e1000: Choose which set of props to migrate

When we're using the subsection we migrate both
the 'props' and 'tso_props' data; when we're not using
the subsection (to migrate to 2.11 or old machine types) we've
got to choose what to migrate in the main structure.

If we're using the subsection migrate 'props' in the main structure.
If we're not using the subsection then migrate the last one
that changed, which gives behaviour similar to the old behaviour.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>

hw/net/e1000.c

@@ -130,6 +130,7 @@ typedef struct E1000State_st {
 #define E1000_FLAG_TSO (1 << E1000_FLAG_TSO_BIT)
     uint32_t compat_flags;
     bool received_tx_tso;
+    bool use_tso_for_migration;
     e1000x_txd_props mig_props;
 } E1000State;
 
@@ -622,9 +623,11 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
     if (dtype == E1000_TXD_CMD_DEXT) {    /* context descriptor */
         if (le32_to_cpu(xp->cmd_and_length) & E1000_TXD_CMD_TSE) {
             e1000x_read_tx_ctx_descr(xp, &tp->tso_props);
+            s->use_tso_for_migration = 1;
             tp->tso_frames = 0;
         } else {
             e1000x_read_tx_ctx_descr(xp, &tp->props);
+            s->use_tso_for_migration = 0;
         }
         return;
     } else if (dtype == (E1000_TXD_CMD_DEXT | E1000_TXD_DTYP_D)) {
@@ -1366,7 +1369,20 @@ static int e1000_pre_save(void *opaque)
         s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
     }
 
-    s->mig_props = s->tx.props;
+    /* Decide which set of props to migrate in the main structure */
+    if (chkflag(TSO) || !s->use_tso_for_migration) {
+        /* Either we're migrating with the extra subsection, in which
+         * case the mig_props is always 'props' OR
+         * we've not got the subsection, but 'props' was the last
+         * updated.
+         */
+        s->mig_props = s->tx.props;
+    } else {
+        /* We're not using the subsection, and 'tso_props' was
+         * the last updated.
+         */
+        s->mig_props = s->tx.tso_props;
+    }
     return 0;
 }