perf data: Add doc when no conversion support compiled

This adds documentation on the environment variables needed to the
message telling that no conversion support is compiled in.

Committer testing:

  $ make -C tools/perf install
  $ perf data convert --all --to-ctf myctftrace
  No conversion support compiled in. perf should be compiled with environment variables LIBBABELTRACE=1 and LIBBABELTRACE_DIR=/path/to/libbabeltrace/
  $

Signed-off-by: Geneviève Bastien <gbastien@versatic.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Francis Deslauriers <francis.deslauriers@efficios.com>
Cc: Julien Desfossez <jdesfossez@efficios.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170727181205.24843-3-gbastien@versatic.net
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-data.c b/tools/perf/builtin-data.c
index 0adb5f82335ad22534a6f7d91e4fc3b34086bb47..46cd8490baf452cc70739c605e4cdab79d9060be 100644 (file)
--- a/tools/perf/builtin-data.c
+++ b/tools/perf/builtin-data.c
@@ -69,7 +69,7 @@ static int cmd_data_convert(int argc, const char **argv)
        };
 
 #ifndef HAVE_LIBBABELTRACE_SUPPORT
-       pr_err("No conversion support compiled in.\n");
+       pr_err("No conversion support compiled in. perf should be compiled with environment variables LIBBABELTRACE=1 and LIBBABELTRACE_DIR=/path/to/libbabeltrace/\n");
        return -1;
 #endif