1 files changed, 25 insertions, 37 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index adf592e867..d74f6701b5 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -47,6 +47,8 @@ struct BlockBackend {
      * can be used to restore those options in the new BDS on insert) */
     BlockBackendRootState root_state;
 
+    bool enable_write_cache;
+
     /* I/O stats (display with "info blockstats"). */
     BlockAcctStats stats;
 
@@ -160,6 +162,8 @@ BlockBackend *blk_new_open(const char *filename, const char *reference,
         return NULL;
     }
 
+    blk_set_enable_write_cache(blk, true);
+
     return blk;
 }
 
@@ -372,23 +376,6 @@ BlockDriverState *blk_bs(BlockBackend *blk)
 }
 
 /*
- * Changes the BlockDriverState attached to @blk
- */
-void blk_set_bs(BlockBackend *blk, BlockDriverState *bs)
-{
-    bdrv_ref(bs);
-
-    if (blk->root) {
-        blk->root->bs->blk = NULL;
-        bdrv_root_unref_child(blk->root);
-    }
-    assert(bs->blk == NULL);
-
-    blk->root = bdrv_root_attach_child(bs, "root", &child_root);
-    bs->blk = blk;
-}
-
-/*
  * Return @blk's DriveInfo if any, else null.
  */
 DriveInfo *blk_legacy_dinfo(BlockBackend *blk)
@@ -712,11 +699,17 @@ static int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
                                       unsigned int bytes, QEMUIOVector *qiov,
                                       BdrvRequestFlags flags)
 {
-    int ret = blk_check_byte_request(blk, offset, bytes);
+    int ret;
+
+    ret = blk_check_byte_request(blk, offset, bytes);
     if (ret < 0) {
         return ret;
     }
 
+    if (!blk->enable_write_cache) {
+        flags |= BDRV_REQ_FUA;
+    }
+
     return bdrv_co_do_pwritev(blk_bs(blk), offset, bytes, qiov, flags);
 }
 
@@ -1223,28 +1216,12 @@ int blk_is_sg(BlockBackend *blk)
 
 int blk_enable_write_cache(BlockBackend *blk)
 {
-    BlockDriverState *bs = blk_bs(blk);
-
-    if (bs) {
-        return bdrv_enable_write_cache(bs);
-    } else {
-        return !!(blk->root_state.open_flags & BDRV_O_CACHE_WB);
-    }
+    return blk->enable_write_cache;
 }
 
 void blk_set_enable_write_cache(BlockBackend *blk, bool wce)
 {
-    BlockDriverState *bs = blk_bs(blk);
-
-    if (bs) {
-        bdrv_set_enable_write_cache(bs, wce);
-    } else {
-        if (wce) {
-            blk->root_state.open_flags |= BDRV_O_CACHE_WB;
-        } else {
-            blk->root_state.open_flags &= ~BDRV_O_CACHE_WB;
-        }
-    }
+    blk->enable_write_cache = wce;
 }
 
 void blk_invalidate_cache(BlockBackend *blk, Error **errp)
@@ -1505,11 +1482,22 @@ int blk_discard(BlockBackend *blk, int64_t sector_num, int nb_sectors)
 int blk_save_vmstate(BlockBackend *blk, const uint8_t *buf,
                      int64_t pos, int size)
 {
+    int ret;
+
     if (!blk_is_available(blk)) {
         return -ENOMEDIUM;
     }
 
-    return bdrv_save_vmstate(blk_bs(blk), buf, pos, size);
+    ret = bdrv_save_vmstate(blk_bs(blk), buf, pos, size);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret == size && !blk->enable_write_cache) {
+        ret = bdrv_flush(blk_bs(blk));
+    }
+
+    return ret < 0 ? ret : size;
 }
 
 int blk_load_vmstate(BlockBackend *blk, uint8_t *buf, int64_t pos, int size)