Re: [Qemu-devel] [PATCH 3/3] replay: introduce block devices record/replay

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> From: Kevin Wolf [mailto:kwolf@redhat.com]
> Am 25.02.2016 um 10:06 hat Pavel Dovgalyuk geschrieben:
> > There is one problem with flush event - callbacks for flush are called for
> > all layers and I couldn't synchronize them correctly yet.
> > I'll probably have to add new callback to block driver, which handles
> > flush request for the whole stack of the drivers.
> 
> Flushes should be treated more or less the same a writes, I think.

But bdrv_co_flush has different structure and does not allow synchronization
of the top layer. Here is the patch for fixing this:

diff --git a/block/io.c b/block/io.c
index a69bfc4..9e05dfe 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2369,6 +2369,12 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
     }
 
     tracked_request_begin(&req, bs, 0, 0, BDRV_TRACKED_FLUSH);
+    /* Write back all layers by calling one driver function */
+    if (bs->drv->bdrv_co_flush) {
+        ret = bs->drv->bdrv_co_flush(bs);
+        goto out;
+    }
+    
     /* Write back cached data to the OS even with cache=unsafe */
     BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
     if (bs->drv->bdrv_co_flush_to_os) {
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 9ef823a..9cc2c58 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -176,6 +176,13 @@ struct BlockDriver {
     int (*bdrv_inactivate)(BlockDriverState *bs);
 
     /*
+     * Flushes all data for all layers by calling bdrv_co_flush for underlying
+     * layers, if needed. This function is needed for deterministic
+     * synchronization of the flush finishing callback.
+     */
+    int coroutine_fn (*bdrv_co_flush)(BlockDriverState *bs);
+    
+    /*
      * Flushes all data that was already written to the OS all the way down to
      * the disk (for example raw-posix calls fsync()).
      */


Then I'll have just to implement bdrv_co_flush for blkreplay layer.
This callback will manually invoke bdrv_co_flush for underlying layer
allowing synchronization of finishing callback.

Pavel Dovgalyuk