P2V
P2V(vol, sd->sd_pos, bp->bio_offset, &virtual, ©);
P2V(vol, sd->sd_pos, bp->bio_offset, &virtual, ©);
P2V(vol, sd->sd_pos, bp->bio_offset, &virtual, ©);
P2V(vol, sd->sd_pos, sd->sd_rebuild_pos, &virtual, ©);
P2V(vol, sd->sd_pos, sd->sd_rebuild_pos + len, &vend, ©);