M_DATABUF
explicit_bzero(M_DATABUF(m), M_SIZE(m));
KASSERT(m->m_data >= M_DATABUF(m));
return m->m_data - M_DATABUF(m);
KASSERT(M_DATABUF(m) + M_SIZE(m) >= (m->m_data + m->m_len));
return M_DATABUF(m) + M_SIZE(m) - (m->m_data + m->m_len);
KASSERT(m->m_data == M_DATABUF(m)); /* newly-allocated check */
m->m_data = M_DATABUF(m) + ((M_SIZE(m) - (len)) &~ (sizeof(long) - 1));
m->m_data - M_DATABUF(m), m->m_len);
head = M_DATABUF(m0);