// 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\n", start, end, where);
        for (i = start; i <= end; i++)
                if(bfs_move_block(i, where + i, sb)) {
                        dprintf("failed to move block %08lx -> %08lx\n", 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)\n",
                                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)\n", 
                                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)\n", 
                                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\n",
                                                                inode->i_ino);
                        goto out;
                }
        } else
                err = 0;

        dprintf("c=%d, b=%08lx, phys=%08lx (moved)\n",
                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 = {
        .set_page_dirty = __set_page_dirty_buffers,
        .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;