trace: Warn the user when not available

From: Arnaldo Carvalho de Melo <[email protected]>

When the audit-libs devel package is not found at build time we disable the 'trace' command, as we are not able to map syscall numbers to strings, but then the message the user is presented is cryptic:

[root@zoo linux]# trace ls
perf: 'ls' is not a perf-command. See 'perf --help'.

Fix it by presenting a more helpful message:

[root@zoo linux]# trace l
trace command not available: missing audit-libs devel package at build time.

---
 tools/perf/perf.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index 431798a4110d..78f7b920e548 100644
@@ -481,14 +481,18 @@ int main(int argc, const char **argv)
 		fprintf(stderr, "cannot handle %s internally", cmd);
 		goto out;
 	}
-#ifdef HAVE_LIBAUDIT_SUPPORT
 	if (!prefixcmp(cmd, "trace")) {
+#ifdef HAVE_LIBAUDIT_SUPPORT
 		set_buildid_dir();
 		setup_path();
 		argv[0] = "trace";
 		return cmd_trace(argc, argv, NULL);
-	}
+#else
+		fprintf(stderr,
+			"trace command not available: missing audit-libs devel package at build time.\n");
+		goto out;
 #endif
+	}
 	/* Look for flags.. */
 	argv++;
 	argc--;

1.9.3

From: Arnaldo Carvalho de Melo <[email protected]>

We were just showing "libperl: OFF", unlike other features where we present the user with a message helping have a feature built in.

Fix it by adding the following message:

config/Makefile:450: Missing perl devel files. Disabling perl scripting support, consider installing perl-ExtUtils-Embed

---
 tools/perf/config/Makefile | 1 +
 1 file changed, 1 insertion(+)

index 729bbdf5cec7..319426f632fc 100644
@@ -447,6 +447,7 @@ else
   ifneq ($(feature-libperl), 1)
     CFLAGS += -DNO_LIBPERL
     NO_LIBPERL := 1
+    msg := $(warning Missing perl devel files. Disabling perl scripting support, consider installing perl-ExtUtils-Embed);
   else
     LDFLAGS += $(PERL_EMBED_LDFLAGS)
     EXTLIBS += $(PERL_EMBED_LIBADD)

1.9.3