Re: [PATCH v2] perf ftrace: Detect whether ftrace is enabled on system

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Wed, Sep 11, 2024 at 11:15:19AM +0100, James Clark wrote:
> On 11/09/2024 11:01, Changbin Du wrote:
> > To make error messages more accurate, this change detects whether ftrace is
> > enabled on system by checking trace file "set_ftrace_pid".

<SNIP>

> > @@ -1583,6 +1601,11 @@ int cmd_ftrace(int argc, const char **argv)
> >   	if (!check_ftrace_capable())
> >   		return -1;
> > +	if (!is_ftrace_supported()) {
> > +		pr_err("ftrace is not supported on this system\n");
> > +		return -ENOTSUP;
> > +	}
> > +
> >   	ret = perf_config(perf_ftrace_config, &ftrace);
> >   	if (ret < 0)
> >   		return -1;
> 
> Reviewed-by: James Clark <james.clark@linaro.org>

Applied and added these comments:

Committer testing:

Doing it in an unprivileged toolbox container on Fedora 40:

Before:

  acme@number:~/git/perf-tools-next$ toolbox enter perf
  ⬢[acme@toolbox perf-tools-next]$ sudo su -
  ⬢[root@toolbox ~]# ~acme/bin/perf ftrace
  failed to reset ftrace
  ⬢[root@toolbox ~]#

After this patch:

  ⬢[root@toolbox ~]# ~acme/bin/perf ftrace
  ftrace is not supported on this system
  ⬢[root@toolbox ~]#

Maybe we could check if we are in such as situation, inside an
unprivileged container, and provide a HINT line?

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Changbin Du <changbin.du@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>