block-coroutine-wrapper: Introduce no_co_wrapper

Some functions must not be called from coroutine context. The common
pattern to use them anyway from a coroutine is running them in a BH and
letting the calling coroutine yield to be woken up when the BH is
completed.

Instead of manually writing such wrappers, add support for generating
them to block-coroutine-wrapper.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230126172432.436111-2-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/block/block-common.h

@@ -54,6 +54,20 @@
 #define co_wrapper_bdrv_rdlock         no_coroutine_fn
 #define co_wrapper_mixed_bdrv_rdlock   no_coroutine_fn coroutine_mixed_fn
 
+/*
+ * no_co_wrapper: Function specifier used by block-coroutine-wrapper.py
+ *
+ * Function specifier which does nothing but mark functions to be generated by
+ * scripts/block-coroutine-wrapper.py.
+ *
+ * A no_co_wrapper function declaration creates a coroutine_fn wrapper around
+ * functions that must not be called in coroutine context. It achieves this by
+ * scheduling a BH in the bottom half that runs the respective non-coroutine
+ * function. The coroutine yields after scheduling the BH and is reentered when
+ * the wrapped function returns.
+ */
+#define no_co_wrapper
+
 #include "block/blockjob.h"
 
 /* block.c */

scripts/block-coroutine-wrapper.py

@@ -63,8 +63,8 @@ def __init__(self, param_decl: str) -> None:
 
 
 class FuncDecl:
-    def __init__(self, return_type: str, name: str, args: str,
-                 variant: str) -> None:
+    def __init__(self, wrapper_type: str, return_type: str, name: str,
+                 args: str, variant: str) -> None:
         self.return_type = return_type.strip()
         self.name = name.strip()
         self.struct_name = snake_to_camel(self.name)
@@ -72,8 +72,21 @@ def __init__(self, return_type: str, name: str, args: str,
         self.create_only_co = 'mixed' not in variant
         self.graph_rdlock = 'bdrv_rdlock' in variant
 
-        subsystem, subname = self.name.split('_', 1)
-        self.co_name = f'{subsystem}_co_{subname}'
+        self.wrapper_type = wrapper_type
+
+        if wrapper_type == 'co':
+            subsystem, subname = self.name.split('_', 1)
+            self.target_name = f'{subsystem}_co_{subname}'
+        else:
+            assert wrapper_type == 'no_co'
+            subsystem, co_infix, subname = self.name.split('_', 2)
+            if co_infix != 'co':
+                raise ValueError(f"Invalid no_co function name: {self.name}")
+            if not self.create_only_co:
+                raise ValueError(f"no_co function can't be mixed: {self.name}")
+            if self.graph_rdlock:
+                raise ValueError(f"no_co function can't be rdlock: {self.name}")
+            self.target_name = f'{subsystem}_{subname}'
 
         t = self.args[0].type
         if t == 'BlockDriverState *':
@@ -105,7 +118,8 @@ def gen_block(self, format: str) -> str:
 
 # Match wrappers declared with a co_wrapper mark
 func_decl_re = re.compile(r'^(?P<return_type>[a-zA-Z][a-zA-Z0-9_]* [\*]?)'
-                          r'\s*co_wrapper'
+                          r'(\s*coroutine_fn)?'
+                          r'\s*(?P<wrapper_type>(no_)?co)_wrapper'
                           r'(?P<variant>(_[a-z][a-z0-9_]*)?)\s*'
                           r'(?P<wrapper_name>[a-z][a-z0-9_]*)'
                           r'\((?P<args>[^)]*)\);$', re.MULTILINE)
@@ -113,7 +127,8 @@ def gen_block(self, format: str) -> str:
 
 def func_decl_iter(text: str) -> Iterator:
     for m in func_decl_re.finditer(text):
-        yield FuncDecl(return_type=m.group('return_type'),
+        yield FuncDecl(wrapper_type=m.group('wrapper_type'),
+                       return_type=m.group('return_type'),
                        name=m.group('wrapper_name'),
                        args=m.group('args'),
                        variant=m.group('variant'))
@@ -133,7 +148,7 @@ def create_mixed_wrapper(func: FuncDecl) -> str:
     """
     Checks if we are already in coroutine
     """
-    name = func.co_name
+    name = func.target_name
     struct_name = func.struct_name
     graph_assume_lock = 'assume_graph_lock();' if func.graph_rdlock else ''
 
@@ -163,7 +178,7 @@ def create_co_wrapper(func: FuncDecl) -> str:
     """
     Assumes we are not in coroutine, and creates one
     """
-    name = func.co_name
+    name = func.target_name
     struct_name = func.struct_name
     return f"""\
 {func.return_type} {func.name}({ func.gen_list('{decl}') })
@@ -183,10 +198,11 @@ def create_co_wrapper(func: FuncDecl) -> str:
 }}"""
 
 
-def gen_wrapper(func: FuncDecl) -> str:
+def gen_co_wrapper(func: FuncDecl) -> str:
     assert not '_co_' in func.name
+    assert func.wrapper_type == 'co'
 
-    name = func.co_name
+    name = func.target_name
     struct_name = func.struct_name
 
     graph_lock=''
@@ -225,11 +241,56 @@ def gen_wrapper(func: FuncDecl) -> str:
 {creation_function(func)}"""
 
 
+def gen_no_co_wrapper(func: FuncDecl) -> str:
+    assert '_co_' in func.name
+    assert func.wrapper_type == 'no_co'
+
+    name = func.target_name
+    struct_name = func.struct_name
+
+    return f"""\
+/*
+ * Wrappers for {name}
+ */
+
+typedef struct {struct_name} {{
+    Coroutine *co;
+    {func.return_field}
+{ func.gen_block('    {decl};') }
+}} {struct_name};
+
+static void {name}_bh(void *opaque)
+{{
+    {struct_name} *s = opaque;
+
+    {func.get_result}{name}({ func.gen_list('s->{name}') });
+
+    aio_co_wake(s->co);
+}}
+
+{func.return_type} coroutine_fn {func.name}({ func.gen_list('{decl}') })
+{{
+    {struct_name} s = {{
+        .co = qemu_coroutine_self(),
+{ func.gen_block('        .{name} = {name},') }
+    }};
+    assert(qemu_in_coroutine());
+
+    aio_bh_schedule_oneshot(qemu_get_aio_context(), {name}_bh, &s);
+    qemu_coroutine_yield();
+
+    {func.ret}
+}}"""
+
+
 def gen_wrappers(input_code: str) -> str:
     res = ''
     for func in func_decl_iter(input_code):
         res += '\n\n\n'
-        res += gen_wrapper(func)
+        if func.wrapper_type == 'co':
+            res += gen_co_wrapper(func)
+        else:
+            res += gen_no_co_wrapper(func)
 
     return res