block: Introduce BlockDriver.bdrv_drain callback
Drivers can have internal request sources that generate 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.
Update the comments of bdrv_drain and bdrv_drained_begin accordingly.
Like bdrv_requests_pending(), we should consider all the children of bs.
Before, the while loop just works, as bdrv_requests_pending() already
tracks its children; now we mustn't miss the callback, so recurse down
explicitly.
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1447064214-29930-9-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/io.c b/block/io.c
index 4ecb171..adc1eab 100644
--- a/block/io.c
+++ b/block/io.c
@@ -237,8 +237,21 @@
return false;
}
+static void bdrv_drain_recurse(BlockDriverState *bs)
+{
+ BdrvChild *child;
+
+ if (bs->drv && bs->drv->bdrv_drain) {
+ bs->drv->bdrv_drain(bs);
+ }
+ QLIST_FOREACH(child, &bs->children, next) {
+ bdrv_drain_recurse(child->bs);
+ }
+}
+
/*
- * Wait for pending requests to complete on a single BlockDriverState subtree
+ * Wait for pending requests to complete on a single BlockDriverState subtree,
+ * and suspend block driver's internal I/O until next request arrives.
*
* Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
* AioContext.
@@ -251,6 +264,7 @@
{
bool busy = true;
+ bdrv_drain_recurse(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 84991d9..3a24913 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -295,6 +295,12 @@
*/
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;
};
