text: /*
   *   Copyright (C) International Business Machines Corp., 2000-2005
   *   Portions Copyright (C) Christoph Hellwig, 2001-2002
   *
   *   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 02111-1307 USA
   */
  
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/bio.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/buffer_head.h>
  #include <linux/mempool.h>
  #include <linux/seq_file.h>
  #include "jfs_incore.h"
  #include "jfs_superblock.h"
  #include "jfs_filsys.h"
  #include "jfs_metapage.h"
  #include "jfs_txnmgr.h"
  #include "jfs_debug.h"
  
  #ifdef CONFIG_JFS_STATISTICS
  static struct {
  	uint	pagealloc;	/* # of page allocations */
  	uint	pagefree;	/* # of page frees */
  	uint	lockwait;	/* # of sleeping lock_metapage() calls */
  } mpStat;
  #endif
  
  #define metapage_locked(mp) test_bit(META_locked, &(mp)->flag)
  #define trylock_metapage(mp) test_and_set_bit_lock(META_locked, &(mp)->flag)
  
  static inline void unlock_metapage(struct metapage *mp)
  {
  	clear_bit_unlock(META_locked, &mp->flag);
  	wake_up(&mp->wait);
  }
  
  static inline void __lock_metapage(struct metapage *mp)
  {
  	DECLARE_WAITQUEUE(wait, current);
  	INCREMENT(mpStat.lockwait);
  	add_wait_queue_exclusive(&mp->wait, &wait);
  	do {
  		set_current_state(TASK_UNINTERRUPTIBLE);
  		if (metapage_locked(mp)) {
  			unlock_page(mp->page);
  			io_schedule();
  			lock_page(mp->page);
  		}
  	} while (trylock_metapage(mp));
  	__set_current_state(TASK_RUNNING);
  	remove_wait_queue(&mp->wait, &wait);
  }
  
  /*
   * Must have mp->page locked
   */
  static inline void lock_metapage(struct metapage *mp)
  {
  	if (trylock_metapage(mp))
  		__lock_metapage(mp);
  }
  
  #define METAPOOL_MIN_PAGES 32
  static struct kmem_cache *metapage_cache;
  static mempool_t *metapage_mempool;
  
  #define MPS_PER_PAGE (PAGE_SIZE >> L2PSIZE)
  
  #if MPS_PER_PAGE > 1
  
  struct meta_anchor {
  	int mp_count;
  	atomic_t io_count;
  	struct metapage *mp[MPS_PER_PAGE];
  };
  #define mp_anchor(page) ((struct meta_anchor *)page_private(page))
  
  static inline struct metapage *page_to_mp(struct page *page, int offset)
  {
  	if (!PagePrivate(page))
  		return NULL;
  	return mp_anchor(page)->mp[offset >> L2PSIZE];
  }
  
  static inline int insert_metapage(struct page *page, struct metapage *mp)
  {
  	struct meta_anchor *a;
  	int index;
  	int l2mp_blocks;	/* log2 blocks per metapage */
  
  	if (PagePrivate(page))
  		a = mp_anchor(page);
  	else {
  		a = kzalloc(sizeof(struct meta_anchor), GFP_NOFS);
  		if (!a)
  			return -ENOMEM;
  		set_page_private(page, (unsigned long)a);
  		SetPagePrivate(page);
  		kmap(page);
  	}
  
  	if (mp) {
  		l2mp_blocks = L2PSIZE - page->mapping->host->i_blkbits;
  		index = (mp->index >> l2mp_blocks) & (MPS_PER_PAGE - 1);
  		a->mp_count++;
  		a->mp[index] = mp;
  	}
  
  	return 0;
  }
  
  static inline void remove_metapage(struct page *page, struct metapage *mp)
  {
  	struct meta_anchor *a = mp_anchor(page);
  	int l2mp_blocks = L2PSIZE - page->mapping->host->i_blkbits;
  	int index;
  
  	index = (mp->index >> l2mp_blocks) & (MPS_PER_PAGE - 1);
  
  	BUG_ON(a->mp[index] != mp);
  
  	a->mp[index] = NULL;
  	if (--a->mp_count == 0) {
  		kfree(a);
  		set_page_private(page, 0);
  		ClearPagePrivate(page);
  		kunmap(page);
  	}
  }
  
  static inline void inc_io(struct page *page)
  {
  	atomic_inc(&mp_anchor(page)->io_count);
  }
  
  static inline void dec_io(struct page *page, void (*handler) (struct page *))
  {
  	if (atomic_dec_and_test(&mp_anchor(page)->io_count))
  		handler(page);
  }
  
  #else
  static inline struct metapage *page_to_mp(struct page *page, int offset)
  {
  	return PagePrivate(page) ? (struct metapage *)page_private(page) : NULL;
  }
  
  static inline int insert_metapage(struct page *page, struct metapage *mp)
  {
  	if (mp) {
  		set_page_private(page, (unsigned long)mp);
  		SetPagePrivate(page);
  		kmap(page);
  	}
  	return 0;
  }
  
  static inline void remove_metapage(struct page *page, struct metapage *mp)
  {
  	set_page_private(page, 0);
  	ClearPagePrivate(page);
  	kunmap(page);
  }
  
  #define inc_io(page) do {} while(0)
  #define dec_io(page, handler) handler(page)
  
  #endif
  
  static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
  {
  	struct metapage *mp = mempool_alloc(metapage_mempool, gfp_mask);
  
  	if (mp) {
  		mp->lid = 0;
  		mp->lsn = 0;
  		mp->data = NULL;
  		mp->clsn = 0;
  		mp->log = NULL;
  		init_waitqueue_head(&mp->wait);
  	}
  	return mp;
  }
  
  static inline void free_metapage(struct metapage *mp)
  {
  	mempool_free(mp, metapage_mempool);
  }
  
  int __init metapage_init(void)
  {
  	/*
  	 * Allocate the metapage structures
  	 */
  	metapage_cache = kmem_cache_create("jfs_mp", sizeof(struct metapage),
  					   0, 0, NULL);
  	if (metapage_cache == NULL)
  		return -ENOMEM;
  
  	metapage_mempool = mempool_create_slab_pool(METAPOOL_MIN_PAGES,
  						    metapage_cache);
  
  	if (metapage_mempool == NULL) {
  		kmem_cache_destroy(metapage_cache);
  		return -ENOMEM;
  	}
  
  	return 0;
  }
  
  void metapage_exit(void)
  {
  	mempool_destroy(metapage_mempool);
  	kmem_cache_destroy(metapage_cache);
  }
  
  static inline void drop_metapage(struct page *page, struct metapage *mp)
  {
  	if (mp->count || mp->nohomeok || test_bit(META_dirty, &mp->flag) ||
  	    test_bit(META_io, &mp->flag))
  		return;
  	remove_metapage(page, mp);
  	INCREMENT(mpStat.pagefree);
  	free_metapage(mp);
  }
  
  /*
   * Metapage address space operations
   */
  
  static sector_t metapage_get_blocks(struct inode *inode, sector_t lblock,
  				    int *len)
  {
  	int rc = 0;
  	int xflag;
  	s64 xaddr;
  	sector_t file_blocks = (inode->i_size + inode->i_sb->s_blocksize - 1) >>
  			       inode->i_blkbits;
  
  	if (lblock >= file_blocks)
  		return 0;
  	if (lblock + *len > file_blocks)
  		*len = file_blocks - lblock;
  
  	if (inode->i_ino) {
  		rc = xtLookup(inode, (s64)lblock, *len, &xflag, &xaddr, len, 0);
  		if ((rc == 0) && *len)
  			lblock = (sector_t)xaddr;
  		else
  			lblock = 0;
  	} /* else no mapping */
  
  	return lblock;
  }
  
  static void last_read_complete(struct page *page)
  {
  	if (!PageError(page))
  		SetPageUptodate(page);
  	unlock_page(page);
  }
  
  static void metapage_read_end_io(struct bio *bio)
  {
  	struct page *page = bio->bi_private;
  
  	if (bio->bi_status) {
  		printk(KERN_ERR "metapage_read_end_io: I/O error\n");
  		SetPageError(page);
  	}
  
  	dec_io(page, last_read_complete);
  	bio_put(bio);
  }
  
  static void remove_from_logsync(struct metapage *mp)
  {
  	struct jfs_log *log = mp->log;
  	unsigned long flags;
  /*
   * This can race.  Recheck that log hasn't been set to null, and after
   * acquiring logsync lock, recheck lsn
   */
  	if (!log)
  		return;
  
  	LOGSYNC_LOCK(log, flags);
  	if (mp->lsn) {
  		mp->log = NULL;
  		mp->lsn = 0;
  		mp->clsn = 0;
  		log->count--;
  		list_del(&mp->synclist);
  	}
  	LOGSYNC_UNLOCK(log, flags);
  }
  
  static void last_write_complete(struct page *page)
  {
  	struct metapage *mp;
  	unsigned int offset;
  
  	for (offset = 0; offset < PAGE_SIZE; offset += PSIZE) {
  		mp = page_to_mp(page, offset);
  		if (mp && test_bit(META_io, &mp->flag)) {
  			if (mp->lsn)
  				remove_from_logsync(mp);
  			clear_bit(META_io, &mp->flag);
  		}
  		/*
  		 * I'd like to call drop_metapage here, but I don't think it's
  		 * safe unless I have the page locked
  		 */
  	}
  	end_page_writeback(page);
  }
  
  static void metapage_write_end_io(struct bio *bio)
  {
  	struct page *page = bio->bi_private;
  
  	BUG_ON(!PagePrivate(page));
  
  	if (bio->bi_status) {
  		printk(KERN_ERR "metapage_write_end_io: I/O error\n");
  		SetPageError(page);
  	}
  	dec_io(page, last_write_complete);
  	bio_put(bio);
  }
  
  static int metapage_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct bio *bio = NULL;
  	int block_offset;	/* block offset of mp within page */
  	struct inode *inode = page->mapping->host;
  	int blocks_per_mp = JFS_SBI(inode->i_sb)->nbperpage;
  	int len;
  	int xlen;
  	struct metapage *mp;
  	int redirty = 0;
  	sector_t lblock;
  	int nr_underway = 0;
  	sector_t pblock;
  	sector_t next_block = 0;
  	sector_t page_start;
  	unsigned long bio_bytes = 0;
  	unsigned long bio_offset = 0;
  	int offset;
  	int bad_blocks = 0;
  
  	page_start = (sector_t)page->index <<
  		     (PAGE_SHIFT - inode->i_blkbits);
  	BUG_ON(!PageLocked(page));
  	BUG_ON(PageWriteback(page));
  	set_page_writeback(page);
  
  	for (offset = 0; offset < PAGE_SIZE; offset += PSIZE) {
  		mp = page_to_mp(page, offset);
  
  		if (!mp || !test_bit(META_dirty, &mp->flag))
  			continue;
  
  		if (mp->nohomeok && !test_bit(META_forcewrite, &mp->flag)) {
  			redirty = 1;
  			/*
  			 * Make sure this page isn't blocked indefinitely.
  			 * If the journal isn't undergoing I/O, push it
  			 */
  			if (mp->log && !(mp->log->cflag & logGC_PAGEOUT))
  				jfs_flush_journal(mp->log, 0);
  			continue;
  		}
  
  		clear_bit(META_dirty, &mp->flag);
  		set_bit(META_io, &mp->flag);
  		block_offset = offset >> inode->i_blkbits;
  		lblock = page_start + block_offset;
  		if (bio) {
  			if (xlen && lblock == next_block) {
  				/* Contiguous, in memory & on disk */
  				len = min(xlen, blocks_per_mp);
  				xlen -= len;
  				bio_bytes += len << inode->i_blkbits;
  				continue;
  			}
  			/* Not contiguous */
  			if (bio_add_page(bio, page, bio_bytes, bio_offset) <
  			    bio_bytes)
  				goto add_failed;
  			/*
  			 * Increment counter before submitting i/o to keep
  			 * count from hitting zero before we're through
  			 */
  			inc_io(page);
  			if (!bio->bi_iter.bi_size)
  				goto dump_bio;
  			submit_bio(bio);
  			nr_underway++;
  			bio = NULL;
  		} else
  			inc_io(page);
  		xlen = (PAGE_SIZE - offset) >> inode->i_blkbits;
  		pblock = metapage_get_blocks(inode, lblock, &xlen);
  		if (!pblock) {
  			printk(KERN_ERR "JFS: metapage_get_blocks failed\n");
  			/*
  			 * We already called inc_io(), but can't cancel it
  			 * with dec_io() until we're done with the page
  			 */
  			bad_blocks++;
  			continue;
  		}
  		len = min(xlen, (int)JFS_SBI(inode->i_sb)->nbperpage);
  
  		bio = bio_alloc(GFP_NOFS, 1);
  		bio_set_dev(bio, inode->i_sb->s_bdev);
  		bio->bi_iter.bi_sector = pblock << (inode->i_blkbits - 9);
  		bio->bi_end_io = metapage_write_end_io;
  		bio->bi_private = page;
  		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
  
  		/* Don't call bio_add_page yet, we may add to this vec */
  		bio_offset = offset;
  		bio_bytes = len << inode->i_blkbits;
  
  		xlen -= len;
  		next_block = lblock + len;
  	}
  	if (bio) {
  		if (bio_add_page(bio, page, bio_bytes, bio_offset) < bio_bytes)
  				goto add_failed;
  		if (!bio->bi_iter.bi_size)
  			goto dump_bio;
  
  		submit_bio(bio);
  		nr_underway++;
  	}
  	if (redirty)
  		redirty_page_for_writepage(wbc, page);
  
  	unlock_page(page);
  
  	if (bad_blocks)
  		goto err_out;
  
  	if (nr_underway == 0)
  		end_page_writeback(page);
  
  	return 0;
  add_failed:
  	/* We should never reach here, since we're only adding one vec */
  	printk(KERN_ERR "JFS: bio_add_page failed unexpectedly\n");
  	goto skip;
  dump_bio:
  	print_hex_dump(KERN_ERR, "JFS: dump of bio: ", DUMP_PREFIX_ADDRESS, 16,
  		       4, bio, sizeof(*bio), 0);
  skip:
  	bio_put(bio);
  	unlock_page(page);
  	dec_io(page, last_write_complete);
  err_out:
  	while (bad_blocks--)
  		dec_io(page, last_write_complete);
  	return -EIO;
  }
  
  static int metapage_readpage(struct file *fp, struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	struct bio *bio = NULL;
  	int block_offset;
  	int blocks_per_page = PAGE_SIZE >> inode->i_blkbits;
  	sector_t page_start;	/* address of page in fs blocks */
  	sector_t pblock;
  	int xlen;
  	unsigned int len;
  	int offset;
  
  	BUG_ON(!PageLocked(page));
  	page_start = (sector_t)page->index <<
  		     (PAGE_SHIFT - inode->i_blkbits);
  
  	block_offset = 0;
  	while (block_offset < blocks_per_page) {
  		xlen = blocks_per_page - block_offset;
  		pblock = metapage_get_blocks(inode, page_start + block_offset,
  					     &xlen);
  		if (pblock) {
  			if (!PagePrivate(page))
  				insert_metapage(page, NULL);
  			inc_io(page);
  			if (bio)
  				submit_bio(bio);
  
  			bio = bio_alloc(GFP_NOFS, 1);
  			bio_set_dev(bio, inode->i_sb->s_bdev);
  			bio->bi_iter.bi_sector =
  				pblock << (inode->i_blkbits - 9);
  			bio->bi_end_io = metapage_read_end_io;
  			bio->bi_private = page;
  			bio_set_op_attrs(bio, REQ_OP_READ, 0);
  			len = xlen << inode->i_blkbits;
  			offset = block_offset << inode->i_blkbits;
  			if (bio_add_page(bio, page, len, offset) < len)
  				goto add_failed;
  			block_offset += xlen;
  		} else
  			block_offset++;
  	}
  	if (bio)
  		submit_bio(bio);
  	else
  		unlock_page(page);
  
  	return 0;
  
  add_failed:
  	printk(KERN_ERR "JFS: bio_add_page failed unexpectedly\n");
  	bio_put(bio);
  	dec_io(page, last_read_complete);
  	return -EIO;
  }
  
  static int metapage_releasepage(struct page *page, gfp_t gfp_mask)
  {
  	struct metapage *mp;
  	int ret = 1;
  	int offset;
  
  	for (offset = 0; offset < PAGE_SIZE; offset += PSIZE) {
  		mp = page_to_mp(page, offset);
  
  		if (!mp)
  			continue;
  
  		jfs_info("metapage_releasepage: mp = 0x%p", mp);
  		if (mp->count || mp->nohomeok ||
  		    test_bit(META_dirty, &mp->flag)) {
  			jfs_info("count = %ld, nohomeok = %d", mp->count,
  				 mp->nohomeok);
  			ret = 0;
  			continue;
  		}
  		if (mp->lsn)
  			remove_from_logsync(mp);
  		remove_metapage(page, mp);
  		INCREMENT(mpStat.pagefree);
  		free_metapage(mp);
  	}
  	return ret;
  }
  
  static void metapage_invalidatepage(struct page *page, unsigned int offset,
  				    unsigned int length)
  {
  	BUG_ON(offset || length < PAGE_SIZE);
  
  	BUG_ON(PageWriteback(page));
  
  	metapage_releasepage(page, 0);
  }
  
  const struct address_space_operations jfs_metapage_aops = {
  	.readpage	= metapage_readpage,
  	.writepage	= metapage_writepage,
  	.releasepage	= metapage_releasepage,
  	.invalidatepage	= metapage_invalidatepage,
  	.set_page_dirty	= __set_page_dirty_nobuffers,
  };
  
  struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
  				unsigned int size, int absolute,
  				unsigned long new)
  {
  	int l2BlocksPerPage;
  	int l2bsize;
  	struct address_space *mapping;
  	struct metapage *mp = NULL;
  	struct page *page;
  	unsigned long page_index;
  	unsigned long page_offset;
  
  	jfs_info("__get_metapage: ino = %ld, lblock = 0x%lx, abs=%d",
  		 inode->i_ino, lblock, absolute);
  
  	l2bsize = inode->i_blkbits;
  	l2BlocksPerPage = PAGE_SHIFT - l2bsize;
  	page_index = lblock >> l2BlocksPerPage;
  	page_offset = (lblock - (page_index << l2BlocksPerPage)) << l2bsize;
  	if ((page_offset + size) > PAGE_SIZE) {
  		jfs_err("MetaData crosses page boundary!!");
  		jfs_err("lblock = %lx, size  = %d", lblock, size);
  		dump_stack();
  		return NULL;
  	}
  	if (absolute)
  		mapping = JFS_SBI(inode->i_sb)->direct_inode->i_mapping;
  	else {
  		/*
  		 * If an nfs client tries to read an inode that is larger
  		 * than any existing inodes, we may try to read past the
  		 * end of the inode map
  		 */
  		if ((lblock << inode->i_blkbits) >= inode->i_size)
  			return NULL;
  		mapping = inode->i_mapping;
  	}
  
  	if (new && (PSIZE == PAGE_SIZE)) {
  		page = grab_cache_page(mapping, page_index);
  		if (!page) {
  			jfs_err("grab_cache_page failed!");
  			return NULL;
  		}
  		SetPageUptodate(page);
  	} else {
  		page = read_mapping_page(mapping, page_index, NULL);
  		if (IS_ERR(page) || !PageUptodate(page)) {
  			jfs_err("read_mapping_page failed!");
  			return NULL;
  		}
  		lock_page(page);
  	}
  
  	mp = page_to_mp(page, page_offset);
  	if (mp) {
  		if (mp->logical_size != size) {
  			jfs_error(inode->i_sb,
  				  "get_mp->logical_size != size\n");
  			jfs_err("logical_size = %d, size = %d",
  				mp->logical_size, size);
  			dump_stack();
  			goto unlock;
  		}
  		mp->count++;
  		lock_metapage(mp);
  		if (test_bit(META_discard, &mp->flag)) {
  			if (!new) {
  				jfs_error(inode->i_sb,
  					  "using a discarded metapage\n");
  				discard_metapage(mp);
  				goto unlock;
  			}
  			clear_bit(META_discard, &mp->flag);
  		}
  	} else {
  		INCREMENT(mpStat.pagealloc);
  		mp = alloc_metapage(GFP_NOFS);
  		if (!mp)
  			goto unlock;
  		mp->page = page;
  		mp->sb = inode->i_sb;
  		mp->flag = 0;
  		mp->xflag = COMMIT_PAGE;
  		mp->count = 1;
  		mp->nohomeok = 0;
  		mp->logical_size = size;
  		mp->data = page_address(page) + page_offset;
  		mp->index = lblock;
  		if (unlikely(insert_metapage(page, mp))) {
  			free_metapage(mp);
  			goto unlock;
  		}
  		lock_metapage(mp);
  	}
  
  	if (new) {
  		jfs_info("zeroing mp = 0x%p", mp);
  		memset(mp->data, 0, PSIZE);
  	}
  
  	unlock_page(page);
  	jfs_info("__get_metapage: returning = 0x%p data = 0x%p", mp, mp->data);
  	return mp;
  
  unlock:
  	unlock_page(page);
  	return NULL;
  }
  
  void grab_metapage(struct metapage * mp)
  {
  	jfs_info("grab_metapage: mp = 0x%p", mp);
  	get_page(mp->page);
  	lock_page(mp->page);
  	mp->count++;
  	lock_metapage(mp);
  	unlock_page(mp->page);
  }
  
  void force_metapage(struct metapage *mp)
  {
  	struct page *page = mp->page;
  	jfs_info("force_metapage: mp = 0x%p", mp);
  	set_bit(META_forcewrite, &mp->flag);
  	clear_bit(META_sync, &mp->flag);
  	get_page(page);
  	lock_page(page);
  	set_page_dirty(page);
  	if (write_one_page(page))
  		jfs_error(mp->sb, "write_one_page() failed\n");
  	clear_bit(META_forcewrite, &mp->flag);
  	put_page(page);
  }
  
  void hold_metapage(struct metapage *mp)
  {
  	lock_page(mp->page);
  }
  
  void put_metapage(struct metapage *mp)
  {
  	if (mp->count || mp->nohomeok) {
  		/* Someone else will release this */
  		unlock_page(mp->page);
  		return;
  	}
  	get_page(mp->page);
  	mp->count++;
  	lock_metapage(mp);
  	unlock_page(mp->page);
  	release_metapage(mp);
  }
  
  void release_metapage(struct metapage * mp)
  {
  	struct page *page = mp->page;
  	jfs_info("release_metapage: mp = 0x%p, flag = 0x%lx", mp, mp->flag);
  
  	BUG_ON(!page);
  
  	lock_page(page);
  	unlock_metapage(mp);
  
  	assert(mp->count);
  	if (--mp->count || mp->nohomeok) {
  		unlock_page(page);
  		put_page(page);
  		return;
  	}
  
  	if (test_bit(META_dirty, &mp->flag)) {
  		set_page_dirty(page);
  		if (test_bit(META_sync, &mp->flag)) {
  			clear_bit(META_sync, &mp->flag);
  			if (write_one_page(page))
  				jfs_error(mp->sb, "write_one_page() failed\n");
  			lock_page(page); /* write_one_page unlocks the page */
  		}
  	} else if (mp->lsn)	/* discard_metapage doesn't remove it */
  		remove_from_logsync(mp);
  
  	/* Try to keep metapages from using up too much memory */
  	drop_metapage(page, mp);
  
  	unlock_page(page);
  	put_page(page);
  }
  
  void __invalidate_metapages(struct inode *ip, s64 addr, int len)
  {
  	sector_t lblock;
  	int l2BlocksPerPage = PAGE_SHIFT - ip->i_blkbits;
  	int BlocksPerPage = 1 << l2BlocksPerPage;
  	/* All callers are interested in block device's mapping */
  	struct address_space *mapping =
  		JFS_SBI(ip->i_sb)->direct_inode->i_mapping;
  	struct metapage *mp;
  	struct page *page;
  	unsigned int offset;
  
  	/*
  	 * Mark metapages to discard.  They will eventually be
  	 * released, but should not be written.
  	 */
  	for (lblock = addr & ~(BlocksPerPage - 1); lblock < addr + len;
  	     lblock += BlocksPerPage) {
  		page = find_lock_page(mapping, lblock >> l2BlocksPerPage);
  		if (!page)
  			continue;
  		for (offset = 0; offset < PAGE_SIZE; offset += PSIZE) {
  			mp = page_to_mp(page, offset);
  			if (!mp)
  				continue;
  			if (mp->index < addr)
  				continue;
  			if (mp->index >= addr + len)
  				break;
  
  			clear_bit(META_dirty, &mp->flag);
  			set_bit(META_discard, &mp->flag);
  			if (mp->lsn)
  				remove_from_logsync(mp);
  		}
  		unlock_page(page);
  		put_page(page);
  	}
  }
  
  #ifdef CONFIG_JFS_STATISTICS
  static int jfs_mpstat_proc_show(struct seq_file *m, void *v)
  {
  	seq_printf(m,
  		       "JFS Metapage statistics\n"
  		       "=======================\n"
  		       "page allocations = %d\n"
  		       "page frees = %d\n"
  		       "lock waits = %d\n",
  		       mpStat.pagealloc,
  		       mpStat.pagefree,
  		       mpStat.lockwait);
  	return 0;
  }
  
  static int jfs_mpstat_proc_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, jfs_mpstat_proc_show, NULL);
  }
  
  const struct file_operations jfs_mpstat_proc_fops = {
  	.open		= jfs_mpstat_proc_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= single_release,
  };
  #endif
  