perf trace: Allow syscall arg formatters to request non suppression of zeros

Commit-ID:  d47737d524174a81b80c487fe07de3ee2458ee32
Gitweb:     http://git.kernel.org/tip/d47737d524174a81b80c487fe07de3ee2458ee32
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Mon, 17 Jul 2017 15:59:03 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Tue, 18 Jul 2017 23:14:24 -0300

perf trace: Allow syscall arg formatters to request non suppression of zeros

The 'perf trace' tool is suppressing args set to zero, with the exception of string tables (strarrays), which are kinda like enums, i.e. we have maps to go from numbers to strings.

But the 'cmd' fcntl arg requires more specialized treatment, as its value will regulate if the next fcntl syscall arg, 'arg', should be ignored (not used) and also how to format the syscall return (fd, file flags, etc), so add a 'show_zero" bool to struct syscall_arg_fmt, to regulate this more explicitely.

Will be used in a following patch with fcntl, here is just the mechanism.

---
 tools/perf/builtin-trace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index 32778a6..b842bd9 100644
@@ -604,6 +604,7 @@ static size_t syscall_arg__scnprintf_getrandom_flags(char *bf, size_t size,
 struct syscall_arg_fmt {
 	size_t	   (*scnprintf)(char *bf, size_t size, struct syscall_arg *arg);
 	void	   *parm;
+	bool	   show_zero;
 };
 
 static struct syscall_fmt {

@@ -1428,7 +1429,8 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
  			 */
 			if (val == 0 &&
 			    !(sc->arg_fmt &&
-			      (sc->arg_fmt[arg.idx].scnprintf == SCA_STRARRAY ||
+			      (sc->arg_fmt[arg.idx].show_zero ||
+			       sc->arg_fmt[arg.idx].scnprintf == SCA_STRARRAY ||
 			       sc->arg_fmt[arg.idx].scnprintf == SCA_STRARRAYS) &&
 			      sc->arg_fmt[arg.idx].parm))
 				continue;