SBUF_FINISHED
KASSERT((s->s_flags & SBUF_FINISHED) == state,
SBUF_CLEARFLAG(s, SBUF_FINISHED);
#define SBUF_ISFINISHED(s) ((s)->s_flags & SBUF_FINISHED)
SBUF_SETFLAG(s, SBUF_FINISHED);
assert_sbuf_state(s, SBUF_FINISHED);