[Qemu-devel] [PATCH V2] net: Fix dealing with packets when runstate changes

[zhanghailiang]

For all NICs(except virtio-net) emulated by qemu,
Such as e1000, rtl8139, pcnet and ne2k_pci,
Qemu can still receive packets when VM is not running.
If this happened in *migration's* last PAUSE VM stage,
The new dirty RAM related to the packets will be missed,
And this will lead serious network fault in VM.

To avoid this, we forbid receiving packets in generic net code when
VM is not running. Also, when the runstate changes back to running,
we definitely need to flush queues to get packets flowing again.

Here we implement this in the net layer:
(1) Judge the vm runstate in qemu_can_send_packet
(2) Add a member 'VMChangeStateEntry *vmstate' to struct NICState,
Which will listen for VM runstate changes.
(3) Register a handler function for VMstate change.
When vm changes back to running, we flush all queues in the callback function.
(4) Remove checking vm state in virtio_net_can_receive

Signed-off-by: zhanghailiang <address@hidden>
---
v2:
- remove the superfluous check of nc->received_disabled 
---
 hw/net/virtio-net.c |  4 ----
 include/net/net.h   |  2 ++
 net/net.c           | 31 +++++++++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 268eff9..287d762 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -839,10 +839,6 @@ static int virtio_net_can_receive(NetClientState *nc)
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
     VirtIONetQueue *q = virtio_net_get_subqueue(nc);
 
-    if (!vdev->vm_running) {
-        return 0;
-    }
-
     if (nc->queue_index >= n->curr_queues) {
         return 0;
     }
diff --git a/include/net/net.h b/include/net/net.h
index ed594f9..a294277 100644
--- a/include/net/net.h
+++ b/include/net/net.h
@@ -8,6 +8,7 @@
 #include "net/queue.h"
 #include "migration/vmstate.h"
 #include "qapi-types.h"
+#include "sysemu/sysemu.h"
 
 #define MAX_QUEUE_NUM 1024
 
@@ -96,6 +97,7 @@ typedef struct NICState {
     NICConf *conf;
     void *opaque;
     bool peer_deleted;
+    VMChangeStateEntry *vmstate;
 } NICState;
 
 NetClientState *qemu_find_netdev(const char *id);
diff --git a/net/net.c b/net/net.c
index 6d930ea..113a37b 100644
--- a/net/net.c
+++ b/net/net.c
@@ -242,6 +242,28 @@ NetClientState *qemu_new_net_client(NetClientInfo *info,
     return nc;
 }
 
+static void nic_vmstate_change_handler(void *opaque,
+                                       int running,
+                                       RunState state)
+{
+    NICState *nic = opaque;
+    NetClientState *nc;
+    int i, queues;
+
+    if (!running) {
+        return;
+    }
+
+    queues = MAX(1, nic->conf->peers.queues);
+    for (i = 0; i < queues; i++) {
+        nc = &nic->ncs[i];
+        if (nc->info->can_receive && !nc->info->can_receive(nc)) {
+            continue;
+        }
+        qemu_flush_queued_packets(nc);
+    }
+}
+
 NICState *qemu_new_nic(NetClientInfo *info,
                        NICConf *conf,
                        const char *model,
@@ -259,6 +281,8 @@ NICState *qemu_new_nic(NetClientInfo *info,
     nic->ncs = (void *)nic + info->size;
     nic->conf = conf;
     nic->opaque = opaque;
+    nic->vmstate = qemu_add_vm_change_state_handler(nic_vmstate_change_handler,
+                                                    nic);
 
     for (i = 0; i < queues; i++) {
         qemu_net_client_setup(&nic->ncs[i], info, peers[i], model, name,
@@ -379,6 +403,7 @@ void qemu_del_nic(NICState *nic)
         qemu_free_net_client(nc);
     }
 
+    qemu_del_vm_change_state_handler(nic->vmstate);
     g_free(nic);
 }
 
@@ -452,6 +477,12 @@ void qemu_set_vnet_hdr_len(NetClientState *nc, int len)
 
 int qemu_can_send_packet(NetClientState *sender)
 {
+    int vmstat = runstate_is_running();
+
+    if (!vmstat) {
+        return 0;
+    }
+
     if (!sender->peer) {
         return 1;
     }
-- 
1.7.12.4