block: Drop permissions when migration completes

With image locking, permissions affect other qemu processes as well. We
want to be sure that the destination can run, so let's drop permissions
on the source when migration completes.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

block.c

@@ -4019,7 +4019,7 @@ void bdrv_invalidate_cache_all(Error **errp)
 static int bdrv_inactivate_recurse(BlockDriverState *bs,
                                    bool setting_flag)
 {
-    BdrvChild *child;
+    BdrvChild *child, *parent;
     int ret;
 
     if (!setting_flag && bs->drv->bdrv_inactivate) {
@@ -4038,6 +4038,16 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs,
 
     if (setting_flag) {
         bs->open_flags |= BDRV_O_INACTIVE;
+
+        QLIST_FOREACH(parent, &bs->parents, next_parent) {
+            if (parent->role->inactivate) {
+                ret = parent->role->inactivate(parent);
+                if (ret < 0) {
+                    bs->open_flags &= ~BDRV_O_INACTIVE;
+                    return ret;
+                }
+            }
+        }
     }
     return 0;
 }

block/block-backend.c

@@ -156,6 +156,30 @@ static void blk_root_activate(BdrvChild *child, Error **errp)
     }
 }
 
+static int blk_root_inactivate(BdrvChild *child)
+{
+    BlockBackend *blk = child->opaque;
+
+    if (blk->disable_perm) {
+        return 0;
+    }
+
+    /* Only inactivate BlockBackends for guest devices (which are inactive at
+     * this point because the VM is stopped) and unattached monitor-owned
+     * BlockBackends. If there is still any other user like a block job, then
+     * we simply can't inactivate the image. */
+    if (!blk->dev && !blk->name[0]) {
+        return -EPERM;
+    }
+
+    blk->disable_perm = true;
+    if (blk->root) {
+        bdrv_child_try_set_perm(blk->root, 0, BLK_PERM_ALL, &error_abort);
+    }
+
+    return 0;
+}
+
 static const BdrvChildRole child_root = {
     .inherit_options    = blk_root_inherit_options,
 
@@ -168,6 +192,7 @@ static const BdrvChildRole child_root = {
     .drained_end        = blk_root_drained_end,
 
     .activate           = blk_root_activate,
+    .inactivate         = blk_root_inactivate,
 };
 
 /*

include/block/block_int.h

@@ -473,10 +473,11 @@ struct BdrvChildRole {
     void (*drained_begin)(BdrvChild *child);
     void (*drained_end)(BdrvChild *child);
 
-    /* Notifies the parent that the child has been activated (e.g. when
-     * migration is completing) and it can start requesting permissions and
-     * doing I/O on it. */
+    /* Notifies the parent that the child has been activated/inactivated (e.g.
+     * when migration is completing) and it can start/stop requesting
+     * permissions and doing I/O on it. */
     void (*activate)(BdrvChild *child, Error **errp);
+    int (*inactivate)(BdrvChild *child);
 
     void (*attach)(BdrvChild *child);
     void (*detach)(BdrvChild *child);