static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask)
{
    hwaddr pa;
    pa = vq->vring.used + offsetof(VRingUsed, flags);
    stw_phys(pa, lduw_phys(pa) & ~mask);
}
static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask)
{
    hwaddr pa;
    pa = vq->vring.used + offsetof(VRingUsed, flags);
    stw_phys(pa, lduw_phys(pa) & ~mask);
}