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SubjectRe: [PATCH v3] tools/lib/traceevent: Replace str_error_r() with an open coded implementation
On Tue, 2 Oct 2018 17:55:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@goodmis.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@alumni.cmu.edu>
> Reported-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.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;
> + }

Bah, I now get warnings that sys_nerr and sys_errlist are deprecated.

OK, so going back to just using the racy strerror() should be good
enough, as this incompatibility with strerror_r() is a disaster!

-- Steve


> return 0;
> }
>

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