dir.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.
 *
 * dir.c
 */

/*
 * This file implements code to read directories from disk.
 *
 * See namei.c for a description of directory organisation on disk.
 */

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

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

static const unsigned char squashfs_filetype_table[] = {
    DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_FIFO, DT_SOCK
};

/*
 * Lookup offset (f_pos) in the directory index, returning the
 * metadata block containing it.
 *
 * If we get an error reading the index then return the part of the index
 * (if any) we have managed to read - the index isn't essential, just
 * quicker.
 */
static int get_dir_index_using_offset(struct super_block *sb,
    u64 *next_block, int *next_offset, u64 index_start, int index_offset,
    int i_count, u64 f_pos)
{
    struct squashfs_sb_info *msblk = sb->s_fs_info;
    int err, i, index, length = 0;
    struct squashfs_dir_index dir_index;

    TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
                    i_count, f_pos);

    /*
     * Translate from external f_pos to the internal f_pos.  This
     * is offset by 3 because we invent "." and ".." entries which are
     * not actually stored in the directory.
     */
    if (f_pos <= 3)
        return f_pos;
    f_pos -= 3;

    for (i = 0; i < i_count; i++) {
        err = squashfs_read_metadata(sb, &dir_index, &index_start,
                &index_offset, sizeof(dir_index));
        if (err < 0)
            break;

        index = le32_to_cpu(dir_index.index);
        if (index > f_pos)
            /*
             * Found the index we're looking for.
             */
            break;

        err = squashfs_read_metadata(sb, NULL, &index_start,
                &index_offset, le32_to_cpu(dir_index.size) + 1);
        if (err < 0)
            break;

        length = index;
        *next_block = le32_to_cpu(dir_index.start_block) +
                    msblk->directory_table;
    }

    *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;

    /*
     * Translate back from internal f_pos to external f_pos.
     */
    return length + 3;
}


static int squashfs_readdir(struct file *file, void *dirent, filldir_t filldir)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
    u64 block = squashfs_i(inode)->start + msblk->directory_table;
    int offset = squashfs_i(inode)->offset, length, dir_count, size,
                type, err;
    unsigned int inode_number;
    struct squashfs_dir_header dirh;
    struct squashfs_dir_entry *dire;

    TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);

    dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
    if (dire == NULL) {
        ERROR("Failed to allocate squashfs_dir_entry\n");
        goto finish;
    }

    /*
     * Return "." and  ".." entries as the first two filenames in the
     * directory.  To maximise compression these two entries are not
     * stored in the directory, and so we invent them here.
     *
     * It also means that the external f_pos is offset by 3 from the
     * on-disk directory f_pos.
     */
    while (file->f_pos < 3) {
        char *name;
        int i_ino;

        if (file->f_pos == 0) {
            name = ".";
            size = 1;
            i_ino = inode->i_ino;
        } else {
            name = "..";
            size = 2;
            i_ino = squashfs_i(inode)->parent;
        }

        TRACE("Calling filldir(%p, %s, %d, %lld, %d, %d)\n",
                dirent, name, size, file->f_pos, i_ino,
                squashfs_filetype_table[1]);

        if (filldir(dirent, name, size, file->f_pos, i_ino,
                squashfs_filetype_table[1]) < 0) {
                TRACE("Filldir returned less than 0\n");
            goto finish;
        }

        file->f_pos += size;
    }

    length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
                squashfs_i(inode)->dir_idx_start,
                squashfs_i(inode)->dir_idx_offset,
                squashfs_i(inode)->dir_idx_cnt,
                file->f_pos);

    while (length < i_size_read(inode)) {
        /*
         * Read directory header
         */
        err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
                    &offset, sizeof(dirh));
        if (err < 0)
            goto failed_read;

        length += sizeof(dirh);

        dir_count = le32_to_cpu(dirh.count) + 1;

        if (dir_count > SQUASHFS_DIR_COUNT)
            goto failed_read;

        while (dir_count--) {
            /*
             * Read directory entry.
             */
            err = squashfs_read_metadata(inode->i_sb, dire, &block,
                    &offset, sizeof(*dire));
            if (err < 0)
                goto failed_read;

            size = le16_to_cpu(dire->size) + 1;

            /* size should never be larger than SQUASHFS_NAME_LEN */
            if (size > SQUASHFS_NAME_LEN)
                goto failed_read;

            err = squashfs_read_metadata(inode->i_sb, dire->name,
                    &block, &offset, size);
            if (err < 0)
                goto failed_read;

            length += sizeof(*dire) + size;

            if (file->f_pos >= length)
                continue;

            dire->name[size] = '\0';
            inode_number = le32_to_cpu(dirh.inode_number) +
                ((short) le16_to_cpu(dire->inode_number));
            type = le16_to_cpu(dire->type);

            TRACE("Calling filldir(%p, %s, %d, %lld, %x:%x, %d, %d)"
                    "\n", dirent, dire->name, size,
                    file->f_pos,
                    le32_to_cpu(dirh.start_block),
                    le16_to_cpu(dire->offset),
                    inode_number,
                    squashfs_filetype_table[type]);

            if (filldir(dirent, dire->name, size, file->f_pos,
                    inode_number,
                    squashfs_filetype_table[type]) < 0) {
                TRACE("Filldir returned less than 0\n");
                goto finish;
            }

            file->f_pos = length;
        }
    }

finish:
    kfree(dire);
    return 0;

failed_read:
    ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
    kfree(dire);
    return 0;
}


const struct file_operations squashfs_dir_ops = {
    .read = generic_read_dir,
    .readdir = squashfs_readdir,
    .llseek = default_llseek,
};