veristat: Add more veristat control over verifier log options

Add --log-size to be able to customize log buffer sent to bpf() syscall
for BPF program verification logging.

Add --log-fixed to enforce BPF_LOG_FIXED behavior for BPF verifier log.
This is useful in unlikely event that beginning of truncated verifier
log is more important than the end of it (which with rotating verifier
log behavior is the default now).
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230406234205.323208-6-andrii@kernel.org

tools/testing/selftests/bpf/veristat.c

@@ -141,12 +141,15 @@ static struct env {
 	bool verbose;
 	bool debug;
 	bool quiet;
-	int log_level;
 	enum resfmt out_fmt;
 	bool show_version;
 	bool comparison_mode;
 	bool replay_mode;
 
+	int log_level;
+	int log_size;
+	bool log_fixed;
+
 	struct verif_stats *prog_stats;
 	int prog_stat_cnt;
 
@@ -193,12 +196,19 @@ const char argp_program_doc[] =
 "   OR: veristat -C <baseline.csv> <comparison.csv>\n"
 "   OR: veristat -R <results.csv>\n";
 
+enum {
+	OPT_LOG_FIXED = 1000,
+	OPT_LOG_SIZE = 1001,
+};
+
 static const struct argp_option opts[] = {
 	{ NULL, 'h', NULL, OPTION_HIDDEN, "Show the full help" },
 	{ "version", 'V', NULL, 0, "Print version" },
 	{ "verbose", 'v', NULL, 0, "Verbose mode" },
-	{ "log-level", 'l', "LEVEL", 0, "Verifier log level (default 0 for normal mode, 1 for verbose mode)" },
 	{ "debug", 'd', NULL, 0, "Debug mode (turns on libbpf debug logging)" },
+	{ "log-level", 'l', "LEVEL", 0, "Verifier log level (default 0 for normal mode, 1 for verbose mode)" },
+	{ "log-fixed", OPT_LOG_FIXED, NULL, 0, "Disable verifier log rotation" },
+	{ "log-size", OPT_LOG_SIZE, "BYTES", 0, "Customize verifier log size (default to 16MB)" },
 	{ "quiet", 'q', NULL, 0, "Quiet mode" },
 	{ "emit", 'e', "SPEC", 0, "Specify stats to be emitted" },
 	{ "sort", 's', "SPEC", 0, "Specify sort order" },
@@ -263,6 +273,17 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state)
 			argp_usage(state);
 		}
 		break;
+	case OPT_LOG_FIXED:
+		env.log_fixed = true;
+		break;
+	case OPT_LOG_SIZE:
+		errno = 0;
+		env.log_size = strtol(arg, NULL, 10);
+		if (errno) {
+			fprintf(stderr, "invalid log size: %s\n", arg);
+			argp_usage(state);
+		}
+		break;
 	case 'C':
 		env.comparison_mode = true;
 		break;
@@ -929,8 +950,8 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf
 {
 	const char *prog_name = bpf_program__name(prog);
 	const char *base_filename = basename(filename);
-	size_t buf_sz = sizeof(verif_log_buf);
-	char *buf = verif_log_buf;
+	char *buf;
+	int buf_sz, log_level;
 	struct verif_stats *stats;
 	int err = 0;
 	void *tmp;
@@ -948,18 +969,23 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf
 	memset(stats, 0, sizeof(*stats));
 
 	if (env.verbose) {
-		buf_sz = 16 * 1024 * 1024;
+		buf_sz = env.log_size ? env.log_size : 16 * 1024 * 1024;
 		buf = malloc(buf_sz);
 		if (!buf)
 			return -ENOMEM;
-		bpf_program__set_log_buf(prog, buf, buf_sz);
-		bpf_program__set_log_level(prog, env.log_level | 4); /* stats + log */
+		/* ensure we always request stats */
+		log_level = env.log_level | 4 | (env.log_fixed ? 8 : 0);
 	} else {
-		bpf_program__set_log_buf(prog, buf, buf_sz);
-		bpf_program__set_log_level(prog, 4); /* only verifier stats */
+		buf = verif_log_buf;
+		buf_sz = sizeof(verif_log_buf);
+		/* request only verifier stats */
+		log_level = 4 | (env.log_fixed ? 8 : 0);
 	}
 	verif_log_buf[0] = '\0';
 
+	bpf_program__set_log_buf(prog, buf, buf_sz);
+	bpf_program__set_log_level(prog, log_level);
+
 	/* increase chances of successful BPF object loading */
 	fixup_obj(obj, prog, base_filename);