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

[Markus Armbruster]

"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?

>      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?

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