vhost-user: add a migration blocker If VHOST_USER_PROTOCOL_F_LOG_SHMFD is not announced, block vhost-user migration. The blocker is removed in vhost_dev_cleanup(). Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Thibaut Collet <thibaut.collet@6wind.com>

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 2709c4e..fb3aa40 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c

@@ -15,6 +15,7 @@
 #include "qemu/error-report.h"
 #include "qemu/sockets.h"
 #include "exec/ram_addr.h"
+#include "migration/migration.h"
 
 #include <fcntl.h>
 #include <unistd.h>
@@ -442,6 +443,14 @@
         }
     }
 
+    if (dev->migration_blocker == NULL &&
+        !virtio_has_feature(dev->protocol_features,
+                            VHOST_USER_PROTOCOL_F_LOG_SHMFD)) {
+        error_setg(&dev->migration_blocker,
+                   "Migration disabled: vhost-user backend lacks "
+                   "VHOST_USER_PROTOCOL_F_LOG_SHMFD feature.");
+    }
+
     return 0;
 }
 

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 65c09bf..a553256 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c

@@ -961,6 +961,8 @@
     uint64_t features;
     int i, r;
 
+    hdev->migration_blocker = NULL;
+
     if (vhost_set_backend_type(hdev, backend_type) < 0) {
         close((uintptr_t)opaque);
         return -1;
@@ -1012,12 +1014,18 @@
         .eventfd_del = vhost_eventfd_del,
         .priority = 10
     };
-    hdev->migration_blocker = NULL;
-    if (!(hdev->features & (0x1ULL << VHOST_F_LOG_ALL))) {
-        error_setg(&hdev->migration_blocker,
-                   "Migration disabled: vhost lacks VHOST_F_LOG_ALL feature.");
+
+    if (hdev->migration_blocker == NULL) {
+        if (!(hdev->features & (0x1ULL << VHOST_F_LOG_ALL))) {
+            error_setg(&hdev->migration_blocker,
+                       "Migration disabled: vhost lacks VHOST_F_LOG_ALL feature.");
+        }
+    }
+
+    if (hdev->migration_blocker != NULL) {
         migrate_add_blocker(hdev->migration_blocker);
     }
+
     hdev->mem = g_malloc0(offsetof(struct vhost_memory, regions));
     hdev->n_mem_sections = 0;
     hdev->mem_sections = NULL;