This patch modifies `bpftool map dump [-j|-p] id <map-id>` to json-
print and pretty-json-print map dump. It calls btf_dumper introduced in
previous patch to accomplish this.

The patch only prints debug info when -j or -p flags are supplied. Then
too, if the map has associated btf data loaded. Otherwise the usual
debug-less output is printed.

Signed-off-by: Okash Khawaja <osk@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>

---
 tools/bpf/bpftool/map.c |   94 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 91 insertions(+), 3 deletions(-)

--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -43,9 +43,13 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <linux/err.h>
 
 #include <bpf.h>
 
+#include "json_writer.h"
+#include "btf.h"
+#include "btf_dumper.h"
 #include "main.h"
 
 static const char * const map_type_name[] = {
@@ -508,6 +512,83 @@ static int do_show(int argc, char **argv
 	return errno == ENOENT ? 0 : -1;
 }
 
+
+static int do_dump_btf(struct btf *btf, struct bpf_map_info *map_info,
+		void *key, void *value)
+{
+	int ret;
+
+	jsonw_start_object(json_wtr);
+	jsonw_name(json_wtr, "key");
+
+	ret = btf_dumper_type(btf, json_wtr, map_info->btf_key_type_id, key);
+	if (ret)
+		goto out;
+
+	jsonw_end_object(json_wtr);
+
+	jsonw_start_object(json_wtr);
+	jsonw_name(json_wtr, "value");
+
+	ret = btf_dumper_type(btf, json_wtr, map_info->btf_value_type_id,
+			value);
+
+out:
+	/* end of root object */
+	jsonw_end_object(json_wtr);
+
+	return ret;
+}
+
+static struct btf *get_btf(struct bpf_map_info *map_info)
+{
+	int btf_fd = bpf_btf_get_fd_by_id(map_info->btf_id);
+	struct bpf_btf_info btf_info = { 0 };
+	__u32 len = sizeof(btf_info);
+	uint32_t last_size;
+	int err;
+	struct btf *btf = NULL;
+	void *ptr = NULL, *temp_ptr;
+
+	if (btf_fd < 0)
+		return NULL;
+
+	btf_info.btf_size = 4096;
+	do {
+		last_size = btf_info.btf_size;
+		temp_ptr = realloc(ptr, last_size);
+		if (!temp_ptr) {
+			p_err("unable allocate memory for debug info.");
+			goto exit_free;
+		}
+
+		ptr = temp_ptr;
+		bzero(ptr, last_size);
+		btf_info.btf = ptr_to_u64(ptr);
+		err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
+	} while (!err && btf_info.btf_size > last_size && last_size == 4096);
+
+	if (err || btf_info.btf_size > last_size) {
+		p_info("can't get btf info. debug info won't be displayed. error: %s",
+				err ? strerror(errno) : "exceeds size retry");
+		goto exit_free;
+	}
+
+	btf = btf__new((uint8_t *) btf_info.btf,
+			btf_info.btf_size, NULL);
+	if (IS_ERR(btf)) {
+		printf("error when initialising btf: %s\n",
+				strerror(PTR_ERR(btf)));
+		btf = NULL;
+	}
+
+exit_free:
+	close(btf_fd);
+	free(ptr);
+
+	return btf;
+}
+
 static int do_dump(int argc, char **argv)
 {
 	void *key, *value, *prev_key;
@@ -516,6 +597,7 @@ static int do_dump(int argc, char **argv
 	__u32 len = sizeof(info);
 	int err;
 	int fd;
+	struct btf *btf = NULL;
 
 	if (argc != 2)
 		usage();
@@ -538,6 +620,8 @@ static int do_dump(int argc, char **argv
 		goto exit_free;
 	}
 
+	btf = get_btf(&info);
+
 	prev_key = NULL;
 	if (json_output)
 		jsonw_start_array(json_wtr);
@@ -550,9 +634,12 @@ static int do_dump(int argc, char **argv
 		}
 
 		if (!bpf_map_lookup_elem(fd, key, value)) {
-			if (json_output)
-				print_entry_json(&info, key, value);
-			else
+			if (json_output) {
+				if (btf)
+					do_dump_btf(btf, &info, key, value);
+				else
+					print_entry_json(&info, key, value);
+			} else
 				print_entry_plain(&info, key, value);
 		} else {
 			if (json_output) {
@@ -584,6 +671,7 @@ exit_free:
 	free(key);
 	free(value);
 	close(fd);
+	btf__free(btf);
 
 	return err;
 }