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linux
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datastream.c
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/* * linux/fs/befs/datastream.c * * Copyright (C) 2001 Will Dyson <will_dyson@pobox.com> * * Based on portions of file.c by Makoto Kato <m_kato@ga2.so-net.ne.jp> * * Many thanks to Dominic Giampaolo, author of "Practical File System * Design with the Be File System", for such a helpful book. * */ #include <linux/kernel.h> #include <linux/buffer_head.h> #include <linux/string.h> #include "befs.h" #include "datastream.h" #include "io.h" const befs_inode_addr BAD_IADDR = { 0, 0, 0 }; static int befs_find_brun_direct(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run); static int befs_find_brun_indirect(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run); static int befs_find_brun_dblindirect(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run); /** * befs_read_datastream - get buffer_head containing data, starting from pos. * @sb: Filesystem superblock * @ds: datastream to find data with * @pos: start of data * @off: offset of data in buffer_head->b_data * * Returns pointer to buffer_head containing data starting with offset @off, * if you don't need to know offset just set @off = NULL. */ struct buffer_head * befs_read_datastream(struct super_block *sb, const befs_data_stream *ds, befs_off_t pos, uint *off) { struct buffer_head *bh; befs_block_run run; befs_blocknr_t block; /* block coresponding to pos */ befs_debug(sb, "---> %s %llu", __func__, pos); block = pos >> BEFS_SB(sb)->block_shift; if (off) *off = pos - (block << BEFS_SB(sb)->block_shift); if (befs_fblock2brun(sb, ds, block, &run) != BEFS_OK) { befs_error(sb, "BeFS: Error finding disk addr of block %lu", (unsigned long)block); befs_debug(sb, "<--- %s ERROR", __func__); return NULL; } bh = befs_bread_iaddr(sb, run); if (!bh) { befs_error(sb, "BeFS: Error reading block %lu from datastream", (unsigned long)block); return NULL; } befs_debug(sb, "<--- %s read data, starting at %llu", __func__, pos); return bh; } /** * befs_fblock2brun - give back block run for fblock * @sb: the superblock * @data: datastream to read from * @fblock: the blocknumber with the file position to find * @run: The found run is passed back through this pointer * * Takes a file position and gives back a brun who's starting block * is block number fblock of the file. * * Returns BEFS_OK or BEFS_ERR. * * Calls specialized functions for each of the three possible * datastream regions. */ int befs_fblock2brun(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t fblock, befs_block_run *run) { int err; befs_off_t pos = fblock << BEFS_SB(sb)->block_shift; if (pos < data->max_direct_range) { err = befs_find_brun_direct(sb, data, fblock, run); } else if (pos < data->max_indirect_range) { err = befs_find_brun_indirect(sb, data, fblock, run); } else if (pos < data->max_double_indirect_range) { err = befs_find_brun_dblindirect(sb, data, fblock, run); } else { befs_error(sb, "befs_fblock2brun() was asked to find block %lu, " "which is not mapped by the datastream\n", (unsigned long)fblock); err = BEFS_ERR; } return err; } /** * befs_read_lsmylink - read long symlink from datastream. * @sb: Filesystem superblock * @ds: Datastream to read from * @buff: Buffer in which to place long symlink data * @len: Length of the long symlink in bytes * * Returns the number of bytes read */ size_t befs_read_lsymlink(struct super_block *sb, const befs_data_stream *ds, void *buff, befs_off_t len) { befs_off_t bytes_read = 0; /* bytes readed */ u16 plen; struct buffer_head *bh; befs_debug(sb, "---> %s length: %llu", __func__, len); while (bytes_read < len) { bh = befs_read_datastream(sb, ds, bytes_read, NULL); if (!bh) { befs_error(sb, "BeFS: Error reading datastream block " "starting from %llu", bytes_read); befs_debug(sb, "<--- %s ERROR", __func__); return bytes_read; } plen = ((bytes_read + BEFS_SB(sb)->block_size) < len) ? BEFS_SB(sb)->block_size : len - bytes_read; memcpy(buff + bytes_read, bh->b_data, plen); brelse(bh); bytes_read += plen; } befs_debug(sb, "<--- %s read %u bytes", __func__, (unsigned int) bytes_read); return bytes_read; } /** * befs_count_blocks - blocks used by a file * @sb: Filesystem superblock * @ds: Datastream of the file * * Counts the number of fs blocks that the file represented by * inode occupies on the filesystem, counting both regular file * data and filesystem metadata (and eventually attribute data * when we support attributes) */ befs_blocknr_t befs_count_blocks(struct super_block *sb, const befs_data_stream *ds) { befs_blocknr_t blocks; befs_blocknr_t datablocks; /* File data blocks */ befs_blocknr_t metablocks; /* FS metadata blocks */ struct befs_sb_info *befs_sb = BEFS_SB(sb); befs_debug(sb, "---> %s", __func__); datablocks = ds->size >> befs_sb->block_shift; if (ds->size & (befs_sb->block_size - 1)) datablocks += 1; metablocks = 1; /* Start with 1 block for inode */ /* Size of indirect block */ if (ds->size > ds->max_direct_range) metablocks += ds->indirect.len; /* * Double indir block, plus all the indirect blocks it maps. * In the double-indirect range, all block runs of data are * BEFS_DBLINDIR_BRUN_LEN blocks long. Therefore, we know * how many data block runs are in the double-indirect region, * and from that we know how many indirect blocks it takes to * map them. We assume that the indirect blocks are also * BEFS_DBLINDIR_BRUN_LEN blocks long. */ if (ds->size > ds->max_indirect_range && ds->max_indirect_range != 0) { uint dbl_bytes; uint dbl_bruns; uint indirblocks; dbl_bytes = ds->max_double_indirect_range - ds->max_indirect_range; dbl_bruns = dbl_bytes / (befs_sb->block_size * BEFS_DBLINDIR_BRUN_LEN); indirblocks = dbl_bruns / befs_iaddrs_per_block(sb); metablocks += ds->double_indirect.len; metablocks += indirblocks; } blocks = datablocks + metablocks; befs_debug(sb, "<--- %s %u blocks", __func__, (unsigned int)blocks); return blocks; } /** * befs_find_brun_direct - find a direct block run in the datastream * @sb: the superblock * @data: the datastream * @blockno: the blocknumber to find * @run: The found run is passed back through this pointer * * Finds the block run that starts at file block number blockno * in the file represented by the datastream data, if that * blockno is in the direct region of the datastream. * * Return value is BEFS_OK if the blockrun is found, BEFS_ERR * otherwise. * * Algorithm: * Linear search. Checks each element of array[] to see if it * contains the blockno-th filesystem block. This is necessary * because the block runs map variable amounts of data. Simply * keeps a count of the number of blocks searched so far (sum), * incrementing this by the length of each block run as we come * across it. Adds sum to *count before returning (this is so * you can search multiple arrays that are logicaly one array, * as in the indirect region code). * * When/if blockno is found, if blockno is inside of a block * run as stored on disk, we offset the start and length members * of the block run, so that blockno is the start and len is * still valid (the run ends in the same place). */ static int befs_find_brun_direct(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run) { int i; const befs_block_run *array = data->direct; befs_blocknr_t sum; befs_debug(sb, "---> %s, find %lu", __func__, (unsigned long)blockno); for (i = 0, sum = 0; i < BEFS_NUM_DIRECT_BLOCKS; sum += array[i].len, i++) { if (blockno >= sum && blockno < sum + (array[i].len)) { int offset = blockno - sum; run->allocation_group = array[i].allocation_group; run->start = array[i].start + offset; run->len = array[i].len - offset; befs_debug(sb, "---> %s, " "found %lu at direct[%d]", __func__, (unsigned long)blockno, i); return BEFS_OK; } } befs_error(sb, "%s failed to find file block %lu", __func__, (unsigned long)blockno); befs_debug(sb, "---> %s ERROR", __func__); return BEFS_ERR; } /** * befs_find_brun_indirect - find a block run in the datastream * @sb: the superblock * @data: the datastream * @blockno: the blocknumber to find * @run: The found run is passed back through this pointer * * Finds the block run that starts at file block number blockno * in the file represented by the datastream data, if that * blockno is in the indirect region of the datastream. * * Return value is BEFS_OK if the blockrun is found, BEFS_ERR * otherwise. * * Algorithm: * For each block in the indirect run of the datastream, read * it in and search through it for search_blk. * * XXX: * Really should check to make sure blockno is inside indirect * region. */ static int befs_find_brun_indirect(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run) { int i, j; befs_blocknr_t sum = 0; befs_blocknr_t indir_start_blk; befs_blocknr_t search_blk; struct buffer_head *indirblock; befs_disk_block_run *array; befs_block_run indirect = data->indirect; befs_blocknr_t indirblockno = iaddr2blockno(sb, &indirect); int arraylen = befs_iaddrs_per_block(sb); befs_debug(sb, "---> %s, find %lu", __func__, (unsigned long)blockno); indir_start_blk = data->max_direct_range >> BEFS_SB(sb)->block_shift; search_blk = blockno - indir_start_blk; /* Examine blocks of the indirect run one at a time */ for (i = 0; i < indirect.len; i++) { indirblock = sb_bread(sb, indirblockno + i); if (indirblock == NULL) { befs_error(sb, "---> %s failed to read " "disk block %lu from the indirect brun", __func__, (unsigned long)indirblockno + i); befs_debug(sb, "<--- %s ERROR", __func__); return BEFS_ERR; } array = (befs_disk_block_run *) indirblock->b_data; for (j = 0; j < arraylen; ++j) { int len = fs16_to_cpu(sb, array[j].len); if (search_blk >= sum && search_blk < sum + len) { int offset = search_blk - sum; run->allocation_group = fs32_to_cpu(sb, array[j].allocation_group); run->start = fs16_to_cpu(sb, array[j].start) + offset; run->len = fs16_to_cpu(sb, array[j].len) - offset; brelse(indirblock); befs_debug(sb, "<--- %s found file block " "%lu at indirect[%d]", __func__, (unsigned long)blockno, j + (i * arraylen)); return BEFS_OK; } sum += len; } brelse(indirblock); } /* Only fallthrough is an error */ befs_error(sb, "BeFS: %s failed to find " "file block %lu", __func__, (unsigned long)blockno); befs_debug(sb, "<--- %s ERROR", __func__); return BEFS_ERR; } /** * befs_find_brun_dblindirect - find a block run in the datastream * @sb: the superblock * @data: the datastream * @blockno: the blocknumber to find * @run: The found run is passed back through this pointer * * Finds the block run that starts at file block number blockno * in the file represented by the datastream data, if that * blockno is in the double-indirect region of the datastream. * * Return value is BEFS_OK if the blockrun is found, BEFS_ERR * otherwise. * * Algorithm: * The block runs in the double-indirect region are different. * They are always allocated 4 fs blocks at a time, so each * block run maps a constant amount of file data. This means * that we can directly calculate how many block runs into the * double-indirect region we need to go to get to the one that * maps a particular filesystem block. * * We do this in two stages. First we calculate which of the * inode addresses in the double-indirect block will point us * to the indirect block that contains the mapping for the data, * then we calculate which of the inode addresses in that * indirect block maps the data block we are after. * * Oh, and once we've done that, we actually read in the blocks * that contain the inode addresses we calculated above. Even * though the double-indirect run may be several blocks long, * we can calculate which of those blocks will contain the index * we are after and only read that one. We then follow it to * the indirect block and perform a similar process to find * the actual block run that maps the data block we are interested * in. * * Then we offset the run as in befs_find_brun_array() and we are * done. */ static int befs_find_brun_dblindirect(struct super_block *sb, const befs_data_stream *data, befs_blocknr_t blockno, befs_block_run *run) { int dblindir_indx; int indir_indx; int offset; int dbl_which_block; int which_block; int dbl_block_indx; int block_indx; off_t dblindir_leftover; befs_blocknr_t blockno_at_run_start; struct buffer_head *dbl_indir_block; struct buffer_head *indir_block; befs_block_run indir_run; befs_disk_inode_addr *iaddr_array; befs_blocknr_t indir_start_blk = data->max_indirect_range >> BEFS_SB(sb)->block_shift; off_t dbl_indir_off = blockno - indir_start_blk; /* number of data blocks mapped by each of the iaddrs in * the indirect block pointed to by the double indirect block */ size_t iblklen = BEFS_DBLINDIR_BRUN_LEN; /* number of data blocks mapped by each of the iaddrs in * the double indirect block */ size_t diblklen = iblklen * befs_iaddrs_per_block(sb) * BEFS_DBLINDIR_BRUN_LEN; befs_debug(sb, "---> %s find %lu", __func__, (unsigned long)blockno); /* First, discover which of the double_indir->indir blocks * contains pos. Then figure out how much of pos that * accounted for. Then discover which of the iaddrs in * the indirect block contains pos. */ dblindir_indx = dbl_indir_off / diblklen; dblindir_leftover = dbl_indir_off % diblklen; indir_indx = dblindir_leftover / diblklen; /* Read double indirect block */ dbl_which_block = dblindir_indx / befs_iaddrs_per_block(sb); if (dbl_which_block > data->double_indirect.len) { befs_error(sb, "The double-indirect index calculated by " "%s, %d, is outside the range " "of the double-indirect block", __func__, dblindir_indx); return BEFS_ERR; } dbl_indir_block = sb_bread(sb, iaddr2blockno(sb, &data->double_indirect) + dbl_which_block); if (dbl_indir_block == NULL) { befs_error(sb, "%s couldn't read the " "double-indirect block at blockno %lu", __func__, (unsigned long) iaddr2blockno(sb, &data->double_indirect) + dbl_which_block); return BEFS_ERR; } dbl_block_indx = dblindir_indx - (dbl_which_block * befs_iaddrs_per_block(sb)); iaddr_array = (befs_disk_inode_addr *) dbl_indir_block->b_data; indir_run = fsrun_to_cpu(sb, iaddr_array[dbl_block_indx]); brelse(dbl_indir_block); /* Read indirect block */ which_block = indir_indx / befs_iaddrs_per_block(sb); if (which_block > indir_run.len) { befs_error(sb, "The indirect index calculated by " "%s, %d, is outside the range " "of the indirect block", __func__, indir_indx); return BEFS_ERR; } indir_block = sb_bread(sb, iaddr2blockno(sb, &indir_run) + which_block); if (indir_block == NULL) { befs_error(sb, "%s couldn't read the indirect block " "at blockno %lu", __func__, (unsigned long) iaddr2blockno(sb, &indir_run) + which_block); return BEFS_ERR; } block_indx = indir_indx - (which_block * befs_iaddrs_per_block(sb)); iaddr_array = (befs_disk_inode_addr *) indir_block->b_data; *run = fsrun_to_cpu(sb, iaddr_array[block_indx]); brelse(indir_block); blockno_at_run_start = indir_start_blk; blockno_at_run_start += diblklen * dblindir_indx; blockno_at_run_start += iblklen * indir_indx; offset = blockno - blockno_at_run_start; run->start += offset; run->len -= offset; befs_debug(sb, "Found file block %lu in double_indirect[%d][%d]," " double_indirect_leftover = %lu", (unsigned long) blockno, dblindir_indx, indir_indx, dblindir_leftover); return BEFS_OK; }
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