uipc_stream_sbspace
space = uipc_stream_sbspace(sb);
space = uipc_stream_sbspace(sb);
if (uipc_stream_sbspace(sb) >= sb->sb_lowat)
kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);
kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);
while ((*space = uipc_stream_sbspace(sb)) < need &&