migration/rdma: Check for postcopy sooner

It makes no sense first try to see if there is an rdma error and then
do nothing on postcopy stage.  Change it so we check we are in
postcopy before doing anything.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230504114443.23891-6-quintela@redhat.com>

migration/rdma.c

@@ -3234,6 +3234,10 @@ static size_t qemu_rdma_save_page(QEMUFile *f,
     RDMAContext *rdma;
     int ret;
 
+    if (migration_in_postcopy()) {
+        return RAM_SAVE_CONTROL_NOT_SUPP;
+    }
+
     RCU_READ_LOCK_GUARD();
     rdma = qatomic_rcu_read(&rioc->rdmaout);
 
@@ -3243,10 +3247,6 @@ static size_t qemu_rdma_save_page(QEMUFile *f,
 
     CHECK_ERROR_STATE();
 
-    if (migration_in_postcopy()) {
-        return RAM_SAVE_CONTROL_NOT_SUPP;
-    }
-
     qemu_fflush(f);
 
     /*
@@ -3866,6 +3866,10 @@ static int qemu_rdma_registration_start(QEMUFile *f,
     QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(qemu_file_get_ioc(f));
     RDMAContext *rdma;
 
+    if (migration_in_postcopy()) {
+        return 0;
+    }
+
     RCU_READ_LOCK_GUARD();
     rdma = qatomic_rcu_read(&rioc->rdmaout);
     if (!rdma) {
@@ -3874,10 +3878,6 @@ static int qemu_rdma_registration_start(QEMUFile *f,
 
     CHECK_ERROR_STATE();
 
-    if (migration_in_postcopy()) {
-        return 0;
-    }
-
     trace_qemu_rdma_registration_start(flags);
     qemu_put_be64(f, RAM_SAVE_FLAG_HOOK);
     qemu_fflush(f);
@@ -3897,6 +3897,10 @@ static int qemu_rdma_registration_stop(QEMUFile *f,
     RDMAControlHeader head = { .len = 0, .repeat = 1 };
     int ret = 0;
 
+    if (migration_in_postcopy()) {
+        return 0;
+    }
+
     RCU_READ_LOCK_GUARD();
     rdma = qatomic_rcu_read(&rioc->rdmaout);
     if (!rdma) {
@@ -3905,10 +3909,6 @@ static int qemu_rdma_registration_stop(QEMUFile *f,
 
     CHECK_ERROR_STATE();
 
-    if (migration_in_postcopy()) {
-        return 0;
-    }
-
     qemu_fflush(f);
     ret = qemu_rdma_drain_cq(f, rdma);