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@lougher.demon.co.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/zlib.h>
  43#include <linux/slab.h>
  44
  45#include "squashfs_fs.h"
  46#include "squashfs_fs_sb.h"
  47#include "squashfs_fs_i.h"
  48#include "squashfs.h"
  49
  50/*
  51 * Look-up inode number (ino) in table, returning the inode location.
  52 */
  53static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
  54{
  55        struct squashfs_sb_info *msblk = sb->s_fs_info;
  56        int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
  57        int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
  58        u64 start = le64_to_cpu(msblk->inode_lookup_table[blk]);
  59        __le64 ino;
  60        int err;
  61
  62        TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
  63
  64        err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
  65        if (err < 0)
  66                return err;
  67
  68        TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
  69                (u64) le64_to_cpu(ino));
  70
  71        return le64_to_cpu(ino);
  72}
  73
  74
  75static struct dentry *squashfs_export_iget(struct super_block *sb,
  76        unsigned int ino_num)
  77{
  78        long long ino;
  79        struct dentry *dentry = ERR_PTR(-ENOENT);
  80
  81        TRACE("Entered squashfs_export_iget\n");
  82
  83        ino = squashfs_inode_lookup(sb, ino_num);
  84        if (ino >= 0)
  85                dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
  86
  87        return dentry;
  88}
  89
  90
  91static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
  92                struct fid *fid, int fh_len, int fh_type)
  93{
  94        if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
  95                        || fh_len < 2)
  96                return NULL;
  97
  98        return squashfs_export_iget(sb, fid->i32.ino);
  99}
 100
 101
 102static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
 103                struct fid *fid, int fh_len, int fh_type)
 104{
 105        if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
 106                return NULL;
 107
 108        return squashfs_export_iget(sb, fid->i32.parent_ino);
 109}
 110
 111
 112static struct dentry *squashfs_get_parent(struct dentry *child)
 113{
 114        struct inode *inode = child->d_inode;
 115        unsigned int parent_ino = squashfs_i(inode)->parent;
 116
 117        return squashfs_export_iget(inode->i_sb, parent_ino);
 118}
 119
 120
 121/*
 122 * Read uncompressed inode lookup table indexes off disk into memory
 123 */
 124__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
 125                u64 lookup_table_start, unsigned int inodes)
 126{
 127        unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
 128        __le64 *inode_lookup_table;
 129        int err;
 130
 131        TRACE("In read_inode_lookup_table, length %d\n", length);
 132
 133        /* Allocate inode lookup table indexes */
 134        inode_lookup_table = kmalloc(length, GFP_KERNEL);
 135        if (inode_lookup_table == NULL) {
 136                ERROR("Failed to allocate inode lookup table\n");
 137                return ERR_PTR(-ENOMEM);
 138        }
 139
 140        err = squashfs_read_table(sb, inode_lookup_table, lookup_table_start,
 141                        length);
 142        if (err < 0) {
 143                ERROR("unable to read inode lookup table\n");
 144                kfree(inode_lookup_table);
 145                return ERR_PTR(err);
 146        }
 147
 148        return inode_lookup_table;
 149}
 150
 151
 152const struct export_operations squashfs_export_ops = {
 153        .fh_to_dentry = squashfs_fh_to_dentry,
 154        .fh_to_parent = squashfs_fh_to_parent,
 155        .get_parent = squashfs_get_parent
 156};
 157