Re: [PATCH 3/3] tracing: make tp_printk work on syscall tracepoints

[Jeff Xie]

Hi steve,

On Sat, Apr 9, 2022 at 5:18 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Wed, 30 Mar 2022 00:39:31 +0800
> Jeff Xie <xiehuan09@xxxxxxxxx> wrote:
>
> First, patch 1 and 2 can be folded into this patch. Making something
> "available for future use" is not a reason to break up patches. It will not
> help in bisecting, and its not something to be backported.
>
> Next, the tracing subsystem follows the "Capitalize first letter" for
> subjects:
>
>  "tracing: Make tp_printk work on syscall tracepoints"
>
> > Adding printk for syscall tracepoints for the tp_printk work.
>
> Need to add much more content to the above. Your cover letter would work.
>
>     Currently the tp_printk option has no effect on syscall tracepoint.
>     When adding the kernel option parameter tp_printk, then:
>
>     echo 1 > /sys/kernel/debug/tracing/events/syscalls/enable
>
>     When running any application, no trace information is printed on the
>     terminal.
>
>     Now added printk for syscall tracepoints.
>
> As commit logs should be self explanatory per commit. The cover letter was,
> but this patch was lacking.

Thanks a lot for these detailed suggestions.

>
> >
> > Signed-off-by: Jeff Xie <xiehuan09@xxxxxxxxx>
> > ---
> >  kernel/trace/trace_syscalls.c | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >
> > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> > index f755bde42fd0..9798122166d3 100644
> > --- a/kernel/trace/trace_syscalls.c
> > +++ b/kernel/trace/trace_syscalls.c
> > @@ -290,6 +290,25 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
> >       return ret;
> >  }
> >
> > +static void syscall_output_printk(struct trace_entry *ent,
> > +             struct trace_event_file *trace_file, struct trace_array *tr)
> > +{
> > +     unsigned long flags;
> > +     struct trace_iterator *iter = tracepoint_print_iter;
> > +     struct trace_event *event = &trace_file->event_call->event;
> > +
> > +     spin_lock_irqsave(&tracepoint_iter_lock, flags);
> > +
> > +     trace_seq_init(&iter->seq);
> > +     iter->ent = ent;
> > +     iter->tr = tr;
> > +     event->funcs->trace(iter, 0, event);
> > +     trace_seq_putc(&iter->seq, 0);
> > +     pr_info("%s", iter->seq.buffer);
> > +
> > +     spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
> > +}
> > +
> >  static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
> >  {
> >       struct trace_array *tr = data;
> > @@ -333,6 +352,9 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
> >       syscall_get_arguments(current, regs, args);
> >       memcpy(entry->args, args, sizeof(unsigned long) * sys_data->nb_args);
> >
> > +     if (static_key_false(&tracepoint_printk_key.key))
> > +             syscall_output_printk(&entry->ent, trace_file, tr);
> > +
> >       event_trigger_unlock_commit(trace_file, buffer, event, entry,
> >                                   trace_ctx);
>
>
> >  }
> > @@ -376,6 +398,9 @@ static void ftrace_syscall_exit(void *data, struct pt_regs *regs, long ret)
> >       entry->nr = syscall_nr;
> >       entry->ret = syscall_get_return_value(current, regs);
> >
> > +     if (static_key_false(&tracepoint_printk_key.key))
> > +             syscall_output_printk(&entry->ent, trace_file, tr);
> > +
>
> Instead of reimplementing the logic, just convert the syscall code to use,
> trace_event_buffer_reserve() and trace_event_buffer_commit(), and then you
> not only get tp_printk() for syscalls, but also other features as well.

Thanks, I will prepare the V2.

> -- Steve
>
>
> >       event_trigger_unlock_commit(trace_file, buffer, event, entry,
> >                                   trace_ctx);
> >  }
>
---
JeffXie