linux-kernel - Re: [PATCH v2] tools/lib/traceevent: Replace str_error

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Date:   Mon, 24 Sep 2018 20:07:17 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>
Subject: Re: [PATCH v2] tools/lib/traceevent: Replace str_error_r() with an
 open coded implementation

On Fri, Sep 21, 2018 at 03:20:37PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> While working on having PowerTop use libtracevent as a shared object
> library, Tzvetomir hit "str_error_r not defined". This was added by commit
> c3cec9e68f12d ("tools lib traceevent: Use str_error_r()") because
> strerror_r() has two definitions, where one is GNU specific, and the other
> is XSI complient. The strerror_r() is in a wrapper str_error_r() to keep the
> code from having to worry about which compiler is being used.
> 
> The problem is that str_error_r() is external to libtraceevent, and not part
> of the library. If it is used as a shared object then the tools using it
> will need to define that function. I do not want that function defined in
> libtraceevent itself, as it is out of scope for that library.
> 
> As there's only a single instance of this call, I replaced it with an open
> coded algorithm that just uses strerror() and strncpy() to place the error
> message in the given buffer. We don't need to worry about the errors that
> strerror_r() returns. If the buffer isn't big enough, we simply truncate it.
> 
> Reported-by: Tzvetomir Stoyanov <tstoyanov@...are.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

> ---
> 
> Changes from v1:
> 
>  - Account for buflen being zero (do nothing).
> 
>  tools/lib/traceevent/event-parse.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index 7980fc6c3bac..ba7570646d2c 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -18,7 +18,6 @@
>  #include <errno.h>
>  #include <stdint.h>
>  #include <limits.h>
> -#include <linux/string.h>
>  #include <linux/time64.h>
>  
>  #include <netinet/in.h>
> @@ -6215,7 +6214,12 @@ int tep_strerror(struct tep_handle *pevent __maybe_unused,
>  	const char *msg;
>  
>  	if (errnum >= 0) {
> -		str_error_r(errnum, buf, buflen);
> +		const char *error_str = strerror(errnum);
> +
> +		if (buflen > 0) {
> +			strncpy(buf, error_str, buflen);
> +			buf[buflen - 1] = 0;
> +		}
>  		return 0;
>  	}
>  
> -- 
> 2.13.6
>