fs/squashfs/dir.c

   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  * dir.c
  22  */
  23
  24 /*
  25  * This file implements code to read directories from disk.
  26  *
  27  * See namei.c for a description of directory organisation on disk.
  28  */
  29
  30 #include <linux/fs.h>
  31 #include <linux/vfs.h>
  32 #include <linux/slab.h>
  33
  34 #include "squashfs_fs.h"
  35 #include "squashfs_fs_sb.h"
  36 #include "squashfs_fs_i.h"
  37 #include "squashfs.h"
  38
  39 static const unsigned char squashfs_filetype_table[] = {
  40         DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_FIFO, DT_SOCK
  41 };
  42
  43 /*
  44  * Lookup offset (f_pos) in the directory index, returning the
  45  * metadata block containing it.
  46  *
  47  * If we get an error reading the index then return the part of the index
  48  * (if any) we have managed to read - the index isn't essential, just
  49  * quicker.
  50  */
  51 static int get_dir_index_using_offset(struct super_block *sb,
  52         u64 *next_block, int *next_offset, u64 index_start, int index_offset,
  53         int i_count, u64 f_pos)
  54 {
  55         struct squashfs_sb_info *msblk = sb->s_fs_info;
  56         int err, i, index, length = 0;
  57         unsigned int size;
  58         struct squashfs_dir_index dir_index;
  59
  60         TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
  61                                         i_count, f_pos);
  62
  63         /*
  64          * Translate from external f_pos to the internal f_pos.  This
  65          * is offset by 3 because we invent "." and ".." entries which are
  66          * not actually stored in the directory.
  67          */
  68         if (f_pos <= 3)
  69                 return f_pos;
  70         f_pos -= 3;
  71
  72         for (i = 0; i < i_count; i++) {
  73                 err = squashfs_read_metadata(sb, &dir_index, &index_start,
  74                                 &index_offset, sizeof(dir_index));
  75                 if (err < 0)
  76                         break;
  77
  78                 index = le32_to_cpu(dir_index.index);
  79                 if (index > f_pos)
  80                         /*
  81                          * Found the index we're looking for.
  82                          */
  83                         break;
  84
  85                 size = le32_to_cpu(dir_index.size) + 1;
  86
  87                 /* size should never be larger than SQUASHFS_NAME_LEN */
  88                 if (size > SQUASHFS_NAME_LEN)
  89                         break;
  90
  91                 err = squashfs_read_metadata(sb, NULL, &index_start,
  92                                 &index_offset, size);
  93                 if (err < 0)
  94                         break;
  95
  96                 length = index;
  97                 *next_block = le32_to_cpu(dir_index.start_block) +
  98                                         msblk->directory_table;
  99         }
 100
 101         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
 102
 103         /*
 104          * Translate back from internal f_pos to external f_pos.
 105          */
 106         return length + 3;
 107 }
 108
 109
 110 static int squashfs_readdir(struct file *file, struct dir_context *ctx)
 111 {
 112         struct inode *inode = file_inode(file);
 113         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 114         u64 block = squashfs_i(inode)->start + msblk->directory_table;
 115         int offset = squashfs_i(inode)->offset, length, err;
 116         unsigned int inode_number, dir_count, size, type;
 117         struct squashfs_dir_header dirh;
 118         struct squashfs_dir_entry *dire;
 119
 120         TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);
 121
 122         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 123         if (dire == NULL) {
 124                 ERROR("Failed to allocate squashfs_dir_entry\n");
 125                 goto finish;
 126         }
 127
 128         /*
 129          * Return "." and  ".." entries as the first two filenames in the
 130          * directory.  To maximise compression these two entries are not
 131          * stored in the directory, and so we invent them here.
 132          *
 133          * It also means that the external f_pos is offset by 3 from the
 134          * on-disk directory f_pos.
 135          */
 136         while (ctx->pos < 3) {
 137                 char *name;
 138                 int i_ino;
 139
 140                 if (ctx->pos == 0) {
 141                         name = ".";
 142                         size = 1;
 143                         i_ino = inode->i_ino;
 144                 } else {
 145                         name = "..";
 146                         size = 2;
 147                         i_ino = squashfs_i(inode)->parent;
 148                 }
 149
 150                 if (!dir_emit(ctx, name, size, i_ino,
 151                                 squashfs_filetype_table[1]))
 152                         goto finish;
 153
 154                 ctx->pos += size;
 155         }
 156
 157         length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
 158                                 squashfs_i(inode)->dir_idx_start,
 159                                 squashfs_i(inode)->dir_idx_offset,
 160                                 squashfs_i(inode)->dir_idx_cnt,
 161                                 ctx->pos);
 162
 163         while (length < i_size_read(inode)) {
 164                 /*
 165                  * Read directory header
 166                  */
 167                 err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
 168                                         &offset, sizeof(dirh));
 169                 if (err < 0)
 170                         goto failed_read;
 171
 172                 length += sizeof(dirh);
 173
 174                 dir_count = le32_to_cpu(dirh.count) + 1;
 175
 176                 if (dir_count > SQUASHFS_DIR_COUNT)
 177                         goto failed_read;
 178
 179                 while (dir_count--) {
 180                         /*
 181                          * Read directory entry.
 182                          */
 183                         err = squashfs_read_metadata(inode->i_sb, dire, &block,
 184                                         &offset, sizeof(*dire));
 185                         if (err < 0)
 186                                 goto failed_read;
 187
 188                         size = le16_to_cpu(dire->size) + 1;
 189
 190                         /* size should never be larger than SQUASHFS_NAME_LEN */
 191                         if (size > SQUASHFS_NAME_LEN)
 192                                 goto failed_read;
 193
 194                         err = squashfs_read_metadata(inode->i_sb, dire->name,
 195                                         &block, &offset, size);
 196                         if (err < 0)
 197                                 goto failed_read;
 198
 199                         length += sizeof(*dire) + size;
 200
 201                         if (ctx->pos >= length)
 202                                 continue;
 203
 204                         dire->name[size] = '\0';
 205                         inode_number = le32_to_cpu(dirh.inode_number) +
 206                                 ((short) le16_to_cpu(dire->inode_number));
 207                         type = le16_to_cpu(dire->type);
 208
 209                         if (type > SQUASHFS_MAX_DIR_TYPE)
 210                                 goto failed_read;
 211
 212                         if (!dir_emit(ctx, dire->name, size,
 213                                         inode_number,
 214                                         squashfs_filetype_table[type]))
 215                                 goto finish;
 216
 217                         ctx->pos = length;
 218                 }
 219         }
 220
 221 finish:
 222         kfree(dire);
 223         return 0;
 224
 225 failed_read:
 226         ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
 227         kfree(dire);
 228         return 0;
 229 }
 230
 231
 232 const struct file_operations squashfs_dir_ops = {
 233         .read = generic_read_dir,
 234         .iterate_shared = squashfs_readdir,
 235         .llseek = generic_file_llseek,
 236 };