C_IBS
{ "bs", f_bs, C_BS, C_BS|C_IBS|C_OBS|C_OSYNC },
{ "ibs", f_ibs, C_IBS, C_BS|C_IBS },
ddflags |= C_IBS|C_OBS;
if (ddflags & C_BS && ddflags & (C_IBS|C_OBS))