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  */
  53 static 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
  75 static 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
  91 static 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
 102 static 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
 112 static 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
 152 const 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 };