[PATCH v8 16/43] block: Flush all children in generic code

[Max Reitz <mreitz@redhat.com>]

If the driver does not support .bdrv_co_flush() so bdrv_co_flush()
itself has to flush the children of the given node, it should not flush
just bs->file->bs, but in fact all children that might have been written
to (judging from the permissions taken on them).

This is a bug fix for qcow2 images with an external data file, as they
so far did not flush that data_file node.

In any case, the BLKDBG_EVENT() should be emitted on the primary child,
because that is where a blkdebug node would be if there is any.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
 block/io.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/block/io.c b/block/io.c
index 6f9402117e..8d777cd0ec 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2771,6 +2771,8 @@ static int coroutine_fn bdrv_flush_co_entry(void *opaque)
 
 int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
 {
+    BdrvChild *primary_child = bdrv_primary_child(bs);
+    BdrvChild *child;
     int current_gen;
     int ret = 0;
 
@@ -2800,7 +2802,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
     }
 
     /* Write back cached data to the OS even with cache=unsafe */
-    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
+    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_OS);
     if (bs->drv->bdrv_co_flush_to_os) {
         ret = bs->drv->bdrv_co_flush_to_os(bs);
         if (ret < 0) {
@@ -2810,15 +2812,15 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
 
     /* But don't actually force it to the disk with cache=unsafe */
     if (bs->open_flags & BDRV_O_NO_FLUSH) {
-        goto flush_parent;
+        goto flush_children;
     }
 
     /* Check if we really need to flush anything */
     if (bs->flushed_gen == current_gen) {
-        goto flush_parent;
+        goto flush_children;
     }
 
-    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK);
+    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_DISK);
     if (!bs->drv) {
         /* bs->drv->bdrv_co_flush() might have ejected the BDS
          * (even in case of apparent success) */
@@ -2862,8 +2864,17 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
     /* Now flush the underlying protocol.  It will also have BDRV_O_NO_FLUSH
      * in the case of cache=unsafe, so there are no useless flushes.
      */
-flush_parent:
-    ret = bs->file ? bdrv_co_flush(bs->file->bs) : 0;
+flush_children:
+    ret = 0;
+    QLIST_FOREACH(child, &bs->children, next) {
+        if (child->perm & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) {
+            int this_child_ret = bdrv_co_flush(child->bs);
+            if (!ret) {
+                ret = this_child_ret;
+            }
+        }
+    }
+
 out:
     /* Notify any pending flushes that we have completed */
     if (ret == 0) {
-- 
2.26.2