namei.c revision 0b77ad632ce83f94aa24e028e1ce98ceec518944
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/zlib.h> 61 62#include "squashfs_fs.h" 63#include "squashfs_fs_sb.h" 64#include "squashfs_fs_i.h" 65#include "squashfs.h" 66 67/* 68 * Lookup name in the directory index, returning the location of the metadata 69 * block containing it, and the directory index this represents. 70 * 71 * If we get an error reading the index then return the part of the index 72 * (if any) we have managed to read - the index isn't essential, just 73 * quicker. 74 */ 75static int get_dir_index_using_name(struct super_block *sb, 76 long long *next_block, int *next_offset, 77 long long index_start, int index_offset, 78 int i_count, const char *name, int len) 79{ 80 struct squashfs_sb_info *msblk = sb->s_fs_info; 81 int i, size, length = 0, err; 82 struct squashfs_dir_index *index; 83 char *str; 84 85 TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count); 86 87 str = kmalloc(sizeof(*index) + (SQUASHFS_NAME_LEN + 1) * 2, GFP_KERNEL); 88 if (str == NULL) { 89 ERROR("Failed to allocate squashfs_dir_index\n"); 90 goto out; 91 } 92 93 index = (struct squashfs_dir_index *) (str + SQUASHFS_NAME_LEN + 1); 94 strncpy(str, name, len); 95 str[len] = '\0'; 96 97 for (i = 0; i < i_count; i++) { 98 err = squashfs_read_metadata(sb, index, &index_start, 99 &index_offset, sizeof(*index)); 100 if (err < 0) 101 break; 102 103 104 size = le32_to_cpu(index->size) + 1; 105 106 err = squashfs_read_metadata(sb, index->name, &index_start, 107 &index_offset, size); 108 if (err < 0) 109 break; 110 111 index->name[size] = '\0'; 112 113 if (strcmp(index->name, str) > 0) 114 break; 115 116 length = le32_to_cpu(index->index); 117 *next_block = le32_to_cpu(index->start_block) + 118 msblk->directory_table; 119 } 120 121 *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE; 122 kfree(str); 123 124out: 125 /* 126 * Return index (f_pos) of the looked up metadata block. Translate 127 * from internal f_pos to external f_pos which is offset by 3 because 128 * we invent "." and ".." entries which are not actually stored in the 129 * directory. 130 */ 131 return length + 3; 132} 133 134 135static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry, 136 struct nameidata *nd) 137{ 138 const unsigned char *name = dentry->d_name.name; 139 int len = dentry->d_name.len; 140 struct inode *inode = NULL; 141 struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info; 142 struct squashfs_dir_header dirh; 143 struct squashfs_dir_entry *dire; 144 long long block = SQUASHFS_I(dir)->start + msblk->directory_table; 145 int offset = SQUASHFS_I(dir)->offset; 146 int err, length = 0, dir_count, size; 147 148 TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset); 149 150 dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL); 151 if (dire == NULL) { 152 ERROR("Failed to allocate squashfs_dir_entry\n"); 153 return ERR_PTR(-ENOMEM); 154 } 155 156 if (len > SQUASHFS_NAME_LEN) 157 return ERR_PTR(-ENAMETOOLONG); 158 159 length = get_dir_index_using_name(dir->i_sb, &block, &offset, 160 SQUASHFS_I(dir)->dir_idx_start, 161 SQUASHFS_I(dir)->dir_idx_offset, 162 SQUASHFS_I(dir)->dir_idx_cnt, name, len); 163 164 while (length < i_size_read(dir)) { 165 /* 166 * Read directory header. 167 */ 168 err = squashfs_read_metadata(dir->i_sb, &dirh, &block, 169 &offset, sizeof(dirh)); 170 if (err < 0) 171 goto read_failure; 172 173 length += sizeof(dirh); 174 175 dir_count = le32_to_cpu(dirh.count) + 1; 176 while (dir_count--) { 177 /* 178 * Read directory entry. 179 */ 180 err = squashfs_read_metadata(dir->i_sb, dire, &block, 181 &offset, sizeof(*dire)); 182 if (err < 0) 183 goto read_failure; 184 185 size = le16_to_cpu(dire->size) + 1; 186 187 err = squashfs_read_metadata(dir->i_sb, dire->name, 188 &block, &offset, size); 189 if (err < 0) 190 goto read_failure; 191 192 length += sizeof(*dire) + size; 193 194 if (name[0] < dire->name[0]) 195 goto exit_lookup; 196 197 if (len == size && !strncmp(name, dire->name, len)) { 198 unsigned int blk, off, ino_num; 199 long long ino; 200 blk = le32_to_cpu(dirh.start_block); 201 off = le16_to_cpu(dire->offset); 202 ino_num = le32_to_cpu(dirh.inode_number) + 203 (short) le16_to_cpu(dire->inode_number); 204 ino = SQUASHFS_MKINODE(blk, off); 205 206 TRACE("calling squashfs_iget for directory " 207 "entry %s, inode %x:%x, %d\n", name, 208 blk, off, ino_num); 209 210 inode = squashfs_iget(dir->i_sb, ino, ino_num); 211 if (IS_ERR(inode)) 212 return ERR_CAST(inode); 213 214 goto exit_lookup; 215 } 216 } 217 } 218 219exit_lookup: 220 kfree(dire); 221 if (inode) 222 return d_splice_alias(inode, dentry); 223 d_add(dentry, inode); 224 return ERR_PTR(0); 225 226read_failure: 227 ERROR("Unable to read directory block [%llx:%x]\n", 228 SQUASHFS_I(dir)->start + msblk->directory_table, 229 SQUASHFS_I(dir)->offset); 230 return ERR_PTR(err); 231} 232 233 234const struct inode_operations squashfs_dir_inode_ops = { 235 .lookup = squashfs_lookup 236}; 237