block.c

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/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <[email protected]>
 *
 * 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;
}