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         struct squashfs_dir_index dir_index;
  58
  59         TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
  60                                         i_count, f_pos);
  61
  62         /*
  63          * Translate from external f_pos to the internal f_pos.  This
  64          * is offset by 3 because we invent "." and ".." entries which are
  65          * not actually stored in the directory.
  66          */
  67         if (f_pos <= 3)
  68                 return f_pos;
  69         f_pos -= 3;
  70
  71         for (i = 0; i < i_count; i++) {
  72                 err = squashfs_read_metadata(sb, &dir_index, &index_start,
  73                                 &index_offset, sizeof(dir_index));
  74                 if (err < 0)
  75                         break;
  76
  77                 index = le32_to_cpu(dir_index.index);
  78                 if (index > f_pos)
  79                         /*
  80                          * Found the index we're looking for.
  81                          */
  82                         break;
  83
  84                 err = squashfs_read_metadata(sb, NULL, &index_start,
  85                                 &index_offset, le32_to_cpu(dir_index.size) + 1);
  86                 if (err < 0)
  87                         break;
  88
  89                 length = index;
  90                 *next_block = le32_to_cpu(dir_index.start_block) +
  91                                         msblk->directory_table;
  92         }
  93
  94         *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
  95
  96         /*
  97          * Translate back from internal f_pos to external f_pos.
  98          */
  99         return length + 3;
 100 }
 101
 102
 103 static int squashfs_readdir(struct file *file, struct dir_context *ctx)
 104 {
 105         struct inode *inode = file_inode(file);
 106         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 107         u64 block = squashfs_i(inode)->start + msblk->directory_table;
 108         int offset = squashfs_i(inode)->offset, length, dir_count, size,
 109                                 type, err;
 110         unsigned int inode_number;
 111         struct squashfs_dir_header dirh;
 112         struct squashfs_dir_entry *dire;
 113
 114         TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);
 115
 116         dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 117         if (dire == NULL) {
 118                 ERROR("Failed to allocate squashfs_dir_entry\n");
 119                 goto finish;
 120         }
 121
 122         /*
 123          * Return "." and  ".." entries as the first two filenames in the
 124          * directory.  To maximise compression these two entries are not
 125          * stored in the directory, and so we invent them here.
 126          *
 127          * It also means that the external f_pos is offset by 3 from the
 128          * on-disk directory f_pos.
 129          */
 130         while (ctx->pos < 3) {
 131                 char *name;
 132                 int i_ino;
 133
 134                 if (ctx->pos == 0) {
 135                         name = ".";
 136                         size = 1;
 137                         i_ino = inode->i_ino;
 138                 } else {
 139                         name = "..";
 140                         size = 2;
 141                         i_ino = squashfs_i(inode)->parent;
 142                 }
 143
 144                 if (!dir_emit(ctx, name, size, i_ino,
 145                                 squashfs_filetype_table[1]))
 146                         goto finish;
 147
 148                 ctx->pos += size;
 149         }
 150
 151         length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
 152                                 squashfs_i(inode)->dir_idx_start,
 153                                 squashfs_i(inode)->dir_idx_offset,
 154                                 squashfs_i(inode)->dir_idx_cnt,
 155                                 ctx->pos);
 156
 157         while (length < i_size_read(inode)) {
 158                 /*
 159                  * Read directory header
 160                  */
 161                 err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
 162                                         &offset, sizeof(dirh));
 163                 if (err < 0)
 164                         goto failed_read;
 165
 166                 length += sizeof(dirh);
 167
 168                 dir_count = le32_to_cpu(dirh.count) + 1;
 169
 170                 if (dir_count > SQUASHFS_DIR_COUNT)
 171                         goto failed_read;
 172
 173                 while (dir_count--) {
 174                         /*
 175                          * Read directory entry.
 176                          */
 177                         err = squashfs_read_metadata(inode->i_sb, dire, &block,
 178                                         &offset, sizeof(*dire));
 179                         if (err < 0)
 180                                 goto failed_read;
 181
 182                         size = le16_to_cpu(dire->size) + 1;
 183
 184                         /* size should never be larger than SQUASHFS_NAME_LEN */
 185                         if (size > SQUASHFS_NAME_LEN)
 186                                 goto failed_read;
 187
 188                         err = squashfs_read_metadata(inode->i_sb, dire->name,
 189                                         &block, &offset, size);
 190                         if (err < 0)
 191                                 goto failed_read;
 192
 193                         length += sizeof(*dire) + size;
 194
 195                         if (ctx->pos >= length)
 196                                 continue;
 197
 198                         dire->name[size] = '\0';
 199                         inode_number = le32_to_cpu(dirh.inode_number) +
 200                                 ((short) le16_to_cpu(dire->inode_number));
 201                         type = le16_to_cpu(dire->type);
 202
 203                         if (!dir_emit(ctx, dire->name, size,
 204                                         inode_number,
 205                                         squashfs_filetype_table[type]))
 206                                 goto finish;
 207
 208                         ctx->pos = length;
 209                 }
 210         }
 211
 212 finish:
 213         kfree(dire);
 214         return 0;
 215
 216 failed_read:
 217         ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
 218         kfree(dire);
 219         return 0;
 220 }
 221
 222
 223 const struct file_operations squashfs_dir_ops = {
 224         .read = generic_read_dir,
 225         .iterate = squashfs_readdir,
 226         .llseek = default_llseek,
 227 };