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-rw-r--r--include/sysemu/block-backend-io.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/sysemu/block-backend-io.h b/include/sysemu/block-backend-io.h
index bb25493ba1..851a44de96 100644
--- a/include/sysemu/block-backend-io.h
+++ b/include/sysemu/block-backend-io.h
@@ -90,6 +90,11 @@ void blk_iostatus_set_err(BlockBackend *blk, int error);
 int blk_get_max_iov(BlockBackend *blk);
 int blk_get_max_hw_iov(BlockBackend *blk);
 
+/*
+ * blk_io_plug/unplug are thread-local operations. This means that multiple
+ * IOThreads can simultaneously call plug/unplug, but the caller must ensure
+ * that each unplug() is called in the same IOThread of the matching plug().
+ */
 void coroutine_fn blk_co_io_plug(BlockBackend *blk);
 void co_wrapper blk_io_plug(BlockBackend *blk);