fs/nilfs2/mdt.c - linux - Git at Google

 /*
  * mdt.c - meta data file for NILFS
  *
  * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
  *
  * 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.
  *
  * Written by Ryusuke Konishi.
  */

 #include <linux/buffer_head.h>
 #include <linux/mpage.h>
 #include <linux/mm.h>
 #include <linux/writeback.h>
 #include <linux/backing-dev.h>
 #include <linux/swap.h>
 #include <linux/slab.h>
 #include "nilfs.h"
 #include "btnode.h"
 #include "segment.h"
 #include "page.h"
 #include "mdt.h"

 #include <trace/events/nilfs2.h>

 #define NILFS_MDT_MAX_RA_BLOCKS		(16 - 1)


 static int
 nilfs_mdt_insert_new_block(struct inode *inode, unsigned long block,
 			   struct buffer_head *bh,
 			   void (*init_block)(struct inode *,
 					      struct buffer_head *, void *))
 {
 	struct nilfs_inode_info *ii = NILFS_I(inode);
 	void *kaddr;
 	int ret;

 	/* Caller exclude read accesses using page lock */

 	/* set_buffer_new(bh); */
 	bh->b_blocknr = 0;

 	ret = nilfs_bmap_insert(ii->i_bmap, block, (unsigned long)bh);
 	if (unlikely(ret))
 		return ret;

 	set_buffer_mapped(bh);

 	kaddr = kmap_atomic(bh->b_page);
 	memset(kaddr + bh_offset(bh), 0, 1 << inode->i_blkbits);
 	if (init_block)
 		init_block(inode, bh, kaddr);
 	flush_dcache_page(bh->b_page);
 	kunmap_atomic(kaddr);

 	set_buffer_uptodate(bh);
 	mark_buffer_dirty(bh);
 	nilfs_mdt_mark_dirty(inode);

 	trace_nilfs2_mdt_insert_new_block(inode, inode->i_ino, block);

 	return 0;
 }

 static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
 				  struct buffer_head **out_bh,
 				  void (*init_block)(struct inode *,
 						     struct buffer_head *,
 						     void *))
 {
 	struct super_block *sb = inode->i_sb;
 	struct nilfs_transaction_info ti;
 	struct buffer_head *bh;
 	int err;

 	nilfs_transaction_begin(sb, &ti, 0);

 	err = -ENOMEM;
 	bh = nilfs_grab_buffer(inode, inode->i_mapping, block, 0);
 	if (unlikely(!bh))
 		goto failed_unlock;

 	err = -EEXIST;
 	if (buffer_uptodate(bh))
 		goto failed_bh;

 	wait_on_buffer(bh);
 	if (buffer_uptodate(bh))
 		goto failed_bh;

 	bh->b_bdev = sb->s_bdev;
 	err = nilfs_mdt_insert_new_block(inode, block, bh, init_block);
 	if (likely(!err)) {
 		get_bh(bh);
 		*out_bh = bh;
 	}

  failed_bh:
 	unlock_page(bh->b_page);
 	put_page(bh->b_page);
 	brelse(bh);

  failed_unlock:
 	if (likely(!err))
 		err = nilfs_transaction_commit(sb);
 	else
 		nilfs_transaction_abort(sb);

 	return err;
 }

 static int
 nilfs_mdt_submit_block(struct inode *inode, unsigned long blkoff,
 		       int mode, struct buffer_head **out_bh)
 {
 	struct buffer_head *bh;
 	__u64 blknum = 0;
 	int ret = -ENOMEM;

 	bh = nilfs_grab_buffer(inode, inode->i_mapping, blkoff, 0);
 	if (unlikely(!bh))
 		goto failed;

 	ret = -EEXIST; /* internal code */
 	if (buffer_uptodate(bh))
 		goto out;

 	if (mode == READA) {
 		if (!trylock_buffer(bh)) {
 			ret = -EBUSY;
 			goto failed_bh;
 		}
 	} else /* mode == READ */
 		lock_buffer(bh);

 	if (buffer_uptodate(bh)) {
 		unlock_buffer(bh);
 		goto out;
 	}

 	ret = nilfs_bmap_lookup(NILFS_I(inode)->i_bmap, blkoff, &blknum);
 	if (unlikely(ret)) {
 		unlock_buffer(bh);
 		goto failed_bh;
 	}
 	map_bh(bh, inode->i_sb, (sector_t)blknum);

 	bh->b_end_io = end_buffer_read_sync;
 	get_bh(bh);
 	submit_bh(mode, bh);
 	ret = 0;

 	trace_nilfs2_mdt_submit_block(inode, inode->i_ino, blkoff, mode);
  out:
 	get_bh(bh);
 	*out_bh = bh;

  failed_bh:
 	unlock_page(bh->b_page);
 	put_page(bh->b_page);
 	brelse(bh);
  failed:
 	return ret;
 }

 static int nilfs_mdt_read_block(struct inode *inode, unsigned long block,
 				int readahead, struct buffer_head **out_bh)
 {
 	struct buffer_head *first_bh, *bh;
 	unsigned long blkoff;
 	int i, nr_ra_blocks = NILFS_MDT_MAX_RA_BLOCKS;
 	int err;

 	err = nilfs_mdt_submit_block(inode, block, READ, &first_bh);
 	if (err == -EEXIST) /* internal code */
 		goto out;

 	if (unlikely(err))
 		goto failed;

 	if (readahead) {
 		blkoff = block + 1;
 		for (i = 0; i < nr_ra_blocks; i++, blkoff++) {
 			err = nilfs_mdt_submit_block(inode, blkoff, READA, &bh);
 			if (likely(!err || err == -EEXIST))
 				brelse(bh);
 			else if (err != -EBUSY)
 				break;
 				/* abort readahead if bmap lookup failed */
 			if (!buffer_locked(first_bh))
 				goto out_no_wait;
 		}
 	}

 	wait_on_buffer(first_bh);

  out_no_wait:
 	err = -EIO;
 	if (!buffer_uptodate(first_bh))
 		goto failed_bh;
  out:
 	*out_bh = first_bh;
 	return 0;

  failed_bh:
 	brelse(first_bh);
  failed:
 	return err;
 }

 /**
  * nilfs_mdt_get_block - read or create a buffer on meta data file.
  * @inode: inode of the meta data file
  * @blkoff: block offset
  * @create: create flag
  * @init_block: initializer used for newly allocated block
  * @out_bh: output of a pointer to the buffer_head
  *
  * nilfs_mdt_get_block() looks up the specified buffer and tries to create
  * a new buffer if @create is not zero.  On success, the returned buffer is
  * assured to be either existing or formatted using a buffer lock on success.
  * @out_bh is substituted only when zero is returned.
  *
  * Return Value: On success, it returns 0. On error, the following negative
  * error code is returned.
  *
  * %-ENOMEM - Insufficient memory available.
  *
  * %-EIO - I/O error
  *
  * %-ENOENT - the specified block does not exist (hole block)
  *
  * %-EROFS - Read only filesystem (for create mode)
  */
 int nilfs_mdt_get_block(struct inode *inode, unsigned long blkoff, int create,
 			void (*init_block)(struct inode *,
 					   struct buffer_head *, void *),
 			struct buffer_head **out_bh)
 {
 	int ret;

 	/* Should be rewritten with merging nilfs_mdt_read_block() */
  retry:
 	ret = nilfs_mdt_read_block(inode, blkoff, !create, out_bh);
 	if (!create || ret != -ENOENT)
 		return ret;

 	ret = nilfs_mdt_create_block(inode, blkoff, out_bh, init_block);
 	if (unlikely(ret == -EEXIST)) {
 		/* create = 0; */  /* limit read-create loop retries */
 		goto retry;
 	}
 	return ret;
 }

 /**
  * nilfs_mdt_find_block - find and get a buffer on meta data file.
  * @inode: inode of the meta data file
  * @start: start block offset (inclusive)
  * @end: end block offset (inclusive)
  * @blkoff: block offset
  * @out_bh: place to store a pointer to buffer_head struct
  *
  * nilfs_mdt_find_block() looks up an existing block in range of
  * [@start, @end] and stores pointer to a buffer head of the block to
  * @out_bh, and block offset to @blkoff, respectively.  @out_bh and
  * @blkoff are substituted only when zero is returned.
  *
  * Return Value: On success, it returns 0. On error, the following negative
  * error code is returned.
  *
  * %-ENOMEM - Insufficient memory available.
  *
  * %-EIO - I/O error
  *
  * %-ENOENT - no block was found in the range
  */
 int nilfs_mdt_find_block(struct inode *inode, unsigned long start,
 			 unsigned long end, unsigned long *blkoff,
 			 struct buffer_head **out_bh)
 {
 	__u64 next;
 	int ret;

 	if (unlikely(start > end))
 		return -ENOENT;

 	ret = nilfs_mdt_read_block(inode, start, true, out_bh);
 	if (!ret) {
 		*blkoff = start;
 		goto out;
 	}
 	if (unlikely(ret != -ENOENT || start == ULONG_MAX))
 		goto out;

 	ret = nilfs_bmap_seek_key(NILFS_I(inode)->i_bmap, start + 1, &next);
 	if (!ret) {
 		if (next <= end) {
 			ret = nilfs_mdt_read_block(inode, next, true, out_bh);
 			if (!ret)
 				*blkoff = next;
 		} else {
 			ret = -ENOENT;
 		}
 	}
 out:
 	return ret;
 }

 /**
  * nilfs_mdt_delete_block - make a hole on the meta data file.
  * @inode: inode of the meta data file
  * @block: block offset
  *
  * Return Value: On success, zero is returned.
  * On error, one of the following negative error code is returned.
  *
  * %-ENOMEM - Insufficient memory available.
  *
  * %-EIO - I/O error
  */
 int nilfs_mdt_delete_block(struct inode *inode, unsigned long block)
 {
 	struct nilfs_inode_info *ii = NILFS_I(inode);
 	int err;

 	err = nilfs_bmap_delete(ii->i_bmap, block);
 	if (!err || err == -ENOENT) {
 		nilfs_mdt_mark_dirty(inode);
 		nilfs_mdt_forget_block(inode, block);
 	}
 	return err;
 }

 /**
  * nilfs_mdt_forget_block - discard dirty state and try to remove the page
  * @inode: inode of the meta data file
  * @block: block offset
  *
  * nilfs_mdt_forget_block() clears a dirty flag of the specified buffer, and
  * tries to release the page including the buffer from a page cache.
  *
  * Return Value: On success, 0 is returned. On error, one of the following
  * negative error code is returned.
  *
  * %-EBUSY - page has an active buffer.
  *
  * %-ENOENT - page cache has no page addressed by the offset.
  */
 int nilfs_mdt_forget_block(struct inode *inode, unsigned long block)
 {
 	pgoff_t index = (pgoff_t)block >>
 		(PAGE_SHIFT - inode->i_blkbits);
 	struct page *page;
 	unsigned long first_block;
 	int ret = 0;
 	int still_dirty;

 	page = find_lock_page(inode->i_mapping, index);
 	if (!page)
 		return -ENOENT;

 	wait_on_page_writeback(page);

 	first_block = (unsigned long)index <<
 		(PAGE_SHIFT - inode->i_blkbits);
 	if (page_has_buffers(page)) {
 		struct buffer_head *bh;

 		bh = nilfs_page_get_nth_block(page, block - first_block);
 		nilfs_forget_buffer(bh);
 	}
 	still_dirty = PageDirty(page);
 	unlock_page(page);
 	put_page(page);

 	if (still_dirty ||
 	    invalidate_inode_pages2_range(inode->i_mapping, index, index) != 0)
 		ret = -EBUSY;
 	return ret;
 }

 /**
  * nilfs_mdt_mark_block_dirty - mark a block on the meta data file dirty.
  * @inode: inode of the meta data file
  * @block: block offset
  *
  * Return Value: On success, it returns 0. On error, the following negative
  * error code is returned.
  *
  * %-ENOMEM - Insufficient memory available.
  *
  * %-EIO - I/O error
  *
  * %-ENOENT - the specified block does not exist (hole block)
  */
 int nilfs_mdt_mark_block_dirty(struct inode *inode, unsigned long block)
 {
 	struct buffer_head *bh;
 	int err;

 	err = nilfs_mdt_read_block(inode, block, 0, &bh);
 	if (unlikely(err))
 		return err;
 	mark_buffer_dirty(bh);
 	nilfs_mdt_mark_dirty(inode);
 	brelse(bh);
 	return 0;
 }

 int nilfs_mdt_fetch_dirty(struct inode *inode)
 {
 	struct nilfs_inode_info *ii = NILFS_I(inode);

 	if (nilfs_bmap_test_and_clear_dirty(ii->i_bmap)) {
 		set_bit(NILFS_I_DIRTY, &ii->i_state);
 		return 1;
 	}
 	return test_bit(NILFS_I_DIRTY, &ii->i_state);
 }

 static int
 nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 {
 	struct inode *inode = page->mapping->host;
 	struct super_block *sb;
 	int err = 0;

 	if (inode && (inode->i_sb->s_flags & MS_RDONLY)) {
 		/*
 		 * It means that filesystem was remounted in read-only
 		 * mode because of error or metadata corruption. But we
 		 * have dirty pages that try to be flushed in background.
 		 * So, here we simply discard this dirty page.
 		 */
 		nilfs_clear_dirty_page(page, false);
 		unlock_page(page);
 		return -EROFS;
 	}

 	redirty_page_for_writepage(wbc, page);
 	unlock_page(page);

 	if (!inode)
 		return 0;

 	sb = inode->i_sb;

 	if (wbc->sync_mode == WB_SYNC_ALL)
 		err = nilfs_construct_segment(sb);
 	else if (wbc->for_reclaim)
 		nilfs_flush_segment(sb, inode->i_ino);

 	return err;
 }


 static const struct address_space_operations def_mdt_aops = {
 	.writepage		= nilfs_mdt_write_page,
 };

 static const struct inode_operations def_mdt_iops;
 static const struct file_operations def_mdt_fops;


 int nilfs_mdt_init(struct inode *inode, gfp_t gfp_mask, size_t objsz)
 {
 	struct nilfs_mdt_info *mi;

 	mi = kzalloc(max(sizeof(*mi), objsz), GFP_NOFS);
 	if (!mi)
 		return -ENOMEM;

 	init_rwsem(&mi->mi_sem);
 	inode->i_private = mi;

 	inode->i_mode = S_IFREG;
 	mapping_set_gfp_mask(inode->i_mapping, gfp_mask);

 	inode->i_op = &def_mdt_iops;
 	inode->i_fop = &def_mdt_fops;
 	inode->i_mapping->a_ops = &def_mdt_aops;

 	return 0;
 }

 void nilfs_mdt_set_entry_size(struct inode *inode, unsigned entry_size,
 			      unsigned header_size)
 {
 	struct nilfs_mdt_info *mi = NILFS_MDT(inode);

 	mi->mi_entry_size = entry_size;
 	mi->mi_entries_per_block = (1 << inode->i_blkbits) / entry_size;
 	mi->mi_first_entry_offset = DIV_ROUND_UP(header_size, entry_size);
 }

 /**
  * nilfs_mdt_setup_shadow_map - setup shadow map and bind it to metadata file
  * @inode: inode of the metadata file
  * @shadow: shadow mapping
  */
 int nilfs_mdt_setup_shadow_map(struct inode *inode,
 			       struct nilfs_shadow_map *shadow)
 {
 	struct nilfs_mdt_info *mi = NILFS_MDT(inode);

 	INIT_LIST_HEAD(&shadow->frozen_buffers);
 	address_space_init_once(&shadow->frozen_data);
 	nilfs_mapping_init(&shadow->frozen_data, inode);
 	address_space_init_once(&shadow->frozen_btnodes);
 	nilfs_mapping_init(&shadow->frozen_btnodes, inode);
 	mi->mi_shadow = shadow;
 	return 0;
 }

 /**
  * nilfs_mdt_save_to_shadow_map - copy bmap and dirty pages to shadow map
  * @inode: inode of the metadata file
  */
 int nilfs_mdt_save_to_shadow_map(struct inode *inode)
 {
 	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
 	struct nilfs_inode_info *ii = NILFS_I(inode);
 	struct nilfs_shadow_map *shadow = mi->mi_shadow;
 	int ret;

 	ret = nilfs_copy_dirty_pages(&shadow->frozen_data, inode->i_mapping);
 	if (ret)
 		goto out;

 	ret = nilfs_copy_dirty_pages(&shadow->frozen_btnodes,
 				     &ii->i_btnode_cache);
 	if (ret)
 		goto out;

 	nilfs_bmap_save(ii->i_bmap, &shadow->bmap_store);
  out:
 	return ret;
 }

 int nilfs_mdt_freeze_buffer(struct inode *inode, struct buffer_head *bh)
 {
 	struct nilfs_shadow_map *shadow = NILFS_MDT(inode)->mi_shadow;
 	struct buffer_head *bh_frozen;
 	struct page *page;
 	int blkbits = inode->i_blkbits;

 	page = grab_cache_page(&shadow->frozen_data, bh->b_page->index);
 	if (!page)
 		return -ENOMEM;

 	if (!page_has_buffers(page))
 		create_empty_buffers(page, 1 << blkbits, 0);

 	bh_frozen = nilfs_page_get_nth_block(page, bh_offset(bh) >> blkbits);

 	if (!buffer_uptodate(bh_frozen))
 		nilfs_copy_buffer(bh_frozen, bh);
 	if (list_empty(&bh_frozen->b_assoc_buffers)) {
 		list_add_tail(&bh_frozen->b_assoc_buffers,
 			      &shadow->frozen_buffers);
 		set_buffer_nilfs_redirected(bh);
 	} else {
 		brelse(bh_frozen); /* already frozen */
 	}

 	unlock_page(page);
 	put_page(page);
 	return 0;
 }

 struct buffer_head *
 nilfs_mdt_get_frozen_buffer(struct inode *inode, struct buffer_head *bh)
 {
 	struct nilfs_shadow_map *shadow = NILFS_MDT(inode)->mi_shadow;
 	struct buffer_head *bh_frozen = NULL;
 	struct page *page;
 	int n;

 	page = find_lock_page(&shadow->frozen_data, bh->b_page->index);
 	if (page) {
 		if (page_has_buffers(page)) {
 			n = bh_offset(bh) >> inode->i_blkbits;
 			bh_frozen = nilfs_page_get_nth_block(page, n);
 		}
 		unlock_page(page);
 		put_page(page);
 	}
 	return bh_frozen;
 }

 static void nilfs_release_frozen_buffers(struct nilfs_shadow_map *shadow)
 {
 	struct list_head *head = &shadow->frozen_buffers;
 	struct buffer_head *bh;

 	while (!list_empty(head)) {
 		bh = list_first_entry(head, struct buffer_head,
 				      b_assoc_buffers);
 		list_del_init(&bh->b_assoc_buffers);
 		brelse(bh); /* drop ref-count to make it releasable */
 	}
 }

 /**
  * nilfs_mdt_restore_from_shadow_map - restore dirty pages and bmap state
  * @inode: inode of the metadata file
  */
 void nilfs_mdt_restore_from_shadow_map(struct inode *inode)
 {
 	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
 	struct nilfs_inode_info *ii = NILFS_I(inode);
 	struct nilfs_shadow_map *shadow = mi->mi_shadow;

 	down_write(&mi->mi_sem);

 	if (mi->mi_palloc_cache)
 		nilfs_palloc_clear_cache(inode);

 	nilfs_clear_dirty_pages(inode->i_mapping, true);
 	nilfs_copy_back_pages(inode->i_mapping, &shadow->frozen_data);

 	nilfs_clear_dirty_pages(&ii->i_btnode_cache, true);
 	nilfs_copy_back_pages(&ii->i_btnode_cache, &shadow->frozen_btnodes);

 	nilfs_bmap_restore(ii->i_bmap, &shadow->bmap_store);

 	up_write(&mi->mi_sem);
 }

 /**
  * nilfs_mdt_clear_shadow_map - truncate pages in shadow map caches
  * @inode: inode of the metadata file
  */
 void nilfs_mdt_clear_shadow_map(struct inode *inode)
 {
 	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
 	struct nilfs_shadow_map *shadow = mi->mi_shadow;

 	down_write(&mi->mi_sem);
 	nilfs_release_frozen_buffers(shadow);
 	truncate_inode_pages(&shadow->frozen_data, 0);
 	truncate_inode_pages(&shadow->frozen_btnodes, 0);
 	up_write(&mi->mi_sem);
 }
	/*
	* mdt.c - meta data file for NILFS
	*
	* Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
	*
	* 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.
	*
	* Written by Ryusuke Konishi.
	*/

	#include <linux/buffer_head.h>
	#include <linux/mpage.h>
	#include <linux/mm.h>
	#include <linux/writeback.h>
	#include <linux/backing-dev.h>
	#include <linux/swap.h>
	#include <linux/slab.h>
	#include "nilfs.h"
	#include "btnode.h"
	#include "segment.h"
	#include "page.h"
	#include "mdt.h"

	#include <trace/events/nilfs2.h>

	#define NILFS_MDT_MAX_RA_BLOCKS (16 - 1)


	static int
	nilfs_mdt_insert_new_block(struct inode *inode, unsigned long block,
	struct buffer_head *bh,
	void (init_block)(struct inode ,
	struct buffer_head , void ))
	{
	struct nilfs_inode_info *ii = NILFS_I(inode);
	void *kaddr;
	int ret;

	/* Caller exclude read accesses using page lock */

	/* set_buffer_new(bh); */
	bh->b_blocknr = 0;

	ret = nilfs_bmap_insert(ii->i_bmap, block, (unsigned long)bh);
	if (unlikely(ret))
	return ret;

	set_buffer_mapped(bh);

	kaddr = kmap_atomic(bh->b_page);
	memset(kaddr + bh_offset(bh), 0, 1 << inode->i_blkbits);
	if (init_block)
	init_block(inode, bh, kaddr);
	flush_dcache_page(bh->b_page);
	kunmap_atomic(kaddr);

	set_buffer_uptodate(bh);
	mark_buffer_dirty(bh);
	nilfs_mdt_mark_dirty(inode);

	trace_nilfs2_mdt_insert_new_block(inode, inode->i_ino, block);

	return 0;
	}

	static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
	struct buffer_head **out_bh,
	void (init_block)(struct inode ,
	struct buffer_head *,
	void *))
	{
	struct super_block *sb = inode->i_sb;
	struct nilfs_transaction_info ti;
	struct buffer_head *bh;
	int err;

	nilfs_transaction_begin(sb, &ti, 0);

	err = -ENOMEM;
	bh = nilfs_grab_buffer(inode, inode->i_mapping, block, 0);
	if (unlikely(!bh))
	goto failed_unlock;

	err = -EEXIST;
	if (buffer_uptodate(bh))
	goto failed_bh;

	wait_on_buffer(bh);
	if (buffer_uptodate(bh))
	goto failed_bh;

	bh->b_bdev = sb->s_bdev;
	err = nilfs_mdt_insert_new_block(inode, block, bh, init_block);
	if (likely(!err)) {
	get_bh(bh);
	*out_bh = bh;
	}

	failed_bh:
	unlock_page(bh->b_page);
	put_page(bh->b_page);
	brelse(bh);

	failed_unlock:
	if (likely(!err))
	err = nilfs_transaction_commit(sb);
	else
	nilfs_transaction_abort(sb);

	return err;
	}

	static int
	nilfs_mdt_submit_block(struct inode *inode, unsigned long blkoff,
	int mode, struct buffer_head **out_bh)
	{
	struct buffer_head *bh;
	__u64 blknum = 0;
	int ret = -ENOMEM;

	bh = nilfs_grab_buffer(inode, inode->i_mapping, blkoff, 0);
	if (unlikely(!bh))
	goto failed;

	ret = -EEXIST; /* internal code */
	if (buffer_uptodate(bh))
	goto out;

	if (mode == READA) {
	if (!trylock_buffer(bh)) {
	ret = -EBUSY;
	goto failed_bh;
	}
	} else /* mode == READ */
	lock_buffer(bh);

	if (buffer_uptodate(bh)) {
	unlock_buffer(bh);
	goto out;
	}

	ret = nilfs_bmap_lookup(NILFS_I(inode)->i_bmap, blkoff, &blknum);
	if (unlikely(ret)) {
	unlock_buffer(bh);
	goto failed_bh;
	}
	map_bh(bh, inode->i_sb, (sector_t)blknum);

	bh->b_end_io = end_buffer_read_sync;
	get_bh(bh);
	submit_bh(mode, bh);
	ret = 0;

	trace_nilfs2_mdt_submit_block(inode, inode->i_ino, blkoff, mode);
	out:
	get_bh(bh);
	*out_bh = bh;

	failed_bh:
	unlock_page(bh->b_page);
	put_page(bh->b_page);
	brelse(bh);
	failed:
	return ret;
	}

	static int nilfs_mdt_read_block(struct inode *inode, unsigned long block,
	int readahead, struct buffer_head **out_bh)
	{
	struct buffer_head first_bh, bh;
	unsigned long blkoff;
	int i, nr_ra_blocks = NILFS_MDT_MAX_RA_BLOCKS;
	int err;

	err = nilfs_mdt_submit_block(inode, block, READ, &first_bh);
	if (err == -EEXIST) /* internal code */
	goto out;

	if (unlikely(err))
	goto failed;

	if (readahead) {
	blkoff = block + 1;
	for (i = 0; i < nr_ra_blocks; i++, blkoff++) {
	err = nilfs_mdt_submit_block(inode, blkoff, READA, &bh);
	if (likely(!err \|\| err == -EEXIST))
	brelse(bh);
	else if (err != -EBUSY)
	break;
	/* abort readahead if bmap lookup failed */
	if (!buffer_locked(first_bh))
	goto out_no_wait;
	}
	}

	wait_on_buffer(first_bh);

	out_no_wait:
	err = -EIO;
	if (!buffer_uptodate(first_bh))
	goto failed_bh;
	out:
	*out_bh = first_bh;
	return 0;

	failed_bh:
	brelse(first_bh);
	failed:
	return err;
	}

	/**
	* nilfs_mdt_get_block - read or create a buffer on meta data file.
	* @inode: inode of the meta data file
	* @blkoff: block offset
	* @create: create flag
	* @init_block: initializer used for newly allocated block
	* @out_bh: output of a pointer to the buffer_head
	*
	* nilfs_mdt_get_block() looks up the specified buffer and tries to create
	* a new buffer if @create is not zero. On success, the returned buffer is
	* assured to be either existing or formatted using a buffer lock on success.
	* @out_bh is substituted only when zero is returned.
	*
	* Return Value: On success, it returns 0. On error, the following negative
	* error code is returned.
	*
	* %-ENOMEM - Insufficient memory available.
	*
	* %-EIO - I/O error
	*
	* %-ENOENT - the specified block does not exist (hole block)
	*
	* %-EROFS - Read only filesystem (for create mode)
	*/
	int nilfs_mdt_get_block(struct inode *inode, unsigned long blkoff, int create,
	void (init_block)(struct inode ,
	struct buffer_head , void ),
	struct buffer_head **out_bh)
	{
	int ret;

	/* Should be rewritten with merging nilfs_mdt_read_block() */
	retry:
	ret = nilfs_mdt_read_block(inode, blkoff, !create, out_bh);
	if (!create \|\| ret != -ENOENT)
	return ret;

	ret = nilfs_mdt_create_block(inode, blkoff, out_bh, init_block);
	if (unlikely(ret == -EEXIST)) {
	/* create = 0; / / limit read-create loop retries */
	goto retry;
	}
	return ret;
	}

	/**
	* nilfs_mdt_find_block - find and get a buffer on meta data file.
	* @inode: inode of the meta data file
	* @start: start block offset (inclusive)
	* @end: end block offset (inclusive)
	* @blkoff: block offset
	* @out_bh: place to store a pointer to buffer_head struct
	*
	* nilfs_mdt_find_block() looks up an existing block in range of
	* [@start, @end] and stores pointer to a buffer head of the block to
	* @out_bh, and block offset to @blkoff, respectively. @out_bh and
	* @blkoff are substituted only when zero is returned.
	*
	* Return Value: On success, it returns 0. On error, the following negative
	* error code is returned.
	*
	* %-ENOMEM - Insufficient memory available.
	*
	* %-EIO - I/O error
	*
	* %-ENOENT - no block was found in the range
	*/
	int nilfs_mdt_find_block(struct inode *inode, unsigned long start,
	unsigned long end, unsigned long *blkoff,
	struct buffer_head **out_bh)
	{
	__u64 next;
	int ret;

	if (unlikely(start > end))
	return -ENOENT;

	ret = nilfs_mdt_read_block(inode, start, true, out_bh);
	if (!ret) {
	*blkoff = start;
	goto out;
	}
	if (unlikely(ret != -ENOENT \|\| start == ULONG_MAX))
	goto out;

	ret = nilfs_bmap_seek_key(NILFS_I(inode)->i_bmap, start + 1, &next);
	if (!ret) {
	if (next <= end) {
	ret = nilfs_mdt_read_block(inode, next, true, out_bh);
	if (!ret)
	*blkoff = next;
	} else {
	ret = -ENOENT;
	}
	}
	out:
	return ret;
	}

	/**
	* nilfs_mdt_delete_block - make a hole on the meta data file.
	* @inode: inode of the meta data file
	* @block: block offset
	*
	* Return Value: On success, zero is returned.
	* On error, one of the following negative error code is returned.
	*
	* %-ENOMEM - Insufficient memory available.
	*
	* %-EIO - I/O error
	*/
	int nilfs_mdt_delete_block(struct inode *inode, unsigned long block)
	{
	struct nilfs_inode_info *ii = NILFS_I(inode);
	int err;

	err = nilfs_bmap_delete(ii->i_bmap, block);
	if (!err \|\| err == -ENOENT) {
	nilfs_mdt_mark_dirty(inode);
	nilfs_mdt_forget_block(inode, block);
	}
	return err;
	}

	/**
	* nilfs_mdt_forget_block - discard dirty state and try to remove the page
	* @inode: inode of the meta data file
	* @block: block offset
	*
	* nilfs_mdt_forget_block() clears a dirty flag of the specified buffer, and
	* tries to release the page including the buffer from a page cache.
	*
	* Return Value: On success, 0 is returned. On error, one of the following
	* negative error code is returned.
	*
	* %-EBUSY - page has an active buffer.
	*
	* %-ENOENT - page cache has no page addressed by the offset.
	*/
	int nilfs_mdt_forget_block(struct inode *inode, unsigned long block)
	{
	pgoff_t index = (pgoff_t)block >>
	(PAGE_SHIFT - inode->i_blkbits);
	struct page *page;
	unsigned long first_block;
	int ret = 0;
	int still_dirty;

	page = find_lock_page(inode->i_mapping, index);
	if (!page)
	return -ENOENT;

	wait_on_page_writeback(page);

	first_block = (unsigned long)index <<
	(PAGE_SHIFT - inode->i_blkbits);
	if (page_has_buffers(page)) {
	struct buffer_head *bh;

	bh = nilfs_page_get_nth_block(page, block - first_block);
	nilfs_forget_buffer(bh);
	}
	still_dirty = PageDirty(page);
	unlock_page(page);
	put_page(page);

	if (still_dirty \|\|
	invalidate_inode_pages2_range(inode->i_mapping, index, index) != 0)
	ret = -EBUSY;
	return ret;
	}

	/**
	* nilfs_mdt_mark_block_dirty - mark a block on the meta data file dirty.
	* @inode: inode of the meta data file
	* @block: block offset
	*
	* Return Value: On success, it returns 0. On error, the following negative
	* error code is returned.
	*
	* %-ENOMEM - Insufficient memory available.
	*
	* %-EIO - I/O error
	*
	* %-ENOENT - the specified block does not exist (hole block)
	*/
	int nilfs_mdt_mark_block_dirty(struct inode *inode, unsigned long block)
	{
	struct buffer_head *bh;
	int err;

	err = nilfs_mdt_read_block(inode, block, 0, &bh);
	if (unlikely(err))
	return err;
	mark_buffer_dirty(bh);
	nilfs_mdt_mark_dirty(inode);
	brelse(bh);
	return 0;
	}

	int nilfs_mdt_fetch_dirty(struct inode *inode)
	{
	struct nilfs_inode_info *ii = NILFS_I(inode);

	if (nilfs_bmap_test_and_clear_dirty(ii->i_bmap)) {
	set_bit(NILFS_I_DIRTY, &ii->i_state);
	return 1;
	}
	return test_bit(NILFS_I_DIRTY, &ii->i_state);
	}

	static int
	nilfs_mdt_write_page(struct page page, struct writeback_control wbc)
	{
	struct inode *inode = page->mapping->host;
	struct super_block *sb;
	int err = 0;

	if (inode && (inode->i_sb->s_flags & MS_RDONLY)) {
	/*
	* It means that filesystem was remounted in read-only
	* mode because of error or metadata corruption. But we
	* have dirty pages that try to be flushed in background.
	* So, here we simply discard this dirty page.
	*/
	nilfs_clear_dirty_page(page, false);
	unlock_page(page);
	return -EROFS;
	}

	redirty_page_for_writepage(wbc, page);
	unlock_page(page);

	if (!inode)
	return 0;

	sb = inode->i_sb;

	if (wbc->sync_mode == WB_SYNC_ALL)
	err = nilfs_construct_segment(sb);
	else if (wbc->for_reclaim)
	nilfs_flush_segment(sb, inode->i_ino);

	return err;
	}


	static const struct address_space_operations def_mdt_aops = {
	.writepage = nilfs_mdt_write_page,
	};

	static const struct inode_operations def_mdt_iops;
	static const struct file_operations def_mdt_fops;


	int nilfs_mdt_init(struct inode *inode, gfp_t gfp_mask, size_t objsz)
	{
	struct nilfs_mdt_info *mi;

	mi = kzalloc(max(sizeof(*mi), objsz), GFP_NOFS);
	if (!mi)
	return -ENOMEM;

	init_rwsem(&mi->mi_sem);
	inode->i_private = mi;

	inode->i_mode = S_IFREG;
	mapping_set_gfp_mask(inode->i_mapping, gfp_mask);

	inode->i_op = &def_mdt_iops;
	inode->i_fop = &def_mdt_fops;
	inode->i_mapping->a_ops = &def_mdt_aops;

	return 0;
	}

	void nilfs_mdt_set_entry_size(struct inode *inode, unsigned entry_size,
	unsigned header_size)
	{
	struct nilfs_mdt_info *mi = NILFS_MDT(inode);

	mi->mi_entry_size = entry_size;
	mi->mi_entries_per_block = (1 << inode->i_blkbits) / entry_size;
	mi->mi_first_entry_offset = DIV_ROUND_UP(header_size, entry_size);
	}

	/**
	* nilfs_mdt_setup_shadow_map - setup shadow map and bind it to metadata file
	* @inode: inode of the metadata file
	* @shadow: shadow mapping
	*/
	int nilfs_mdt_setup_shadow_map(struct inode *inode,
	struct nilfs_shadow_map *shadow)
	{
	struct nilfs_mdt_info *mi = NILFS_MDT(inode);

	INIT_LIST_HEAD(&shadow->frozen_buffers);
	address_space_init_once(&shadow->frozen_data);
	nilfs_mapping_init(&shadow->frozen_data, inode);
	address_space_init_once(&shadow->frozen_btnodes);
	nilfs_mapping_init(&shadow->frozen_btnodes, inode);
	mi->mi_shadow = shadow;
	return 0;
	}

	/**
	* nilfs_mdt_save_to_shadow_map - copy bmap and dirty pages to shadow map
	* @inode: inode of the metadata file
	*/
	int nilfs_mdt_save_to_shadow_map(struct inode *inode)
	{
	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
	struct nilfs_inode_info *ii = NILFS_I(inode);
	struct nilfs_shadow_map *shadow = mi->mi_shadow;
	int ret;

	ret = nilfs_copy_dirty_pages(&shadow->frozen_data, inode->i_mapping);
	if (ret)
	goto out;

	ret = nilfs_copy_dirty_pages(&shadow->frozen_btnodes,
	&ii->i_btnode_cache);
	if (ret)
	goto out;

	nilfs_bmap_save(ii->i_bmap, &shadow->bmap_store);
	out:
	return ret;
	}

	int nilfs_mdt_freeze_buffer(struct inode inode, struct buffer_head bh)
	{
	struct nilfs_shadow_map *shadow = NILFS_MDT(inode)->mi_shadow;
	struct buffer_head *bh_frozen;
	struct page *page;
	int blkbits = inode->i_blkbits;

	page = grab_cache_page(&shadow->frozen_data, bh->b_page->index);
	if (!page)
	return -ENOMEM;

	if (!page_has_buffers(page))
	create_empty_buffers(page, 1 << blkbits, 0);

	bh_frozen = nilfs_page_get_nth_block(page, bh_offset(bh) >> blkbits);

	if (!buffer_uptodate(bh_frozen))
	nilfs_copy_buffer(bh_frozen, bh);
	if (list_empty(&bh_frozen->b_assoc_buffers)) {
	list_add_tail(&bh_frozen->b_assoc_buffers,
	&shadow->frozen_buffers);
	set_buffer_nilfs_redirected(bh);
	} else {
	brelse(bh_frozen); /* already frozen */
	}

	unlock_page(page);
	put_page(page);
	return 0;
	}

	struct buffer_head *
	nilfs_mdt_get_frozen_buffer(struct inode inode, struct buffer_head bh)
	{
	struct nilfs_shadow_map *shadow = NILFS_MDT(inode)->mi_shadow;
	struct buffer_head *bh_frozen = NULL;
	struct page *page;
	int n;

	page = find_lock_page(&shadow->frozen_data, bh->b_page->index);
	if (page) {
	if (page_has_buffers(page)) {
	n = bh_offset(bh) >> inode->i_blkbits;
	bh_frozen = nilfs_page_get_nth_block(page, n);
	}
	unlock_page(page);
	put_page(page);
	}
	return bh_frozen;
	}

	static void nilfs_release_frozen_buffers(struct nilfs_shadow_map *shadow)
	{
	struct list_head *head = &shadow->frozen_buffers;
	struct buffer_head *bh;

	while (!list_empty(head)) {
	bh = list_first_entry(head, struct buffer_head,
	b_assoc_buffers);
	list_del_init(&bh->b_assoc_buffers);
	brelse(bh); /* drop ref-count to make it releasable */
	}
	}

	/**
	* nilfs_mdt_restore_from_shadow_map - restore dirty pages and bmap state
	* @inode: inode of the metadata file
	*/
	void nilfs_mdt_restore_from_shadow_map(struct inode *inode)
	{
	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
	struct nilfs_inode_info *ii = NILFS_I(inode);
	struct nilfs_shadow_map *shadow = mi->mi_shadow;

	down_write(&mi->mi_sem);

	if (mi->mi_palloc_cache)
	nilfs_palloc_clear_cache(inode);

	nilfs_clear_dirty_pages(inode->i_mapping, true);
	nilfs_copy_back_pages(inode->i_mapping, &shadow->frozen_data);

	nilfs_clear_dirty_pages(&ii->i_btnode_cache, true);
	nilfs_copy_back_pages(&ii->i_btnode_cache, &shadow->frozen_btnodes);

	nilfs_bmap_restore(ii->i_bmap, &shadow->bmap_store);

	up_write(&mi->mi_sem);
	}

	/**
	* nilfs_mdt_clear_shadow_map - truncate pages in shadow map caches
	* @inode: inode of the metadata file
	*/
	void nilfs_mdt_clear_shadow_map(struct inode *inode)
	{
	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
	struct nilfs_shadow_map *shadow = mi->mi_shadow;

	down_write(&mi->mi_sem);
	nilfs_release_frozen_buffers(shadow);
	truncate_inode_pages(&shadow->frozen_data, 0);
	truncate_inode_pages(&shadow->frozen_btnodes, 0);
	up_write(&mi->mi_sem);
	}