OpenCloudOS-Kernel/fs/gfs2/aops.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
 * Copyright (C) 2004-2008 Red Hat, Inc.  All rights reserved.
 */

#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;
	xa_mark_t 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(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
		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(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
		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
 *
 * Calls try_to_free_buffers() to free the buffers and put the page if the
 * buffers can be released.
 *
 * Returns: 1 if the page was put or else 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);
			if (!list_empty(&bd->bd_list))
				list_del_init(&bd->bd_list);
			bd->bd_bh = NULL;
			bh->b_private = NULL;
			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);
	struct gfs2_sbd *sdp = GFS2_SB(inode);

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