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@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  * 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
  61 #include "squashfs_fs.h"
  62 #include "squashfs_fs_sb.h"
  63 #include "squashfs_fs_i.h"
  64 #include "squashfs.h"
  65
  66 /*
  67  * Lookup name in the directory index, returning the location of the metadata
  68  * block containing it, and the directory index this represents.
  69  *
  70  * If we get an error reading the index then return the part of the index
  71  * (if any) we have managed to read - the index isn't essential, just
  72  * quicker.
  73  */
  74 static int get_dir_index_using_name(struct super_block *sb,
  75                         u64 *next_block, int *next_offset, u64 index_start,
  76                         int index_offset, int i_count, const char *name,
  77                         int len)
  78 {
  79         struct squashfs_sb_info *msblk = sb->s_fs_info;
  80         int i, size, length = 0, err;
  81         struct squashfs_dir_index *index;
  82         char *str;
  83
  84         TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
  85
  86         index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
  87         if (index == NULL) {
  88                 ERROR("Failed to allocate squashfs_dir_index\n");
  89                 goto out;
  90         }
  91
  92         str = &index->name[SQUASHFS_NAME_LEN + 1];
  93         strncpy(str, name, len);
  94         str[len] = '\0';
  95
  96         for (i = 0; i < i_count; i++) {
  97                 err = squashfs_read_metadata(sb, index, &index_start,
  98                                         &index_offset, sizeof(*index));
  99                 if (err < 0)
 100                         break;
 101
 102
 103                 size = le32_to_cpu(index->size) + 1;
 104
 105                 err = squashfs_read_metadata(sb, index->name, &index_start,
 106                                         &index_offset, size);
 107                 if (err < 0)
 108                         break;
 109
 110                 index->name[size] = '\0';
 111
 112                 if (strcmp(index->name, str) > 0)
 113                         break;
 114
 115                 length = le32_to_cpu(index->index);
 116                 *next_block = le32_to_cpu(index->start_block) +
 117                                         msblk->directory_table;
 118         }
 119
 120         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
 121         kfree(index);
 122
 123 out:
 124         /*
 125          * Return index (f_pos) of the looked up metadata block.  Translate
 126          * from internal f_pos to external f_pos which is offset by 3 because
 127          * we invent "." and ".." entries which are not actually stored in the
 128          * directory.
 129          */
 130         return length + 3;
 131 }
 132
 133
 134 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 135                                  struct nameidata *nd)
 136 {
 137         const unsigned char *name = dentry->d_name.name;
 138         int len = dentry->d_name.len;
 139         struct inode *inode = NULL;
 140         struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
 141         struct squashfs_dir_header dirh;
 142         struct squashfs_dir_entry *dire;
 143         u64 block = squashfs_i(dir)->start + msblk->directory_table;
 144         int offset = squashfs_i(dir)->offset;
 145         int err, length = 0, dir_count, size;
 146
 147         TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
 148
 149         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 150         if (dire == NULL) {
 151                 ERROR("Failed to allocate squashfs_dir_entry\n");
 152                 return ERR_PTR(-ENOMEM);
 153         }
 154
 155         if (len > SQUASHFS_NAME_LEN) {
 156                 err = -ENAMETOOLONG;
 157                 goto failed;
 158         }
 159
 160         length = get_dir_index_using_name(dir->i_sb, &block, &offset,
 161                                 squashfs_i(dir)->dir_idx_start,
 162                                 squashfs_i(dir)->dir_idx_offset,
 163                                 squashfs_i(dir)->dir_idx_cnt, name, len);
 164
 165         while (length < i_size_read(dir)) {
 166                 /*
 167                  * Read directory header.
 168                  */
 169                 err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
 170                                 &offset, sizeof(dirh));
 171                 if (err < 0)
 172                         goto read_failure;
 173
 174                 length += sizeof(dirh);
 175
 176                 dir_count = le32_to_cpu(dirh.count) + 1;
 177                 while (dir_count--) {
 178                         /*
 179                          * Read directory entry.
 180                          */
 181                         err = squashfs_read_metadata(dir->i_sb, dire, &block,
 182                                         &offset, sizeof(*dire));
 183                         if (err < 0)
 184                                 goto read_failure;
 185
 186                         size = le16_to_cpu(dire->size) + 1;
 187
 188                         err = squashfs_read_metadata(dir->i_sb, dire->name,
 189                                         &block, &offset, size);
 190                         if (err < 0)
 191                                 goto read_failure;
 192
 193                         length += sizeof(*dire) + size;
 194
 195                         if (name[0] < dire->name[0])
 196                                 goto exit_lookup;
 197
 198                         if (len == size && !strncmp(name, dire->name, len)) {
 199                                 unsigned int blk, off, ino_num;
 200                                 long long ino;
 201                                 blk = le32_to_cpu(dirh.start_block);
 202                                 off = le16_to_cpu(dire->offset);
 203                                 ino_num = le32_to_cpu(dirh.inode_number) +
 204                                         (short) le16_to_cpu(dire->inode_number);
 205                                 ino = SQUASHFS_MKINODE(blk, off);
 206
 207                                 TRACE("calling squashfs_iget for directory "
 208                                         "entry %s, inode  %x:%x, %d\n", name,
 209                                         blk, off, ino_num);
 210
 211                                 inode = squashfs_iget(dir->i_sb, ino, ino_num);
 212                                 if (IS_ERR(inode)) {
 213                                         err = PTR_ERR(inode);
 214                                         goto failed;
 215                                 }
 216
 217                                 goto exit_lookup;
 218                         }
 219                 }
 220         }
 221
 222 exit_lookup:
 223         kfree(dire);
 224         if (inode)
 225                 return d_splice_alias(inode, dentry);
 226         d_add(dentry, inode);
 227         return ERR_PTR(0);
 228
 229 read_failure:
 230         ERROR("Unable to read directory block [%llx:%x]\n",
 231                 squashfs_i(dir)->start + msblk->directory_table,
 232                 squashfs_i(dir)->offset);
 233 failed:
 234         kfree(dire);
 235         return ERR_PTR(err);
 236 }
 237
 238
 239 const struct inode_operations squashfs_dir_inode_ops = {
 240         .lookup = squashfs_lookup
 241 };