block: Move enable_write_cache to BB level

Whether a write cache is used or not is a decision that concerns the
user (e.g. the guest device) rather than the backend. It was already
logically part of the BB level as bdrv_move_feature_fields() always kept
it on top of the BDS tree; with this patch, the core of it (the actual
flag and the additional flushes) is also implemented there.

Direct callers of bdrv_open() must pass BDRV_O_CACHE_WB now if bs
doesn't have a BlockBackend attached.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/block/io.c b/block/io.c
index b588435..939e4f1 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1160,7 +1160,7 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
     }
     bdrv_debug_event(bs, BLKDBG_PWRITEV_DONE);
 
-    if (ret == 0 && !bs->enable_write_cache) {
+    if (ret == 0 && (flags & BDRV_REQ_FUA)) {
         ret = bdrv_co_flush(bs);
     }