datastream.c

linux 内核源代码

		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, "---> befs_find_brun_direct(), "
				   "found %lu at direct[%d]", blockno, i);
			return BEFS_OK;
		}
	}

	befs_debug(sb, "---> befs_find_brun_direct() ERROR");
	return BEFS_ERR;
}

/*
	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.
	
	sb: the superblock
	data: the datastream
	blockno: the blocknumber to find
	run: The found run is passed back through this pointer
	
	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.
	
	2001-11-15 Will Dyson
*/
static int
befs_find_brun_indirect(struct super_block *sb,
			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, "---> befs_find_brun_indirect(), find %lu", 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 = befs_bread(sb, indirblockno + i);
		if (indirblock == NULL) {
			befs_debug(sb,
				   "---> befs_find_brun_indirect() failed to "
				   "read disk block %lu from the indirect brun",
				   indirblockno + i);
			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,
					   "<--- befs_find_brun_indirect() found "
					   "file block %lu at indirect[%d]",
					   blockno, j + (i * arraylen));
				return BEFS_OK;
			}
			sum += len;
		}

		brelse(indirblock);
	}

	/* Only fallthrough is an error */
	befs_error(sb, "BeFS: befs_find_brun_indirect() failed to find "
		   "file block %lu", blockno);

	befs_debug(sb, "<--- befs_find_brun_indirect() ERROR");
	return BEFS_ERR;
}

/*
	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.
	
	sb: the superblock
	data: the datastream
	blockno: the blocknumber to find
	run: The found run is passed back through this pointer
	
	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.
	
	2001-11-15 Will Dyson
*/
static int
befs_find_brun_dblindirect(struct super_block *sb,
			   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 = NULL;
	befs_sb_info *befs_sb = BEFS_SB(sb);

	befs_blocknr_t indir_start_blk =
	    data->max_indirect_range >> befs_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, "---> befs_find_brun_dblindirect() find %lu", 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 "
			   "befs_read_brun_dblindirect(), %d, is outside the range "
			   "of the double-indirect block", dblindir_indx);
		return BEFS_ERR;
	}

	dbl_indir_block =
	    befs_bread(sb, iaddr2blockno(sb, &data->double_indirect) +
					dbl_which_block);
	if (dbl_indir_block == NULL) {
		befs_error(sb, "befs_read_brun_dblindirect() couldn't read the "
			   "double-indirect block at blockno %lu",
			   iaddr2blockno(sb,
					 &data->double_indirect) +
			   dbl_which_block);
		brelse(dbl_indir_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);
	iaddr_array = NULL;

	/* 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 "
			   "befs_read_brun_dblindirect(), %d, is outside the range "
			   "of the indirect block", indir_indx);
		return BEFS_ERR;
	}

	indir_block =
	    befs_bread(sb, iaddr2blockno(sb, &indir_run) + which_block);
	if (indir_block == NULL) {
		befs_error(sb, "befs_read_brun_dblindirect() couldn't read the "
			   "indirect block at blockno %lu",
			   iaddr2blockno(sb, &indir_run) + which_block);
		brelse(indir_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);
	iaddr_array = NULL;

	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",
		   blockno, dblindir_indx, indir_indx, dblindir_leftover);

	return BEFS_OK;
}