migration: refactor init_dirty_bitmap_migration

Split out handling one bs, it is needed for the following commit, which
will handle BlockBackends separately.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200521220648.3255-2-vsementsov@virtuozzo.com>
[eblake: shorter subject line]
Signed-off-by: Eric Blake <eblake@redhat.com>

migration/block-dirty-bitmap.c

@@ -268,57 +268,66 @@ static void dirty_bitmap_mig_cleanup(void)
 }
 
 /* Called with iothread lock taken. */
-static int init_dirty_bitmap_migration(void)
+static int add_bitmaps_to_list(BlockDriverState *bs, const char *bs_name)
 {
-    BlockDriverState *bs;
     BdrvDirtyBitmap *bitmap;
     DirtyBitmapMigBitmapState *dbms;
     Error *local_err = NULL;
 
-    dirty_bitmap_mig_state.bulk_completed = false;
-    dirty_bitmap_mig_state.prev_bs = NULL;
-    dirty_bitmap_mig_state.prev_bitmap = NULL;
-    dirty_bitmap_mig_state.no_bitmaps = false;
+    FOR_EACH_DIRTY_BITMAP(bs, bitmap) {
+        if (!bdrv_dirty_bitmap_name(bitmap)) {
+            continue;
+        }
 
-    for (bs = bdrv_next_all_states(NULL); bs; bs = bdrv_next_all_states(bs)) {
-        const char *name = bdrv_get_device_or_node_name(bs);
+        if (!bs_name || strcmp(bs_name, "") == 0) {
+            error_report("Found bitmap '%s' in unnamed node %p. It can't "
+                         "be migrated", bdrv_dirty_bitmap_name(bitmap), bs);
+            return -1;
+        }
 
-        FOR_EACH_DIRTY_BITMAP(bs, bitmap) {
-            if (!bdrv_dirty_bitmap_name(bitmap)) {
-                continue;
-            }
+        if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT, &local_err)) {
+            error_report_err(local_err);
+            return -1;
+        }
 
-            if (!name || strcmp(name, "") == 0) {
-                error_report("Found bitmap '%s' in unnamed node %p. It can't "
-                             "be migrated", bdrv_dirty_bitmap_name(bitmap), bs);
-                goto fail;
-            }
+        bdrv_ref(bs);
+        bdrv_dirty_bitmap_set_busy(bitmap, true);
+
+        dbms = g_new0(DirtyBitmapMigBitmapState, 1);
+        dbms->bs = bs;
+        dbms->node_name = bs_name;
+        dbms->bitmap = bitmap;
+        dbms->total_sectors = bdrv_nb_sectors(bs);
+        dbms->sectors_per_chunk = CHUNK_SIZE * 8 *
+            bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
+        if (bdrv_dirty_bitmap_enabled(bitmap)) {
+            dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_ENABLED;
+        }
+        if (bdrv_dirty_bitmap_get_persistence(bitmap)) {
+            dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
+        }
 
-            if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT,
-                                        &local_err)) {
-                error_report_err(local_err);
-                goto fail;
-            }
+        QSIMPLEQ_INSERT_TAIL(&dirty_bitmap_mig_state.dbms_list,
+                             dbms, entry);
+    }
 
-            bdrv_ref(bs);
-            bdrv_dirty_bitmap_set_busy(bitmap, true);
-
-            dbms = g_new0(DirtyBitmapMigBitmapState, 1);
-            dbms->bs = bs;
-            dbms->node_name = name;
-            dbms->bitmap = bitmap;
-            dbms->total_sectors = bdrv_nb_sectors(bs);
-            dbms->sectors_per_chunk = CHUNK_SIZE * 8 *
-                bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
-            if (bdrv_dirty_bitmap_enabled(bitmap)) {
-                dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_ENABLED;
-            }
-            if (bdrv_dirty_bitmap_get_persistence(bitmap)) {
-                dbms->flags |= DIRTY_BITMAP_MIG_START_FLAG_PERSISTENT;
-            }
+    return 0;
+}
+
+/* Called with iothread lock taken. */
+static int init_dirty_bitmap_migration(void)
+{
+    BlockDriverState *bs;
+    DirtyBitmapMigBitmapState *dbms;
+
+    dirty_bitmap_mig_state.bulk_completed = false;
+    dirty_bitmap_mig_state.prev_bs = NULL;
+    dirty_bitmap_mig_state.prev_bitmap = NULL;
+    dirty_bitmap_mig_state.no_bitmaps = false;
 
-            QSIMPLEQ_INSERT_TAIL(&dirty_bitmap_mig_state.dbms_list,
-                                 dbms, entry);
+    for (bs = bdrv_next_all_states(NULL); bs; bs = bdrv_next_all_states(bs)) {
+        if (add_bitmaps_to_list(bs, bdrv_get_device_or_node_name(bs))) {
+            goto fail;
         }
     }