Merge branch 'bpf-bpftool-json-fixes'

Quentin Monnet says:

====================
These are two minor fixes to avoid breaking JSON output in batch mode. The
first one makes bpftool output a "null" JSON object, as expected in batch
mode if nothing else is to be printed, when dumping program instructions
into an output file. The second one replaces a call to "perror()" with
something that does not break JSON when parsing input file for batch mode.
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/main.c

@@ -244,7 +244,7 @@ static int do_batch(int argc, char **argv)
 	}
 
 	if (errno && errno != ENOENT) {
-		perror("reading batch file failed");
+		p_err("reading batch file failed: %s", strerror(errno));
 		err = -1;
 	} else {
 		p_info("processed %d lines", lines);

tools/bpf/bpftool/prog.c

@@ -774,6 +774,9 @@ static int do_dump(int argc, char **argv)
 			      n < 0 ? strerror(errno) : "short write");
 			goto err_free;
 		}
+
+		if (json_output)
+			jsonw_null(json_wtr);
 	} else {
 		if (member_len == &info.jited_prog_len) {
 			const char *name = NULL;