virtio-balloon: Rip out qemu_balloon_inhibit()

The only remaining special case is postcopy. It cannot handle
concurrent discards yet, which would result in requesting already sent
pages from the source. Special-case it in virtio-balloon instead.

Introduce migration_in_incoming_postcopy(), to find out if incoming
postcopy is active.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-7-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

migration/migration.c

diff --git a/migration/migration.c b/migration/migration.c
index 481a590..d365d82 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1772,6 +1772,13 @@
     return migration_in_postcopy() && s->postcopy_after_devices;
 }
 
+bool migration_in_incoming_postcopy(void)
+{
+    PostcopyState ps = postcopy_state_get();
+
+    return ps >= POSTCOPY_INCOMING_DISCARD && ps < POSTCOPY_INCOMING_END;
+}
+
 bool migration_is_idle(void)
 {
     MigrationState *s = current_migration;