[Qemu-devel] [PATCH 11/12] block: Introduce BlockDriver.bdrv_drain callback

[Fam Zheng <famz@redhat.com>]

Drivers can have internal request sources that generates IO, like the
need_check_timer in QED. Since we want quiesced periods that contain
nested event loops in block layer, we need to have a way to disable such
event sources.

Block drivers must implement the "bdrv_drain" callback if it has any
internal sources that can generate I/O activity, like a timer or a
worker thread (even in a library) that can schedule QEMUBH in an
asynchronous callback.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/io.c                | 3 +++
 include/block/block_int.h | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/block/io.c b/block/io.c
index b0dde7f..ad4b456 100644
--- a/block/io.c
+++ b/block/io.c
@@ -247,6 +247,9 @@ void bdrv_drain(BlockDriverState *bs)
 {
     bool busy = true;
 
+    if (bs->drv && bs->drv->bdrv_drain) {
+        bs->drv->bdrv_drain(bs);
+    }
     while (busy) {
         /* Keep iterating */
          bdrv_flush_io_queue(bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 7c58221..99359b2 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -288,6 +288,12 @@ struct BlockDriver {
      */
     int (*bdrv_probe_geometry)(BlockDriverState *bs, HDGeometry *geo);
 
+    /**
+     * Drain and stop any internal sources of requests in the driver, and
+     * remain so until next I/O callback (e.g. bdrv_co_writev) is called.
+     */
+    void (*bdrv_drain)(BlockDriverState *bs);
+
     QLIST_ENTRY(BlockDriver) list;
 };
 
-- 
2.5.3