tools: bpftool: make error message from getopt_long() JSON-friendly

If `getopt_long()` meets an unknown option, it prints its own error
message to standard error output. While this does not strictly break
JSON output, it is the only case bpftool prints something to standard
error output if JSON output is required. All other errors are printed on
standard output as JSON objects, so that an external program does not
have to parse stderr.

This is changed by setting the global variable `opterr` to 0.
Furthermore, p_err() is used to reproduce the error message in a more
JSON-friendly way, so that users still get to know what the erroneous
option is.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index d72dd73a4016641f37ed4245abe0d62cf4827de7..d294bc8168bed8cc72f8926c6947b98aba0cbcc6 100644 (file)
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -288,6 +288,7 @@ int main(int argc, char **argv)
        hash_init(prog_table.table);
        hash_init(map_table.table);
 
+       opterr = 0;
        while ((opt = getopt_long(argc, argv, "Vhpjf",
                                  options, NULL)) >= 0) {
                switch (opt) {
@@ -313,7 +314,11 @@ int main(int argc, char **argv)
                        show_pinned = true;
                        break;
                default:
-                       usage();
+                       p_err("unrecognized option '%s'", argv[optind - 1]);
+                       if (json_output)
+                               clean_and_exit(-1);
+                       else
+                               usage();
                }
        }