[Qemu-devel] [PATCH v6 11/12] qed: Implement .bdrv_drain

[Fam Zheng <famz@redhat.com>]

The "need_check_timer" is used to clear the "NEED_CHECK" flag in the
image header after a grace period once metadata update has finished. In
compliance to the bdrv_drain semantics we should make sure it remains
deleted once .bdrv_drain is called.

We cannot reuse qed_need_check_timer_cb because it calls bdrv_aio_flush
with a completion callback that starts more I/O, bdrv_drain cannot cope
with this. Also the assertions in qed_need_check_timer_cb and
qed_unplug_allocating_write_reqs are not guaranteed in the case of
bdrv_qed_drain.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/qed.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/block/qed.c b/block/qed.c
index 5ea05d4..d63a7de 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -375,6 +375,20 @@ static void bdrv_qed_attach_aio_context(BlockDriverState *bs,
     }
 }
 
+static void bdrv_qed_drain(BlockDriverState *bs)
+{
+    BDRVQEDState *s = bs->opaque;
+    int ret;
+
+    /* Cancel timer and start doing I/O that were meant to happen when it
+     * fires, that way we get bdrv_drain() taking care of the requests
+     * correctly. */
+    qed_cancel_need_check_timer(s);
+    qed_plug_allocating_write_reqs(s);
+    ret = bdrv_flush(s->bs);
+    qed_clear_need_check(s, ret);
+}
+
 static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
                          Error **errp)
 {
@@ -1676,6 +1690,7 @@ static BlockDriver bdrv_qed = {
     .bdrv_check               = bdrv_qed_check,
     .bdrv_detach_aio_context  = bdrv_qed_detach_aio_context,
     .bdrv_attach_aio_context  = bdrv_qed_attach_aio_context,
+    .bdrv_drain               = bdrv_qed_drain,
 };
 
 static void bdrv_qed_init(void)
-- 
2.4.3