LXR linux/fs/squashfs/export.c

   1/*
   2 * Squashfs - a compressed read only filesystem for Linux
   3 *
   4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   5 * Phillip Lougher <phillip@squashfs.org.uk>
   6 *
   7 * This program is free software; you can redistribute it and/or
   8 * modify it under the terms of the GNU General Public License
   9 * as published by the Free Software Foundation; either version 2,
  10 * or (at your option) any later version.
  11 *
  12 * This program is distributed in the hope that it will be useful,
  13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 * GNU General Public License for more details.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, write to the Free Software
  19 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  20 *
  21 * export.c
  22 */
  23
  24/*
  25 * This file implements code to make Squashfs filesystems exportable (NFS etc.)
  26 *
  27 * The export code uses an inode lookup table to map inode numbers passed in
  28 * filehandles to an inode location on disk.  This table is stored compressed
  29 * into metadata blocks.  A second index table is used to locate these.  This
  30 * second index table for speed of access (and because it is small) is read at
  31 * mount time and cached in memory.
  32 *
  33 * The inode lookup table is used only by the export code, inode disk
  34 * locations are directly encoded in directories, enabling direct access
  35 * without an intermediate lookup for all operations except the export ops.
  36 */
  37
  38#include <linux/fs.h>
  39#include <linux/vfs.h>
  40#include <linux/dcache.h>
  41#include <linux/exportfs.h>
  42#include <linux/slab.h>
  43
  44#include "squashfs_fs.h"
  45#include "squashfs_fs_sb.h"
  46#include "squashfs_fs_i.h"
  47#include "squashfs.h"
  48
  49/*
  50 * Look-up inode number (ino) in table, returning the inode location.
  51 */
  52static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
  53{
  54        struct squashfs_sb_info *msblk = sb->s_fs_info;
  55        int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
  56        int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
  57        u64 start = le64_to_cpu(msblk->inode_lookup_table[blk]);
  58        __le64 ino;
  59        int err;
  60
  61        TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
  62
  63        err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
  64        if (err < 0)
  65                return err;
  66
  67        TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
  68                (u64) le64_to_cpu(ino));
  69
  70        return le64_to_cpu(ino);
  71}
  72
  73
  74static struct dentry *squashfs_export_iget(struct super_block *sb,
  75        unsigned int ino_num)
  76{
  77        long long ino;
  78        struct dentry *dentry = ERR_PTR(-ENOENT);
  79
  80        TRACE("Entered squashfs_export_iget\n");
  81
  82        ino = squashfs_inode_lookup(sb, ino_num);
  83        if (ino >= 0)
  84                dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
  85
  86        return dentry;
  87}
  88
  89
  90static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
  91                struct fid *fid, int fh_len, int fh_type)
  92{
  93        if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
  94                        || fh_len < 2)
  95                return NULL;
  96
  97        return squashfs_export_iget(sb, fid->i32.ino);
  98}
  99
 100
 101static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
 102                struct fid *fid, int fh_len, int fh_type)
 103{
 104        if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
 105                return NULL;
 106
 107        return squashfs_export_iget(sb, fid->i32.parent_ino);
 108}
 109
 110
 111static struct dentry *squashfs_get_parent(struct dentry *child)
 112{
 113        struct inode *inode = child->d_inode;
 114        unsigned int parent_ino = squashfs_i(inode)->parent;
 115
 116        return squashfs_export_iget(inode->i_sb, parent_ino);
 117}
 118
 119
 120/*
 121 * Read uncompressed inode lookup table indexes off disk into memory
 122 */
 123__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
 124                u64 lookup_table_start, u64 next_table, unsigned int inodes)
 125{
 126        unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
 127        __le64 *table;
 128
 129        TRACE("In read_inode_lookup_table, length %d\n", length);
 130
 131        /* Sanity check values */
 132
 133        /* there should always be at least one inode */
 134        if (inodes == 0)
 135                return ERR_PTR(-EINVAL);
 136
 137        /* length bytes should not extend into the next table - this check
 138         * also traps instances where lookup_table_start is incorrectly larger
 139         * than the next table start
 140         */
 141        if (lookup_table_start + length > next_table)
 142                return ERR_PTR(-EINVAL);
 143
 144        table = squashfs_read_table(sb, lookup_table_start, length);
 145
 146        /*
 147         * table[0] points to the first inode lookup table metadata block,
 148         * this should be less than lookup_table_start
 149         */
 150        if (!IS_ERR(table) && le64_to_cpu(table[0]) >= lookup_table_start) {
 151                kfree(table);
 152                return ERR_PTR(-EINVAL);
 153        }
 154
 155        return table;
 156}
 157
 158
 159const struct export_operations squashfs_export_ops = {
 160        .fh_to_dentry = squashfs_fh_to_dentry,
 161        .fh_to_parent = squashfs_fh_to_parent,
 162        .get_parent = squashfs_get_parent
 163};
 164