linux-kernel - Re: [PATCH v2 1/3] tracing/syscalls: Rename variable 'nr' to 'syscall

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Message-ID: <56CF4877.8000107@gmail.com>
Date:	Fri, 26 Feb 2016 03:31:19 +0900
From:	Taeung Song <treeze.taeung@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2 1/3] tracing/syscalls: Rename variable 'nr' to
 'syscall_nr'

Hi, Arnaldo

On 02/26/2016 02:57 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Feb 26, 2016 at 02:38:57AM +0900, Taeung Song escreveu:
>> There is a problem about duplicated variable name i.e.
>>      # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_io_getevents/format
>>      name: sys_enter_io_getevents
>>      ID: 739
>>      format:
>>              field:unsigned short common_type; offset:0;  size:2; signed:0;
>>              field:unsigned char common_flags; offset:2;  size:1; signed:0;
>>              field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
>>              field:int common_pid;offset:4;size:4;signed:1;
>>              field:int nr;                     offset:8;  size:4; signed:1;
>>              field:aio_context_t ctx_id;       offset:16; size:8; signed:0;
>>              field:long min_nr;                offset:24; size:8; signed:0;
>>              field:long nr;                    offset:32; size:8; signed:0;
>>              field:struct io_event * events;   offset:40; size:8; signed:0;
>>              field:struct timespec * timeout;  offset:48; size:8; signed:0;
>>
>>              print fmt: "ctx_id: 0x%08lx, min_nr: 0x%08lx, nr: 0x%08lx,
>>                          events: 0x%08lx, timeout: 0x%08lx", ((unsigned long)(REC->ctx_id)),
>>                          ((unsigned long)(REC->min_nr)), ((unsigned long)(REC->nr)),
>>                          ((unsigned long)(REC->events)), ((unsigned long)(REC->timeout))
>>
>> As above 'int nr;' and 'long nr;' variables have
>> duplicated name so problems are occurred in perf-script i.e.
>>
>>      # perf record -e syscalls:*
>>      # perf script -g python
>>      # perf script -s perf-script.py
>>        File "perf-script.py", line 8694
>>          def syscalls__sys_enter_io_getevents(event_name, context, common_cpu,
>>      SyntaxError: duplicate argument 'nr' in function definition
>>      Error running python script perf-script.py
>
> Please test this with 'perf trace', which this patch breaks, this patch
> should make it understand this 3rd variation of the non common list of
> fields in syscall tracepoints:

OK, I will test it.
But IMHO, I think the bottom change has a problem.
Because sys_enter_io_getevent() has a argument 'long nr'.
So this if statement must not have strcmp(sc->args->name, "nr") == 0.

+ if (sc->args && strcmp(sc->args->name, "syscall_nr") == 0) {

I think the above instance seem better than the bottom.

+	if (sc->args && (strcmp(sc->args->name, "syscall_nr") || 
strcmp(sc->args->name, "nr")) == 0) {

But I'll test again with perf-trace.
And then will say the result.

>
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 20916dd77aac..b31eed102a83 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -1724,8 +1724,8 @@ static int trace__read_syscall_info(struct trace *trace, int id)
>
>   	sc->args = sc->tp_format->format.fields;
>   	sc->nr_args = sc->tp_format->format.nr_fields;
> -	/* drop nr field - not relevant here; does not exist on older kernels */
> -	if (sc->args && strcmp(sc->args->name, "nr") == 0) {
> +	/* drop (syscall_)?nr field - not relevant here; does not exist on older kernels */
> +	if (sc->args && (strcmp(sc->args->name, "syscall_nr") || strcmp(sc->args->name, "nr")) == 0) {
>   		sc->args = sc->args->next;
>   		--sc->nr_args;
>   	}
>
>
> ----------------------
>
> But then I wonder if it wouldn't be better to prefix this with double
> underscores, making it "__syscall_nr" :-\
>

I so agree. Low probability but the name 'syscall_nr' may also
have similar problems.

Thanks,
Taeung