export.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.
 *
 * export.c
 */

/*
 * This file implements code to make Squashfs filesystems exportable (NFS etc.)
 *
 * The export code uses an inode lookup table to map inode numbers passed in
 * filehandles to an inode location on disk.  This table is stored compressed
 * into metadata blocks.  A second index table is used to locate these.  This
 * second index table for speed of access (and because it is small) is read at
 * mount time and cached in memory.
 *
 * The inode lookup table is used only by the export code, inode disk
 * locations are directly encoded in directories, enabling direct access
 * without an intermediate lookup for all operations except the export ops.
 */

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

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

/*
 * Look-up inode number (ino) in table, returning the inode location.
 */
static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
{
    struct squashfs_sb_info *msblk = sb->s_fs_info;
    int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
    int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
    u64 start = le64_to_cpu(msblk->inode_lookup_table[blk]);
    __le64 ino;
    int err;

    TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);

    err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
    if (err < 0)
        return err;

    TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
        (u64) le64_to_cpu(ino));

    return le64_to_cpu(ino);
}


static struct dentry *squashfs_export_iget(struct super_block *sb,
    unsigned int ino_num)
{
    long long ino;
    struct dentry *dentry = ERR_PTR(-ENOENT);

    TRACE("Entered squashfs_export_iget\n");

    ino = squashfs_inode_lookup(sb, ino_num);
    if (ino >= 0)
        dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));

    return dentry;
}


static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
        struct fid *fid, int fh_len, int fh_type)
{
    if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
            || fh_len < 2)
        return NULL;

    return squashfs_export_iget(sb, fid->i32.ino);
}


static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
        struct fid *fid, int fh_len, int fh_type)
{
    if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
        return NULL;

    return squashfs_export_iget(sb, fid->i32.parent_ino);
}


static struct dentry *squashfs_get_parent(struct dentry *child)
{
    struct inode *inode = child->d_inode;
    unsigned int parent_ino = squashfs_i(inode)->parent;

    return squashfs_export_iget(inode->i_sb, parent_ino);
}


/*
 * Read uncompressed inode lookup table indexes off disk into memory
 */
__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
        u64 lookup_table_start, u64 next_table, unsigned int inodes)
{
    unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
    __le64 *table;

    TRACE("In read_inode_lookup_table, length %d\n", length);

    /* Sanity check values */

    /* there should always be at least one inode */
    if (inodes == 0)
        return ERR_PTR(-EINVAL);

    /* length bytes should not extend into the next table - this check
     * also traps instances where lookup_table_start is incorrectly larger
     * than the next table start
     */
    if (lookup_table_start + length > next_table)
        return ERR_PTR(-EINVAL);

    table = squashfs_read_table(sb, lookup_table_start, length);

    /*
     * table[0] points to the first inode lookup table metadata block,
     * this should be less than lookup_table_start
     */
    if (!IS_ERR(table) && le64_to_cpu(table[0]) >= lookup_table_start) {
        kfree(table);
        return ERR_PTR(-EINVAL);
    }

    return table;
}


const struct export_operations squashfs_export_ops = {
    .fh_to_dentry = squashfs_fh_to_dentry,
    .fh_to_parent = squashfs_fh_to_parent,
    .get_parent = squashfs_get_parent
};