scripts: add block-coroutine-wrapper.py

We have a very frequent pattern of creating a coroutine from a function
with several arguments:

  - create a structure to pack parameters
  - create _entry function to call original function taking parameters
    from struct
  - do different magic to handle completion: set ret to NOT_DONE or
    EINPROGRESS or use separate bool field
  - fill the struct and create coroutine from _entry function with this
    struct as a parameter
  - do coroutine enter and BDRV_POLL_WHILE loop

Let's reduce code duplication by generating coroutine wrappers.

This patch adds scripts/block-coroutine-wrapper.py together with some
friends, which will generate functions with declared prototypes marked
by the 'generated_co_wrapper' specifier.

The usage of new code generation is as follows:

    1. define the coroutine function somewhere

        int coroutine_fn bdrv_co_NAME(...) {...}

    2. declare in some header file

        int generated_co_wrapper bdrv_NAME(...);

       with same list of parameters (generated_co_wrapper is
       defined in "include/block/block.h").

    3. Make sure the block_gen_c declaration in block/meson.build
       mentions the file with your marker function.

Still, no function is now marked, this work is for the following
commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924185414.28642-5-vsementsov@virtuozzo.com>
[Added encoding='utf-8' to open() calls as requested by Vladimir. Fixed
typo and grammar issues pointed out by Eric Blake. Removed clang-format
dependency that caused build test issues.
--Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/block-coroutine-wrapper.py

@@ -0,0 +1,167 @@
+#! /usr/bin/env python3
+"""Generate coroutine wrappers for block subsystem.
+
+The program parses one or several concatenated c files from stdin,
+searches for functions with the 'generated_co_wrapper' specifier
+and generates corresponding wrappers on stdout.
+
+Usage: block-coroutine-wrapper.py generated-file.c FILE.[ch]...
+
+Copyright (c) 2020 Virtuozzo International GmbH.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+import sys
+import re
+from typing import Iterator
+
+
+def gen_header():
+    copyright = re.sub('^.*Copyright', 'Copyright', __doc__, flags=re.DOTALL)
+    copyright = re.sub('^(?=.)', ' * ', copyright.strip(), flags=re.MULTILINE)
+    copyright = re.sub('^$', ' *', copyright, flags=re.MULTILINE)
+    return f"""\
+/*
+ * File is generated by scripts/block-coroutine-wrapper.py
+ *
+{copyright}
+ */
+
+#include "qemu/osdep.h"
+#include "block/coroutines.h"
+#include "block/block-gen.h"
+#include "block/block_int.h"\
+"""
+
+
+class ParamDecl:
+    param_re = re.compile(r'(?P<decl>'
+                          r'(?P<type>.*[ *])'
+                          r'(?P<name>[a-z][a-z0-9_]*)'
+                          r')')
+
+    def __init__(self, param_decl: str) -> None:
+        m = self.param_re.match(param_decl.strip())
+        if m is None:
+            raise ValueError(f'Wrong parameter declaration: "{param_decl}"')
+        self.decl = m.group('decl')
+        self.type = m.group('type')
+        self.name = m.group('name')
+
+
+class FuncDecl:
+    def __init__(self, return_type: str, name: str, args: str) -> None:
+        self.return_type = return_type.strip()
+        self.name = name.strip()
+        self.args = [ParamDecl(arg.strip()) for arg in args.split(',')]
+
+    def gen_list(self, format: str) -> str:
+        return ', '.join(format.format_map(arg.__dict__) for arg in self.args)
+
+    def gen_block(self, format: str) -> str:
+        return '\n'.join(format.format_map(arg.__dict__) for arg in self.args)
+
+
+# Match wrappers declared with a generated_co_wrapper mark
+func_decl_re = re.compile(r'^int\s*generated_co_wrapper\s*'
+                          r'(?P<wrapper_name>[a-z][a-z0-9_]*)'
+                          r'\((?P<args>[^)]*)\);$', re.MULTILINE)
+
+
+def func_decl_iter(text: str) -> Iterator:
+    for m in func_decl_re.finditer(text):
+        yield FuncDecl(return_type='int',
+                       name=m.group('wrapper_name'),
+                       args=m.group('args'))
+
+
+def snake_to_camel(func_name: str) -> str:
+    """
+    Convert underscore names like 'some_function_name' to camel-case like
+    'SomeFunctionName'
+    """
+    words = func_name.split('_')
+    words = [w[0].upper() + w[1:] for w in words]
+    return ''.join(words)
+
+
+def gen_wrapper(func: FuncDecl) -> str:
+    assert func.name.startswith('bdrv_')
+    assert not func.name.startswith('bdrv_co_')
+    assert func.return_type == 'int'
+    assert func.args[0].type in ['BlockDriverState *', 'BdrvChild *']
+
+    name = 'bdrv_co_' + func.name[5:]
+    bs = 'bs' if func.args[0].type == 'BlockDriverState *' else 'child->bs'
+    struct_name = snake_to_camel(name)
+
+    return f"""\
+/*
+ * Wrappers for {name}
+ */
+
+typedef struct {struct_name} {{
+    BdrvPollCo poll_state;
+{ func.gen_block('    {decl};') }
+}} {struct_name};
+
+static void coroutine_fn {name}_entry(void *opaque)
+{{
+    {struct_name} *s = opaque;
+
+    s->poll_state.ret = {name}({ func.gen_list('s->{name}') });
+    s->poll_state.in_progress = false;
+
+    aio_wait_kick();
+}}
+
+int {func.name}({ func.gen_list('{decl}') })
+{{
+    if (qemu_in_coroutine()) {{
+        return {name}({ func.gen_list('{name}') });
+    }} else {{
+        {struct_name} s = {{
+            .poll_state.bs = {bs},
+            .poll_state.in_progress = true,
+
+{ func.gen_block('            .{name} = {name},') }
+        }};
+
+        s.poll_state.co = qemu_coroutine_create({name}_entry, &s);
+
+        return bdrv_poll_co(&s.poll_state);
+    }}
+}}"""
+
+
+def gen_wrappers(input_code: str) -> str:
+    res = ''
+    for func in func_decl_iter(input_code):
+        res += '\n\n\n'
+        res += gen_wrapper(func)
+
+    return res
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 3:
+        exit(f'Usage: {sys.argv[0]} OUT_FILE.c IN_FILE.[ch]...')
+
+    with open(sys.argv[1], 'w', encoding='utf-8') as f_out:
+        f_out.write(gen_header())
+        for fname in sys.argv[2:]:
+            with open(fname, encoding='utf-8') as f_in:
+                f_out.write(gen_wrappers(f_in.read()))
+                f_out.write('\n')