/*
 * OMFS (as used by RIO Karma) file operations.
 * Copyright (C) 2005 Bob Copeland <me@bobcopeland.com>
 * Released under GPL v2.
 */

#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)) {
                        be64_add_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 */
        be32_add_cpu(&oe->e_extent_count, 1);

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 void omfs_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);
                omfs_truncate(inode);
        }
}

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))
                omfs_write_failed(mapping, pos + len);

        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 = new_sync_read,
        .write = new_sync_write,
        .read_iter = generic_file_read_iter,
        .write_iter = generic_file_write_iter,
        .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 = inode_newsize_ok(inode, attr->ia_size);
                if (error)
                        return error;
                truncate_setsize(inode, attr->ia_size);
                omfs_truncate(inode);
        }

        setattr_copy(inode, attr);
        mark_inode_dirty(inode);
        return 0;
}

const struct inode_operations omfs_file_inops = {
        .setattr = omfs_setattr,
};

const struct address_space_operations omfs_aops = {
        .readpage = omfs_readpage,
        .readpages = omfs_readpages,
        .writepage = omfs_writepage,
        .writepages = omfs_writepages,
        .write_begin = omfs_write_begin,
        .write_end = generic_write_end,
        .bmap = omfs_bmap,
};