Re: [Qemu-devel] [PATCH v5 3/6] libvhost-user: Support tracking inflight I/O in shared memory

[Jason Wang]

On 2019/1/22 下午4:31, elohi...@gmail.com wrote:
+static int
+vu_queue_inflight_get(VuDev *dev, VuVirtq *vq, int desc_idx)
+{
+    if (!has_feature(dev->protocol_features,
+        VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
+        return 0;
+    }
+
+    if (unlikely(!vq->inflight)) {
+        return -1;
+    }
+
+    vq->inflight->desc[desc_idx].inuse = 1;
+
+    vq->inflight->desc[desc_idx].avail_idx = vq->last_avail_idx;
+
+    return 0;
+}
+
+static int
+vu_queue_inflight_pre_put(VuDev *dev, VuVirtq *vq, int desc_idx)
+{
+    if (!has_feature(dev->protocol_features,
+        VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
+        return 0;
+    }
+
+    if (unlikely(!vq->inflight)) {
+        return -1;
+    }
+
+    vq->inflight->desc[desc_idx].used_idx = vq->used_idx;
+
+    barrier();
+
+    vq->inflight->desc[desc_idx].version++;
+
+    return 0;
+}


You probably need WRITE_ONCE() semantic (e.g volatile) to make sure the 
value reach memory.

Thanks