The BlockBackend quiesce_counter is greater than zero during drained
sections. Add an API to check whether the BlockBackend is in a drained
section.

The next patch will use this API.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/sysemu/block-backend-global-state.h | 1 +
 block/block-backend.c                       | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/sysemu/block-backend-global-state.h b/include/sysemu/block-backend-global-state.h
index 2b6d27db7c..ac7cbd6b5e 100644
--- a/include/sysemu/block-backend-global-state.h
+++ b/include/sysemu/block-backend-global-state.h
@@ -78,6 +78,7 @@ void blk_activate(BlockBackend *blk, Error **errp);
 int blk_make_zero(BlockBackend *blk, BdrvRequestFlags flags);
 void blk_aio_cancel(BlockAIOCB *acb);
 int blk_commit_all(void);
+bool blk_in_drain(BlockBackend *blk);
 void blk_drain(BlockBackend *blk);
 void blk_drain_all(void);
 void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
diff --git a/block/block-backend.c b/block/block-backend.c
index 9e0f48692a..e0a1d9ec0f 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1270,6 +1270,13 @@ blk_check_byte_request(BlockBackend *blk, int64_t offset, int64_t bytes)
     return 0;
 }
 
+/* Are we currently in a drained section? */
+bool blk_in_drain(BlockBackend *blk)
+{
+    GLOBAL_STATE_CODE(); /* change to IO_OR_GS_CODE(), if necessary */
+    return qatomic_read(&blk->quiesce_counter);
+}
+
 /* To be called between exactly one pair of blk_inc/dec_in_flight() */
 static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
 {
-- 
2.39.2