text: // SPDX-License-Identifier: GPL-2.0+
  /*
   * alloc.c - NILFS dat/inode allocator
   *
   * Copyright (C) 2006-2008 Nippon Telegraph and Telephone Corporation.
   *
   * Originally written by Koji Sato.
   * Two allocators were unified by Ryusuke Konishi and Amagai Yoshiji.
   */
  
  #include <linux/types.h>
  #include <linux/buffer_head.h>
  #include <linux/fs.h>
  #include <linux/bitops.h>
  #include <linux/slab.h>
  #include "mdt.h"
  #include "alloc.h"
  
  
  /**
   * nilfs_palloc_groups_per_desc_block - get the number of groups that a group
   *					descriptor block can maintain
   * @inode: inode of metadata file using this allocator
   */
  static inline unsigned long
  nilfs_palloc_groups_per_desc_block(const struct inode *inode)
  {
  	return i_blocksize(inode) /
  		sizeof(struct nilfs_palloc_group_desc);
  }
  
  /**
   * nilfs_palloc_groups_count - get maximum number of groups
   * @inode: inode of metadata file using this allocator
   */
  static inline unsigned long
  nilfs_palloc_groups_count(const struct inode *inode)
  {
  	return 1UL << (BITS_PER_LONG - (inode->i_blkbits + 3 /* log2(8) */));
  }
  
  /**
   * nilfs_palloc_init_blockgroup - initialize private variables for allocator
   * @inode: inode of metadata file using this allocator
   * @entry_size: size of the persistent object
   */
  int nilfs_palloc_init_blockgroup(struct inode *inode, unsigned int entry_size)
  {
  	struct nilfs_mdt_info *mi = NILFS_MDT(inode);
  
  	mi->mi_bgl = kmalloc(sizeof(*mi->mi_bgl), GFP_NOFS);
  	if (!mi->mi_bgl)
  		return -ENOMEM;
  
  	bgl_lock_init(mi->mi_bgl);
  
  	nilfs_mdt_set_entry_size(inode, entry_size, 0);
  
  	mi->mi_blocks_per_group =
  		DIV_ROUND_UP(nilfs_palloc_entries_per_group(inode),
  			     mi->mi_entries_per_block) + 1;
  		/*
  		 * Number of blocks in a group including entry blocks
  		 * and a bitmap block
  		 */
  	mi->mi_blocks_per_desc_block =
  		nilfs_palloc_groups_per_desc_block(inode) *
  		mi->mi_blocks_per_group + 1;
  		/*
  		 * Number of blocks per descriptor including the
  		 * descriptor block
  		 */
  	return 0;
  }
  
  /**
   * nilfs_palloc_group - get group number and offset from an entry number
   * @inode: inode of metadata file using this allocator
   * @nr: serial number of the entry (e.g. inode number)
   * @offset: pointer to store offset number in the group
   */
  static unsigned long nilfs_palloc_group(const struct inode *inode, __u64 nr,
  					unsigned long *offset)
  {
  	__u64 group = nr;
  
  	*offset = do_div(group, nilfs_palloc_entries_per_group(inode));
  	return group;
  }
  
  /**
   * nilfs_palloc_desc_blkoff - get block offset of a group descriptor block
   * @inode: inode of metadata file using this allocator
   * @group: group number
   *
   * nilfs_palloc_desc_blkoff() returns block offset of the descriptor
   * block which contains a descriptor of the specified group.
   */
  static unsigned long
  nilfs_palloc_desc_blkoff(const struct inode *inode, unsigned long group)
  {
  	unsigned long desc_block =
  		group / nilfs_palloc_groups_per_desc_block(inode);
  	return desc_block * NILFS_MDT(inode)->mi_blocks_per_desc_block;
  }
  
  /**
   * nilfs_palloc_bitmap_blkoff - get block offset of a bitmap block
   * @inode: inode of metadata file using this allocator
   * @group: group number
   *
   * nilfs_palloc_bitmap_blkoff() returns block offset of the bitmap
   * block used to allocate/deallocate entries in the specified group.
   */
  static unsigned long
  nilfs_palloc_bitmap_blkoff(const struct inode *inode, unsigned long group)
  {
  	unsigned long desc_offset =
  		group % nilfs_palloc_groups_per_desc_block(inode);
  	return nilfs_palloc_desc_blkoff(inode, group) + 1 +
  		desc_offset * NILFS_MDT(inode)->mi_blocks_per_group;
  }
  
  /**
   * nilfs_palloc_group_desc_nfrees - get the number of free entries in a group
   * @desc: pointer to descriptor structure for the group
   * @lock: spin lock protecting @desc
   */
  static unsigned long
  nilfs_palloc_group_desc_nfrees(const struct nilfs_palloc_group_desc *desc,
  			       spinlock_t *lock)
  {
  	unsigned long nfree;
  
  	spin_lock(lock);
  	nfree = le32_to_cpu(desc->pg_nfrees);
  	spin_unlock(lock);
  	return nfree;
  }
  
  /**
   * nilfs_palloc_group_desc_add_entries - adjust count of free entries
   * @desc: pointer to descriptor structure for the group
   * @lock: spin lock protecting @desc
   * @n: delta to be added
   */
  static u32
  nilfs_palloc_group_desc_add_entries(struct nilfs_palloc_group_desc *desc,
  				    spinlock_t *lock, u32 n)
  {
  	u32 nfree;
  
  	spin_lock(lock);
  	le32_add_cpu(&desc->pg_nfrees, n);
  	nfree = le32_to_cpu(desc->pg_nfrees);
  	spin_unlock(lock);
  	return nfree;
  }
  
  /**
   * nilfs_palloc_entry_blkoff - get block offset of an entry block
   * @inode: inode of metadata file using this allocator
   * @nr: serial number of the entry (e.g. inode number)
   */
  static unsigned long
  nilfs_palloc_entry_blkoff(const struct inode *inode, __u64 nr)
  {
  	unsigned long group, group_offset;
  
  	group = nilfs_palloc_group(inode, nr, &group_offset);
  
  	return nilfs_palloc_bitmap_blkoff(inode, group) + 1 +
  		group_offset / NILFS_MDT(inode)->mi_entries_per_block;
  }
  
  /**
   * nilfs_palloc_desc_block_init - initialize buffer of a group descriptor block
   * @inode: inode of metadata file
   * @bh: buffer head of the buffer to be initialized
   * @kaddr: kernel address mapped for the page including the buffer
   */
  static void nilfs_palloc_desc_block_init(struct inode *inode,
  					 struct buffer_head *bh, void *kaddr)
  {
  	struct nilfs_palloc_group_desc *desc = kaddr + bh_offset(bh);
  	unsigned long n = nilfs_palloc_groups_per_desc_block(inode);
  	__le32 nfrees;
  
  	nfrees = cpu_to_le32(nilfs_palloc_entries_per_group(inode));
  	while (n-- > 0) {
  		desc->pg_nfrees = nfrees;
  		desc++;
  	}
  }
  
  static int nilfs_palloc_get_block(struct inode *inode, unsigned long blkoff,
  				  int create,
  				  void (*init_block)(struct inode *,
  						     struct buffer_head *,
  						     void *),
  				  struct buffer_head **bhp,
  				  struct nilfs_bh_assoc *prev,
  				  spinlock_t *lock)
  {
  	int ret;
  
  	spin_lock(lock);
  	if (prev->bh && blkoff == prev->blkoff) {
  		get_bh(prev->bh);
  		*bhp = prev->bh;
  		spin_unlock(lock);
  		return 0;
  	}
  	spin_unlock(lock);
  
  	ret = nilfs_mdt_get_block(inode, blkoff, create, init_block, bhp);
  	if (!ret) {
  		spin_lock(lock);
  		/*
  		 * The following code must be safe for change of the
  		 * cache contents during the get block call.
  		 */
  		brelse(prev->bh);
  		get_bh(*bhp);
  		prev->bh = *bhp;
  		prev->blkoff = blkoff;
  		spin_unlock(lock);
  	}
  	return ret;
  }
  
  /**
   * nilfs_palloc_delete_block - delete a block on the persistent allocator file
   * @inode: inode of metadata file using this allocator
   * @blkoff: block offset
   * @prev: nilfs_bh_assoc struct of the last used buffer
   * @lock: spin lock protecting @prev
   */
  static int nilfs_palloc_delete_block(struct inode *inode, unsigned long blkoff,
  				     struct nilfs_bh_assoc *prev,
  				     spinlock_t *lock)
  {
  	spin_lock(lock);
  	if (prev->bh && blkoff == prev->blkoff) {
  		brelse(prev->bh);
  		prev->bh = NULL;
  	}
  	spin_unlock(lock);
  	return nilfs_mdt_delete_block(inode, blkoff);
  }
  
  /**
   * nilfs_palloc_get_desc_block - get buffer head of a group descriptor block
   * @inode: inode of metadata file using this allocator
   * @group: group number
   * @create: create flag
   * @bhp: pointer to store the resultant buffer head
   */
  static int nilfs_palloc_get_desc_block(struct inode *inode,
  				       unsigned long group,
  				       int create, struct buffer_head **bhp)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	return nilfs_palloc_get_block(inode,
  				      nilfs_palloc_desc_blkoff(inode, group),
  				      create, nilfs_palloc_desc_block_init,
  				      bhp, &cache->prev_desc, &cache->lock);
  }
  
  /**
   * nilfs_palloc_get_bitmap_block - get buffer head of a bitmap block
   * @inode: inode of metadata file using this allocator
   * @group: group number
   * @create: create flag
   * @bhp: pointer to store the resultant buffer head
   */
  static int nilfs_palloc_get_bitmap_block(struct inode *inode,
  					 unsigned long group,
  					 int create, struct buffer_head **bhp)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	return nilfs_palloc_get_block(inode,
  				      nilfs_palloc_bitmap_blkoff(inode, group),
  				      create, NULL, bhp,
  				      &cache->prev_bitmap, &cache->lock);
  }
  
  /**
   * nilfs_palloc_delete_bitmap_block - delete a bitmap block
   * @inode: inode of metadata file using this allocator
   * @group: group number
   */
  static int nilfs_palloc_delete_bitmap_block(struct inode *inode,
  					    unsigned long group)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	return nilfs_palloc_delete_block(inode,
  					 nilfs_palloc_bitmap_blkoff(inode,
  								    group),
  					 &cache->prev_bitmap, &cache->lock);
  }
  
  /**
   * nilfs_palloc_get_entry_block - get buffer head of an entry block
   * @inode: inode of metadata file using this allocator
   * @nr: serial number of the entry (e.g. inode number)
   * @create: create flag
   * @bhp: pointer to store the resultant buffer head
   */
  int nilfs_palloc_get_entry_block(struct inode *inode, __u64 nr,
  				 int create, struct buffer_head **bhp)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	return nilfs_palloc_get_block(inode,
  				      nilfs_palloc_entry_blkoff(inode, nr),
  				      create, NULL, bhp,
  				      &cache->prev_entry, &cache->lock);
  }
  
  /**
   * nilfs_palloc_delete_entry_block - delete an entry block
   * @inode: inode of metadata file using this allocator
   * @nr: serial number of the entry
   */
  static int nilfs_palloc_delete_entry_block(struct inode *inode, __u64 nr)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	return nilfs_palloc_delete_block(inode,
  					 nilfs_palloc_entry_blkoff(inode, nr),
  					 &cache->prev_entry, &cache->lock);
  }
  
  /**
   * nilfs_palloc_block_get_group_desc - get kernel address of a group descriptor
   * @inode: inode of metadata file using this allocator
   * @group: group number
   * @bh: buffer head of the buffer storing the group descriptor block
   * @kaddr: kernel address mapped for the page including the buffer
   */
  static struct nilfs_palloc_group_desc *
  nilfs_palloc_block_get_group_desc(const struct inode *inode,
  				  unsigned long group,
  				  const struct buffer_head *bh, void *kaddr)
  {
  	return (struct nilfs_palloc_group_desc *)(kaddr + bh_offset(bh)) +
  		group % nilfs_palloc_groups_per_desc_block(inode);
  }
  
  /**
   * nilfs_palloc_block_get_entry - get kernel address of an entry
   * @inode: inode of metadata file using this allocator
   * @nr: serial number of the entry (e.g. inode number)
   * @bh: buffer head of the buffer storing the entry block
   * @kaddr: kernel address mapped for the page including the buffer
   */
  void *nilfs_palloc_block_get_entry(const struct inode *inode, __u64 nr,
  				   const struct buffer_head *bh, void *kaddr)
  {
  	unsigned long entry_offset, group_offset;
  
  	nilfs_palloc_group(inode, nr, &group_offset);
  	entry_offset = group_offset % NILFS_MDT(inode)->mi_entries_per_block;
  
  	return kaddr + bh_offset(bh) +
  		entry_offset * NILFS_MDT(inode)->mi_entry_size;
  }
  
  /**
   * nilfs_palloc_find_available_slot - find available slot in a group
   * @bitmap: bitmap of the group
   * @target: offset number of an entry in the group (start point)
   * @bsize: size in bits
   * @lock: spin lock protecting @bitmap
   */
  static int nilfs_palloc_find_available_slot(unsigned char *bitmap,
  					    unsigned long target,
  					    unsigned int bsize,
  					    spinlock_t *lock)
  {
  	int pos, end = bsize;
  
  	if (likely(target < bsize)) {
  		pos = target;
  		do {
  			pos = nilfs_find_next_zero_bit(bitmap, end, pos);
  			if (pos >= end)
  				break;
  			if (!nilfs_set_bit_atomic(lock, pos, bitmap))
  				return pos;
  		} while (++pos < end);
  
  		end = target;
  	}
  
  	/* wrap around */
  	for (pos = 0; pos < end; pos++) {
  		pos = nilfs_find_next_zero_bit(bitmap, end, pos);
  		if (pos >= end)
  			break;
  		if (!nilfs_set_bit_atomic(lock, pos, bitmap))
  			return pos;
  	}
  
  	return -ENOSPC;
  }
  
  /**
   * nilfs_palloc_rest_groups_in_desc_block - get the remaining number of groups
   *					    in a group descriptor block
   * @inode: inode of metadata file using this allocator
   * @curr: current group number
   * @max: maximum number of groups
   */
  static unsigned long
  nilfs_palloc_rest_groups_in_desc_block(const struct inode *inode,
  				       unsigned long curr, unsigned long max)
  {
  	return min_t(unsigned long,
  		     nilfs_palloc_groups_per_desc_block(inode) -
  		     curr % nilfs_palloc_groups_per_desc_block(inode),
  		     max - curr + 1);
  }
  
  /**
   * nilfs_palloc_count_desc_blocks - count descriptor blocks number
   * @inode: inode of metadata file using this allocator
   * @desc_blocks: descriptor blocks number [out]
   */
  static int nilfs_palloc_count_desc_blocks(struct inode *inode,
  					    unsigned long *desc_blocks)
  {
  	__u64 blknum;
  	int ret;
  
  	ret = nilfs_bmap_last_key(NILFS_I(inode)->i_bmap, &blknum);
  	if (likely(!ret))
  		*desc_blocks = DIV_ROUND_UP(
  			(unsigned long)blknum,
  			NILFS_MDT(inode)->mi_blocks_per_desc_block);
  	return ret;
  }
  
  /**
   * nilfs_palloc_mdt_file_can_grow - check potential opportunity for
   *					MDT file growing
   * @inode: inode of metadata file using this allocator
   * @desc_blocks: known current descriptor blocks count
   */
  static inline bool nilfs_palloc_mdt_file_can_grow(struct inode *inode,
  						    unsigned long desc_blocks)
  {
  	return (nilfs_palloc_groups_per_desc_block(inode) * desc_blocks) <
  			nilfs_palloc_groups_count(inode);
  }
  
  /**
   * nilfs_palloc_count_max_entries - count max number of entries that can be
   *					described by descriptor blocks count
   * @inode: inode of metadata file using this allocator
   * @nused: current number of used entries
   * @nmaxp: max number of entries [out]
   */
  int nilfs_palloc_count_max_entries(struct inode *inode, u64 nused, u64 *nmaxp)
  {
  	unsigned long desc_blocks = 0;
  	u64 entries_per_desc_block, nmax;
  	int err;
  
  	err = nilfs_palloc_count_desc_blocks(inode, &desc_blocks);
  	if (unlikely(err))
  		return err;
  
  	entries_per_desc_block = (u64)nilfs_palloc_entries_per_group(inode) *
  				nilfs_palloc_groups_per_desc_block(inode);
  	nmax = entries_per_desc_block * desc_blocks;
  
  	if (nused == nmax &&
  			nilfs_palloc_mdt_file_can_grow(inode, desc_blocks))
  		nmax += entries_per_desc_block;
  
  	if (nused > nmax)
  		return -ERANGE;
  
  	*nmaxp = nmax;
  	return 0;
  }
  
  /**
   * nilfs_palloc_prepare_alloc_entry - prepare to allocate a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the allocation
   */
  int nilfs_palloc_prepare_alloc_entry(struct inode *inode,
  				     struct nilfs_palloc_req *req)
  {
  	struct buffer_head *desc_bh, *bitmap_bh;
  	struct nilfs_palloc_group_desc *desc;
  	unsigned char *bitmap;
  	void *desc_kaddr, *bitmap_kaddr;
  	unsigned long group, maxgroup, ngroups;
  	unsigned long group_offset, maxgroup_offset;
  	unsigned long n, entries_per_group;
  	unsigned long i, j;
  	spinlock_t *lock;
  	int pos, ret;
  
  	ngroups = nilfs_palloc_groups_count(inode);
  	maxgroup = ngroups - 1;
  	group = nilfs_palloc_group(inode, req->pr_entry_nr, &group_offset);
  	entries_per_group = nilfs_palloc_entries_per_group(inode);
  
  	for (i = 0; i < ngroups; i += n) {
  		if (group >= ngroups) {
  			/* wrap around */
  			group = 0;
  			maxgroup = nilfs_palloc_group(inode, req->pr_entry_nr,
  						      &maxgroup_offset) - 1;
  		}
  		ret = nilfs_palloc_get_desc_block(inode, group, 1, &desc_bh);
  		if (ret < 0)
  			return ret;
  		desc_kaddr = kmap(desc_bh->b_page);
  		desc = nilfs_palloc_block_get_group_desc(
  			inode, group, desc_bh, desc_kaddr);
  		n = nilfs_palloc_rest_groups_in_desc_block(inode, group,
  							   maxgroup);
  		for (j = 0; j < n; j++, desc++, group++) {
  			lock = nilfs_mdt_bgl_lock(inode, group);
  			if (nilfs_palloc_group_desc_nfrees(desc, lock) > 0) {
  				ret = nilfs_palloc_get_bitmap_block(
  					inode, group, 1, &bitmap_bh);
  				if (ret < 0)
  					goto out_desc;
  				bitmap_kaddr = kmap(bitmap_bh->b_page);
  				bitmap = bitmap_kaddr + bh_offset(bitmap_bh);
  				pos = nilfs_palloc_find_available_slot(
  					bitmap, group_offset,
  					entries_per_group, lock);
  				if (pos >= 0) {
  					/* found a free entry */
  					nilfs_palloc_group_desc_add_entries(
  						desc, lock, -1);
  					req->pr_entry_nr =
  						entries_per_group * group + pos;
  					kunmap(desc_bh->b_page);
  					kunmap(bitmap_bh->b_page);
  
  					req->pr_desc_bh = desc_bh;
  					req->pr_bitmap_bh = bitmap_bh;
  					return 0;
  				}
  				kunmap(bitmap_bh->b_page);
  				brelse(bitmap_bh);
  			}
  
  			group_offset = 0;
  		}
  
  		kunmap(desc_bh->b_page);
  		brelse(desc_bh);
  	}
  
  	/* no entries left */
  	return -ENOSPC;
  
   out_desc:
  	kunmap(desc_bh->b_page);
  	brelse(desc_bh);
  	return ret;
  }
  
  /**
   * nilfs_palloc_commit_alloc_entry - finish allocation of a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the allocation
   */
  void nilfs_palloc_commit_alloc_entry(struct inode *inode,
  				     struct nilfs_palloc_req *req)
  {
  	mark_buffer_dirty(req->pr_bitmap_bh);
  	mark_buffer_dirty(req->pr_desc_bh);
  	nilfs_mdt_mark_dirty(inode);
  
  	brelse(req->pr_bitmap_bh);
  	brelse(req->pr_desc_bh);
  }
  
  /**
   * nilfs_palloc_commit_free_entry - finish deallocating a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the removal
   */
  void nilfs_palloc_commit_free_entry(struct inode *inode,
  				    struct nilfs_palloc_req *req)
  {
  	struct nilfs_palloc_group_desc *desc;
  	unsigned long group, group_offset;
  	unsigned char *bitmap;
  	void *desc_kaddr, *bitmap_kaddr;
  	spinlock_t *lock;
  
  	group = nilfs_palloc_group(inode, req->pr_entry_nr, &group_offset);
  	desc_kaddr = kmap(req->pr_desc_bh->b_page);
  	desc = nilfs_palloc_block_get_group_desc(inode, group,
  						 req->pr_desc_bh, desc_kaddr);
  	bitmap_kaddr = kmap(req->pr_bitmap_bh->b_page);
  	bitmap = bitmap_kaddr + bh_offset(req->pr_bitmap_bh);
  	lock = nilfs_mdt_bgl_lock(inode, group);
  
  	if (!nilfs_clear_bit_atomic(lock, group_offset, bitmap))
  		nilfs_warn(inode->i_sb,
  			   "%s (ino=%lu): entry number %llu already freed",
  			   __func__, inode->i_ino,
  			   (unsigned long long)req->pr_entry_nr);
  	else
  		nilfs_palloc_group_desc_add_entries(desc, lock, 1);
  
  	kunmap(req->pr_bitmap_bh->b_page);
  	kunmap(req->pr_desc_bh->b_page);
  
  	mark_buffer_dirty(req->pr_desc_bh);
  	mark_buffer_dirty(req->pr_bitmap_bh);
  	nilfs_mdt_mark_dirty(inode);
  
  	brelse(req->pr_bitmap_bh);
  	brelse(req->pr_desc_bh);
  }
  
  /**
   * nilfs_palloc_abort_alloc_entry - cancel allocation of a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the allocation
   */
  void nilfs_palloc_abort_alloc_entry(struct inode *inode,
  				    struct nilfs_palloc_req *req)
  {
  	struct nilfs_palloc_group_desc *desc;
  	void *desc_kaddr, *bitmap_kaddr;
  	unsigned char *bitmap;
  	unsigned long group, group_offset;
  	spinlock_t *lock;
  
  	group = nilfs_palloc_group(inode, req->pr_entry_nr, &group_offset);
  	desc_kaddr = kmap(req->pr_desc_bh->b_page);
  	desc = nilfs_palloc_block_get_group_desc(inode, group,
  						 req->pr_desc_bh, desc_kaddr);
  	bitmap_kaddr = kmap(req->pr_bitmap_bh->b_page);
  	bitmap = bitmap_kaddr + bh_offset(req->pr_bitmap_bh);
  	lock = nilfs_mdt_bgl_lock(inode, group);
  
  	if (!nilfs_clear_bit_atomic(lock, group_offset, bitmap))
  		nilfs_warn(inode->i_sb,
  			   "%s (ino=%lu): entry number %llu already freed",
  			   __func__, inode->i_ino,
  			   (unsigned long long)req->pr_entry_nr);
  	else
  		nilfs_palloc_group_desc_add_entries(desc, lock, 1);
  
  	kunmap(req->pr_bitmap_bh->b_page);
  	kunmap(req->pr_desc_bh->b_page);
  
  	brelse(req->pr_bitmap_bh);
  	brelse(req->pr_desc_bh);
  
  	req->pr_entry_nr = 0;
  	req->pr_bitmap_bh = NULL;
  	req->pr_desc_bh = NULL;
  }
  
  /**
   * nilfs_palloc_prepare_free_entry - prepare to deallocate a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the removal
   */
  int nilfs_palloc_prepare_free_entry(struct inode *inode,
  				    struct nilfs_palloc_req *req)
  {
  	struct buffer_head *desc_bh, *bitmap_bh;
  	unsigned long group, group_offset;
  	int ret;
  
  	group = nilfs_palloc_group(inode, req->pr_entry_nr, &group_offset);
  	ret = nilfs_palloc_get_desc_block(inode, group, 1, &desc_bh);
  	if (ret < 0)
  		return ret;
  	ret = nilfs_palloc_get_bitmap_block(inode, group, 1, &bitmap_bh);
  	if (ret < 0) {
  		brelse(desc_bh);
  		return ret;
  	}
  
  	req->pr_desc_bh = desc_bh;
  	req->pr_bitmap_bh = bitmap_bh;
  	return 0;
  }
  
  /**
   * nilfs_palloc_abort_free_entry - cancel deallocating a persistent object
   * @inode: inode of metadata file using this allocator
   * @req: nilfs_palloc_req structure exchanged for the removal
   */
  void nilfs_palloc_abort_free_entry(struct inode *inode,
  				   struct nilfs_palloc_req *req)
  {
  	brelse(req->pr_bitmap_bh);
  	brelse(req->pr_desc_bh);
  
  	req->pr_entry_nr = 0;
  	req->pr_bitmap_bh = NULL;
  	req->pr_desc_bh = NULL;
  }
  
  /**
   * nilfs_palloc_freev - deallocate a set of persistent objects
   * @inode: inode of metadata file using this allocator
   * @entry_nrs: array of entry numbers to be deallocated
   * @nitems: number of entries stored in @entry_nrs
   */
  int nilfs_palloc_freev(struct inode *inode, __u64 *entry_nrs, size_t nitems)
  {
  	struct buffer_head *desc_bh, *bitmap_bh;
  	struct nilfs_palloc_group_desc *desc;
  	unsigned char *bitmap;
  	void *desc_kaddr, *bitmap_kaddr;
  	unsigned long group, group_offset;
  	__u64 group_min_nr, last_nrs[8];
  	const unsigned long epg = nilfs_palloc_entries_per_group(inode);
  	const unsigned int epb = NILFS_MDT(inode)->mi_entries_per_block;
  	unsigned int entry_start, end, pos;
  	spinlock_t *lock;
  	int i, j, k, ret;
  	u32 nfree;
  
  	for (i = 0; i < nitems; i = j) {
  		int change_group = false;
  		int nempties = 0, n = 0;
  
  		group = nilfs_palloc_group(inode, entry_nrs[i], &group_offset);
  		ret = nilfs_palloc_get_desc_block(inode, group, 0, &desc_bh);
  		if (ret < 0)
  			return ret;
  		ret = nilfs_palloc_get_bitmap_block(inode, group, 0,
  						    &bitmap_bh);
  		if (ret < 0) {
  			brelse(desc_bh);
  			return ret;
  		}
  
  		/* Get the first entry number of the group */
  		group_min_nr = (__u64)group * epg;
  
  		bitmap_kaddr = kmap(bitmap_bh->b_page);
  		bitmap = bitmap_kaddr + bh_offset(bitmap_bh);
  		lock = nilfs_mdt_bgl_lock(inode, group);
  
  		j = i;
  		entry_start = rounddown(group_offset, epb);
  		do {
  			if (!nilfs_clear_bit_atomic(lock, group_offset,
  						    bitmap)) {
  				nilfs_warn(inode->i_sb,
  					   "%s (ino=%lu): entry number %llu already freed",
  					   __func__, inode->i_ino,
  					   (unsigned long long)entry_nrs[j]);
  			} else {
  				n++;
  			}
  
  			j++;
  			if (j >= nitems || entry_nrs[j] < group_min_nr ||
  			    entry_nrs[j] >= group_min_nr + epg) {
  				change_group = true;
  			} else {
  				group_offset = entry_nrs[j] - group_min_nr;
  				if (group_offset >= entry_start &&
  				    group_offset < entry_start + epb) {
  					/* This entry is in the same block */
  					continue;
  				}
  			}
  
  			/* Test if the entry block is empty or not */
  			end = entry_start + epb;
  			pos = nilfs_find_next_bit(bitmap, end, entry_start);
  			if (pos >= end) {
  				last_nrs[nempties++] = entry_nrs[j - 1];
  				if (nempties >= ARRAY_SIZE(last_nrs))
  					break;
  			}
  
  			if (change_group)
  				break;
  
  			/* Go on to the next entry block */
  			entry_start = rounddown(group_offset, epb);
  		} while (true);
  
  		kunmap(bitmap_bh->b_page);
  		mark_buffer_dirty(bitmap_bh);
  		brelse(bitmap_bh);
  
  		for (k = 0; k < nempties; k++) {
  			ret = nilfs_palloc_delete_entry_block(inode,
  							      last_nrs[k]);
  			if (ret && ret != -ENOENT)
  				nilfs_warn(inode->i_sb,
  					   "error %d deleting block that object (entry=%llu, ino=%lu) belongs to",
  					   ret, (unsigned long long)last_nrs[k],
  					   inode->i_ino);
  		}
  
  		desc_kaddr = kmap_atomic(desc_bh->b_page);
  		desc = nilfs_palloc_block_get_group_desc(
  			inode, group, desc_bh, desc_kaddr);
  		nfree = nilfs_palloc_group_desc_add_entries(desc, lock, n);
  		kunmap_atomic(desc_kaddr);
  		mark_buffer_dirty(desc_bh);
  		nilfs_mdt_mark_dirty(inode);
  		brelse(desc_bh);
  
  		if (nfree == nilfs_palloc_entries_per_group(inode)) {
  			ret = nilfs_palloc_delete_bitmap_block(inode, group);
  			if (ret && ret != -ENOENT)
  				nilfs_warn(inode->i_sb,
  					   "error %d deleting bitmap block of group=%lu, ino=%lu",
  					   ret, group, inode->i_ino);
  		}
  	}
  	return 0;
  }
  
  void nilfs_palloc_setup_cache(struct inode *inode,
  			      struct nilfs_palloc_cache *cache)
  {
  	NILFS_MDT(inode)->mi_palloc_cache = cache;
  	spin_lock_init(&cache->lock);
  }
  
  void nilfs_palloc_clear_cache(struct inode *inode)
  {
  	struct nilfs_palloc_cache *cache = NILFS_MDT(inode)->mi_palloc_cache;
  
  	spin_lock(&cache->lock);
  	brelse(cache->prev_desc.bh);
  	brelse(cache->prev_bitmap.bh);
  	brelse(cache->prev_entry.bh);
  	cache->prev_desc.bh = NULL;
  	cache->prev_bitmap.bh = NULL;
  	cache->prev_entry.bh = NULL;
  	spin_unlock(&cache->lock);
  }
  
  void nilfs_palloc_destroy_cache(struct inode *inode)
  {
  	nilfs_palloc_clear_cache(inode);
  	NILFS_MDT(inode)->mi_palloc_cache = NULL;
  }
  