sndbuf_getblocks
u_int64_t sndbuf_getblocks(struct snd_dbuf *b);
a->blocks = sndbuf_getblocks(bs) - rdch->blocks;
rdch->blocks = sndbuf_getblocks(bs);
a->blocks = sndbuf_getblocks(bs) - wrch->blocks;
wrch->blocks = sndbuf_getblocks(bs);