Better ways to validate map via BTF?

[Jesper Dangaard Brouer <brouer@redhat.com>]

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Hi Andrii,

Is there are better way to validate that a userspace BPF-program uses
the correct map via BTF?

Below and in attached patch, I'm using bpf_obj_get_info_by_fd() to get
some map-info, and check info.value_size and info.max_entries match
what I expect.  What I really want, is to check that "map-value" have
same struct layout as:

 struct config {
	__u32 action;
	int ifindex;
	__u32 options;
 };

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer


static void check_config_map_fd_info(int map_fd) {
	struct bpf_map_info info = { 0 };
	__u32 info_len = sizeof(info);
	__u32 exp_value_size = sizeof(struct config);
	__u32 exp_entries = 1;
	int err;

	/* BPF-info via bpf-syscall */
	err = bpf_obj_get_info_by_fd(map_fd, &info, &info_len);
	if (err) {
		fprintf(stderr, "ERR: %s() can't get info - %s\n",
			__func__,  strerror(errno));
		exit(EXIT_FAIL_BPF);
	}

	if (exp_value_size != info.value_size) {
		fprintf(stderr, "ERR: %s() "
			"Map value size(%d) mismatch expected size(%d)\n",
			__func__, info.value_size, exp_value_size);
		exit(EXIT_FAIL_BPF);
	}

	if (exp_entries != info.max_entries) {
		fprintf(stderr, "ERR: %s() "
			"Map max_entries(%d) mismatch expected entries(%d)\n",
			__func__, info.max_entries, exp_entries);
		exit(EXIT_FAIL_BPF);
	}
}


struct config {
	__u32 action;
	int ifindex;
	__u32 options;
};


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samples/bpf: xdp_rxq_info check that map have expected size

From: Jesper Dangaard Brouer <brouer@redhat.com>

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 samples/bpf/xdp_rxq_info_user.c |   33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
index 51e0d810e070..fa60731fdbad 100644
--- a/samples/bpf/xdp_rxq_info_user.c
+++ b/samples/bpf/xdp_rxq_info_user.c
@@ -453,6 +453,35 @@ static void stats_poll(int interval, int action, __u32 cfg_opt)
 	free_stats_record(prev);
 }
 
+static void check_config_map_fd_info(int map_fd) {
+	struct bpf_map_info info = { 0 };
+	__u32 info_len = sizeof(info);
+	__u32 exp_value_size = sizeof(struct config);
+	__u32 exp_entries = 1;
+	int err;
+
+	/* BPF-info via bpf-syscall */
+	err = bpf_obj_get_info_by_fd(map_fd, &info, &info_len);
+	if (err) {
+		fprintf(stderr, "ERR: %s() can't get info - %s\n",
+			__func__,  strerror(errno));
+		exit(EXIT_FAIL_BPF);
+	}
+
+	if (exp_value_size != info.value_size) {
+		fprintf(stderr, "ERR: %s() "
+			"Map value size(%d) mismatch expected size(%d)\n",
+			__func__, info.value_size, exp_value_size);
+		exit(EXIT_FAIL_BPF);
+	}
+
+	if (exp_entries != info.max_entries) {
+		fprintf(stderr, "ERR: %s() "
+			"Map max_entries(%d) mismatch expected entries(%d)\n",
+			__func__, info.max_entries, exp_entries);
+		exit(EXIT_FAIL_BPF);
+	}
+}
 
 int main(int argc, char **argv)
 {
@@ -461,7 +490,7 @@ int main(int argc, char **argv)
 	struct bpf_prog_load_attr prog_load_attr = {
 		.prog_type	= BPF_PROG_TYPE_XDP,
 	};
-	struct bpf_prog_info info = {};
+	struct bpf_prog_info info = { 0 };
 	__u32 info_len = sizeof(info);
 	int prog_fd, map_fd, opt, err;
 	bool use_separators = true;
@@ -490,6 +519,7 @@ int main(int argc, char **argv)
 		return EXIT_FAIL;
 
 	map = bpf_map__next(NULL, obj);
+//	map =  bpf_object__find_map_by_name(obj, "config");
 	stats_global_map = bpf_map__next(map, obj);
 	rx_queue_index_map = bpf_map__next(stats_global_map, obj);
 	if (!map || !stats_global_map || !rx_queue_index_map) {
@@ -581,6 +611,7 @@ int main(int argc, char **argv)
 		setlocale(LC_NUMERIC, "en_US");
 
 	/* User-side setup ifindex in config_map */
+	check_config_map_fd_info(map_fd);
 	err = bpf_map_update_elem(map_fd, &key, &cfg, 0);
 	if (err) {
 		fprintf(stderr, "Store config failed (err:%d)\n", err);