[Qemu-block] [RFC PATCH 2/7] block: Block "device IO" during bdrv_drain and bdrv_drain_all

[Fam Zheng]

We don't want new requests from guest, so block the operation around the
nested poll.

Signed-off-by: Fam Zheng <address@hidden>
---
 block/io.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/block/io.c b/block/io.c
index 1ce62c4..d369de3 100644
--- a/block/io.c
+++ b/block/io.c
@@ -289,9 +289,15 @@ static bool bdrv_drain_one(BlockDriverState *bs)
  */
 void bdrv_drain(BlockDriverState *bs)
 {
+    Error *blocker = NULL;
+
+    error_setg(&blocker, "bdrv_drain in progress");
+    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
     while (bdrv_drain_one(bs)) {
         /* Keep iterating */
     }
+    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
+    error_free(blocker);
 }
 
 /*
@@ -311,6 +317,9 @@ void bdrv_drain_all(void)
     /* Always run first iteration so any pending completion BHs run */
     bool busy = true;
     BlockDriverState *bs = NULL;
+    Error *blocker = NULL;
+
+    error_setg(&blocker, "bdrv_drain_all in progress");
 
     while ((bs = bdrv_next(bs))) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
@@ -319,6 +328,7 @@ void bdrv_drain_all(void)
         if (bs->job) {
             block_job_pause(bs->job);
         }
+        bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
         aio_context_release(aio_context);
     }
 
@@ -343,8 +353,10 @@ void bdrv_drain_all(void)
         if (bs->job) {
             block_job_resume(bs->job);
         }
+        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
         aio_context_release(aio_context);
     }
+    error_free(blocker);
 }
 
 /**
-- 
1.9.3