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

[Arnaldo Carvalho de Melo]

Em Mon, Feb 19, 2018 at 10:33:29AM +0800, changbin...@intel.com escreveu:
> From: Changbin Du 
> 
> Before this change, the '--graph-funcs', '--nograph-funcs' and
> '--trace-funcs' options didn't work as expected when the  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@jouet ~]# perf ftrace -a --graph-depth 1 --graph-funcs abcdefg
failed to set tracing filters
[root@jouet ~]#

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

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

- Arnaldo

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

[Namhyung Kim]

On Mon, Feb 19, 2018 at 10:33:29AM +0800, changbin...@intel.com wrote:
> From: Changbin Du 
> 
> Before this change, the '--graph-funcs', '--nograph-funcs' and
> '--trace-funcs' options didn't work as expected when the  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.
> 
> Cc: Namhyung Kim 
> Signed-off-by: Changbin Du 

Acked-by: Namhyung Kim 

Thanks,
Namhyung


> 
> ---
> v4: check strdup() return. (Kim)
> v3: Took Kim's suggestion that add a space after function name.
> v2: Rebase.
> ---
>  tools/perf/builtin-ftrace.c | 18 --
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 25a42ac..f42f228 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -72,6 +72,7 @@ static int __write_tracing_file(const char *name, const 
> char *val, bool append)
>   ssize_t size = strlen(val);
>   int flags = O_WRONLY;
>   char errbuf[512];
> + char *val_copy;
>  
>   file = get_tracing_file(name);
>   if (!file) {
> @@ -91,12 +92,23 @@ static int __write_tracing_file(const char *name, const 
> char *val, bool append)
>   goto out;
>   }
>  
> - if (write(fd, val, size) == size)
> + /*
> +  * Copy the original value and append a '\n'. Without this,
> +  * the kernel can hide possible errors.
> +  */
> + val_copy = strdup(val);
> + if (!val_copy)
> + goto out_close;
> + val_copy[size] = '\n';
> +
> + if (write(fd, val_copy, size + 1) == size + 1)
>   ret = 0;
>   else
>   pr_debug("write '%s' to tracing/%s failed: %s\n",
>val, name, str_error_r(errno, errbuf, sizeof(errbuf)));
>  
> + free(val_copy);
> +out_close:
>   close(fd);
>  out:
>   put_tracing_file(file);
> @@ -280,8 +292,10 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int 
> argc, const char **argv)
>   signal(SIGCHLD, sig_handler);
>   signal(SIGPIPE, sig_handler);
>  
> - if (reset_tracing_files(ftrace) < 0)
> + if (reset_tracing_files(ftrace) < 0) {
> + pr_err("failed to reset ftrace\n");
>   goto out;
> + }
>  
>   /* reset ftrace buffer */
>   if (write_tracing_file("trace", "0") < 0)
> -- 
> 2.7.4
>