read_ahead
sector_t read_ahead = min((sector_t) MAX_READ_AHEAD_BLOCKS,
dm_bufio_prefetch(reader->client, block_number, read_ahead);
read_ahead(reader, 0);
read_ahead(reader, block_number + 1);
switch(lparam->read_ahead) {
u8 read_ahead; /* read ahead, no read ahead, adaptive read
uint8_t read_ahead;
struct file_ra_state read_ahead;
log->page_size, NULL, &log->read_ahead);