sndbuf_getbufofs
bcopy(from, sndbuf_getbufofs(b, sndbuf_getfreeptr(b)), l);
bcopy(sndbuf_getbufofs(b, sndbuf_getreadyptr(b)), to, l);
void *sndbuf_getbufofs(struct snd_dbuf *b, unsigned int ofs);
off = sndbuf_getbufofs(bs, p);
off = sndbuf_getbufofs(bs, p);
*offset = (uintptr_t)sndbuf_getbufofs(c->bufsoft, *offset);