/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * block.c
 */

/*
 * This file implements the low-level routines to read and decompress
 * datablocks and metadata blocks.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/buffer_head.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"
#include "decompressor.h"

/*
 * Read the metadata block length, this is stored in the first two
 * bytes of the metadata block.
 */
static struct buffer_head *get_block_length(struct super_block *sb,
                        u64 *cur_index, int *offset, int *length)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        struct buffer_head *bh;

        bh = sb_bread(sb, *cur_index);
        if (bh == NULL)
                return NULL;

        if (msblk->devblksize - *offset == 1) {
                *length = (unsigned char) bh->b_data[*offset];
                put_bh(bh);
                bh = sb_bread(sb, ++(*cur_index));
                if (bh == NULL)
                        return NULL;
                *length |= (unsigned char) bh->b_data[0] << 8;
                *offset = 1;
        } else {
                *length = (unsigned char) bh->b_data[*offset] |
                        (unsigned char) bh->b_data[*offset + 1] << 8;
                *offset += 2;

                if (*offset == msblk->devblksize) {
                        put_bh(bh);
                        bh = sb_bread(sb, ++(*cur_index));
                        if (bh == NULL)
                                return NULL;
                        *offset = 0;
                }
        }

        return bh;
}


/*
 * Read and decompress a metadata block or datablock.  Length is non-zero
 * if a datablock is being read (the size is stored elsewhere in the
 * filesystem), otherwise the length is obtained from the first two bytes of
 * the metadata block.  A bit in the length field indicates if the block
 * is stored uncompressed in the filesystem (usually because compression
 * generated a larger block - this does occasionally happen with compression
 * algorithms).
 */
int squashfs_read_data(struct super_block *sb, void **buffer, u64 index,
                        int length, u64 *next_index, int srclength, int pages)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        struct buffer_head **bh;
        int offset = index & ((1 << msblk->devblksize_log2) - 1);
        u64 cur_index = index >> msblk->devblksize_log2;
        int bytes, compressed, b = 0, k = 0, page = 0, avail;

        bh = kcalloc(((srclength + msblk->devblksize - 1)
                >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
        if (bh == NULL)
                return -ENOMEM;

        if (length) {
                /*
                 * Datablock.
                 */
                bytes = -offset;
                compressed = SQUASHFS_COMPRESSED_BLOCK(length);
                length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
                if (next_index)
                        *next_index = index + length;

                TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
                        index, compressed ? "" : "un", length, srclength);

                if (length < 0 || length > srclength ||
                                (index + length) > msblk->bytes_used)
                        goto read_failure;

                for (b = 0; bytes < length; b++, cur_index++) {
                        bh[b] = sb_getblk(sb, cur_index);
                        if (bh[b] == NULL)
                                goto block_release;
                        bytes += msblk->devblksize;
                }
                ll_rw_block(READ, b, bh);
        } else {
                /*
                 * Metadata block.
                 */
                if ((index + 2) > msblk->bytes_used)
                        goto read_failure;

                bh[0] = get_block_length(sb, &cur_index, &offset, &length);
                if (bh[0] == NULL)
                        goto read_failure;
                b = 1;

                bytes = msblk->devblksize - offset;
                compressed = SQUASHFS_COMPRESSED(length);
                length = SQUASHFS_COMPRESSED_SIZE(length);
                if (next_index)
                        *next_index = index + length + 2;

                TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
                                compressed ? "" : "un", length);

                if (length < 0 || length > srclength ||
                                        (index + length) > msblk->bytes_used)
                        goto block_release;

                for (; bytes < length; b++) {
                        bh[b] = sb_getblk(sb, ++cur_index);
                        if (bh[b] == NULL)
                                goto block_release;
                        bytes += msblk->devblksize;
                }
                ll_rw_block(READ, b - 1, bh + 1);
        }

        if (compressed) {
                length = squashfs_decompress(msblk, buffer, bh, b, offset,
                         length, srclength, pages);
                if (length < 0)
                        goto read_failure;
        } else {
                /*
                 * Block is uncompressed.
                 */
                int i, in, pg_offset = 0;

                for (i = 0; i < b; i++) {
                        wait_on_buffer(bh[i]);
                        if (!buffer_uptodate(bh[i]))
                                goto block_release;
                }

                for (bytes = length; k < b; k++) {
                        in = min(bytes, msblk->devblksize - offset);
                        bytes -= in;
                        while (in) {
                                if (pg_offset == PAGE_CACHE_SIZE) {
                                        page++;
                                        pg_offset = 0;
                                }
                                avail = min_t(int, in, PAGE_CACHE_SIZE -
                                                pg_offset);
                                memcpy(buffer[page] + pg_offset,
                                                bh[k]->b_data + offset, avail);
                                in -= avail;
                                pg_offset += avail;
                                offset += avail;
                        }
                        offset = 0;
                        put_bh(bh[k]);
                }
        }

        kfree(bh);
        return length;

block_release:
        for (; k < b; k++)
                put_bh(bh[k]);

read_failure:
        ERROR("squashfs_read_data failed to read block 0x%llx\n",
                                        (unsigned long long) index);
        kfree(bh);
        return -EIO;
}