/*
   * OMFS (as used by RIO Karma) file operations.
   * Copyright (C) 2005 Bob Copeland <me@bobcopeland.com>
   * Released under GPL v2.
   */
  
  #include <linux/version.h>
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/buffer_head.h>
  #include <linux/mpage.h>
  #include "omfs.h"

  static u32 omfs_max_extents(struct omfs_sb_info *sbi, int offset)
  {
  	return (sbi->s_sys_blocksize - offset -
  		sizeof(struct omfs_extent)) /
  		sizeof(struct omfs_extent_entry) + 1;
  }

  void omfs_make_empty_table(struct buffer_head *bh, int offset)
  {
  	struct omfs_extent *oe = (struct omfs_extent *) &bh->b_data[offset];

  	oe->e_next = ~cpu_to_be64(0ULL);

  	oe->e_extent_count = cpu_to_be32(1),
  	oe->e_fill = cpu_to_be32(0x22),

  	oe->e_entry.e_cluster = ~cpu_to_be64(0ULL);
  	oe->e_entry.e_blocks = ~cpu_to_be64(0ULL);

  }
  
  int omfs_shrink_inode(struct inode *inode)
  {
  	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
  	struct omfs_extent *oe;
  	struct omfs_extent_entry *entry;
  	struct buffer_head *bh;
  	u64 next, last;
  	u32 extent_count;

  	u32 max_extents;

  	int ret;
  
  	/* traverse extent table, freeing each entry that is greater
  	 * than inode->i_size;
  	 */
  	next = inode->i_ino;
  
  	/* only support truncate -> 0 for now */
  	ret = -EIO;
  	if (inode->i_size != 0)
  		goto out;

  	bh = omfs_bread(inode->i_sb, next);

  	if (!bh)
  		goto out;
  
  	oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);

  	max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);

  
  	for (;;) {

  		if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next))
  			goto out_brelse;

  
  		extent_count = be32_to_cpu(oe->e_extent_count);

  
  		if (extent_count > max_extents)
  			goto out_brelse;

  		last = next;
  		next = be64_to_cpu(oe->e_next);
  		entry = &oe->e_entry;
  
  		/* ignore last entry as it is the terminator */
  		for (; extent_count > 1; extent_count--) {
  			u64 start, count;
  			start = be64_to_cpu(entry->e_cluster);
  			count = be64_to_cpu(entry->e_blocks);
  
  			omfs_clear_range(inode->i_sb, start, (int) count);
  			entry++;
  		}
  		omfs_make_empty_table(bh, (char *) oe - bh->b_data);
  		mark_buffer_dirty(bh);
  		brelse(bh);
  
  		if (last != inode->i_ino)
  			omfs_clear_range(inode->i_sb, last, sbi->s_mirrors);
  
  		if (next == ~0)
  			break;

  		bh = omfs_bread(inode->i_sb, next);

  		if (!bh)
  			goto out;
  		oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);

  		max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);

  	}
  	ret = 0;
  out:
  	return ret;

  out_brelse:
  	brelse(bh);
  	return ret;

  }
  
  static void omfs_truncate(struct inode *inode)
  {
  	omfs_shrink_inode(inode);
  	mark_inode_dirty(inode);
  }
  
  /*
   * Add new blocks to the current extent, or create new entries/continuations
   * as necessary.
   */
  static int omfs_grow_extent(struct inode *inode, struct omfs_extent *oe,
  			u64 *ret_block)
  {
  	struct omfs_extent_entry *terminator;
  	struct omfs_extent_entry *entry = &oe->e_entry;
  	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
  	u32 extent_count = be32_to_cpu(oe->e_extent_count);
  	u64 new_block = 0;
  	u32 max_count;
  	int new_count;
  	int ret = 0;
  
  	/* reached the end of the extent table with no blocks mapped.
  	 * there are three possibilities for adding: grow last extent,
  	 * add a new extent to the current extent table, and add a
  	 * continuation inode.  in last two cases need an allocator for
  	 * sbi->s_cluster_size
  	 */
  
  	/* TODO: handle holes */
  
  	/* should always have a terminator */
  	if (extent_count < 1)
  		return -EIO;
  
  	/* trivially grow current extent, if next block is not taken */
  	terminator = entry + extent_count - 1;
  	if (extent_count > 1) {
  		entry = terminator-1;
  		new_block = be64_to_cpu(entry->e_cluster) +
  			be64_to_cpu(entry->e_blocks);
  
  		if (omfs_allocate_block(inode->i_sb, new_block)) {
  			entry->e_blocks =
  				cpu_to_be64(be64_to_cpu(entry->e_blocks) + 1);
  			terminator->e_blocks = ~(cpu_to_be64(
  				be64_to_cpu(~terminator->e_blocks) + 1));
  			goto out;
  		}
  	}

  	max_count = omfs_max_extents(sbi, OMFS_EXTENT_START);

  
  	/* TODO: add a continuation block here */
  	if (be32_to_cpu(oe->e_extent_count) > max_count-1)
  		return -EIO;
  
  	/* try to allocate a new cluster */
  	ret = omfs_allocate_range(inode->i_sb, 1, sbi->s_clustersize,
  		&new_block, &new_count);
  	if (ret)
  		goto out_fail;
  
  	/* copy terminator down an entry */
  	entry = terminator;
  	terminator++;
  	memcpy(terminator, entry, sizeof(struct omfs_extent_entry));
  
  	entry->e_cluster = cpu_to_be64(new_block);
  	entry->e_blocks = cpu_to_be64((u64) new_count);
  
  	terminator->e_blocks = ~(cpu_to_be64(
  		be64_to_cpu(~terminator->e_blocks) + (u64) new_count));
  
  	/* write in new entry */
  	oe->e_extent_count = cpu_to_be32(1 + be32_to_cpu(oe->e_extent_count));
  
  out:
  	*ret_block = new_block;
  out_fail:
  	return ret;
  }
  
  /*
   * Scans across the directory table for a given file block number.
   * If block not found, return 0.
   */
  static sector_t find_block(struct inode *inode, struct omfs_extent_entry *ent,
  			sector_t block, int count, int *left)
  {
  	/* count > 1 because of terminator */
  	sector_t searched = 0;
  	for (; count > 1; count--) {
  		int numblocks = clus_to_blk(OMFS_SB(inode->i_sb),
  			be64_to_cpu(ent->e_blocks));
  
  		if (block >= searched  &&
  		    block < searched + numblocks) {
  			/*
  			 * found it at cluster + (block - searched)
  			 * numblocks - (block - searched) is remainder
  			 */
  			*left = numblocks - (block - searched);
  			return clus_to_blk(OMFS_SB(inode->i_sb),
  				be64_to_cpu(ent->e_cluster)) +
  				block - searched;
  		}
  		searched += numblocks;
  		ent++;
  	}
  	return 0;
  }
  
  static int omfs_get_block(struct inode *inode, sector_t block,
  			  struct buffer_head *bh_result, int create)
  {
  	struct buffer_head *bh;
  	sector_t next, offset;
  	int ret;

  	u64 uninitialized_var(new_block);

  	u32 max_extents;

  	int extent_count;
  	struct omfs_extent *oe;
  	struct omfs_extent_entry *entry;
  	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
  	int max_blocks = bh_result->b_size >> inode->i_blkbits;
  	int remain;
  
  	ret = -EIO;

  	bh = omfs_bread(inode->i_sb, inode->i_ino);

  	if (!bh)
  		goto out;
  
  	oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);

  	max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);

  	next = inode->i_ino;
  
  	for (;;) {
  
  		if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next))
  			goto out_brelse;
  
  		extent_count = be32_to_cpu(oe->e_extent_count);
  		next = be64_to_cpu(oe->e_next);
  		entry = &oe->e_entry;

  		if (extent_count > max_extents)
  			goto out_brelse;

  		offset = find_block(inode, entry, block, extent_count, &remain);
  		if (offset > 0) {
  			ret = 0;
  			map_bh(bh_result, inode->i_sb, offset);
  			if (remain > max_blocks)
  				remain = max_blocks;
  			bh_result->b_size = (remain << inode->i_blkbits);
  			goto out_brelse;
  		}
  		if (next == ~0)
  			break;
  
  		brelse(bh);

  		bh = omfs_bread(inode->i_sb, next);

  		if (!bh)
  			goto out;
  		oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);

  		max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);

  	}
  	if (create) {
  		ret = omfs_grow_extent(inode, oe, &new_block);
  		if (ret == 0) {
  			mark_buffer_dirty(bh);
  			mark_inode_dirty(inode);
  			map_bh(bh_result, inode->i_sb,
  					clus_to_blk(sbi, new_block));
  		}
  	}
  out_brelse:
  	brelse(bh);
  out:
  	return ret;
  }
  
  static int omfs_readpage(struct file *file, struct page *page)
  {
  	return block_read_full_page(page, omfs_get_block);
  }
  
  static int omfs_readpages(struct file *file, struct address_space *mapping,
  		struct list_head *pages, unsigned nr_pages)
  {
  	return mpage_readpages(mapping, pages, nr_pages, omfs_get_block);
  }
  
  static int omfs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	return block_write_full_page(page, omfs_get_block, wbc);
  }
  
  static int
  omfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
  {
  	return mpage_writepages(mapping, wbc, omfs_get_block);
  }
  
  static int omfs_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,
  				omfs_get_block);
  	if (unlikely(ret)) {
  		loff_t isize = mapping->host->i_size;
  		if (pos + len > isize)
  			vmtruncate(mapping->host, isize);
  	}
  
  	return ret;

  }
  
  static sector_t omfs_bmap(struct address_space *mapping, sector_t block)
  {
  	return generic_block_bmap(mapping, block, omfs_get_block);
  }

  const struct file_operations omfs_file_operations = {

  	.llseek = generic_file_llseek,
  	.read = do_sync_read,
  	.write = do_sync_write,
  	.aio_read = generic_file_aio_read,
  	.aio_write = generic_file_aio_write,
  	.mmap = generic_file_mmap,

  	.fsync = generic_file_fsync,

  	.splice_read = generic_file_splice_read,
  };

  static int omfs_setattr(struct dentry *dentry, struct iattr *attr)
  {
  	struct inode *inode = dentry->d_inode;
  	int error;
  
  	error = inode_change_ok(inode, attr);
  	if (error)
  		return error;

  
  	if ((attr->ia_valid & ATTR_SIZE) &&
  	    attr->ia_size != i_size_read(inode)) {
  		error = vmtruncate(inode, attr->ia_size);
  		if (error)
  			return error;
  	}
  
  	setattr_copy(inode, attr);
  	mark_inode_dirty(inode);
  	return 0;

  }

  const struct inode_operations omfs_file_inops = {

  	.setattr = omfs_setattr,

  	.truncate = omfs_truncate
  };

  const struct address_space_operations omfs_aops = {

  	.readpage = omfs_readpage,
  	.readpages = omfs_readpages,
  	.writepage = omfs_writepage,
  	.writepages = omfs_writepages,
  	.sync_page = block_sync_page,
  	.write_begin = omfs_write_begin,
  	.write_end = generic_write_end,
  	.bmap = omfs_bmap,
  };