fs/squashfs/namei.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  * namei.c
  22  */
  23
  24 /*
  25  * This file implements code to do filename lookup in directories.
  26  *
  27  * Like inodes, directories are packed into compressed metadata blocks, stored
  28  * in a directory table.  Directories are accessed using the start address of
  29  * the metablock containing the directory and the offset into the
  30  * decompressed block (<block, offset>).
  31  *
  32  * Directories are organised in a slightly complex way, and are not simply
  33  * a list of file names.  The organisation takes advantage of the
  34  * fact that (in most cases) the inodes of the files will be in the same
  35  * compressed metadata block, and therefore, can share the start block.
  36  * Directories are therefore organised in a two level list, a directory
  37  * header containing the shared start block value, and a sequence of directory
  38  * entries, each of which share the shared start block.  A new directory header
  39  * is written once/if the inode start block changes.  The directory
  40  * header/directory entry list is repeated as many times as necessary.
  41  *
  42  * Directories are sorted, and can contain a directory index to speed up
  43  * file lookup.  Directory indexes store one entry per metablock, each entry
  44  * storing the index/filename mapping to the first directory header
  45  * in each metadata block.  Directories are sorted in alphabetical order,
  46  * and at lookup the index is scanned linearly looking for the first filename
  47  * alphabetically larger than the filename being looked up.  At this point the
  48  * location of the metadata block the filename is in has been found.
  49  * The general idea of the index is ensure only one metadata block needs to be
  50  * decompressed to do a lookup irrespective of the length of the directory.
  51  * This scheme has the advantage that it doesn't require extra memory overhead
  52  * and doesn't require much extra storage on disk.
  53  */
  54
  55 #include <linux/fs.h>
  56 #include <linux/vfs.h>
  57 #include <linux/slab.h>
  58 #include <linux/string.h>
  59 #include <linux/dcache.h>
  60 #include <linux/xattr.h>
  61
  62 #include "squashfs_fs.h"
  63 #include "squashfs_fs_sb.h"
  64 #include "squashfs_fs_i.h"
  65 #include "squashfs.h"
  66 #include "xattr.h"
  67
  68 /*
  69  * Lookup name in the directory index, returning the location of the metadata
  70  * block containing it, and the directory index this represents.
  71  *
  72  * If we get an error reading the index then return the part of the index
  73  * (if any) we have managed to read - the index isn't essential, just
  74  * quicker.
  75  */
  76 static int get_dir_index_using_name(struct super_block *sb,
  77                         u64 *next_block, int *next_offset, u64 index_start,
  78                         int index_offset, int i_count, const char *name,
  79                         int len)
  80 {
  81         struct squashfs_sb_info *msblk = sb->s_fs_info;
  82         int i, size, length = 0, err;
  83         struct squashfs_dir_index *index;
  84         char *str;
  85
  86         TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
  87
  88         index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
  89         if (index == NULL) {
  90                 ERROR("Failed to allocate squashfs_dir_index\n");
  91                 goto out;
  92         }
  93
  94         str = &index->name[SQUASHFS_NAME_LEN + 1];
  95         strncpy(str, name, len);
  96         str[len] = '\0';
  97
  98         for (i = 0; i < i_count; i++) {
  99                 err = squashfs_read_metadata(sb, index, &index_start,
 100                                         &index_offset, sizeof(*index));
 101                 if (err < 0)
 102                         break;
 103
 104
 105                 size = le32_to_cpu(index->size) + 1;
 106
 107                 err = squashfs_read_metadata(sb, index->name, &index_start,
 108                                         &index_offset, size);
 109                 if (err < 0)
 110                         break;
 111
 112                 index->name[size] = '\0';
 113
 114                 if (strcmp(index->name, str) > 0)
 115                         break;
 116
 117                 length = le32_to_cpu(index->index);
 118                 *next_block = le32_to_cpu(index->start_block) +
 119                                         msblk->directory_table;
 120         }
 121
 122         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
 123         kfree(index);
 124
 125 out:
 126         /*
 127          * Return index (f_pos) of the looked up metadata block.  Translate
 128          * from internal f_pos to external f_pos which is offset by 3 because
 129          * we invent "." and ".." entries which are not actually stored in the
 130          * directory.
 131          */
 132         return length + 3;
 133 }
 134
 135
 136 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 137                                  struct nameidata *nd)
 138 {
 139         const unsigned char *name = dentry->d_name.name;
 140         int len = dentry->d_name.len;
 141         struct inode *inode = NULL;
 142         struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
 143         struct squashfs_dir_header dirh;
 144         struct squashfs_dir_entry *dire;
 145         u64 block = squashfs_i(dir)->start + msblk->directory_table;
 146         int offset = squashfs_i(dir)->offset;
 147         int err, length = 0, dir_count, size;
 148
 149         TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
 150
 151         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 152         if (dire == NULL) {
 153                 ERROR("Failed to allocate squashfs_dir_entry\n");
 154                 return ERR_PTR(-ENOMEM);
 155         }
 156
 157         if (len > SQUASHFS_NAME_LEN) {
 158                 err = -ENAMETOOLONG;
 159                 goto failed;
 160         }
 161
 162         length = get_dir_index_using_name(dir->i_sb, &block, &offset,
 163                                 squashfs_i(dir)->dir_idx_start,
 164                                 squashfs_i(dir)->dir_idx_offset,
 165                                 squashfs_i(dir)->dir_idx_cnt, name, len);
 166
 167         while (length < i_size_read(dir)) {
 168                 /*
 169                  * Read directory header.
 170                  */
 171                 err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
 172                                 &offset, sizeof(dirh));
 173                 if (err < 0)
 174                         goto read_failure;
 175
 176                 length += sizeof(dirh);
 177
 178                 dir_count = le32_to_cpu(dirh.count) + 1;
 179
 180                 /* dir_count should never be larger than 256 */
 181                 if (dir_count > 256)
 182                         goto data_error;
 183
 184                 while (dir_count--) {
 185                         /*
 186                          * Read directory entry.
 187                          */
 188                         err = squashfs_read_metadata(dir->i_sb, dire, &block,
 189                                         &offset, sizeof(*dire));
 190                         if (err < 0)
 191                                 goto read_failure;
 192
 193                         size = le16_to_cpu(dire->size) + 1;
 194
 195                         /* size should never be larger than SQUASHFS_NAME_LEN */
 196                         if (size > SQUASHFS_NAME_LEN)
 197                                 goto data_error;
 198
 199                         err = squashfs_read_metadata(dir->i_sb, dire->name,
 200                                         &block, &offset, size);
 201                         if (err < 0)
 202                                 goto read_failure;
 203
 204                         length += sizeof(*dire) + size;
 205
 206                         if (name[0] < dire->name[0])
 207                                 goto exit_lookup;
 208
 209                         if (len == size && !strncmp(name, dire->name, len)) {
 210                                 unsigned int blk, off, ino_num;
 211                                 long long ino;
 212                                 blk = le32_to_cpu(dirh.start_block);
 213                                 off = le16_to_cpu(dire->offset);
 214                                 ino_num = le32_to_cpu(dirh.inode_number) +
 215                                         (short) le16_to_cpu(dire->inode_number);
 216                                 ino = SQUASHFS_MKINODE(blk, off);
 217
 218                                 TRACE("calling squashfs_iget for directory "
 219                                         "entry %s, inode  %x:%x, %d\n", name,
 220                                         blk, off, ino_num);
 221
 222                                 inode = squashfs_iget(dir->i_sb, ino, ino_num);
 223                                 goto exit_lookup;
 224                         }
 225                 }
 226         }
 227
 228 exit_lookup:
 229         kfree(dire);
 230         return d_splice_alias(inode, dentry);
 231
 232 data_error:
 233         err = -EIO;
 234
 235 read_failure:
 236         ERROR("Unable to read directory block [%llx:%x]\n",
 237                 squashfs_i(dir)->start + msblk->directory_table,
 238                 squashfs_i(dir)->offset);
 239 failed:
 240         kfree(dire);
 241         return ERR_PTR(err);
 242 }
 243
 244
 245 const struct inode_operations squashfs_dir_inode_ops = {
 246         .lookup = squashfs_lookup,
 247         .getxattr = generic_getxattr,
 248         .listxattr = squashfs_listxattr
 249 };