On Tue, Jan 11, 2022 at 6:53 PM John Snow <js...@redhat.com> wrote:
>
> On Thu, Dec 23, 2021 at 6:08 AM Vladimir Sementsov-Ogievskiy
> <vsement...@virtuozzo.com> wrote:
> >
> > Add possibility to generate trace points for each qmp command.
> >
> > We should generate both trace points and trace-events file, for further
> > trace point code generation.
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> > ---
> > scripts/qapi/commands.py | 84 ++++++++++++++++++++++++++++++++++------
> > 1 file changed, 73 insertions(+), 11 deletions(-)
> >
> > diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
> > index 21001bbd6b..9691c11f96 100644
> > --- a/scripts/qapi/commands.py
> > +++ b/scripts/qapi/commands.py
> > @@ -53,7 +53,8 @@ def gen_command_decl(name: str,
> > def gen_call(name: str,
> > arg_type: Optional[QAPISchemaObjectType],
> > boxed: bool,
> > - ret_type: Optional[QAPISchemaType]) -> str:
> > + ret_type: Optional[QAPISchemaType],
> > + add_trace_points: bool) -> str:
> > ret = ''
> >
> > argstr = ''
> > @@ -71,21 +72,65 @@ def gen_call(name: str,
> > if ret_type:
> > lhs = 'retval = '
> >
> > - ret = mcgen('''
> > + qmp_name = f'qmp_{c_name(name)}'
> > + upper = qmp_name.upper()
> > +
> > + if add_trace_points:
> > + ret += mcgen('''
> > +
> > + if (trace_event_get_state_backends(TRACE_%(upper)s)) {
> > + g_autoptr(GString) req_json = qobject_to_json(QOBJECT(args));
> > + trace_%(qmp_name)s("", req_json->str);
> > + }
> > + ''',
> > + upper=upper, qmp_name=qmp_name)
> > +
> > + ret += mcgen('''
> >
> > %(lhs)sqmp_%(c_name)s(%(args)s&err);
> > - error_propagate(errp, err);
> > ''',
> > c_name=c_name(name), args=argstr, lhs=lhs)
> > - if ret_type:
> > - ret += mcgen('''
> > +
> > + ret += mcgen('''
> > if (err) {
> > +''')
> > +
> > + if add_trace_points:
> > + ret += mcgen('''
> > + trace_%(qmp_name)s("FAIL: ", error_get_pretty(err));
> > +''',
> > + qmp_name=qmp_name)
> > +
> > + ret += mcgen('''
> > + error_propagate(errp, err);
> > goto out;
> > }
> > +''')
> > +
> > + if ret_type:
> > + ret += mcgen('''
> >
> > qmp_marshal_output_%(c_name)s(retval, ret, errp);
> > ''',
> > c_name=ret_type.c_name())
> > +
> > + if add_trace_points:
> > + if ret_type:
> > + ret += mcgen('''
> > +
> > + if (trace_event_get_state_backends(TRACE_%(upper)s)) {
> > + g_autoptr(GString) ret_json = qobject_to_json(*ret);
> > + trace_%(qmp_name)s("RET:", ret_json->str);
> > + }
> > + ''',
> > + upper=upper, qmp_name=qmp_name)
> > + else:
> > + ret += mcgen('''
> > +
> > + trace_%(qmp_name)s("SUCCESS", "");
> > + ''',
> > + qmp_name=qmp_name)
> > +
> > return ret
> >
> >
> > @@ -122,10 +167,14 @@ def gen_marshal_decl(name: str) -> str:
> > proto=build_marshal_proto(name))
> >
> >
> > +def gen_trace(name: str) -> str:
> > + return f'qmp_{c_name(name)}(const char *tag, const char *json)
> > "%s%s"\n'
> > +
> > def gen_marshal(name: str,
> > arg_type: Optional[QAPISchemaObjectType],
> > boxed: bool,
> > - ret_type: Optional[QAPISchemaType]) -> str:
> > + ret_type: Optional[QAPISchemaType],
> > + add_trace_points: bool) -> str:
> > have_args = boxed or (arg_type and not arg_type.is_empty())
> > if have_args:
> > assert arg_type is not None
> > @@ -180,7 +229,7 @@ def gen_marshal(name: str,
> > }
> > ''')
> >
> > - ret += gen_call(name, arg_type, boxed, ret_type)
> > + ret += gen_call(name, arg_type, boxed, ret_type, add_trace_points)
> >
> > ret += mcgen('''
> >
> > @@ -238,11 +287,12 @@ def gen_register_command(name: str,
> >
> >
> > class QAPISchemaGenCommandVisitor(QAPISchemaModularCVisitor):
> > - def __init__(self, prefix: str):
> > + def __init__(self, prefix: str, add_trace_points: bool):
> > super().__init__(
> > prefix, 'qapi-commands',
> > ' * Schema-defined QAPI/QMP commands', None, __doc__)
> > self._visited_ret_types: Dict[QAPIGenC, Set[QAPISchemaType]] = {}
> > + self.add_trace_points = add_trace_points
> >
> > def _begin_user_module(self, name: str) -> None:
> > self._visited_ret_types[self._genc] = set()
> > @@ -261,6 +311,15 @@ def _begin_user_module(self, name: str) -> None:
> >
> > ''',
> > commands=commands, visit=visit))
> > +
> > + if self.add_trace_points and c_name(commands) != 'qapi_commands':
> > + self._genc.add(mcgen('''
> > +#include "trace/trace-qapi.h"
> > +#include "qapi/qmp/qjson.h"
> > +#include "trace/trace-%(nm)s_trace_events.h"
> > +''',
> > + nm=c_name(commands)))
> > +
> > self._genh.add(mcgen('''
> > #include "%(types)s.h"
> >
> > @@ -322,7 +381,9 @@ def visit_command(self,
> > with ifcontext(ifcond, self._genh, self._genc):
> > self._genh.add(gen_command_decl(name, arg_type, boxed,
> > ret_type))
> > self._genh.add(gen_marshal_decl(name))
> > - self._genc.add(gen_marshal(name, arg_type, boxed, ret_type))
> > + self._genc.add(gen_marshal(name, arg_type, boxed, ret_type,
> > + self.add_trace_points))
> > + self._gent.add(gen_trace(name))
> > with self._temp_module('./init'):
> > with ifcontext(ifcond, self._genh, self._genc):
> > self._genc.add(gen_register_command(
> > @@ -332,7 +393,8 @@ def visit_command(self,
> >
> > def gen_commands(schema: QAPISchema,
> > output_dir: str,
> > - prefix: str) -> None:
> > - vis = QAPISchemaGenCommandVisitor(prefix)
> > + prefix: str,
> > + add_trace_points: bool) -> None:
> > + vis = QAPISchemaGenCommandVisitor(prefix, add_trace_points)
> > schema.visit(vis)
> > vis.write(output_dir)
> > --
> > 2.31.1
> >
>
> I looked at Stefan's feedback and I want to second his recommendation
> to use _enter and _exit tracepoints, this closely resembles a lot of
> temporary debugging code I've written for jobs/bitmaps over the years
> and find the technique helpful.
>
> --js
>
> (as a tangent ...
>
> I wish I had a much nicer way of doing C generation from Python, this
> is so ugly. It's not your fault, of course. I'm just wondering if the
> mailing list has any smarter ideas for future improvements to the
> mcgen interface, because I find this type of code really hard to
> review.)
Come to think of it, we could use a framework that was originally
designed for HTML templating, but for C instead. Wait! Don't close the
email yet, I have some funny things to write still!!
Downsides:
- New template language
- Complex
Pros:
- Easier to read
- Easier to review
- Avoids reinventing the wheel
- Doesn't even technically add a dependency, since Sphinx already
relies on Jinja ...
- *Extremely* funny
As an example, let's say we had a file
"scripts/qapi/templates/qmp_marshal_output.c" that looked like this:
```
static void qmp_marshal_output_{{c_name}}(
{{c_type}} ret_in,
QObject **ret_out,
Error **errp
) {
Visitor *v;
v = qobject_output_visitor_new_qmp(ret_out);
if (visit_type_{{c_name}}(v, "unused", &ret_in, errp)) {
visit_complete(v, ret_out);
}
visit_free(v);
v = qapi_dealloc_visitor_new();
visit_type_{{c_name}}(v, "unused", &ret_in, NULL);
visit_free(v);
}
```
We could use Jinja to process it from Python like this:
```
import os
from jinja2 import PackageLoader, Environment, FileSystemLoader
env = Environment(loader = FileSystemLoader('./templates/'))
template = env.get_template("qmp_marshal_output.c")
rendered = cgen(template.render(
c_name = "foo",
c_type = "int",
))
print(rendered)
```
You'd get output like this:
```
static void qmp_marshal_output_foo(
int ret_in,
QObject **ret_out,
Error **errp
) {
Visitor *v;
v = qobject_output_visitor_new_qmp(ret_out);
if (visit_type_foo(v, "unused", &ret_in, errp)) {
visit_complete(v, ret_out);
}
visit_free(v);
v = qapi_dealloc_visitor_new();
visit_type_foo(v, "unused", &ret_in, NULL);
visit_free(v);
```
Jinja also supports conditionals and some other logic constructs, so
it'd *probably* apply to most templates we'd want to write, though
admittedly I haven't thought through if it'd actually work everywhere
we'd need it, and I am mostly having a laugh.
...OK, back to work!
--js
