root/fs/befs/datastream.c

DEFINITIONS

1. befs_read_datastream
2. befs_fblock2brun
3. befs_read_lsymlink
4. befs_count_blocks
5. befs_find_brun_direct
6. befs_find_brun_indirect
7. befs_find_brun_dblindirect

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/fs/befs/datastream.c
   4  *
   5  * Copyright (C) 2001 Will Dyson <will_dyson@pobox.com>
   6  *
   7  * Based on portions of file.c by Makoto Kato <m_kato@ga2.so-net.ne.jp>
   8  *
   9  * Many thanks to Dominic Giampaolo, author of "Practical File System
  10  * Design with the Be File System", for such a helpful book.
  11  *
  12  */
  13 
  14 #include <linux/kernel.h>
  15 #include <linux/buffer_head.h>
  16 #include <linux/string.h>
  17 
  18 #include "befs.h"
  19 #include "datastream.h"
  20 #include "io.h"
  21 
  22 const befs_inode_addr BAD_IADDR = { 0, 0, 0 };
  23 
  24 static int befs_find_brun_direct(struct super_block *sb,
  25                                  const befs_data_stream *data,
  26                                  befs_blocknr_t blockno, befs_block_run *run);
  27 
  28 static int befs_find_brun_indirect(struct super_block *sb,
  29                                    const befs_data_stream *data,
  30                                    befs_blocknr_t blockno,
  31                                    befs_block_run *run);
  32 
  33 static int befs_find_brun_dblindirect(struct super_block *sb,
  34                                       const befs_data_stream *data,
  35                                       befs_blocknr_t blockno,
  36                                       befs_block_run *run);
  37 
  38 /**
  39  * befs_read_datastream - get buffer_head containing data, starting from pos.
  40  * @sb: Filesystem superblock
  41  * @ds: datastream to find data with
  42  * @pos: start of data
  43  * @off: offset of data in buffer_head->b_data
  44  *
  45  * Returns pointer to buffer_head containing data starting with offset @off,
  46  * if you don't need to know offset just set @off = NULL.
  47  */
  48 struct buffer_head *
  49 befs_read_datastream(struct super_block *sb, const befs_data_stream *ds,
  50                      befs_off_t pos, uint *off)
  51 {
  52         struct buffer_head *bh;
  53         befs_block_run run;
  54         befs_blocknr_t block;   /* block coresponding to pos */
  55 
  56         befs_debug(sb, "---> %s %llu", __func__, pos);
  57         block = pos >> BEFS_SB(sb)->block_shift;
  58         if (off)
  59                 *off = pos - (block << BEFS_SB(sb)->block_shift);
  60 
  61         if (befs_fblock2brun(sb, ds, block, &run) != BEFS_OK) {
  62                 befs_error(sb, "BeFS: Error finding disk addr of block %lu",
  63                            (unsigned long)block);
  64                 befs_debug(sb, "<--- %s ERROR", __func__);
  65                 return NULL;
  66         }
  67         bh = befs_bread_iaddr(sb, run);
  68         if (!bh) {
  69                 befs_error(sb, "BeFS: Error reading block %lu from datastream",
  70                            (unsigned long)block);
  71                 return NULL;
  72         }
  73 
  74         befs_debug(sb, "<--- %s read data, starting at %llu", __func__, pos);
  75 
  76         return bh;
  77 }
  78 
  79 /**
  80  * befs_fblock2brun - give back block run for fblock
  81  * @sb: the superblock
  82  * @data: datastream to read from
  83  * @fblock: the blocknumber with the file position to find
  84  * @run: The found run is passed back through this pointer
  85  *
  86  * Takes a file position and gives back a brun who's starting block
  87  * is block number fblock of the file.
  88  *
  89  * Returns BEFS_OK or BEFS_ERR.
  90  *
  91  * Calls specialized functions for each of the three possible
  92  * datastream regions.
  93  */
  94 int
  95 befs_fblock2brun(struct super_block *sb, const befs_data_stream *data,
  96                  befs_blocknr_t fblock, befs_block_run *run)
  97 {
  98         int err;
  99         befs_off_t pos = fblock << BEFS_SB(sb)->block_shift;
 100 
 101         if (pos < data->max_direct_range) {
 102                 err = befs_find_brun_direct(sb, data, fblock, run);
 103 
 104         } else if (pos < data->max_indirect_range) {
 105                 err = befs_find_brun_indirect(sb, data, fblock, run);
 106 
 107         } else if (pos < data->max_double_indirect_range) {
 108                 err = befs_find_brun_dblindirect(sb, data, fblock, run);
 109 
 110         } else {
 111                 befs_error(sb,
 112                            "befs_fblock2brun() was asked to find block %lu, "
 113                            "which is not mapped by the datastream\n",
 114                            (unsigned long)fblock);
 115                 err = BEFS_ERR;
 116         }
 117         return err;
 118 }
 119 
 120 /**
 121  * befs_read_lsmylink - read long symlink from datastream.
 122  * @sb: Filesystem superblock
 123  * @ds: Datastream to read from
 124  * @buff: Buffer in which to place long symlink data
 125  * @len: Length of the long symlink in bytes
 126  *
 127  * Returns the number of bytes read
 128  */
 129 size_t
 130 befs_read_lsymlink(struct super_block *sb, const befs_data_stream *ds,
 131                    void *buff, befs_off_t len)
 132 {
 133         befs_off_t bytes_read = 0;      /* bytes readed */
 134         u16 plen;
 135         struct buffer_head *bh;
 136 
 137         befs_debug(sb, "---> %s length: %llu", __func__, len);
 138 
 139         while (bytes_read < len) {
 140                 bh = befs_read_datastream(sb, ds, bytes_read, NULL);
 141                 if (!bh) {
 142                         befs_error(sb, "BeFS: Error reading datastream block "
 143                                    "starting from %llu", bytes_read);
 144                         befs_debug(sb, "<--- %s ERROR", __func__);
 145                         return bytes_read;
 146 
 147                 }
 148                 plen = ((bytes_read + BEFS_SB(sb)->block_size) < len) ?
 149                     BEFS_SB(sb)->block_size : len - bytes_read;
 150                 memcpy(buff + bytes_read, bh->b_data, plen);
 151                 brelse(bh);
 152                 bytes_read += plen;
 153         }
 154 
 155         befs_debug(sb, "<--- %s read %u bytes", __func__, (unsigned int)
 156                    bytes_read);
 157         return bytes_read;
 158 }
 159 
 160 /**
 161  * befs_count_blocks - blocks used by a file
 162  * @sb: Filesystem superblock
 163  * @ds: Datastream of the file
 164  *
 165  * Counts the number of fs blocks that the file represented by
 166  * inode occupies on the filesystem, counting both regular file
 167  * data and filesystem metadata (and eventually attribute data
 168  * when we support attributes)
 169 */
 170 
 171 befs_blocknr_t
 172 befs_count_blocks(struct super_block *sb, const befs_data_stream *ds)
 173 {
 174         befs_blocknr_t blocks;
 175         befs_blocknr_t datablocks;      /* File data blocks */
 176         befs_blocknr_t metablocks;      /* FS metadata blocks */
 177         struct befs_sb_info *befs_sb = BEFS_SB(sb);
 178 
 179         befs_debug(sb, "---> %s", __func__);
 180 
 181         datablocks = ds->size >> befs_sb->block_shift;
 182         if (ds->size & (befs_sb->block_size - 1))
 183                 datablocks += 1;
 184 
 185         metablocks = 1;         /* Start with 1 block for inode */
 186 
 187         /* Size of indirect block */
 188         if (ds->size > ds->max_direct_range)
 189                 metablocks += ds->indirect.len;
 190 
 191         /*
 192          * Double indir block, plus all the indirect blocks it maps.
 193          * In the double-indirect range, all block runs of data are
 194          * BEFS_DBLINDIR_BRUN_LEN blocks long. Therefore, we know
 195          * how many data block runs are in the double-indirect region,
 196          * and from that we know how many indirect blocks it takes to
 197          * map them. We assume that the indirect blocks are also
 198          * BEFS_DBLINDIR_BRUN_LEN blocks long.
 199          */
 200         if (ds->size > ds->max_indirect_range && ds->max_indirect_range != 0) {
 201                 uint dbl_bytes;
 202                 uint dbl_bruns;
 203                 uint indirblocks;
 204 
 205                 dbl_bytes =
 206                     ds->max_double_indirect_range - ds->max_indirect_range;
 207                 dbl_bruns =
 208                     dbl_bytes / (befs_sb->block_size * BEFS_DBLINDIR_BRUN_LEN);
 209                 indirblocks = dbl_bruns / befs_iaddrs_per_block(sb);
 210 
 211                 metablocks += ds->double_indirect.len;
 212                 metablocks += indirblocks;
 213         }
 214 
 215         blocks = datablocks + metablocks;
 216         befs_debug(sb, "<--- %s %u blocks", __func__, (unsigned int)blocks);
 217 
 218         return blocks;
 219 }
 220 
 221 /**
 222  * befs_find_brun_direct - find a direct block run in the datastream
 223  * @sb: the superblock
 224  * @data: the datastream
 225  * @blockno: the blocknumber to find
 226  * @run: The found run is passed back through this pointer
 227  *
 228  * Finds the block run that starts at file block number blockno
 229  * in the file represented by the datastream data, if that
 230  * blockno is in the direct region of the datastream.
 231  *
 232  * Return value is BEFS_OK if the blockrun is found, BEFS_ERR
 233  * otherwise.
 234  *
 235  * Algorithm:
 236  * Linear search. Checks each element of array[] to see if it
 237  * contains the blockno-th filesystem block. This is necessary
 238  * because the block runs map variable amounts of data. Simply
 239  * keeps a count of the number of blocks searched so far (sum),
 240  * incrementing this by the length of each block run as we come
 241  * across it. Adds sum to *count before returning (this is so
 242  * you can search multiple arrays that are logicaly one array,
 243  * as in the indirect region code).
 244  *
 245  * When/if blockno is found, if blockno is inside of a block
 246  * run as stored on disk, we offset the start and length members
 247  * of the block run, so that blockno is the start and len is
 248  * still valid (the run ends in the same place).
 249  */
 250 static int
 251 befs_find_brun_direct(struct super_block *sb, const befs_data_stream *data,
 252                       befs_blocknr_t blockno, befs_block_run *run)
 253 {
 254         int i;
 255         const befs_block_run *array = data->direct;
 256         befs_blocknr_t sum;
 257 
 258         befs_debug(sb, "---> %s, find %lu", __func__, (unsigned long)blockno);
 259 
 260         for (i = 0, sum = 0; i < BEFS_NUM_DIRECT_BLOCKS;
 261              sum += array[i].len, i++) {
 262                 if (blockno >= sum && blockno < sum + (array[i].len)) {
 263                         int offset = blockno - sum;
 264 
 265                         run->allocation_group = array[i].allocation_group;
 266                         run->start = array[i].start + offset;
 267                         run->len = array[i].len - offset;
 268 
 269                         befs_debug(sb, "---> %s, "
 270                                    "found %lu at direct[%d]", __func__,
 271                                    (unsigned long)blockno, i);
 272                         return BEFS_OK;
 273                 }
 274         }
 275 
 276         befs_error(sb, "%s failed to find file block %lu", __func__,
 277                    (unsigned long)blockno);
 278         befs_debug(sb, "---> %s ERROR", __func__);
 279         return BEFS_ERR;
 280 }
 281 
 282 /**
 283  * befs_find_brun_indirect - find a block run in the datastream
 284  * @sb: the superblock
 285  * @data: the datastream
 286  * @blockno: the blocknumber to find
 287  * @run: The found run is passed back through this pointer
 288  *
 289  * Finds the block run that starts at file block number blockno
 290  * in the file represented by the datastream data, if that
 291  * blockno is in the indirect region of the datastream.
 292  *
 293  * Return value is BEFS_OK if the blockrun is found, BEFS_ERR
 294  * otherwise.
 295  *
 296  * Algorithm:
 297  * For each block in the indirect run of the datastream, read
 298  * it in and search through it for search_blk.
 299  *
 300  * XXX:
 301  * Really should check to make sure blockno is inside indirect
 302  * region.
 303  */
 304 static int
 305 befs_find_brun_indirect(struct super_block *sb,
 306                         const befs_data_stream *data,
 307                         befs_blocknr_t blockno,
 308                         befs_block_run *run)
 309 {
 310         int i, j;
 311         befs_blocknr_t sum = 0;
 312         befs_blocknr_t indir_start_blk;
 313         befs_blocknr_t search_blk;
 314         struct buffer_head *indirblock;
 315         befs_disk_block_run *array;
 316 
 317         befs_block_run indirect = data->indirect;
 318         befs_blocknr_t indirblockno = iaddr2blockno(sb, &indirect);
 319         int arraylen = befs_iaddrs_per_block(sb);
 320 
 321         befs_debug(sb, "---> %s, find %lu", __func__, (unsigned long)blockno);
 322 
 323         indir_start_blk = data->max_direct_range >> BEFS_SB(sb)->block_shift;
 324         search_blk = blockno - indir_start_blk;
 325 
 326         /* Examine blocks of the indirect run one at a time */
 327         for (i = 0; i < indirect.len; i++) {
 328                 indirblock = sb_bread(sb, indirblockno + i);
 329                 if (indirblock == NULL) {
 330                         befs_error(sb, "---> %s failed to read "
 331                                    "disk block %lu from the indirect brun",
 332                                    __func__, (unsigned long)indirblockno + i);
 333                         befs_debug(sb, "<--- %s ERROR", __func__);
 334                         return BEFS_ERR;
 335                 }
 336 
 337                 array = (befs_disk_block_run *) indirblock->b_data;
 338 
 339                 for (j = 0; j < arraylen; ++j) {
 340                         int len = fs16_to_cpu(sb, array[j].len);
 341 
 342                         if (search_blk >= sum && search_blk < sum + len) {
 343                                 int offset = search_blk - sum;
 344                                 run->allocation_group =
 345                                     fs32_to_cpu(sb, array[j].allocation_group);
 346                                 run->start =
 347                                     fs16_to_cpu(sb, array[j].start) + offset;
 348                                 run->len =
 349                                     fs16_to_cpu(sb, array[j].len) - offset;
 350 
 351                                 brelse(indirblock);
 352                                 befs_debug(sb,
 353                                            "<--- %s found file block "
 354                                            "%lu at indirect[%d]", __func__,
 355                                            (unsigned long)blockno,
 356                                            j + (i * arraylen));
 357                                 return BEFS_OK;
 358                         }
 359                         sum += len;
 360                 }
 361 
 362                 brelse(indirblock);
 363         }
 364 
 365         /* Only fallthrough is an error */
 366         befs_error(sb, "BeFS: %s failed to find "
 367                    "file block %lu", __func__, (unsigned long)blockno);
 368 
 369         befs_debug(sb, "<--- %s ERROR", __func__);
 370         return BEFS_ERR;
 371 }
 372 
 373 /**
 374  * befs_find_brun_dblindirect - find a block run in the datastream
 375  * @sb: the superblock
 376  * @data: the datastream
 377  * @blockno: the blocknumber to find
 378  * @run: The found run is passed back through this pointer
 379  *
 380  * Finds the block run that starts at file block number blockno
 381  * in the file represented by the datastream data, if that
 382  * blockno is in the double-indirect region of the datastream.
 383  *
 384  * Return value is BEFS_OK if the blockrun is found, BEFS_ERR
 385  * otherwise.
 386  *
 387  * Algorithm:
 388  * The block runs in the double-indirect region are different.
 389  * They are always allocated 4 fs blocks at a time, so each
 390  * block run maps a constant amount of file data. This means
 391  * that we can directly calculate how many block runs into the
 392  * double-indirect region we need to go to get to the one that
 393  * maps a particular filesystem block.
 394  *
 395  * We do this in two stages. First we calculate which of the
 396  * inode addresses in the double-indirect block will point us
 397  * to the indirect block that contains the mapping for the data,
 398  * then we calculate which of the inode addresses in that
 399  * indirect block maps the data block we are after.
 400  *
 401  * Oh, and once we've done that, we actually read in the blocks
 402  * that contain the inode addresses we calculated above. Even
 403  * though the double-indirect run may be several blocks long,
 404  * we can calculate which of those blocks will contain the index
 405  * we are after and only read that one. We then follow it to
 406  * the indirect block and perform a similar process to find
 407  * the actual block run that maps the data block we are interested
 408  * in.
 409  *
 410  * Then we offset the run as in befs_find_brun_array() and we are
 411  * done.
 412  */
 413 static int
 414 befs_find_brun_dblindirect(struct super_block *sb,
 415                            const befs_data_stream *data,
 416                            befs_blocknr_t blockno,
 417                            befs_block_run *run)
 418 {
 419         int dblindir_indx;
 420         int indir_indx;
 421         int offset;
 422         int dbl_which_block;
 423         int which_block;
 424         int dbl_block_indx;
 425         int block_indx;
 426         off_t dblindir_leftover;
 427         befs_blocknr_t blockno_at_run_start;
 428         struct buffer_head *dbl_indir_block;
 429         struct buffer_head *indir_block;
 430         befs_block_run indir_run;
 431         befs_disk_inode_addr *iaddr_array;
 432 
 433         befs_blocknr_t indir_start_blk =
 434             data->max_indirect_range >> BEFS_SB(sb)->block_shift;
 435 
 436         off_t dbl_indir_off = blockno - indir_start_blk;
 437 
 438         /* number of data blocks mapped by each of the iaddrs in
 439          * the indirect block pointed to by the double indirect block
 440          */
 441         size_t iblklen = BEFS_DBLINDIR_BRUN_LEN;
 442 
 443         /* number of data blocks mapped by each of the iaddrs in
 444          * the double indirect block
 445          */
 446         size_t diblklen = iblklen * befs_iaddrs_per_block(sb)
 447             * BEFS_DBLINDIR_BRUN_LEN;
 448 
 449         befs_debug(sb, "---> %s find %lu", __func__, (unsigned long)blockno);
 450 
 451         /* First, discover which of the double_indir->indir blocks
 452          * contains pos. Then figure out how much of pos that
 453          * accounted for. Then discover which of the iaddrs in
 454          * the indirect block contains pos.
 455          */
 456 
 457         dblindir_indx = dbl_indir_off / diblklen;
 458         dblindir_leftover = dbl_indir_off % diblklen;
 459         indir_indx = dblindir_leftover / diblklen;
 460 
 461         /* Read double indirect block */
 462         dbl_which_block = dblindir_indx / befs_iaddrs_per_block(sb);
 463         if (dbl_which_block > data->double_indirect.len) {
 464                 befs_error(sb, "The double-indirect index calculated by "
 465                            "%s, %d, is outside the range "
 466                            "of the double-indirect block", __func__,
 467                            dblindir_indx);
 468                 return BEFS_ERR;
 469         }
 470 
 471         dbl_indir_block =
 472             sb_bread(sb, iaddr2blockno(sb, &data->double_indirect) +
 473                                         dbl_which_block);
 474         if (dbl_indir_block == NULL) {
 475                 befs_error(sb, "%s couldn't read the "
 476                            "double-indirect block at blockno %lu", __func__,
 477                            (unsigned long)
 478                            iaddr2blockno(sb, &data->double_indirect) +
 479                            dbl_which_block);
 480                 return BEFS_ERR;
 481         }
 482 
 483         dbl_block_indx =
 484             dblindir_indx - (dbl_which_block * befs_iaddrs_per_block(sb));
 485         iaddr_array = (befs_disk_inode_addr *) dbl_indir_block->b_data;
 486         indir_run = fsrun_to_cpu(sb, iaddr_array[dbl_block_indx]);
 487         brelse(dbl_indir_block);
 488 
 489         /* Read indirect block */
 490         which_block = indir_indx / befs_iaddrs_per_block(sb);
 491         if (which_block > indir_run.len) {
 492                 befs_error(sb, "The indirect index calculated by "
 493                            "%s, %d, is outside the range "
 494                            "of the indirect block", __func__, indir_indx);
 495                 return BEFS_ERR;
 496         }
 497 
 498         indir_block =
 499             sb_bread(sb, iaddr2blockno(sb, &indir_run) + which_block);
 500         if (indir_block == NULL) {
 501                 befs_error(sb, "%s couldn't read the indirect block "
 502                            "at blockno %lu", __func__, (unsigned long)
 503                            iaddr2blockno(sb, &indir_run) + which_block);
 504                 return BEFS_ERR;
 505         }
 506 
 507         block_indx = indir_indx - (which_block * befs_iaddrs_per_block(sb));
 508         iaddr_array = (befs_disk_inode_addr *) indir_block->b_data;
 509         *run = fsrun_to_cpu(sb, iaddr_array[block_indx]);
 510         brelse(indir_block);
 511 
 512         blockno_at_run_start = indir_start_blk;
 513         blockno_at_run_start += diblklen * dblindir_indx;
 514         blockno_at_run_start += iblklen * indir_indx;
 515         offset = blockno - blockno_at_run_start;
 516 
 517         run->start += offset;
 518         run->len -= offset;
 519 
 520         befs_debug(sb, "Found file block %lu in double_indirect[%d][%d],"
 521                    " double_indirect_leftover = %lu", (unsigned long)
 522                    blockno, dblindir_indx, indir_indx, dblindir_leftover);
 523 
 524         return BEFS_OK;
 525 }