Re: [PATCH v3 2/3] tracing: Add trace_irqsoff tracepoints

[Daniel Wagner]

On 08/30/2016 04:20 PM, Daniel Wagner wrote:
> Just setting the size of the type is not enough. The hist_field_* 
> getter function want to know the offset too:

With this hack here it should work. The COMM generic field is handled via
the tracing_map_ops. We could do it also there but than we need to 
a condition in the trace_map_ops if it is COMM or CPU. 
This shortcut here avoids it:

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 03c0a48..ab8958f 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -152,7 +152,8 @@ EXPORT_SYMBOL_GPL(trace_define_field);
 
 #define __generic_field(type, item, filter_type)                       \
        ret = __trace_define_field(&ftrace_generic_fields, #type,       \
-                                  #item, 0, 0, is_signed_type(type),   \
+                                  #item, 0, sizeof(type),              \
+                                  is_signed_type(type),                \
                                   filter_type);                        \
        if (ret)                                                        \
                return ret;
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f3a960e..77073b7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -75,6 +75,11 @@ static u64 hist_field_log2(struct hist_field *hist_field, 
void *event)
        return (u64) ilog2(roundup_pow_of_two(val));
 }
 
+static u64 hist_field_cpu(struct hist_field *hist_field, void *event)
+{
+       return (u64) smp_processor_id();
+}
+
 #define DEFINE_HIST_FIELD_FN(type)                                     \
 static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
 {                                                                      \
@@ -119,6 +124,7 @@ enum hist_field_flags {
        HIST_FIELD_FL_SYSCALL           = 128,
        HIST_FIELD_FL_STACKTRACE        = 256,
        HIST_FIELD_FL_LOG2              = 512,
+       HIST_FIELD_FL_CPU               = 1024,
 };
 
 struct hist_trigger_attrs {
@@ -371,6 +377,11 @@ static struct hist_field *create_hist_field(struct 
ftrace_event_field *field,
                goto out;
        }
 
+       if (flags & HIST_FIELD_FL_CPU) {
+               hist_field->fn = hist_field_cpu;
+               goto out;
+       }
+
        if (WARN_ON_ONCE(!field))
                goto out;
 
@@ -556,6 +567,11 @@ static int create_key_field(struct hist_trigger_data 
*hist_data,
                        key_size = MAX_FILTER_STR_VAL;
                else
                        key_size = field->size;
+
+               // strcmp(field_name, "cpu") would also work to figure
+               // out if this is a one of the generic fields.
+               if (field->filter_type == FILTER_CPU)
+                       flags |= HIST_FIELD_FL_CPU;
        }
 
        hist_data->fields[key_idx] = create_hist_field(field, flags);