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Linux/fs/squashfs/export.c

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  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 = 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 
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 };
164 

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