[RFC,v4,22/28] COLO: Do checkpoint according to the result of net packets comparing

diff --git a/include/net/colo-nic.h b/include/net/colo-nic.h
index 40dbcfb..67c9807 100644
--- a/include/net/colo-nic.h
+++ b/include/net/colo-nic.h
@@ -19,4 +19,6 @@  void colo_proxy_destroy(int side);
 void colo_add_nic_devices(NetClientState *nc);
 void colo_remove_nic_devices(NetClientState *nc);
 
+int colo_proxy_compare(void);
+
 #endif
diff --git a/migration/colo.c b/migration/colo.c
index dffd6f9..9ef4554 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -25,6 +25,13 @@ 
         }                                                   \
     } while (0)
 
+/*
+* We should not do checkpoint one after another without any time interval,
+* Because this will lead continuous 'stop' status for VM.
+* CHECKPOINT_MIN_PERIOD is the min time limit between two checkpoint action.
+*/
+#define CHECKPOINT_MIN_PERIOD 100  /* unit: ms */
+
 enum {
     COLO_READY = 0x46,
 
@@ -290,6 +297,7 @@  static void *colo_thread(void *opaque)
 {
     MigrationState *s = opaque;
     QEMUFile *colo_control = NULL;
+    int64_t current_time, checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
     int ret;
 
     if (colo_proxy_init(COLO_PRIMARY_MODE) != 0) {
@@ -326,10 +334,36 @@  static void *colo_thread(void *opaque)
     DPRINTF("vm resume to run\n");
 
     while (s->state == MIGRATION_STATUS_COLO) {
+        int proxy_checkpoint_req;
+
+        /* wait for a colo checkpoint */
+        proxy_checkpoint_req = colo_proxy_compare();
+        if (proxy_checkpoint_req < 0) {
+            goto out;
+        } else if (!proxy_checkpoint_req) {
+            /*
+             * No checkpoint is needed, wait for 1ms and then
+             * check if we need checkpoint again
+             */
+            g_usleep(1000);
+            continue;
+        } else {
+            int64_t interval;
+
+            current_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+            interval = current_time - checkpoint_time;
+            if (interval < CHECKPOINT_MIN_PERIOD) {
+                /* Limit the min time between two checkpoint */
+                g_usleep((1000*(CHECKPOINT_MIN_PERIOD - interval)));
+            }
+            DPRINTF("Net packets is not consistent!!!\n");
+        }
+
         /* start a colo checkpoint */
         if (colo_do_checkpoint_transaction(s, colo_control)) {
             goto out;
         }
+        checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
     }
 
 out:
diff --git a/net/colo-nic.c b/net/colo-nic.c
index 38d9bf5..563d661 100644
--- a/net/colo-nic.c
+++ b/net/colo-nic.c
@@ -37,6 +37,9 @@  typedef struct nic_device {
     bool is_up;
 } nic_device;
 
+typedef struct colo_msg {
+    bool is_checkpoint;
+} colo_msg;
 
 typedef struct colo_proxy {
     int sockfd;
@@ -376,3 +379,41 @@  void colo_proxy_destroy(int side)
     cp_info.index = -1;
     colo_nic_side = -1;
 }
+/*
+do checkpoint: return 1
+error: return -1
+do not checkpoint: return 0
+*/
+int colo_proxy_compare(void)
+{
+    uint8_t *buff;
+    int64_t size;
+    struct nlmsghdr *h;
+    struct colo_msg *m;
+    int ret = -1;
+
+    size = colo_proxy_recv(&buff, MSG_DONTWAIT);
+
+    /* timeout, return no checkpoint message. */
+    if (size <= 0) {
+        return 0;
+    }
+
+    h = (struct nlmsghdr *) buff;
+
+    if (h->nlmsg_type == NLMSG_ERROR) {
+        goto out;
+    }
+
+    if (h->nlmsg_len < NLMSG_LENGTH(sizeof(*m))) {
+        goto out;
+    }
+
+    m = NLMSG_DATA(h);
+
+    ret = m->is_checkpoint ? 1 : 0;
+
+out:
+    g_free(buff);
+    return ret;
+}