linux-kernel - Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings

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Date:   Fri, 30 Jun 2017 16:37:47 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Michael Sartain <mikesart@...tmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings

On Fri, Jun 30, 2017 at 2:50 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Fri, 30 Jun 2017 11:17:50 -0600
[..]
>>
>> Signed-off-by: Michael Sartain <mikesart@...tmail.com>
>> ---
>>  kernel/trace/trace.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 59 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 68c214b..ca84c97 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -4692,6 +4692,7 @@ static const struct file_operations tracing_readme_fops = {
>>  static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
>>  {
>>       unsigned int *ptr = v;
>> +     long tgid_check = (long) m->private;
>
> I really don't like the subtle use of having m->private != NULL mean
> this is for tgid listing.
>
> In fact, I don't see the purpose of reusing the seq code. The cmdlines
> and tgid map are quite different. Just create its own functions. I
> don't see the benefit of trying to reuse this except for making the
> code more complex.

I agree with Steven, this patch should be rewritten to use separate
functions and not reuse the other ones as its otherwise really
confusing and not good design.

Thanks,
Joel