linux-kernel - [PATCH v3] tools/lib/traceevent: Replace str_error

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Message-ID: <20181002175539.2ac894c7@gandalf.local.home>
Date:   Tue, 2 Oct 2018 17:55:39 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
        Linux Trace Devel <linux-trace-devel@...r.kernel.org>,
        Colin Patrick McCabe <cmccabe@...mni.cmu.edu>
Subject: [PATCH v3] tools/lib/traceevent: Replace str_error_r() with an open
 coded implementation

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 uses sys_nerr and sys_errlist error array with
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.

The sys_nerr and sys_errlist idea was found here:

  http://www.club.cc.cmu.edu/~cmccabe/blog_strerror.html

Cc: Colin Patrick McCabe <cmccabe@...mni.cmu.edu>
Reported-by: Tzvetomir Stoyanov <tstoyanov@...are.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
Changes since v2:

  Use sys_nerr and sys_errlist idea.

 tools/lib/traceevent/event-parse.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 7980fc6c3bac..d23d10bc5314 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 +6214,13 @@ int tep_strerror(struct tep_handle *pevent __maybe_unused,
 	const char *msg;

 	if (errnum >= 0) {
-		str_error_r(errnum, buf, buflen);
+		if (buflen > 0) {
+			if (errnum < sys_nerr)
+				strncpy(buf, sys_errlist[errnum], buflen);
+			else
+				snprintf(buf, buflen, "Unknown error %d", errnum);
+			buf[buflen - 1] = 0;
+		}
 		return 0;
 	}

-- 
2.13.6