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, length = 0, err; 83 unsigned int size; 84 struct squashfs_dir_index *index; 85 char *str; 86 87 TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count); 88 89 index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL); 90 if (index == NULL) { 91 ERROR("Failed to allocate squashfs_dir_index\n"); 92 goto out; 93 } 94 95 str = &index->name[SQUASHFS_NAME_LEN + 1]; 96 strncpy(str, name, len); 97 str[len] = '\0'; 98 99 for (i = 0; i < i_count; i++) { 100 err = squashfs_read_metadata(sb, index, &index_start, 101 &index_offset, sizeof(*index)); 102 if (err < 0) 103 break; 104 105 106 size = le32_to_cpu(index->size) + 1; 107 if (size > SQUASHFS_NAME_LEN) 108 break; 109 110 err = squashfs_read_metadata(sb, index->name, &index_start, 111 &index_offset, size); 112 if (err < 0) 113 break; 114 115 index->name[size] = '\0'; 116 117 if (strcmp(index->name, str) > 0) 118 break; 119 120 length = le32_to_cpu(index->index); 121 *next_block = le32_to_cpu(index->start_block) + 122 msblk->directory_table; 123 } 124 125 *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE; 126 kfree(index); 127 128 out: 129 /* 130 * Return index (f_pos) of the looked up metadata block. Translate 131 * from internal f_pos to external f_pos which is offset by 3 because 132 * we invent "." and ".." entries which are not actually stored in the 133 * directory. 134 */ 135 return length + 3; 136 } 137 138 139 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry, 140 unsigned int flags) 141 { 142 const unsigned char *name = dentry->d_name.name; 143 int len = dentry->d_name.len; 144 struct inode *inode = NULL; 145 struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info; 146 struct squashfs_dir_header dirh; 147 struct squashfs_dir_entry *dire; 148 u64 block = squashfs_i(dir)->start + msblk->directory_table; 149 int offset = squashfs_i(dir)->offset; 150 int err, length; 151 unsigned int dir_count, size; 152 153 TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset); 154 155 dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL); 156 if (dire == NULL) { 157 ERROR("Failed to allocate squashfs_dir_entry\n"); 158 return ERR_PTR(-ENOMEM); 159 } 160 161 if (len > SQUASHFS_NAME_LEN) { 162 err = -ENAMETOOLONG; 163 goto failed; 164 } 165 166 length = get_dir_index_using_name(dir->i_sb, &block, &offset, 167 squashfs_i(dir)->dir_idx_start, 168 squashfs_i(dir)->dir_idx_offset, 169 squashfs_i(dir)->dir_idx_cnt, name, len); 170 171 while (length < i_size_read(dir)) { 172 /* 173 * Read directory header. 174 */ 175 err = squashfs_read_metadata(dir->i_sb, &dirh, &block, 176 &offset, sizeof(dirh)); 177 if (err < 0) 178 goto read_failure; 179 180 length += sizeof(dirh); 181 182 dir_count = le32_to_cpu(dirh.count) + 1; 183 184 if (dir_count > SQUASHFS_DIR_COUNT) 185 goto data_error; 186 187 while (dir_count--) { 188 /* 189 * Read directory entry. 190 */ 191 err = squashfs_read_metadata(dir->i_sb, dire, &block, 192 &offset, sizeof(*dire)); 193 if (err < 0) 194 goto read_failure; 195 196 size = le16_to_cpu(dire->size) + 1; 197 198 /* size should never be larger than SQUASHFS_NAME_LEN */ 199 if (size > SQUASHFS_NAME_LEN) 200 goto data_error; 201 202 err = squashfs_read_metadata(dir->i_sb, dire->name, 203 &block, &offset, size); 204 if (err < 0) 205 goto read_failure; 206 207 length += sizeof(*dire) + size; 208 209 if (name[0] < dire->name[0]) 210 goto exit_lookup; 211 212 if (len == size && !strncmp(name, dire->name, len)) { 213 unsigned int blk, off, ino_num; 214 long long ino; 215 blk = le32_to_cpu(dirh.start_block); 216 off = le16_to_cpu(dire->offset); 217 ino_num = le32_to_cpu(dirh.inode_number) + 218 (short) le16_to_cpu(dire->inode_number); 219 ino = SQUASHFS_MKINODE(blk, off); 220 221 TRACE("calling squashfs_iget for directory " 222 "entry %s, inode %x:%x, %d\n", name, 223 blk, off, ino_num); 224 225 inode = squashfs_iget(dir->i_sb, ino, ino_num); 226 goto exit_lookup; 227 } 228 } 229 } 230 231 exit_lookup: 232 kfree(dire); 233 return d_splice_alias(inode, dentry); 234 235 data_error: 236 err = -EIO; 237 238 read_failure: 239 ERROR("Unable to read directory block [%llx:%x]\n", 240 squashfs_i(dir)->start + msblk->directory_table, 241 squashfs_i(dir)->offset); 242 failed: 243 kfree(dire); 244 return ERR_PTR(err); 245 } 246 247 248 const struct inode_operations squashfs_dir_inode_ops = { 249 .lookup = squashfs_lookup, 250 .listxattr = squashfs_listxattr 251 }; 252