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diff --git a/docs/devel/block-coroutine-wrapper.rst b/docs/devel/block-coroutine-wrapper.rst
new file mode 100644
index 0000000000..412851986b
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+++ b/docs/devel/block-coroutine-wrapper.rst
@@ -0,0 +1,54 @@
+=======================
+block-coroutine-wrapper
+=======================
+
+A lot of functions in QEMU block layer (see ``block/*``) can only be
+called in coroutine context. Such functions are normally marked by the
+coroutine_fn specifier. Still, sometimes we need to call them from
+non-coroutine context; for this we need to start a coroutine, run the
+needed function from it and wait for the coroutine to finish in a
+BDRV_POLL_WHILE() loop. To run a coroutine we need a function with one
+void* argument. So for each coroutine_fn function which needs a
+non-coroutine interface, we should define a structure to pack the
+parameters, define a separate function to unpack the parameters and
+call the original function and finally define a new interface function
+with same list of arguments as original one, which will pack the
+parameters into a struct, create a coroutine, run it and wait in
+BDRV_POLL_WHILE() loop. It's boring to create such wrappers by hand,
+so we have a script to generate them.
+
+Usage
+=====
+
+Assume we have defined the ``coroutine_fn`` function
+``bdrv_co_foo(<some args>)`` and need a non-coroutine interface for it,
+called ``bdrv_foo(<same args>)``. In this case the script can help. To
+trigger the generation:
+
+1. You need ``bdrv_foo`` declaration somewhere (for example, in
+   ``block/coroutines.h``) with the ``generated_co_wrapper`` mark,
+   like this:
+
+.. code-block:: c
+
+    int generated_co_wrapper bdrv_foo(<some args>);
+
+2. You need to feed this declaration to block-coroutine-wrapper script.
+   For this, add the .h (or .c) file with the declaration to the
+   ``input: files(...)`` list of ``block_gen_c`` target declaration in
+   ``block/meson.build``
+
+You are done. During the build, coroutine wrappers will be generated in
+``<BUILD_DIR>/block/block-gen.c``.
+
+Links
+=====
+
+1. The script location is ``scripts/block-coroutine-wrapper.py``.
+
+2. Generic place for private ``generated_co_wrapper`` declarations is
+   ``block/coroutines.h``, for public declarations:
+   ``include/block/block.h``
+
+3. The core API of generated coroutine wrappers is placed in
+   (not generated) ``block/block-gen.h``
diff --git a/docs/devel/index.rst b/docs/devel/index.rst
index c34b43ec28..5fda2d3509 100644
--- a/docs/devel/index.rst
+++ b/docs/devel/index.rst
@@ -32,3 +32,4 @@ Contents:
    s390-dasd-ipl
    clocks
    qom
+   block-coroutine-wrapper