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SubjectRe: [PATCH 2/2][RFC] tracing: Add extract out softirq names used by irq trace events
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On Fri, 2010-02-26 at 00:48 +0100, Frederic Weisbecker wrote:

>
> And what about a kind of macro that could have two effects:
>
> - define the enum
> - define the nr -> name pairs for resolution
>
> This could be something like:
>
> define_trace_enum(softirq)
> enum_entry(TASKLET, 4), //don't know if it's 4, just an example
> enum_entry(HRTIMER, 5),
> end_trace_enum()

That wont work. Unless it is in a separate file that can be included
over and over again. That is we would need:

** include/linux/softirq_names.h:

define_trace_enum(softirq)
enum_entry(HI, 0),
enum_entry(TIMER, 1),
[...]
end_trace_enum();



** include/trace/define_enum.h:

#define define_trace_enum(name) enum name {
#define enum_entry(a, b) a = b
#define end_trace_enum() }


** include/linux/interrupt.h

/* instead of declaring an enum we have */

#include <trace/define_enum.h>
#include <linux/softirq_names.h>

Here we could do something special with that file.

>
> (My naming sucks, as usual).
>
> In normal headers, it would define an enum:
>
> enum softirq {
> TASKLET = 4,
> HRTIMER = 5,
> };
>
> And in the file that has DEFINE_TRACEPOINT:
>
> /* can be in ftrace_event.h */
> struct resolve_enum {
> const char *name;
> int val;
> };
>
> struct resolve_enum softirq = { //come from define_trace_enum()
> {"TASKLET", 4}, //come from enum_entry()
> {"HRTIMER", 5},
> { NULL, 0}, /* end */
> };
>
> /* This can be used from the trace_event macro */
> const char *softirq_name(int nr)
> {
> return resolve_enum[nr];
> }
>
>
> And then you can get back the struct resolve_enum softirq
> to export the values to debugfs, may be by storing such
> structures in a section (and adding the name of the enum)
>
> This has the advantage of beeing sync with core header
> changes, but this has the drawback of beeing less readable
> to define an enum usable from a TRACE_EVENT (especially
> if I define the naming personally).
>


This just gets ugly and I'm not sure people would like doing this. It
also requires that you number the enums specifically.

A better way could be this:

** include/linux/interrupt.h

#define SOFTIRQ_NAMES \
C(HI), \
C(TIMER), \
[...] \
C(RCU)

#define C(name) name##_SOFTIRQ

enum { SOFTIRQ_NAMES, NR_SOFTIRQS };

#undef C

And in the trace file we could do:

#define C(name) { #name, name##_SOFTIRQ, sizeof(name##_SOFTIRQ) }

struct {
char *name;
int val;
int size;
} softirq_names[] __attribute__((section("trace_syms"))) =
{ SOFTIRQ_NAMES };

#undef C


This way we don't need to number every enum, or have to move the enum
into another file. My question is...

Would the following be acceptable in normal headers?

#define ENUM_NAMES \
C(a), \
C(b), \
...

#define C(name) name

enum { ENUM_NAMES };

#undef C

-- Steve




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