linux-kernel - Re: [PATCH v4] perf ftrace: Append an EOL when write tracing files

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Message-ID: <20180219141300.GE14978@kernel.org>
Date:   Mon, 19 Feb 2018 11:13:00 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     changbin.du@...el.com
Cc:     jolsa@...hat.com, peterz@...radead.org, mingo@...hat.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4] perf ftrace: Append an EOL when write tracing files

Em Mon, Feb 19, 2018 at 10:33:29AM +0800, changbin.du@...el.com escreveu:
> From: Changbin Du <changbin.du@...el.com>
> 
> Before this change, the '--graph-funcs', '--nograph-funcs' and
> '--trace-funcs' options didn't work as expected when the <func> doesn't
> exist. Because the kernel side hid possible errors.
> 
> $ sudo ./perf ftrace -a --graph-depth 1 --graph-funcs abcdefg
>  0)   0.140 us    |  rcu_all_qs();
>  3)   0.304 us    |  mutex_unlock();
>  0)   0.153 us    |  find_vma();
>  3)   0.088 us    |  __fsnotify_parent();
>  0)   6.145 us    |  handle_mm_fault();
>  3)   0.089 us    |  fsnotify();
>  3)   0.161 us    |  __sb_end_write();
>  3)   0.710 us    |  SyS_close();
>  3)   7.848 us    |  exit_to_usermode_loop();
> 
> On above example, I specified function filter 'abcdefg' but all functions
> are enabled. The expected error is hidden.
> 
> The original fix is to make the kernel support '\0' as end of string:
> https://lkml.org/lkml/2018/1/16/116
> 
> But above fix cannot be compatible with old kernels. Then Namhyung Kim
> suggest adding a space after function name.
> 
> This patch will append an '\n' when write tracing file. After this fix,
> the perf will report correct error state. Also let it print an error if
> reset_tracing_files() fails.

Ok, now it prints:

[root@...et ~]# perf ftrace -a --graph-depth 1 --graph-funcs abcdefg
failed to set tracing filters
[root@...et ~]#

which is too vague, i.e. the user is left without knowing what was it
that didn't work in setting the filter.

It would be better to have:

[root@...et ~]# perf ftrace -a --graph-depth 1 --graph-funcs abcdefg
failed to set tracing filters: function 'abcdefg' not found.
[root@...et ~]#

Anyway, this improves the current situation, so I'm applying it.

- Arnaldo