SBUF_AUTOEXTEND
sbuf_new(NULL, NULL, 0, SBUF_AUTOEXTEND)
if ((s->s_flags & SBUF_AUTOEXTEND) == 0) {
if ((flags & SBUF_AUTOEXTEND) != 0)
#define SBUF_CANEXTEND(s) ((s)->s_flags & SBUF_AUTOEXTEND)