linux/fs/squashfs/namei.c
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   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 */
  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                                 unsigned int flags)
 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, 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                if (dir_count > SQUASHFS_DIR_COUNT)
 181                        goto data_error;
 182
 183                while (dir_count--) {
 184                        /*
 185                         * Read directory entry.
 186                         */
 187                        err = squashfs_read_metadata(dir->i_sb, dire, &block,
 188                                        &offset, sizeof(*dire));
 189                        if (err < 0)
 190                                goto read_failure;
 191
 192                        size = le16_to_cpu(dire->size) + 1;
 193
 194                        /* size should never be larger than SQUASHFS_NAME_LEN */
 195                        if (size > SQUASHFS_NAME_LEN)
 196                                goto data_error;
 197
 198                        err = squashfs_read_metadata(dir->i_sb, dire->name,
 199                                        &block, &offset, size);
 200                        if (err < 0)
 201                                goto read_failure;
 202
 203                        length += sizeof(*dire) + size;
 204
 205                        if (name[0] < dire->name[0])
 206                                goto exit_lookup;
 207
 208                        if (len == size && !strncmp(name, dire->name, len)) {
 209                                unsigned int blk, off, ino_num;
 210                                long long ino;
 211                                blk = le32_to_cpu(dirh.start_block);
 212                                off = le16_to_cpu(dire->offset);
 213                                ino_num = le32_to_cpu(dirh.inode_number) +
 214                                        (short) le16_to_cpu(dire->inode_number);
 215                                ino = SQUASHFS_MKINODE(blk, off);
 216
 217                                TRACE("calling squashfs_iget for directory "
 218                                        "entry %s, inode  %x:%x, %d\n", name,
 219                                        blk, off, ino_num);
 220
 221                                inode = squashfs_iget(dir->i_sb, ino, ino_num);
 222                                goto exit_lookup;
 223                        }
 224                }
 225        }
 226
 227exit_lookup:
 228        kfree(dire);
 229        return d_splice_alias(inode, dentry);
 230
 231data_error:
 232        err = -EIO;
 233
 234read_failure:
 235        ERROR("Unable to read directory block [%llx:%x]\n",
 236                squashfs_i(dir)->start + msblk->directory_table,
 237                squashfs_i(dir)->offset);
 238failed:
 239        kfree(dire);
 240        return ERR_PTR(err);
 241}
 242
 243
 244const struct inode_operations squashfs_dir_inode_ops = {
 245        .lookup = squashfs_lookup,
 246        .getxattr = generic_getxattr,
 247        .listxattr = squashfs_listxattr
 248};
 249
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