namei.c

Go to the documentation of this file.

/*
 * 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.
 *
 * namei.c
 */

/*
 * This file implements code to do filename lookup in directories.
 *
 * Like inodes, directories are packed into compressed metadata blocks, stored
 * in a directory table.  Directories are accessed using the start address of
 * the metablock containing the directory and the offset into the
 * decompressed block (<block, offset>).
 *
 * Directories are organised in a slightly complex way, and are not simply
 * a list of file names.  The organisation takes advantage of the
 * fact that (in most cases) the inodes of the files will be in the same
 * compressed metadata block, and therefore, can share the start block.
 * Directories are therefore organised in a two level list, a directory
 * header containing the shared start block value, and a sequence of directory
 * entries, each of which share the shared start block.  A new directory header
 * is written once/if the inode start block changes.  The directory
 * header/directory entry list is repeated as many times as necessary.
 *
 * Directories are sorted, and can contain a directory index to speed up
 * file lookup.  Directory indexes store one entry per metablock, each entry
 * storing the index/filename mapping to the first directory header
 * in each metadata block.  Directories are sorted in alphabetical order,
 * and at lookup the index is scanned linearly looking for the first filename
 * alphabetically larger than the filename being looked up.  At this point the
 * location of the metadata block the filename is in has been found.
 * The general idea of the index is ensure only one metadata block needs to be
 * decompressed to do a lookup irrespective of the length of the directory.
 * This scheme has the advantage that it doesn't require extra memory overhead
 * and doesn't require much extra storage on disk.
 */

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

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

/*
 * Lookup name in the directory index, returning the location of the metadata
 * block containing it, and the directory index this represents.
 *
 * 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_name(struct super_block *sb,
            u64 *next_block, int *next_offset, u64 index_start,
            int index_offset, int i_count, const char *name,
            int len)
{
    struct squashfs_sb_info *msblk = sb->s_fs_info;
    int i, size, length = 0, err;
    struct squashfs_dir_index *index;
    char *str;

    TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);

    index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
    if (index == NULL) {
        ERROR("Failed to allocate squashfs_dir_index\n");
        goto out;
    }

    str = &index->name[SQUASHFS_NAME_LEN + 1];
    strncpy(str, name, len);
    str[len] = '\0';

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


        size = le32_to_cpu(index->size) + 1;

        err = squashfs_read_metadata(sb, index->name, &index_start,
                    &index_offset, size);
        if (err < 0)
            break;

        index->name[size] = '\0';

        if (strcmp(index->name, str) > 0)
            break;

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

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

out:
    /*
     * Return index (f_pos) of the looked up metadata block.  Translate
     * from internal f_pos to external f_pos which is offset by 3 because
     * we invent "." and ".." entries which are not actually stored in the
     * directory.
     */
    return length + 3;
}


static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
                 unsigned int flags)
{
    const unsigned char *name = dentry->d_name.name;
    int len = dentry->d_name.len;
    struct inode *inode = NULL;
    struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
    struct squashfs_dir_header dirh;
    struct squashfs_dir_entry *dire;
    u64 block = squashfs_i(dir)->start + msblk->directory_table;
    int offset = squashfs_i(dir)->offset;
    int err, length, dir_count, size;

    TRACE("Entered squashfs_lookup [%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");
        return ERR_PTR(-ENOMEM);
    }

    if (len > SQUASHFS_NAME_LEN) {
        err = -ENAMETOOLONG;
        goto failed;
    }

    length = get_dir_index_using_name(dir->i_sb, &block, &offset,
                squashfs_i(dir)->dir_idx_start,
                squashfs_i(dir)->dir_idx_offset,
                squashfs_i(dir)->dir_idx_cnt, name, len);

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

        length += sizeof(dirh);

        dir_count = le32_to_cpu(dirh.count) + 1;

        if (dir_count > SQUASHFS_DIR_COUNT)
            goto data_error;

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

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

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

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

            length += sizeof(*dire) + size;

            if (name[0] < dire->name[0])
                goto exit_lookup;

            if (len == size && !strncmp(name, dire->name, len)) {
                unsigned int blk, off, ino_num;
                long long ino;
                blk = le32_to_cpu(dirh.start_block);
                off = le16_to_cpu(dire->offset);
                ino_num = le32_to_cpu(dirh.inode_number) +
                    (short) le16_to_cpu(dire->inode_number);
                ino = SQUASHFS_MKINODE(blk, off);

                TRACE("calling squashfs_iget for directory "
                    "entry %s, inode  %x:%x, %d\n", name,
                    blk, off, ino_num);

                inode = squashfs_iget(dir->i_sb, ino, ino_num);
                goto exit_lookup;
            }
        }
    }

exit_lookup:
    kfree(dire);
    return d_splice_alias(inode, dentry);

data_error:
    err = -EIO;

read_failure:
    ERROR("Unable to read directory block [%llx:%x]\n",
        squashfs_i(dir)->start + msblk->directory_table,
        squashfs_i(dir)->offset);
failed:
    kfree(dire);
    return ERR_PTR(err);
}


const struct inode_operations squashfs_dir_inode_ops = {
    .lookup = squashfs_lookup,
    .getxattr = generic_getxattr,
    .listxattr = squashfs_listxattr
};