Re: [Qemu-block] [Qemu-devel] [PATCH v14 03/21] qapi: add trace events for visitor

[Markus Armbruster]

"Daniel P. Berrange" <address@hidden> writes:

> On Fri, Oct 07, 2016 at 03:59:07PM +0200, Markus Armbruster wrote:
>> "Daniel P. Berrange" <address@hidden> writes:
>> 
>> > Allow tracing of the operation of visitors
>> >
>> > Signed-off-by: Daniel P. Berrange <address@hidden>
>> > ---
>> >  Makefile.objs          |  1 +
>> >  qapi/qapi-visit-core.c | 27 +++++++++++++++++++++++++++
>> >  qapi/trace-events      | 33 +++++++++++++++++++++++++++++++++
>> >  3 files changed, 61 insertions(+)
>> >  create mode 100644 qapi/trace-events
>> >
>> > diff --git a/Makefile.objs b/Makefile.objs
>> > index a8e0224..b3e8aef 100644
>> > --- a/Makefile.objs
>> > +++ b/Makefile.objs
>> > @@ -160,3 +160,4 @@ trace-events-y += target-s390x/trace-events
>> >  trace-events-y += target-ppc/trace-events
>> >  trace-events-y += qom/trace-events
>> >  trace-events-y += linux-user/trace-events
>> > +trace-events-y += qapi/trace-events
>> > diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
>> > index 55f5876..bfcb276 100644
>> > --- a/qapi/qapi-visit-core.c
>> > +++ b/qapi/qapi-visit-core.c
>> > @@ -19,10 +19,12 @@
>> >  #include "qapi/qmp/qerror.h"
>> >  #include "qapi/visitor.h"
>> >  #include "qapi/visitor-impl.h"
>> > +#include "trace.h"
>> >  
>> >  void visit_complete(Visitor *v, void *opaque)
>> >  {
>> >      assert(v->type != VISITOR_OUTPUT || v->complete);
>> > +    trace_visit_complete(v, opaque);
>> 
>> Trace after or before checking the precondition?  Preferences, anyone?
>
> I'm ambivalent, as the assert will crash you either way so
> whether you get a trace event just before the crash seems
> mostly irrelevant to me - the abort stack trace is what
> you'll use to diagnose the crash.

I have a slight preference for trace first, because trace is one call,
while precondition checking can be several.  However, grep shows neither
order is prevalent.  Not worth a respin.

>> >      if (v->complete) {
>> >          v->complete(v, opaque);
>> >      }
>> > @@ -30,6 +32,7 @@ void visit_complete(Visitor *v, void *opaque)
>> >  
>> >  void visit_free(Visitor *v)
>> >  {
>> > +    trace_visit_free(v);
>> >      if (v) {
>> >          v->free(v);
>> >      }
>> > @@ -40,6 +43,7 @@ void visit_start_struct(Visitor *v, const char *name, 
>> > void **obj,
>> >  {
>> >      Error *err = NULL;
>> >  
>> > +    trace_visit_start_struct(v, name, obj, size);
>> >      if (obj) {
>> >          assert(size);
>> >          assert(!(v->type & VISITOR_OUTPUT) || *obj);
>> > @@ -53,6 +57,7 @@ void visit_start_struct(Visitor *v, const char *name, 
>> > void **obj,
>> >  
>> >  void visit_check_struct(Visitor *v, Error **errp)
>> >  {
>> > +    trace_visit_check_struct(v);
>> >      if (v->check_struct) {
>> >          v->check_struct(v, errp);
>> >      }
>> > @@ -60,6 +65,7 @@ void visit_check_struct(Visitor *v, Error **errp)
>> >  
>> >  void visit_end_struct(Visitor *v, void **obj)
>> >  {
>> > +    trace_visit_end_struct(v, obj);
>> >      v->end_struct(v, obj);
>> >  }
>> >  
>> > @@ -69,6 +75,7 @@ void visit_start_list(Visitor *v, const char *name, 
>> > GenericList **list,
>> >      Error *err = NULL;
>> >  
>> >      assert(!list || size >= sizeof(GenericList));
>> > +    trace_visit_start_list(v, name, list, size);
>> >      v->start_list(v, name, list, size, &err);
>> >      if (list && (v->type & VISITOR_INPUT)) {
>> >          assert(!(err && *list));
>> > @@ -79,11 +86,13 @@ void visit_start_list(Visitor *v, const char *name, 
>> > GenericList **list,
>> >  GenericList *visit_next_list(Visitor *v, GenericList *tail, size_t size)
>> >  {
>> >      assert(tail && size >= sizeof(GenericList));
>> > +    trace_visit_next_list(v, tail, size);
>> >      return v->next_list(v, tail, size);
>> >  }
>> >  
>> >  void visit_end_list(Visitor *v, void **obj)
>> >  {
>> > +    trace_visit_end_list(v, obj);
>> >      v->end_list(v, obj);
>> >  }
>> >  
>> > @@ -95,6 +104,7 @@ void visit_start_alternate(Visitor *v, const char *name,
>> >  
>> >      assert(obj && size >= sizeof(GenericAlternate));
>> >      assert(!(v->type & VISITOR_OUTPUT) || *obj);
>> > +    trace_visit_start_alternate(v, name, obj, size, promote_int);
>> >      if (v->start_alternate) {
>> >          v->start_alternate(v, name, obj, size, promote_int, &err);
>> >      }
>> > @@ -106,6 +116,7 @@ void visit_start_alternate(Visitor *v, const char 
>> > *name,
>> >  
>> >  void visit_end_alternate(Visitor *v, void **obj)
>> >  {
>> > +    trace_visit_end_alternate(v, obj);
>> >      if (v->end_alternate) {
>> >          v->end_alternate(v, obj);
>> >      }
>> > @@ -113,6 +124,7 @@ void visit_end_alternate(Visitor *v, void **obj)
>> >  
>> >  bool visit_optional(Visitor *v, const char *name, bool *present)
>> >  {
>> > +    trace_visit_optional(v, name, present);
>> >      if (v->optional) {
>> >          v->optional(v, name, present);
>> >      }
>> > @@ -127,6 +139,7 @@ bool visit_is_input(Visitor *v)
>> >  void visit_type_int(Visitor *v, const char *name, int64_t *obj, Error 
>> > **errp)
>> >  {
>> >      assert(obj);
>> > +    trace_visit_type_int(v, name, obj);
>> >      v->type_int64(v, name, obj, errp);
>> >  }
>> >  
>> > @@ -151,6 +164,7 @@ void visit_type_uint8(Visitor *v, const char *name, 
>> > uint8_t *obj,
>> >                        Error **errp)
>> >  {
>> >      uint64_t value = *obj;
>> > +    trace_visit_type_uint8(v, name, obj);
>> >      visit_type_uintN(v, &value, name, UINT8_MAX, "uint8_t", errp);
>> >      *obj = value;
>> >  }
>> 
>> Putting the trace in the middle of the "value = *obj;
>> visit_type_uintN(v, &value, ...); *obj = value" pattern makes it less
>> visible.
>> 
>> Preserving the pattern requires replacing the initializer by an
>> assignment:
>> 
>>        uint64_t value;
>> 
>>        trace_visit_type_uint8(v, name, obj);
>>        value = *obj;
>>        visit_type_uintN(v, &value, name, UINT8_MAX, "uint8_t", errp);
>>        *obj = value;
>> 
>> Looks slightly more legible to me.  What do you think?
>
> I'm fine with whatever you prefer.

I can touch up this one on commit.