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#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 */ 76static 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 125out: 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 136static 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 if (IS_ERR(inode)) { 224 err = PTR_ERR(inode); 225 goto failed; 226 } 227 228 goto exit_lookup; 229 } 230 } 231 } 232 233exit_lookup: 234 kfree(dire); 235 if (inode) 236 return d_splice_alias(inode, dentry); 237 d_add(dentry, inode); 238 return ERR_PTR(0); 239 240data_error: 241 err = -EIO; 242 243read_failure: 244 ERROR("Unable to read directory block [%llx:%x]\n", 245 squashfs_i(dir)->start + msblk->directory_table, 246 squashfs_i(dir)->offset); 247failed: 248 kfree(dire); 249 return ERR_PTR(err); 250} 251 252 253const struct inode_operations squashfs_dir_inode_ops = { 254 .lookup = squashfs_lookup, 255 .getxattr = generic_getxattr, 256 .listxattr = squashfs_listxattr 257}; 258