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  */
  52 static 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
  74 static 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
  90 static 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
 101 static 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
 111 static struct dentry *squashfs_get_parent(struct dentry *child)
 112 {
 113         struct inode *inode = d_inode(child);
 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
 159 const 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 };