text: /*
   *  linux/fs/sysv/itree.c
   *
   *  Handling of indirect blocks' trees.
   *  AV, Sep--Dec 2000
   */
  
  #include <linux/buffer_head.h>
  #include <linux/mount.h>
  #include <linux/string.h>
  #include "sysv.h"
  
  enum {DIRECT = 10, DEPTH = 4};	/* Have triple indirect */
  
  static inline void dirty_indirect(struct buffer_head *bh, struct inode *inode)
  {
  	mark_buffer_dirty_inode(bh, inode);
  	if (IS_SYNC(inode))
  		sync_dirty_buffer(bh);
  }
  
  static int block_to_path(struct inode *inode, long block, int offsets[DEPTH])
  {
  	struct super_block *sb = inode->i_sb;
  	struct sysv_sb_info *sbi = SYSV_SB(sb);
  	int ptrs_bits = sbi->s_ind_per_block_bits;
  	unsigned long	indirect_blocks = sbi->s_ind_per_block,
  			double_blocks = sbi->s_ind_per_block_2;
  	int n = 0;
  
  	if (block < 0) {
  		printk("sysv_block_map: block < 0\n");
  	} else if (block < DIRECT) {
  		offsets[n++] = block;
  	} else if ( (block -= DIRECT) < indirect_blocks) {
  		offsets[n++] = DIRECT;
  		offsets[n++] = block;
  	} else if ((block -= indirect_blocks) < double_blocks) {
  		offsets[n++] = DIRECT+1;
  		offsets[n++] = block >> ptrs_bits;
  		offsets[n++] = block & (indirect_blocks - 1);
  	} else if (((block -= double_blocks) >> (ptrs_bits * 2)) < indirect_blocks) {
  		offsets[n++] = DIRECT+2;
  		offsets[n++] = block >> (ptrs_bits * 2);
  		offsets[n++] = (block >> ptrs_bits) & (indirect_blocks - 1);
  		offsets[n++] = block & (indirect_blocks - 1);
  	} else {
  		/* nothing */;
  	}
  	return n;
  }
  
  static inline int block_to_cpu(struct sysv_sb_info *sbi, sysv_zone_t nr)
  {
  	return sbi->s_block_base + fs32_to_cpu(sbi, nr);
  }
  
  typedef struct {
  	sysv_zone_t     *p;
  	sysv_zone_t     key;
  	struct buffer_head *bh;
  } Indirect;
  
  static DEFINE_RWLOCK(pointers_lock);
  
  static inline void add_chain(Indirect *p, struct buffer_head *bh, sysv_zone_t *v)
  {
  	p->key = *(p->p = v);
  	p->bh = bh;
  }
  
  static inline int verify_chain(Indirect *from, Indirect *to)
  {
  	while (from <= to && from->key == *from->p)
  		from++;
  	return (from > to);
  }
  
  static inline sysv_zone_t *block_end(struct buffer_head *bh)
  {
  	return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
  }
  
  /*
   * Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
   */
  static Indirect *get_branch(struct inode *inode,
  			    int depth,
  			    int offsets[],
  			    Indirect chain[],
  			    int *err)
  {
  	struct super_block *sb = inode->i_sb;
  	Indirect *p = chain;
  	struct buffer_head *bh;
  
  	*err = 0;
  	add_chain(chain, NULL, SYSV_I(inode)->i_data + *offsets);
  	if (!p->key)
  		goto no_block;
  	while (--depth) {
  		int block = block_to_cpu(SYSV_SB(sb), p->key);
  		bh = sb_bread(sb, block);
  		if (!bh)
  			goto failure;
  		if (!verify_chain(chain, p))
  			goto changed;
  		add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
  		if (!p->key)
  			goto no_block;
  	}
  	return NULL;
  
  changed:
  	brelse(bh);
  	*err = -EAGAIN;
  	goto no_block;
  failure:
  	*err = -EIO;
  no_block:
  	return p;
  }
  
  static int alloc_branch(struct inode *inode,
  			int num,
  			int *offsets,
  			Indirect *branch)
  {
  	int blocksize = inode->i_sb->s_blocksize;
  	int n = 0;
  	int i;
  
  	branch[0].key = sysv_new_block(inode->i_sb);
  	if (branch[0].key) for (n = 1; n < num; n++) {
  		struct buffer_head *bh;
  		int parent;
  		/* Allocate the next block */
  		branch[n].key = sysv_new_block(inode->i_sb);
  		if (!branch[n].key)
  			break;
  		/*
  		 * Get buffer_head for parent block, zero it out and set 
  		 * the pointer to new one, then send parent to disk.
  		 */
  		parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
  		bh = sb_getblk(inode->i_sb, parent);
  		lock_buffer(bh);
  		memset(bh->b_data, 0, blocksize);
  		branch[n].bh = bh;
  		branch[n].p = (sysv_zone_t*) bh->b_data + offsets[n];
  		*branch[n].p = branch[n].key;
  		set_buffer_uptodate(bh);
  		unlock_buffer(bh);
  		dirty_indirect(bh, inode);
  	}
  	if (n == num)
  		return 0;
  
  	/* Allocation failed, free what we already allocated */
  	for (i = 1; i < n; i++)
  		bforget(branch[i].bh);
  	for (i = 0; i < n; i++)
  		sysv_free_block(inode->i_sb, branch[i].key);
  	return -ENOSPC;
  }
  
  static inline int splice_branch(struct inode *inode,
  				Indirect chain[],
  				Indirect *where,
  				int num)
  {
  	int i;
  
  	/* Verify that place we are splicing to is still there and vacant */
  	write_lock(&pointers_lock);
  	if (!verify_chain(chain, where-1) || *where->p)
  		goto changed;
  	*where->p = where->key;
  	write_unlock(&pointers_lock);
  
  	inode->i_ctime = CURRENT_TIME_SEC;
  
  	/* had we spliced it onto indirect block? */
  	if (where->bh)
  		dirty_indirect(where->bh, inode);
  
  	if (IS_SYNC(inode))
  		sysv_sync_inode(inode);
  	else
  		mark_inode_dirty(inode);
  	return 0;
  
  changed:
  	write_unlock(&pointers_lock);
  	for (i = 1; i < num; i++)
  		bforget(where[i].bh);
  	for (i = 0; i < num; i++)
  		sysv_free_block(inode->i_sb, where[i].key);
  	return -EAGAIN;
  }
  
  static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
  {
  	int err = -EIO;
  	int offsets[DEPTH];
  	Indirect chain[DEPTH];
  	struct super_block *sb = inode->i_sb;
  	Indirect *partial;
  	int left;
  	int depth = block_to_path(inode, iblock, offsets);
  
  	if (depth == 0)
  		goto out;
  
  reread:
  	read_lock(&pointers_lock);
  	partial = get_branch(inode, depth, offsets, chain, &err);
  	read_unlock(&pointers_lock);
  
  	/* Simplest case - block found, no allocation needed */
  	if (!partial) {
  got_it:
  		map_bh(bh_result, sb, block_to_cpu(SYSV_SB(sb),
  					chain[depth-1].key));
  		/* Clean up and exit */
  		partial = chain+depth-1; /* the whole chain */
  		goto cleanup;
  	}
  
  	/* Next simple case - plain lookup or failed read of indirect block */
  	if (!create || err == -EIO) {
  cleanup:
  		while (partial > chain) {
  			brelse(partial->bh);
  			partial--;
  		}
  out:
  		return err;
  	}
  
  	/*
  	 * Indirect block might be removed by truncate while we were
  	 * reading it. Handling of that case (forget what we've got and
  	 * reread) is taken out of the main path.
  	 */
  	if (err == -EAGAIN)
  		goto changed;
  
  	left = (chain + depth) - partial;
  	err = alloc_branch(inode, left, offsets+(partial-chain), partial);
  	if (err)
  		goto cleanup;
  
  	if (splice_branch(inode, chain, partial, left) < 0)
  		goto changed;
  
  	set_buffer_new(bh_result);
  	goto got_it;
  
  changed:
  	while (partial > chain) {
  		brelse(partial->bh);
  		partial--;
  	}
  	goto reread;
  }
  
  static inline int all_zeroes(sysv_zone_t *p, sysv_zone_t *q)
  {
  	while (p < q)
  		if (*p++)
  			return 0;
  	return 1;
  }
  
  static Indirect *find_shared(struct inode *inode,
  				int depth,
  				int offsets[],
  				Indirect chain[],
  				sysv_zone_t *top)
  {
  	Indirect *partial, *p;
  	int k, err;
  
  	*top = 0;
  	for (k = depth; k > 1 && !offsets[k-1]; k--)
  		;
  
  	write_lock(&pointers_lock);
  	partial = get_branch(inode, k, offsets, chain, &err);
  	if (!partial)
  		partial = chain + k-1;
  	/*
  	 * If the branch acquired continuation since we've looked at it -
  	 * fine, it should all survive and (new) top doesn't belong to us.
  	 */
  	if (!partial->key && *partial->p) {
  		write_unlock(&pointers_lock);
  		goto no_top;
  	}
  	for (p=partial; p>chain && all_zeroes((sysv_zone_t*)p->bh->b_data,p->p); p--)
  		;
  	/*
  	 * OK, we've found the last block that must survive. The rest of our
  	 * branch should be detached before unlocking. However, if that rest
  	 * of branch is all ours and does not grow immediately from the inode
  	 * it's easier to cheat and just decrement partial->p.
  	 */
  	if (p == chain + k - 1 && p > chain) {
  		p->p--;
  	} else {
  		*top = *p->p;
  		*p->p = 0;
  	}
  	write_unlock(&pointers_lock);
  
  	while (partial > p) {
  		brelse(partial->bh);
  		partial--;
  	}
  no_top:
  	return partial;
  }
  
  static inline void free_data(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q)
  {
  	for ( ; p < q ; p++) {
  		sysv_zone_t nr = *p;
  		if (nr) {
  			*p = 0;
  			sysv_free_block(inode->i_sb, nr);
  			mark_inode_dirty(inode);
  		}
  	}
  }
  
  static void free_branches(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q, int depth)
  {
  	struct buffer_head * bh;
  	struct super_block *sb = inode->i_sb;
  
  	if (depth--) {
  		for ( ; p < q ; p++) {
  			int block;
  			sysv_zone_t nr = *p;
  			if (!nr)
  				continue;
  			*p = 0;
  			block = block_to_cpu(SYSV_SB(sb), nr);
  			bh = sb_bread(sb, block);
  			if (!bh)
  				continue;
  			free_branches(inode, (sysv_zone_t*)bh->b_data,
  					block_end(bh), depth);
  			bforget(bh);
  			sysv_free_block(sb, nr);
  			mark_inode_dirty(inode);
  		}
  	} else
  		free_data(inode, p, q);
  }
  
  void sysv_truncate (struct inode * inode)
  {
  	sysv_zone_t *i_data = SYSV_I(inode)->i_data;
  	int offsets[DEPTH];
  	Indirect chain[DEPTH];
  	Indirect *partial;
  	sysv_zone_t nr = 0;
  	int n;
  	long iblock;
  	unsigned blocksize;
  
  	if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
  	    S_ISLNK(inode->i_mode)))
  		return;
  
  	blocksize = inode->i_sb->s_blocksize;
  	iblock = (inode->i_size + blocksize-1)
  					>> inode->i_sb->s_blocksize_bits;
  
  	block_truncate_page(inode->i_mapping, inode->i_size, get_block);
  
  	n = block_to_path(inode, iblock, offsets);
  	if (n == 0)
  		return;
  
  	if (n == 1) {
  		free_data(inode, i_data+offsets[0], i_data + DIRECT);
  		goto do_indirects;
  	}
  
  	partial = find_shared(inode, n, offsets, chain, &nr);
  	/* Kill the top of shared branch (already detached) */
  	if (nr) {
  		if (partial == chain)
  			mark_inode_dirty(inode);
  		else
  			dirty_indirect(partial->bh, inode);
  		free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
  	}
  	/* Clear the ends of indirect blocks on the shared branch */
  	while (partial > chain) {
  		free_branches(inode, partial->p + 1, block_end(partial->bh),
  				(chain+n-1) - partial);
  		dirty_indirect(partial->bh, inode);
  		brelse (partial->bh);
  		partial--;
  	}
  do_indirects:
  	/* Kill the remaining (whole) subtrees (== subtrees deeper than...) */
  	while (n < DEPTH) {
  		nr = i_data[DIRECT + n - 1];
  		if (nr) {
  			i_data[DIRECT + n - 1] = 0;
  			mark_inode_dirty(inode);
  			free_branches(inode, &nr, &nr+1, n);
  		}
  		n++;
  	}
  	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
  	if (IS_SYNC(inode))
  		sysv_sync_inode (inode);
  	else
  		mark_inode_dirty(inode);
  }
  
  static unsigned sysv_nblocks(struct super_block *s, loff_t size)
  {
  	struct sysv_sb_info *sbi = SYSV_SB(s);
  	int ptrs_bits = sbi->s_ind_per_block_bits;
  	unsigned blocks, res, direct = DIRECT, i = DEPTH;
  	blocks = (size + s->s_blocksize - 1) >> s->s_blocksize_bits;
  	res = blocks;
  	while (--i && blocks > direct) {
  		blocks = ((blocks - direct - 1) >> ptrs_bits) + 1;
  		res += blocks;
  		direct = 1;
  	}
  	return blocks;
  }
  
  int sysv_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
  {
  	struct super_block *s = dentry->d_sb;
  	generic_fillattr(dentry->d_inode, stat);
  	stat->blocks = (s->s_blocksize / 512) * sysv_nblocks(s, stat->size);
  	stat->blksize = s->s_blocksize;
  	return 0;
  }
  
  static int sysv_writepage(struct page *page, struct writeback_control *wbc)
  {
  	return block_write_full_page(page,get_block,wbc);
  }
  
  static int sysv_readpage(struct file *file, struct page *page)
  {
  	return block_read_full_page(page,get_block);
  }
  
  int sysv_prepare_chunk(struct page *page, loff_t pos, unsigned len)
  {
  	return __block_write_begin(page, pos, len, get_block);
  }
  
  static void sysv_write_failed(struct address_space *mapping, loff_t to)
  {
  	struct inode *inode = mapping->host;
  
  	if (to > inode->i_size) {
  		truncate_pagecache(inode, inode->i_size);
  		sysv_truncate(inode);
  	}
  }
  
  static int sysv_write_begin(struct file *file, struct address_space *mapping,
  			loff_t pos, unsigned len, unsigned flags,
  			struct page **pagep, void **fsdata)
  {
  	int ret;
  
  	ret = block_write_begin(mapping, pos, len, flags, pagep, get_block);
  	if (unlikely(ret))
  		sysv_write_failed(mapping, pos + len);
  
  	return ret;
  }
  
  static sector_t sysv_bmap(struct address_space *mapping, sector_t block)
  {
  	return generic_block_bmap(mapping,block,get_block);
  }
  
  const struct address_space_operations sysv_aops = {
  	.readpage = sysv_readpage,
  	.writepage = sysv_writepage,
  	.write_begin = sysv_write_begin,
  	.write_end = generic_write_end,
  	.bmap = sysv_bmap
  };
  