/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
 * Copyright (C) 2004-2008 Red Hat, Inc.  All rights reserved.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License version 2.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/buffer_head.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/fs.h>
#include <linux/writeback.h>
#include <linux/swap.h>
#include <linux/gfs2_ondisk.h>
#include <linux/backing-dev.h>
#include <linux/uio.h>
#include <trace/events/writeback.h>
#include <linux/sched/signal.h>

#include "gfs2.h"
#include "incore.h"
#include "bmap.h"
#include "glock.h"
#include "inode.h"
#include "log.h"
#include "meta_io.h"
#include "quota.h"
#include "trans.h"
#include "rgrp.h"
#include "super.h"
#include "util.h"
#include "glops.h"
#include "aops.h"


void gfs2_page_add_databufs(struct gfs2_inode *ip, struct page *page,
                            unsigned int from, unsigned int len)
{
        struct buffer_head *head = page_buffers(page);
        unsigned int bsize = head->b_size;
        struct buffer_head *bh;
        unsigned int to = from + len;
        unsigned int start, end;

        for (bh = head, start = 0; bh != head || !start;
             bh = bh->b_this_page, start = end) {
                end = start + bsize;
                if (end <= from)
                        continue;
                if (start >= to)
                        break;
                set_buffer_uptodate(bh);
                gfs2_trans_add_data(ip->i_gl, bh);
        }
}

/**
 * gfs2_get_block_noalloc - Fills in a buffer head with details about a block
 * @inode: The inode
 * @lblock: The block number to look up
 * @bh_result: The buffer head to return the result in
 * @create: Non-zero if we may add block to the file
 *
 * Returns: errno
 */

static int gfs2_get_block_noalloc(struct inode *inode, sector_t lblock,
                                  struct buffer_head *bh_result, int create)
{
        int error;

        error = gfs2_block_map(inode, lblock, bh_result, 0);
        if (error)
                return error;
        if (!buffer_mapped(bh_result))
                return -EIO;
        return 0;
}

/**
 * gfs2_writepage_common - Common bits of writepage
 * @page: The page to be written
 * @wbc: The writeback control
 *
 * Returns: 1 if writepage is ok, otherwise an error code or zero if no error.
 */

static int gfs2_writepage_common(struct page *page,
                                 struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        loff_t i_size = i_size_read(inode);
        pgoff_t end_index = i_size >> PAGE_SHIFT;
        unsigned offset;

        if (gfs2_assert_withdraw(sdp, gfs2_glock_is_held_excl(ip->i_gl)))
                goto out;
        if (current->journal_info)
                goto redirty;
        /* Is the page fully outside i_size? (truncate in progress) */
        offset = i_size & (PAGE_SIZE-1);
        if (page->index > end_index || (page->index == end_index && !offset)) {
                page->mapping->a_ops->invalidatepage(page, 0, PAGE_SIZE);
                goto out;
        }
        return 1;
redirty:
        redirty_page_for_writepage(wbc, page);
out:
        unlock_page(page);
        return 0;
}

/**
 * gfs2_writepage - Write page for writeback mappings
 * @page: The page
 * @wbc: The writeback control
 *
 */

static int gfs2_writepage(struct page *page, struct writeback_control *wbc)
{
        int ret;

        ret = gfs2_writepage_common(page, wbc);
        if (ret <= 0)
                return ret;

        return nobh_writepage(page, gfs2_get_block_noalloc, wbc);
}

/* This is the same as calling block_write_full_page, but it also
 * writes pages outside of i_size
 */
static int gfs2_write_full_page(struct page *page, get_block_t *get_block,
                                struct writeback_control *wbc)
{
        struct inode * const inode = page->mapping->host;
        loff_t i_size = i_size_read(inode);
        const pgoff_t end_index = i_size >> PAGE_SHIFT;
        unsigned offset;

        /*
         * The page straddles i_size.  It must be zeroed out on each and every
         * writepage invocation because it may be mmapped.  "A file is mapped
         * in multiples of the page size.  For a file that is not a multiple of
         * the  page size, the remaining memory is zeroed when mapped, and
         * writes to that region are not written out to the file."
         */
        offset = i_size & (PAGE_SIZE-1);
        if (page->index == end_index && offset)
                zero_user_segment(page, offset, PAGE_SIZE);

        return __block_write_full_page(inode, page, get_block, wbc,
                                       end_buffer_async_write);
}

/**
 * __gfs2_jdata_writepage - The core of jdata writepage
 * @page: The page to write
 * @wbc: The writeback control
 *
 * This is shared between writepage and writepages and implements the
 * core of the writepage operation. If a transaction is required then
 * PageChecked will have been set and the transaction will have
 * already been started before this is called.
 */

static int __gfs2_jdata_writepage(struct page *page, struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);

        if (PageChecked(page)) {
                ClearPageChecked(page);
                if (!page_has_buffers(page)) {
                        create_empty_buffers(page, inode->i_sb->s_blocksize,
                                             BIT(BH_Dirty)|BIT(BH_Uptodate));
                }
                gfs2_page_add_databufs(ip, page, 0, sdp->sd_vfs->s_blocksize);
        }
        return gfs2_write_full_page(page, gfs2_get_block_noalloc, wbc);
}

/**
 * gfs2_jdata_writepage - Write complete page
 * @page: Page to write
 * @wbc: The writeback control
 *
 * Returns: errno
 *
 */

static int gfs2_jdata_writepage(struct page *page, struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        int ret;

        if (gfs2_assert_withdraw(sdp, gfs2_glock_is_held_excl(ip->i_gl)))
                goto out;
        if (PageChecked(page) || current->journal_info)
                goto out_ignore;
        ret = __gfs2_jdata_writepage(page, wbc);
        return ret;

out_ignore:
        redirty_page_for_writepage(wbc, page);
out:
        unlock_page(page);
        return 0;
}

/**
 * gfs2_writepages - Write a bunch of dirty pages back to disk
 * @mapping: The mapping to write
 * @wbc: Write-back control
 *
 * Used for both ordered and writeback modes.
 */
static int gfs2_writepages(struct address_space *mapping,
                           struct writeback_control *wbc)
{
        struct gfs2_sbd *sdp = gfs2_mapping2sbd(mapping);
        int ret = mpage_writepages(mapping, wbc, gfs2_get_block_noalloc);

        /*
         * Even if we didn't write any pages here, we might still be holding
         * dirty pages in the ail. We forcibly flush the ail because we don't
         * want balance_dirty_pages() to loop indefinitely trying to write out
         * pages held in the ail that it can't find.
         */
        if (ret == 0)
                set_bit(SDF_FORCE_AIL_FLUSH, &sdp->sd_flags);

        return ret;
}

/**
 * gfs2_write_jdata_pagevec - Write back a pagevec's worth of pages
 * @mapping: The mapping
 * @wbc: The writeback control
 * @pvec: The vector of pages
 * @nr_pages: The number of pages to write
 * @done_index: Page index
 *
 * Returns: non-zero if loop should terminate, zero otherwise
 */

static int gfs2_write_jdata_pagevec(struct address_space *mapping,
                                    struct writeback_control *wbc,
                                    struct pagevec *pvec,
                                    int nr_pages,
                                    pgoff_t *done_index)
{
        struct inode *inode = mapping->host;
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        unsigned nrblocks = nr_pages * (PAGE_SIZE/inode->i_sb->s_blocksize);
        int i;
        int ret;

        ret = gfs2_trans_begin(sdp, nrblocks, nrblocks);
        if (ret < 0)
                return ret;

        for(i = 0; i < nr_pages; i++) {
                struct page *page = pvec->pages[i];

                *done_index = page->index;

                lock_page(page);

                if (unlikely(page->mapping != mapping)) {
continue_unlock:
                        unlock_page(page);
                        continue;
                }

                if (!PageDirty(page)) {
                        /* someone wrote it for us */
                        goto continue_unlock;
                }

                if (PageWriteback(page)) {
                        if (wbc->sync_mode != WB_SYNC_NONE)
                                wait_on_page_writeback(page);
                        else
                                goto continue_unlock;
                }

                BUG_ON(PageWriteback(page));
                if (!clear_page_dirty_for_io(page))
                        goto continue_unlock;

                trace_wbc_writepage(wbc, inode_to_bdi(inode));

                ret = __gfs2_jdata_writepage(page, wbc);
                if (unlikely(ret)) {
                        if (ret == AOP_WRITEPAGE_ACTIVATE) {
                                unlock_page(page);
                                ret = 0;
                        } else {

                                /*
                                 * done_index is set past this page,
                                 * so media errors will not choke
                                 * background writeout for the entire
                                 * file. This has consequences for
                                 * range_cyclic semantics (ie. it may
                                 * not be suitable for data integrity
                                 * writeout).
                                 */
                                *done_index = page->index + 1;
                                ret = 1;
                                break;
                        }
                }

                /*
                 * We stop writing back only if we are not doing
                 * integrity sync. In case of integrity sync we have to
                 * keep going until we have written all the pages
                 * we tagged for writeback prior to entering this loop.
                 */
                if (--wbc->nr_to_write <= 0 && wbc->sync_mode == WB_SYNC_NONE) {
                        ret = 1;
                        break;
                }

        }
        gfs2_trans_end(sdp);
        return ret;
}

/**
 * gfs2_write_cache_jdata - Like write_cache_pages but different
 * @mapping: The mapping to write
 * @wbc: The writeback control
 *
 * The reason that we use our own function here is that we need to
 * start transactions before we grab page locks. This allows us
 * to get the ordering right.
 */

static int gfs2_write_cache_jdata(struct address_space *mapping,
                                  struct writeback_control *wbc)
{
        int ret = 0;
        int done = 0;
        struct pagevec pvec;
        int nr_pages;
        pgoff_t uninitialized_var(writeback_index);
        pgoff_t index;
        pgoff_t end;
        pgoff_t done_index;
        int cycled;
        int range_whole = 0;
        int tag;

        pagevec_init(&pvec);
        if (wbc->range_cyclic) {
                writeback_index = mapping->writeback_index; /* prev offset */
                index = writeback_index;
                if (index == 0)
                        cycled = 1;
                else
                        cycled = 0;
                end = -1;
        } else {
                index = wbc->range_start >> PAGE_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                        range_whole = 1;
                cycled = 1; /* ignore range_cyclic tests */
        }
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;

retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, index, end);
        done_index = index;
        while (!done && (index <= end)) {
                nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
                                tag);
                if (nr_pages == 0)
                        break;

                ret = gfs2_write_jdata_pagevec(mapping, wbc, &pvec, nr_pages, &done_index);
                if (ret)
                        done = 1;
                if (ret > 0)
                        ret = 0;
                pagevec_release(&pvec);
                cond_resched();
        }

        if (!cycled && !done) {
                /*
                 * range_cyclic:
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                cycled = 1;
                index = 0;
                end = writeback_index - 1;
                goto retry;
        }

        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                mapping->writeback_index = done_index;

        return ret;
}


/**
 * gfs2_jdata_writepages - Write a bunch of dirty pages back to disk
 * @mapping: The mapping to write
 * @wbc: The writeback control
 * 
 */

static int gfs2_jdata_writepages(struct address_space *mapping,
                                 struct writeback_control *wbc)
{
        struct gfs2_inode *ip = GFS2_I(mapping->host);
        struct gfs2_sbd *sdp = GFS2_SB(mapping->host);
        int ret;

        ret = gfs2_write_cache_jdata(mapping, wbc);
        if (ret == 0 && wbc->sync_mode == WB_SYNC_ALL) {
                gfs2_log_flush(sdp, ip->i_gl, GFS2_LOG_HEAD_FLUSH_NORMAL |
                               GFS2_LFC_JDATA_WPAGES);
                ret = gfs2_write_cache_jdata(mapping, wbc);
        }
        return ret;
}

/**
 * stuffed_readpage - Fill in a Linux page with stuffed file data
 * @ip: the inode
 * @page: the page
 *
 * Returns: errno
 */

int stuffed_readpage(struct gfs2_inode *ip, struct page *page)
{
        struct buffer_head *dibh;
        u64 dsize = i_size_read(&ip->i_inode);
        void *kaddr;
        int error;

        /*
         * Due to the order of unstuffing files and ->fault(), we can be
         * asked for a zero page in the case of a stuffed file being extended,
         * so we need to supply one here. It doesn't happen often.
         */
        if (unlikely(page->index)) {
                zero_user(page, 0, PAGE_SIZE);
                SetPageUptodate(page);
                return 0;
        }

        error = gfs2_meta_inode_buffer(ip, &dibh);
        if (error)
                return error;

        kaddr = kmap_atomic(page);
        if (dsize > gfs2_max_stuffed_size(ip))
                dsize = gfs2_max_stuffed_size(ip);
        memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode), dsize);
        memset(kaddr + dsize, 0, PAGE_SIZE - dsize);
        kunmap_atomic(kaddr);
        flush_dcache_page(page);
        brelse(dibh);
        SetPageUptodate(page);

        return 0;
}


/**
 * __gfs2_readpage - readpage
 * @file: The file to read a page for
 * @page: The page to read
 *
 * This is the core of gfs2's readpage. It's used by the internal file
 * reading code as in that case we already hold the glock. Also it's
 * called by gfs2_readpage() once the required lock has been granted.
 */

static int __gfs2_readpage(void *file, struct page *page)
{
        struct gfs2_inode *ip = GFS2_I(page->mapping->host);
        struct gfs2_sbd *sdp = GFS2_SB(page->mapping->host);

        int error;

        if (i_blocksize(page->mapping->host) == PAGE_SIZE &&
            !page_has_buffers(page)) {
                error = iomap_readpage(page, &gfs2_iomap_ops);
        } else if (gfs2_is_stuffed(ip)) {
                error = stuffed_readpage(ip, page);
                unlock_page(page);
        } else {
                error = mpage_readpage(page, gfs2_block_map);
        }

        if (unlikely(gfs2_withdrawn(sdp)))
                return -EIO;

        return error;
}

/**
 * gfs2_readpage - read a page of a file
 * @file: The file to read
 * @page: The page of the file
 *
 * This deals with the locking required. We have to unlock and
 * relock the page in order to get the locking in the right
 * order.
 */

static int gfs2_readpage(struct file *file, struct page *page)
{
        struct address_space *mapping = page->mapping;
        struct gfs2_inode *ip = GFS2_I(mapping->host);
        struct gfs2_holder gh;
        int error;

        unlock_page(page);
        gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
        error = gfs2_glock_nq(&gh);
        if (unlikely(error))
                goto out;
        error = AOP_TRUNCATED_PAGE;
        lock_page(page);
        if (page->mapping == mapping && !PageUptodate(page))
                error = __gfs2_readpage(file, page);
        else
                unlock_page(page);
        gfs2_glock_dq(&gh);
out:
        gfs2_holder_uninit(&gh);
        if (error && error != AOP_TRUNCATED_PAGE)
                lock_page(page);
        return error;
}

/**
 * gfs2_internal_read - read an internal file
 * @ip: The gfs2 inode
 * @buf: The buffer to fill
 * @pos: The file position
 * @size: The amount to read
 *
 */

int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
                       unsigned size)
{
        struct address_space *mapping = ip->i_inode.i_mapping;
        unsigned long index = *pos / PAGE_SIZE;
        unsigned offset = *pos & (PAGE_SIZE - 1);
        unsigned copied = 0;
        unsigned amt;
        struct page *page;
        void *p;

        do {
                amt = size - copied;
                if (offset + size > PAGE_SIZE)
                        amt = PAGE_SIZE - offset;
                page = read_cache_page(mapping, index, __gfs2_readpage, NULL);
                if (IS_ERR(page))
                        return PTR_ERR(page);
                p = kmap_atomic(page);
                memcpy(buf + copied, p + offset, amt);
                kunmap_atomic(p);
                put_page(page);
                copied += amt;
                index++;
                offset = 0;
        } while(copied < size);
        (*pos) += size;
        return size;
}

/**
 * gfs2_readpages - Read a bunch of pages at once
 * @file: The file to read from
 * @mapping: Address space info
 * @pages: List of pages to read
 * @nr_pages: Number of pages to read
 *
 * Some notes:
 * 1. This is only for readahead, so we can simply ignore any things
 *    which are slightly inconvenient (such as locking conflicts between
 *    the page lock and the glock) and return having done no I/O. Its
 *    obviously not something we'd want to do on too regular a basis.
 *    Any I/O we ignore at this time will be done via readpage later.
 * 2. We don't handle stuffed files here we let readpage do the honours.
 * 3. mpage_readpages() does most of the heavy lifting in the common case.
 * 4. gfs2_block_map() is relied upon to set BH_Boundary in the right places.
 */

static int gfs2_readpages(struct file *file, struct address_space *mapping,
                          struct list_head *pages, unsigned nr_pages)
{
        struct inode *inode = mapping->host;
        struct gfs2_inode *ip = GFS2_I(inode);
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        struct gfs2_holder gh;
        int ret;

        gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
        ret = gfs2_glock_nq(&gh);
        if (unlikely(ret))
                goto out_uninit;
        if (!gfs2_is_stuffed(ip))
                ret = mpage_readpages(mapping, pages, nr_pages, gfs2_block_map);
        gfs2_glock_dq(&gh);
out_uninit:
        gfs2_holder_uninit(&gh);
        if (unlikely(gfs2_withdrawn(sdp)))
                ret = -EIO;
        return ret;
}

/**
 * adjust_fs_space - Adjusts the free space available due to gfs2_grow
 * @inode: the rindex inode
 */
void adjust_fs_space(struct inode *inode)
{
        struct gfs2_sbd *sdp = GFS2_SB(inode);
        struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
        struct gfs2_inode *l_ip = GFS2_I(sdp->sd_sc_inode);
        struct gfs2_statfs_change_host *m_sc = &sdp->sd_statfs_master;
        struct gfs2_statfs_change_host *l_sc = &sdp->sd_statfs_local;
        struct buffer_head *m_bh, *l_bh;
        u64 fs_total, new_free;

        if (gfs2_trans_begin(sdp, 2 * RES_STATFS, 0) != 0)
                return;

        /* Total up the file system space, according to the latest rindex. */
        fs_total = gfs2_ri_total(sdp);
        if (gfs2_meta_inode_buffer(m_ip, &m_bh) != 0)
                goto out;

        spin_lock(&sdp->sd_statfs_spin);
        gfs2_statfs_change_in(m_sc, m_bh->b_data +
                              sizeof(struct gfs2_dinode));
        if (fs_total > (m_sc->sc_total + l_sc->sc_total))
                new_free = fs_total - (m_sc->sc_total + l_sc->sc_total);
        else
                new_free = 0;
        spin_unlock(&sdp->sd_statfs_spin);
        fs_warn(sdp, "File system extended by %llu blocks.\n",
                (unsigned long long)new_free);
        gfs2_statfs_change(sdp, new_free, new_free, 0);

        if (gfs2_meta_inode_buffer(l_ip, &l_bh) != 0)
                goto out2;
        update_statfs(sdp, m_bh, l_bh);
        brelse(l_bh);
out2:
        brelse(m_bh);
out:
        sdp->sd_rindex_uptodate = 0;
        gfs2_trans_end(sdp);
}

/**
 * gfs2_stuffed_write_end - Write end for stuffed files
 * @inode: The inode
 * @dibh: The buffer_head containing the on-disk inode
 * @pos: The file position
 * @copied: How much was actually copied by the VFS
 * @page: The page
 *
 * This copies the data from the page into the inode block after
 * the inode data structure itself.
 *
 * Returns: copied bytes or errno
 */
int gfs2_stuffed_write_end(struct inode *inode, struct buffer_head *dibh,
                           loff_t pos, unsigned copied,
                           struct page *page)
{
        struct gfs2_inode *ip = GFS2_I(inode);
        u64 to = pos + copied;
        void *kaddr;
        unsigned char *buf = dibh->b_data + sizeof(struct gfs2_dinode);

        BUG_ON(pos + copied > gfs2_max_stuffed_size(ip));

        kaddr = kmap_atomic(page);
        memcpy(buf + pos, kaddr + pos, copied);
        flush_dcache_page(page);
        kunmap_atomic(kaddr);

        WARN_ON(!PageUptodate(page));
        unlock_page(page);
        put_page(page);

        if (copied) {
                if (inode->i_size < to)
                        i_size_write(inode, to);
                mark_inode_dirty(inode);
        }
        return copied;
}

/**
 * jdata_set_page_dirty - Page dirtying function
 * @page: The page to dirty
 *
 * Returns: 1 if it dirtyed the page, or 0 otherwise
 */
 
static int jdata_set_page_dirty(struct page *page)
{
        SetPageChecked(page);
        return __set_page_dirty_buffers(page);
}

/**
 * gfs2_bmap - Block map function
 * @mapping: Address space info
 * @lblock: The block to map
 *
 * Returns: The disk address for the block or 0 on hole or error
 */

static sector_t gfs2_bmap(struct address_space *mapping, sector_t lblock)
{
        struct gfs2_inode *ip = GFS2_I(mapping->host);
        struct gfs2_holder i_gh;
        sector_t dblock = 0;
        int error;

        error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
        if (error)
                return 0;

        if (!gfs2_is_stuffed(ip))
                dblock = generic_block_bmap(mapping, lblock, gfs2_block_map);

        gfs2_glock_dq_uninit(&i_gh);

        return dblock;
}

static void gfs2_discard(struct gfs2_sbd *sdp, struct buffer_head *bh)
{
        struct gfs2_bufdata *bd;

        lock_buffer(bh);
        gfs2_log_lock(sdp);
        clear_buffer_dirty(bh);
        bd = bh->b_private;
        if (bd) {
                if (!list_empty(&bd->bd_list) && !buffer_pinned(bh))
                        list_del_init(&bd->bd_list);
                else
                        gfs2_remove_from_journal(bh, REMOVE_JDATA);
        }
        bh->b_bdev = NULL;
        clear_buffer_mapped(bh);
        clear_buffer_req(bh);
        clear_buffer_new(bh);
        gfs2_log_unlock(sdp);
        unlock_buffer(bh);
}

static void gfs2_invalidatepage(struct page *page, unsigned int offset,
                                unsigned int length)
{
        struct gfs2_sbd *sdp = GFS2_SB(page->mapping->host);
        unsigned int stop = offset + length;
        int partial_page = (offset || length < PAGE_SIZE);
        struct buffer_head *bh, *head;
        unsigned long pos = 0;

        BUG_ON(!PageLocked(page));
        if (!partial_page)
                ClearPageChecked(page);
        if (!page_has_buffers(page))
                goto out;

        bh = head = page_buffers(page);
        do {
                if (pos + bh->b_size > stop)
                        return;

                if (offset <= pos)
                        gfs2_discard(sdp, bh);
                pos += bh->b_size;
                bh = bh->b_this_page;
        } while (bh != head);
out:
        if (!partial_page)
                try_to_release_page(page, 0);
}

/**
 * gfs2_releasepage - free the metadata associated with a page
 * @page: the page that's being released
 * @gfp_mask: passed from Linux VFS, ignored by us
 *
 * Call try_to_free_buffers() if the buffers in this page can be
 * released.
 *
 * Returns: 0
 */

int gfs2_releasepage(struct page *page, gfp_t gfp_mask)
{
        struct address_space *mapping = page->mapping;
        struct gfs2_sbd *sdp = gfs2_mapping2sbd(mapping);
        struct buffer_head *bh, *head;
        struct gfs2_bufdata *bd;

        if (!page_has_buffers(page))
                return 0;

        /*
         * From xfs_vm_releasepage: mm accommodates an old ext3 case where
         * clean pages might not have had the dirty bit cleared.  Thus, it can
         * send actual dirty pages to ->releasepage() via shrink_active_list().
         *
         * As a workaround, we skip pages that contain dirty buffers below.
         * Once ->releasepage isn't called on dirty pages anymore, we can warn
         * on dirty buffers like we used to here again.
         */

        gfs2_log_lock(sdp);
        spin_lock(&sdp->sd_ail_lock);
        head = bh = page_buffers(page);
        do {
                if (atomic_read(&bh->b_count))
                        goto cannot_release;
                bd = bh->b_private;
                if (bd && bd->bd_tr)
                        goto cannot_release;
                if (buffer_dirty(bh) || WARN_ON(buffer_pinned(bh)))
                        goto cannot_release;
                bh = bh->b_this_page;
        } while(bh != head);
        spin_unlock(&sdp->sd_ail_lock);

        head = bh = page_buffers(page);
        do {
                bd = bh->b_private;
                if (bd) {
                        gfs2_assert_warn(sdp, bd->bd_bh == bh);
                        bd->bd_bh = NULL;
                        bh->b_private = NULL;
                        /*
                         * The bd may still be queued as a revoke, in which
                         * case we must not dequeue nor free it.
                         */
                        if (!bd->bd_blkno && !list_empty(&bd->bd_list))
                                list_del_init(&bd->bd_list);
                        if (list_empty(&bd->bd_list))
                                kmem_cache_free(gfs2_bufdata_cachep, bd);
                }

                bh = bh->b_this_page;
        } while (bh != head);
        gfs2_log_unlock(sdp);

        return try_to_free_buffers(page);

cannot_release:
        spin_unlock(&sdp->sd_ail_lock);
        gfs2_log_unlock(sdp);
        return 0;
}

static const struct address_space_operations gfs2_writeback_aops = {
        .writepage = gfs2_writepage,
        .writepages = gfs2_writepages,
        .readpage = gfs2_readpage,
        .readpages = gfs2_readpages,
        .bmap = gfs2_bmap,
        .invalidatepage = gfs2_invalidatepage,
        .releasepage = gfs2_releasepage,
        .direct_IO = noop_direct_IO,
        .migratepage = buffer_migrate_page,
        .is_partially_uptodate = block_is_partially_uptodate,
        .error_remove_page = generic_error_remove_page,
};

static const struct address_space_operations gfs2_ordered_aops = {
        .writepage = gfs2_writepage,
        .writepages = gfs2_writepages,
        .readpage = gfs2_readpage,
        .readpages = gfs2_readpages,
        .set_page_dirty = __set_page_dirty_buffers,
        .bmap = gfs2_bmap,
        .invalidatepage = gfs2_invalidatepage,
        .releasepage = gfs2_releasepage,
        .direct_IO = noop_direct_IO,
        .migratepage = buffer_migrate_page,
        .is_partially_uptodate = block_is_partially_uptodate,
        .error_remove_page = generic_error_remove_page,
};

static const struct address_space_operations gfs2_jdata_aops = {
        .writepage = gfs2_jdata_writepage,
        .writepages = gfs2_jdata_writepages,
        .readpage = gfs2_readpage,
        .readpages = gfs2_readpages,
        .set_page_dirty = jdata_set_page_dirty,
        .bmap = gfs2_bmap,
        .invalidatepage = gfs2_invalidatepage,
        .releasepage = gfs2_releasepage,
        .is_partially_uptodate = block_is_partially_uptodate,
        .error_remove_page = generic_error_remove_page,
};

void gfs2_set_aops(struct inode *inode)
{
        struct gfs2_inode *ip = GFS2_I(inode);

        if (gfs2_is_writeback(ip))
                inode->i_mapping->a_ops = &gfs2_writeback_aops;
        else if (gfs2_is_ordered(ip))
                inode->i_mapping->a_ops = &gfs2_ordered_aops;
        else if (gfs2_is_jdata(ip))
                inode->i_mapping->a_ops = &gfs2_jdata_aops;
        else
                BUG();
}