * Write a cluster to an inode. The cluster may not be allocated yet,
 * in which case it will be. This only exists for buffered writes -
 * O_DIRECT takes a more "traditional" path through the kernel.
 *
 * The caller is responsible for incrementing pos, written counts, etc
 *
 * For file systems that don't support sparse files, pre-allocation
 * and page zeroing up until cpos should be done prior to this
 * function call.
 *
 * Callers should be holding i_sem, and the rw cluster lock.
 *
 * Returns the number of user bytes written, or less than zero for
 * error.
 */
ssize_t ocfs2_buffered_write_cluster(struct file *file, loff_t pos,
                                     size_t count, ocfs2_page_writer *actor,
                                     void *priv)
{
        int ret, credits = OCFS2_INODE_UPDATE_CREDITS;
        ssize_t written = 0;
        u32 phys;
        struct inode *inode = file->f_mapping->host;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        struct buffer_head *di_bh = NULL;
        struct ocfs2_dinode *di;
        struct ocfs2_alloc_context *data_ac = NULL;
        struct ocfs2_alloc_context *meta_ac = NULL;
        handle_t *handle;
        struct ocfs2_write_ctxt wc;

        ocfs2_write_ctxt_init(&wc, osb, pos, count, actor, priv);

        ret = ocfs2_meta_lock(inode, &di_bh, 1);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }
        di = (struct ocfs2_dinode *)di_bh->b_data;

        /*
         * 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_get_clusters(inode, wc.w_cpos, &phys, NULL);
        if (ret) {
                mlog_errno(ret);
                goto out_meta;
        }

        /* phys == 0 means that allocation is required. */
        if (phys == 0) {
                ret = ocfs2_lock_allocators(inode, di, 1, &data_ac, &meta_ac);
                if (ret) {
                        mlog_errno(ret);
                        goto out_meta;
                }

                credits = ocfs2_calc_extend_credits(inode->i_sb, di, 1);
        }

        ret = ocfs2_data_lock(inode, 1);
        if (ret) {
                mlog_errno(ret);
                goto out_meta;
        }

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

        written = ocfs2_write(file, phys, handle, di_bh, data_ac,
                              meta_ac, &wc);
        if (written < 0) {
                ret = written;
                mlog_errno(ret);
                goto out_commit;
        }

        ret = ocfs2_journal_access(handle, inode, di_bh,
                                   OCFS2_JOURNAL_ACCESS_WRITE);
        if (ret) {
                mlog_errno(ret);
                goto out_commit;
        }

        pos += written;
        if (pos > inode->i_size) {
                i_size_write(inode, pos);
                mark_inode_dirty(inode);
        }
        inode->i_blocks = ocfs2_align_bytes_to_sectors((u64)(i_size_read(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);

        ret = ocfs2_journal_dirty(handle, di_bh);
        if (ret)
                mlog_errno(ret);

out_commit:
        ocfs2_commit_trans(osb, handle);

out_data:
        ocfs2_data_unlock(inode, 1);

out_meta:
        up_write(&OCFS2_I(inode)->ip_alloc_sem);
        ocfs2_meta_unlock(inode, 1);

out:
        brelse(di_bh);
        if (data_ac)
                ocfs2_free_alloc_context(data_ac);
        if (meta_ac)
                ocfs2_free_alloc_context(meta_ac);

        return written ? written : ret;
}

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