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 }; 242