migration/block: Use real permissions

Request BLK_PERM_CONSISTENT_READ for the source of block migration, and
handle potential permission errors as good as we can in this place
(which is not very good, but it matches the other failure cases).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

migration/block.c

@@ -379,7 +379,7 @@ static void unset_dirty_tracking(void)
     }
 }
 
-static void init_blk_migration(QEMUFile *f)
+static int init_blk_migration(QEMUFile *f)
 {
     BlockDriverState *bs;
     BlkMigDevState *bmds;
@@ -390,6 +390,8 @@ static void init_blk_migration(QEMUFile *f)
         BlkMigDevState *bmds;
         BlockDriverState *bs;
     } *bmds_bs;
+    Error *local_err = NULL;
+    int ret;
 
     block_mig_state.submitted = 0;
     block_mig_state.read_done = 0;
@@ -411,12 +413,12 @@ static void init_blk_migration(QEMUFile *f)
 
         sectors = bdrv_nb_sectors(bs);
         if (sectors <= 0) {
+            ret = sectors;
             goto out;
         }
 
         bmds = g_new0(BlkMigDevState, 1);
-        /* FIXME Use real permissions */
-        bmds->blk = blk_new(0, BLK_PERM_ALL);
+        bmds->blk = blk_new(BLK_PERM_CONSISTENT_READ, BLK_PERM_ALL);
         bmds->blk_name = g_strdup(bdrv_get_device_name(bs));
         bmds->bulk_completed = 0;
         bmds->total_sectors = sectors;
@@ -446,7 +448,11 @@ static void init_blk_migration(QEMUFile *f)
         BlockDriverState *bs = bmds_bs[i].bs;
 
         if (bmds) {
-            blk_insert_bs(bmds->blk, bs, &error_abort);
+            ret = blk_insert_bs(bmds->blk, bs, &local_err);
+            if (ret < 0) {
+                error_report_err(local_err);
+                goto out;
+            }
 
             alloc_aio_bitmap(bmds);
             error_setg(&bmds->blocker, "block device is in use by migration");
@@ -454,8 +460,10 @@ static void init_blk_migration(QEMUFile *f)
         }
     }
 
+    ret = 0;
 out:
     g_free(bmds_bs);
+    return ret;
 }
 
 /* Called with no lock taken.  */
@@ -706,7 +714,11 @@ static int block_save_setup(QEMUFile *f, void *opaque)
             block_mig_state.submitted, block_mig_state.transferred);
 
     qemu_mutex_lock_iothread();
-    init_blk_migration(f);
+    ret = init_blk_migration(f);
+    if (ret < 0) {
+        qemu_mutex_unlock_iothread();
+        return ret;
+    }
 
     /* start track dirty blocks */
     ret = set_dirty_tracking();