e1000: defer packets until BM enabled

Some guests seem to set BM for e1000 after
enabling RX.
If packets arrive in the window, device is wedged.
Probably works by luck on real hardware, work around
this by making can_receive depend on BM.
Tested-by: NGabriel Somlo <somlo@cmu.edu>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/net/e1000.c

@@ -33,6 +33,7 @@
 #include "sysemu/sysemu.h"
 #include "sysemu/dma.h"
 #include "qemu/iov.h"
+#include "qemu/range.h"
 
 #include "e1000_regs.h"
 
@@ -923,7 +924,9 @@ e1000_can_receive(NetClientState *nc)
     E1000State *s = qemu_get_nic_opaque(nc);
 
     return (s->mac_reg[STATUS] & E1000_STATUS_LU) &&
-        (s->mac_reg[RCTL] & E1000_RCTL_EN) && e1000_has_rxbufs(s, 1);
+        (s->mac_reg[RCTL] & E1000_RCTL_EN) &&
+        (s->parent_obj.config[PCI_COMMAND] & PCI_COMMAND_MASTER) &&
+        e1000_has_rxbufs(s, 1);
 }
 
 static uint64_t rx_desc_base(E1000State *s)
@@ -1529,6 +1532,20 @@ static NetClientInfo net_e1000_info = {
     .link_status_changed = e1000_set_link_status,
 };
 
+static void e1000_write_config(PCIDevice *pci_dev, uint32_t address,
+                                uint32_t val, int len)
+{
+    E1000State *s = E1000(pci_dev);
+
+    pci_default_write_config(pci_dev, address, val, len);
+
+    if (range_covers_byte(address, len, PCI_COMMAND) &&
+        (pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
+        qemu_flush_queued_packets(qemu_get_queue(s->nic));
+    }
+}
+
+
 static int pci_e1000_init(PCIDevice *pci_dev)
 {
     DeviceState *dev = DEVICE(pci_dev);
@@ -1539,6 +1556,8 @@ static int pci_e1000_init(PCIDevice *pci_dev)
     int i;
     uint8_t *macaddr;
 
+    pci_dev->config_write = e1000_write_config;
+
     pci_conf = pci_dev->config;
 
     /* TODO: RST# value should be 0, PCI spec 6.2.4 */