JSON output support for Netlink implementation of --show-ring option

Add --json support for Netlink implementation of --show-ring option
No changes for non-JSON output for this featire.

Example output without --json:
[ethtool-git]$ /ethtool -g enp9s0u2u1u2
Ring parameters for enp9s0u2u1u2:
Pre-set maximums:
RX:		4096
RX Mini:	n/a
RX Jumbo:	n/a
TX:		n/a
Current hardware settings:
RX:		100
RX Mini:	n/a
RX Jumbo:	n/a
TX:		n/a
RX Buf Len:	n/a
CQE Size:	n/a
TX Push:	off
TCP data split:	n/a

Same output with --json:
[ethtool-git]$ ./ethtool --json -g enp9s0u2u1u2
[ {
        "ifname": "enp9s0u2u1u2",
        "rx-max": 4096,
        "rx": 100,
        "tx-push": false
    } ]

Suggested-by: Jakub Kicinski <[email protected]>
Signed-off-by: Maxim Georgiev <[email protected]>

ethtool.c

@@ -5751,6 +5751,7 @@ static const struct option args[] = {
 	},
 	{
 		.opts	= "-g|--show-ring",
+		.json	= true,
 		.func	= do_gring,
 		.nlfunc	= nl_gring,
 		.help	= "Query RX/TX ring parameters"

netlink/rings.c

@@ -21,6 +21,9 @@ int rings_reply_cb(const struct nlmsghdr *nlhdr, void *data)
 	DECLARE_ATTR_TB_INFO(tb);
 	struct nl_context *nlctx = data;
 	unsigned char tcp_hds;
+	char *tcp_hds_fmt;
+	char *tcp_hds_key;
+	char tcp_hds_buf[256];
 	bool silent;
 	int err_ret;
 	int ret;
@@ -34,16 +37,19 @@ int rings_reply_cb(const struct nlmsghdr *nlhdr, void *data)
 	if (!dev_ok(nlctx))
 		return err_ret;
 
+	open_json_object(NULL);
+
 	if (silent)
-		putchar('\n');
-	printf("Ring parameters for %s:\n", nlctx->devname);
-	printf("Pre-set maximums:\n");
+		show_cr();
+	print_string(PRINT_ANY, "ifname", "Ring parameters for %s:\n",
+		     nlctx->devname);
+	print_string(PRINT_FP, NULL, "Pre-set maximums:\n", NULL);
 	show_u32("rx-max", "RX:\t\t", tb[ETHTOOL_A_RINGS_RX_MAX]);
 	show_u32("rx-mini-max", "RX Mini:\t", tb[ETHTOOL_A_RINGS_RX_MINI_MAX]);
 	show_u32("rx-jumbo-max", "RX Jumbo:\t",
 		 tb[ETHTOOL_A_RINGS_RX_JUMBO_MAX]);
 	show_u32("tx-max", "TX:\t\t", tb[ETHTOOL_A_RINGS_TX_MAX]);
-	printf("Current hardware settings:\n");
+	print_string(PRINT_FP, NULL, "Current hardware settings:\n", NULL);
 	show_u32("rx", "RX:\t\t", tb[ETHTOOL_A_RINGS_RX]);
 	show_u32("rx-mini", "RX Mini:\t", tb[ETHTOOL_A_RINGS_RX_MINI]);
 	show_u32("rx-jumbo", "RX Jumbo:\t", tb[ETHTOOL_A_RINGS_RX_JUMBO]);
@@ -52,24 +58,29 @@ int rings_reply_cb(const struct nlmsghdr *nlhdr, void *data)
 	show_u32("cqe-size", "CQE Size:\t", tb[ETHTOOL_A_RINGS_CQE_SIZE]);
 	show_bool("tx-push", "TX Push:\t%s\n", tb[ETHTOOL_A_RINGS_TX_PUSH]);
 
+	tcp_hds_fmt = "TCP data split:\t%s\n";
+	tcp_hds_key = "tcp-data-split";
 	tcp_hds = tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT] ?
 		mnl_attr_get_u8(tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT]) : 0;
-	printf("TCP data split:\t");
 	switch (tcp_hds) {
 	case ETHTOOL_TCP_DATA_SPLIT_UNKNOWN:
-		printf("n/a\n");
+		print_string(PRINT_FP, tcp_hds_key, tcp_hds_fmt, "n/a");
 		break;
 	case ETHTOOL_TCP_DATA_SPLIT_DISABLED:
-		printf("off\n");
+		print_string(PRINT_ANY, tcp_hds_key, tcp_hds_fmt, "off");
 		break;
 	case ETHTOOL_TCP_DATA_SPLIT_ENABLED:
-		printf("on\n");
+		print_string(PRINT_ANY, tcp_hds_key, tcp_hds_fmt, "on");
 		break;
 	default:
-		printf("unknown(%d)\n", tcp_hds);
+		snprintf(tcp_hds_buf, sizeof(tcp_hds_buf),
+			 "unknown(%d)\n", tcp_hds);
+		print_string(PRINT_ANY, tcp_hds_key, tcp_hds_fmt, tcp_hds_buf);
 		break;
 	}
 
+	close_json_object();
+
 	return MNL_CB_OK;
 }
 
@@ -91,7 +102,11 @@ int nl_gring(struct cmd_context *ctx)
 				      ETHTOOL_A_RINGS_HEADER, 0);
 	if (ret < 0)
 		return ret;
-	return nlsock_send_get_request(nlsk, rings_reply_cb);
+
+	new_json_obj(ctx->json);
+	ret = nlsock_send_get_request(nlsk, rings_reply_cb);
+	delete_json_obj();
+	return ret;
 }
 
 /* RINGS_SET */