block-coroutine-wrapper: use qemu_get_current_aio_context()

Use qemu_get_current_aio_context() in mixed wrappers and coroutine
wrappers so that code runs in the caller's AioContext instead of moving
to the BlockDriverState's AioContext. This change is necessary for the
multi-queue block layer where any thread can call into the block layer.

Most wrappers are IO_CODE where it's safe to use the current AioContext
nowadays. BlockDrivers and the core block layer use their own locks and
no longer depend on the AioContext lock for thread-safety.

The bdrv_create() wrapper invokes GLOBAL_STATE code. Using the current
AioContext is safe because this code is only called with the BQL held
from the main loop thread.

The output of qemu-iotests 051 is sensitive to event loop activity.
Update the output because the monitor BH runs at a different time,
causing prompts to be printed differently in the output.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230912231037.826804-6-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

scripts/block-coroutine-wrapper.py

@@ -91,8 +91,6 @@ def __init__(self, wrapper_type: str, return_type: str, name: str,
                 raise ValueError(f"no_co function can't be rdlock: {self.name}")
             self.target_name = f'{subsystem}_{subname}'
 
-        self.ctx = self.gen_ctx()
-
         self.get_result = 's->ret = '
         self.ret = 'return s.ret;'
         self.co_ret = 'return '
@@ -166,7 +164,7 @@ def create_mixed_wrapper(func: FuncDecl) -> str:
         {func.co_ret}{name}({ func.gen_list('{name}') });
     }} else {{
         {struct_name} s = {{
-            .poll_state.ctx = {func.ctx},
+            .poll_state.ctx = qemu_get_current_aio_context(),
             .poll_state.in_progress = true,
 
 { func.gen_block('            .{name} = {name},') }
@@ -190,7 +188,7 @@ def create_co_wrapper(func: FuncDecl) -> str:
 {func.return_type} {func.name}({ func.gen_list('{decl}') })
 {{
     {struct_name} s = {{
-        .poll_state.ctx = {func.ctx},
+        .poll_state.ctx = qemu_get_current_aio_context(),
         .poll_state.in_progress = true,
 
 { func.gen_block('        .{name} = {name},') }