// SPDX-License-Identifier: GPL-2.0

  /*
   *	fs/bfs/file.c
   *	BFS file operations.

   *	Copyright (C) 1999-2018 Tigran Aivazian <aivazian.tigran@gmail.com>

   *
   *	Make the file block allocation algorithm understand the size
   *	of the underlying block device.
   *	Copyright (C) 2007 Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
   *

   */
  
  #include <linux/fs.h>
  #include <linux/buffer_head.h>

  #include "bfs.h"
  
  #undef DEBUG
  
  #ifdef DEBUG
  #define dprintf(x...)	printf(x)
  #else
  #define dprintf(x...)
  #endif

  const struct file_operations bfs_file_operations = {

  	.llseek 	= generic_file_llseek,

  	.read_iter	= generic_file_read_iter,

  	.write_iter	= generic_file_write_iter,

  	.mmap		= generic_file_mmap,

  	.splice_read	= generic_file_splice_read,

  };

  static int bfs_move_block(unsigned long from, unsigned long to,
  					struct super_block *sb)

  {
  	struct buffer_head *bh, *new;
  
  	bh = sb_bread(sb, from);
  	if (!bh)
  		return -EIO;
  	new = sb_getblk(sb, to);
  	memcpy(new->b_data, bh->b_data, bh->b_size);
  	mark_buffer_dirty(new);
  	bforget(bh);
  	brelse(new);
  	return 0;
  }

  static int bfs_move_blocks(struct super_block *sb, unsigned long start,

  				unsigned long end, unsigned long where)

  {
  	unsigned long i;
  
  	dprintf("%08lx-%08lx->%08lx
  ", start, end, where);
  	for (i = start; i <= end; i++)
  		if(bfs_move_block(i, where + i, sb)) {

  			dprintf("failed to move block %08lx -> %08lx
  ", i,
  								where + i);

  			return -EIO;
  		}
  	return 0;
  }

  static int bfs_get_block(struct inode *inode, sector_t block,
  			struct buffer_head *bh_result, int create)

  {

  	unsigned long phys;

  	int err;
  	struct super_block *sb = inode->i_sb;
  	struct bfs_sb_info *info = BFS_SB(sb);
  	struct bfs_inode_info *bi = BFS_I(inode);

  	phys = bi->i_sblock + block;
  	if (!create) {
  		if (phys <= bi->i_eblock) {

  			dprintf("c=%d, b=%08lx, phys=%09lx (granted)
  ",
                                  create, (unsigned long)block, phys);

  			map_bh(bh_result, sb, phys);
  		}
  		return 0;
  	}

  	/*
  	 * If the file is not empty and the requested block is within the
  	 * range of blocks allocated for this file, we can grant it.
  	 */
  	if (bi->i_sblock && (phys <= bi->i_eblock)) {

  		dprintf("c=%d, b=%08lx, phys=%08lx (interim block granted)
  ", 

  				create, (unsigned long)block, phys);

  		map_bh(bh_result, sb, phys);
  		return 0;
  	}

  	/* The file will be extended, so let's see if there is enough space. */
  	if (phys >= info->si_blocks)
  		return -ENOSPC;
  
  	/* The rest has to be protected against itself. */

  	mutex_lock(&info->bfs_lock);

  	/*
  	 * If the last data block for this file is the last allocated
  	 * block, we can extend the file trivially, without moving it
  	 * anywhere.
  	 */

  	if (bi->i_eblock == info->si_lf_eblk) {
  		dprintf("c=%d, b=%08lx, phys=%08lx (simple extension)
  ", 

  				create, (unsigned long)block, phys);

  		map_bh(bh_result, sb, phys);
  		info->si_freeb -= phys - bi->i_eblock;
  		info->si_lf_eblk = bi->i_eblock = phys;
  		mark_inode_dirty(inode);

  		err = 0;
  		goto out;
  	}

  	/* Ok, we have to move this entire file to the next free block. */

  	phys = info->si_lf_eblk + 1;

  	if (phys + block >= info->si_blocks) {
  		err = -ENOSPC;
  		goto out;
  	}
  
  	if (bi->i_sblock) {

  		err = bfs_move_blocks(inode->i_sb, bi->i_sblock, 

  						bi->i_eblock, phys);

  		if (err) {

  			dprintf("failed to move ino=%08lx -> fs corruption
  ",
  								inode->i_ino);

  			goto out;
  		}
  	} else
  		err = 0;

  	dprintf("c=%d, b=%08lx, phys=%08lx (moved)
  ",
                  create, (unsigned long)block, phys);

  	bi->i_sblock = phys;
  	phys += block;
  	info->si_lf_eblk = bi->i_eblock = phys;

  	/*
  	 * This assumes nothing can write the inode back while we are here
  	 * and thus update inode->i_blocks! (XXX)
  	 */

  	info->si_freeb -= bi->i_eblock - bi->i_sblock + 1 - inode->i_blocks;
  	mark_inode_dirty(inode);

  	map_bh(bh_result, sb, phys);
  out:

  	mutex_unlock(&info->bfs_lock);

  	return err;
  }
  
  static int bfs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	return block_write_full_page(page, bfs_get_block, wbc);
  }
  
  static int bfs_readpage(struct file *file, struct page *page)
  {
  	return block_read_full_page(page, bfs_get_block);
  }

  static void bfs_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);

  }

  static int bfs_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,
  				bfs_get_block);

  	if (unlikely(ret))
  		bfs_write_failed(mapping, pos + len);

  
  	return ret;

  }
  
  static sector_t bfs_bmap(struct address_space *mapping, sector_t block)
  {
  	return generic_block_bmap(mapping, block, bfs_get_block);
  }

  const struct address_space_operations bfs_aops = {

  	.readpage	= bfs_readpage,
  	.writepage	= bfs_writepage,

  	.write_begin	= bfs_write_begin,
  	.write_end	= generic_write_end,

  	.bmap		= bfs_bmap,
  };

  const struct inode_operations bfs_file_inops;