[RFC v2 09/14] virtio-net: detect VirtIONet Rx filter mid-migration changes

[Jonah Palmer <jonah.palmer@oracle.com>]

This patch saves the virtio-net device's Rx filter flags as a bit-packed
uint8_t to compare with later during the stop-and-copy phase.

A local enum VirtIONetRxFlags and static inline virtio_net_rx_flags_pack
function is introduced to bit-pack VirtIONet's promisc, allmulti,
alluni, nomulti, nouni, and nobcast into a single byte for easier
comparison.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/net/virtio-net.c            | 28 ++++++++++++++++++++++++++++
 include/hw/virtio/virtio-net.h |  2 ++
 2 files changed, 30 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 88ce33b1d2..42c585142d 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -3864,6 +3864,26 @@ static bool failover_hide_primary_device(DeviceListener *listener,
     return qatomic_read(&n->failover_primary_hidden);
 }
 
+enum VirtIONetRxFlags {
+    VNET_RX_F_PROMISC  = 1u << 0,
+    VNET_RX_F_ALLMULTI = 1u << 1,
+    VNET_RX_F_ALLUNI   = 1u << 2,
+    VNET_RX_F_NOMULTI  = 1u << 3,
+    VNET_RX_F_NOUNI    = 1u << 4,
+    VNET_RX_F_NOBCAST  = 1u << 5,
+};
+
+/* Pack current Rx filter flags into a single uint8_t for comparison */
+static inline uint8_t virtio_net_rx_flags_pack(const VirtIONet *n)
+{
+    return (n->promisc  ? VNET_RX_F_PROMISC  : 0) |
+           (n->allmulti ? VNET_RX_F_ALLMULTI : 0) |
+           (n->alluni   ? VNET_RX_F_ALLUNI   : 0) |
+           (n->nomulti  ? VNET_RX_F_NOMULTI  : 0) |
+           (n->nouni    ? VNET_RX_F_NOUNI    : 0) |
+           (n->nobcast  ? VNET_RX_F_NOBCAST  : 0);
+}
+
 static int virtio_net_early_pre_save(void *opaque)
 {
     VirtIONet *n = opaque;
@@ -3906,6 +3926,9 @@ static int virtio_net_early_pre_save(void *opaque)
         memcpy(vnet_mig->mtable_macs_early, n->mac_table.macs, bytes);
     }
 
+    /* Rx filter flags snapshot */
+    vnet_mig->rx_flags_early = virtio_net_rx_flags_pack(n);
+
     return 0;
 }
 
@@ -4327,6 +4350,11 @@ static bool virtio_net_has_delta(VirtIONet *n, VirtIODevice *vdev)
         }
     }
 
+    /* Has the VirtIONet's Rx filter flags changed? */
+    if (virtio_net_rx_flags_pack(n) != vnet_mig->rx_flags_early) {
+        return true;
+    }
+
     /*
      * Always return true for now until we're able to detect all possible
      * changes to a VirtIONet device.
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 59345f1811..9135d277ff 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -175,6 +175,7 @@ typedef struct VirtIONetQueue {
  * @mtable_uni_overflow_early: Unicast overflow MAC table entries.
  * @mtable_multi_overflow_early: Multicast overflow MAC table entries.
  * @mtable_macs_early: MAC table entries.
+ * @rx_flags_early: Bit-packed RX filters (promisc, allmulti, alluni, etc.).
  */
 typedef struct VirtIONetMigration {
     uint16_t status_early;
@@ -183,6 +184,7 @@ typedef struct VirtIONetMigration {
     uint8_t mtable_uni_overflow_early;
     uint8_t mtable_multi_overflow_early;
     uint8_t *mtable_macs_early;
+    uint8_t rx_flags_early;
 } VirtIONetMigration;
 
 struct VirtIONet {
-- 
2.51.0