tools/bpf: bpftool: add net support

Add "bpftool net" support. Networking devices are enumerated
to dump device index/name associated with xdp progs.

For each networking device, tc classes and qdiscs are enumerated
in order to check their bpf filters.
In addition, root handle and clsact ingress/egress are also checked for
bpf filters.  Not all filter information is printed out. Only ifindex,
kind, filter name, prog_id and tag are printed out, which are good
enough to show attachment information. If the filter action
is a bpf action, its bpf program id, bpf name and tag will be
printed out as well.

For example,
  $ ./bpftool net
  xdp [
  ifindex 2 devname eth0 prog_id 198
  ]
  tc_filters [
  ifindex 2 kind qdisc_htb name prefix_matcher.o:[cls_prefix_matcher_htb]
            prog_id 111727 tag d08fe3b4319bc2fd act []
  ifindex 2 kind qdisc_clsact_ingress name fbflow_icmp
            prog_id 130246 tag 3f265c7f26db62c9 act []
  ifindex 2 kind qdisc_clsact_egress name prefix_matcher.o:[cls_prefix_matcher_clsact]
            prog_id 111726 tag 99a197826974c876
  ifindex 2 kind qdisc_clsact_egress name cls_fg_dscp
            prog_id 108619 tag dc4630674fd72dcc act []
  ifindex 2 kind qdisc_clsact_egress name fbflow_egress
            prog_id 130245 tag 72d2d830d6888d2c
  ]
  $ ./bpftool -jp net
  [{
        "xdp": [{
                "ifindex": 2,
                "devname": "eth0",
                "prog_id": 198
            }
        ],
        "tc_filters": [{
                "ifindex": 2,
                "kind": "qdisc_htb",
                "name": "prefix_matcher.o:[cls_prefix_matcher_htb]",
                "prog_id": 111727,
                "tag": "d08fe3b4319bc2fd",
                "act": []
            },{
                "ifindex": 2,
                "kind": "qdisc_clsact_ingress",
                "name": "fbflow_icmp",
                "prog_id": 130246,
                "tag": "3f265c7f26db62c9",
                "act": []
            },{
                "ifindex": 2,
                "kind": "qdisc_clsact_egress",
                "name": "prefix_matcher.o:[cls_prefix_matcher_clsact]",
                "prog_id": 111726,
                "tag": "99a197826974c876"
            },{
                "ifindex": 2,
                "kind": "qdisc_clsact_egress",
                "name": "cls_fg_dscp",
                "prog_id": 108619,
                "tag": "dc4630674fd72dcc",
                "act": []
            },{
                "ifindex": 2,
                "kind": "qdisc_clsact_egress",
                "name": "fbflow_egress",
                "prog_id": 130245,
                "tag": "72d2d830d6888d2c"
            }
        ]
    }
  ]
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool-net.rst

+================
+bpftool-net
+================
+-------------------------------------------------------------------------------
+tool for inspection of netdev/tc related bpf prog attachments
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **net** *COMMAND*
+
+	*OPTIONS* := { [{ **-j** | **--json** }] [{ **-p** | **--pretty** }] }
+
+	*COMMANDS* :=
+	{ **show** | **list** } [ **dev** name ] | **help**
+
+NET COMMANDS
+============
+
+|	**bpftool** **net { show | list } [ dev name ]**
+|	**bpftool** **net help**
+
+DESCRIPTION
+===========
+	**bpftool net { show | list } [ dev name ]**
+		  List all networking device driver and tc attachment in the system.
+
+                  Output will start with all xdp program attachment, followed by
+                  all tc class/qdisc bpf program attachments. Both xdp programs and
+                  tc programs are ordered based on ifindex number. If multiple bpf
+                  programs attached to the same networking device through **tc filter**,
+                  the order will be first all bpf programs attached to tc classes, then
+                  all bpf programs attached to non clsact qdiscs, and finally all
+                  bpf programs attached to root and clsact qdisc.
+
+	**bpftool net help**
+		  Print short help message.
+
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-v, --version
+		  Print version number (similar to **bpftool version**).
+
+	-j, --json
+		  Generate JSON output. For commands that cannot produce JSON, this
+		  option has no effect.
+
+	-p, --pretty
+		  Generate human-readable JSON output. Implies **-j**.
+
+EXAMPLES
+========
+
+| **# bpftool net**
+
+::
+
+      xdp [
+      ifindex 2 devname eth0 prog_id 198
+      ]
+      tc_filters [
+      ifindex 2 kind qdisc_htb name prefix_matcher.o:[cls_prefix_matcher_htb]
+                prog_id 111727 tag d08fe3b4319bc2fd act []
+      ifindex 2 kind qdisc_clsact_ingress name fbflow_icmp
+                prog_id 130246 tag 3f265c7f26db62c9 act []
+      ifindex 2 kind qdisc_clsact_egress name prefix_matcher.o:[cls_prefix_matcher_clsact]
+                prog_id 111726 tag 99a197826974c876
+      ifindex 2 kind qdisc_clsact_egress name cls_fg_dscp
+                prog_id 108619 tag dc4630674fd72dcc act []
+      ifindex 2 kind qdisc_clsact_egress name fbflow_egress
+                prog_id 130245 tag 72d2d830d6888d2c
+      ]
+
+|
+| **# bpftool -jp net**
+
+::
+
+    [{
+            "xdp": [{
+                    "ifindex": 2,
+                    "devname": "eth0",
+                    "prog_id": 198
+                }
+            ],
+            "tc_filters": [{
+                    "ifindex": 2,
+                    "kind": "qdisc_htb",
+                    "name": "prefix_matcher.o:[cls_prefix_matcher_htb]",
+                    "prog_id": 111727,
+                    "tag": "d08fe3b4319bc2fd",
+                    "act": []
+                },{
+                    "ifindex": 2,
+                    "kind": "qdisc_clsact_ingress",
+                    "name": "fbflow_icmp",
+                    "prog_id": 130246,
+                    "tag": "3f265c7f26db62c9",
+                    "act": []
+                },{
+                    "ifindex": 2,
+                    "kind": "qdisc_clsact_egress",
+                    "name": "prefix_matcher.o:[cls_prefix_matcher_clsact]",
+                    "prog_id": 111726,
+                    "tag": "99a197826974c876"
+                },{
+                    "ifindex": 2,
+                    "kind": "qdisc_clsact_egress",
+                    "name": "cls_fg_dscp",
+                    "prog_id": 108619,
+                    "tag": "dc4630674fd72dcc",
+                    "act": []
+                },{
+                    "ifindex": 2,
+                    "kind": "qdisc_clsact_egress",
+                    "name": "fbflow_egress",
+                    "prog_id": 130245,
+                    "tag": "72d2d830d6888d2c"
+                }
+            ]
+        }
+    ]
+
+
+SEE ALSO
+========
+	**bpftool**\ (8), **bpftool-prog**\ (8), **bpftool-map**\ (8)

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -16,7 +16,7 @@ SYNOPSIS
 
 	**bpftool** **version**
 
-	*OBJECT* := { **map** | **program** | **cgroup** | **perf** }
+	*OBJECT* := { **map** | **program** | **cgroup** | **perf** | **net** }
 
 	*OPTIONS* := { { **-V** | **--version** } | { **-h** | **--help** }
 	| { **-j** | **--json** } [{ **-p** | **--pretty** }] }
@@ -32,6 +32,8 @@ SYNOPSIS
 
 	*PERF-COMMANDS* := { **show** | **list** | **help** }
 
+	*NET-COMMANDS* := { **show** | **list** | **help** }
+
 DESCRIPTION
 ===========
 	*bpftool* allows for inspection and simple modification of BPF objects
@@ -58,4 +60,4 @@ OPTIONS
 SEE ALSO
 ========
 	**bpftool-map**\ (8), **bpftool-prog**\ (8), **bpftool-cgroup**\ (8)
-        **bpftool-perf**\ (8)
+        **bpftool-perf**\ (8), **bpftool-net**\ (8)

tools/bpf/bpftool/bash-completion/bpftool

@@ -494,10 +494,10 @@ _bpftool()
                     _filedir
                     return 0
                     ;;
-		tree)
-		    _filedir
-		    return 0
-		    ;;
+                tree)
+                    _filedir
+                    return 0
+                    ;;
                 attach|detach)
                     local ATTACH_TYPES='ingress egress sock_create sock_ops \
                         device bind4 bind6 post_bind4 post_bind6 connect4 \
@@ -552,6 +552,15 @@ _bpftool()
                     ;;
             esac
             ;;
+        net)
+            case $command in
+                *)
+                    [[ $prev == $object ]] && \
+                        COMPREPLY=( $( compgen -W 'help \
+                            show list' -- "$cur" ) )
+                    ;;
+            esac
+            ;;
     esac
 } &&
 complete -F _bpftool bpftool

tools/bpf/bpftool/main.c

@@ -85,7 +85,7 @@ static int do_help(int argc, char **argv)
 		"       %s batch file FILE\n"
 		"       %s version\n"
 		"\n"
-		"       OBJECT := { prog | map | cgroup | perf }\n"
+		"       OBJECT := { prog | map | cgroup | perf | net }\n"
 		"       " HELP_SPEC_OPTIONS "\n"
 		"",
 		bin_name, bin_name, bin_name);
@@ -215,6 +215,7 @@ static const struct cmd cmds[] = {
 	{ "map",	do_map },
 	{ "cgroup",	do_cgroup },
 	{ "perf",	do_perf },
+	{ "net",	do_net },
 	{ "version",	do_version },
 	{ 0 }
 };

tools/bpf/bpftool/main.h

@@ -136,6 +136,7 @@ int do_map(int argc, char **arg);
 int do_event_pipe(int argc, char **argv);
 int do_cgroup(int argc, char **arg);
 int do_perf(int argc, char **arg);
+int do_net(int argc, char **arg);
 
 int prog_parse_fd(int *argc, char ***argv);
 int map_parse_fd(int *argc, char ***argv);
@@ -165,4 +166,10 @@ struct btf_dumper {
  */
 int btf_dumper_type(const struct btf_dumper *d, __u32 type_id,
 		    const void *data);
+
+struct nlattr;
+struct ifinfomsg;
+struct tcmsg;
+int do_xdp_dump(struct ifinfomsg *ifinfo, struct nlattr **tb);
+int do_filter_dump(struct tcmsg *ifinfo, struct nlattr **tb, const char *kind);
 #endif

tools/bpf/bpftool/net.c

+// SPDX-License-Identifier: GPL-2.0+
+// Copyright (C) 2018 Facebook
+
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <libbpf.h>
+#include <net/if.h>
+#include <linux/if.h>
+#include <linux/rtnetlink.h>
+#include <linux/tc_act/tc_bpf.h>
+#include <sys/socket.h>
+
+#include <bpf.h>
+#include <nlattr.h>
+#include "main.h"
+#include "netlink_dumper.h"
+
+struct bpf_netdev_t {
+	int	*ifindex_array;
+	int	used_len;
+	int	array_len;
+	int	filter_idx;
+};
+
+struct tc_kind_handle {
+	char	kind[64];
+	int	handle;
+};
+
+struct bpf_tcinfo_t {
+	struct tc_kind_handle	*handle_array;
+	int			used_len;
+	int			array_len;
+	bool			is_qdisc;
+};
+
+static int dump_link_nlmsg(void *cookie, void *msg, struct nlattr **tb)
+{
+	struct bpf_netdev_t *netinfo = cookie;
+	struct ifinfomsg *ifinfo = msg;
+
+	if (netinfo->filter_idx > 0 && netinfo->filter_idx != ifinfo->ifi_index)
+		return 0;
+
+	if (netinfo->used_len == netinfo->array_len) {
+		netinfo->ifindex_array = realloc(netinfo->ifindex_array,
+			(netinfo->array_len + 16) * sizeof(int));
+		netinfo->array_len += 16;
+	}
+	netinfo->ifindex_array[netinfo->used_len++] = ifinfo->ifi_index;
+
+	return do_xdp_dump(ifinfo, tb);
+}
+
+static int dump_class_qdisc_nlmsg(void *cookie, void *msg, struct nlattr **tb)
+{
+	struct bpf_tcinfo_t *tcinfo = cookie;
+	struct tcmsg *info = msg;
+
+	if (tcinfo->is_qdisc) {
+		/* skip clsact qdisc */
+		if (tb[TCA_KIND] &&
+		    strcmp(nla_data(tb[TCA_KIND]), "clsact") == 0)
+			return 0;
+		if (info->tcm_handle == 0)
+			return 0;
+	}
+
+	if (tcinfo->used_len == tcinfo->array_len) {
+		tcinfo->handle_array = realloc(tcinfo->handle_array,
+			(tcinfo->array_len + 16) * sizeof(struct tc_kind_handle));
+		tcinfo->array_len += 16;
+	}
+	tcinfo->handle_array[tcinfo->used_len].handle = info->tcm_handle;
+	snprintf(tcinfo->handle_array[tcinfo->used_len].kind,
+		 sizeof(tcinfo->handle_array[tcinfo->used_len].kind),
+		 "%s_%s",
+		 tcinfo->is_qdisc ? "qdisc" : "class",
+		 tb[TCA_KIND] ? nla_getattr_str(tb[TCA_KIND]) : "unknown");
+	tcinfo->used_len++;
+
+	return 0;
+}
+
+static int dump_filter_nlmsg(void *cookie, void *msg, struct nlattr **tb)
+{
+	const char *kind = cookie;
+
+	return do_filter_dump((struct tcmsg *)msg, tb, kind);
+}
+
+static int show_dev_tc_bpf(int sock, unsigned int nl_pid, int ifindex)
+{
+	struct bpf_tcinfo_t tcinfo;
+	int i, handle, ret;
+
+	tcinfo.handle_array = NULL;
+	tcinfo.used_len = 0;
+	tcinfo.array_len = 0;
+
+	tcinfo.is_qdisc = false;
+	ret = nl_get_class(sock, nl_pid, ifindex, dump_class_qdisc_nlmsg,
+			   &tcinfo);
+	if (ret)
+		return ret;
+
+	tcinfo.is_qdisc = true;
+	ret = nl_get_qdisc(sock, nl_pid, ifindex, dump_class_qdisc_nlmsg,
+			   &tcinfo);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < tcinfo.used_len; i++) {
+		ret = nl_get_filter(sock, nl_pid, ifindex,
+				    tcinfo.handle_array[i].handle,
+				    dump_filter_nlmsg,
+				    tcinfo.handle_array[i].kind);
+		if (ret)
+			return ret;
+	}
+
+	/* root, ingress and egress handle */
+	handle = TC_H_ROOT;
+	ret = nl_get_filter(sock, nl_pid, ifindex, handle, dump_filter_nlmsg,
+			    "root");
+	if (ret)
+		return ret;
+
+	handle = TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS);
+	ret = nl_get_filter(sock, nl_pid, ifindex, handle, dump_filter_nlmsg,
+			    "qdisc_clsact_ingress");
+	if (ret)
+		return ret;
+
+	handle = TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS);
+	ret = nl_get_filter(sock, nl_pid, ifindex, handle, dump_filter_nlmsg,
+			    "qdisc_clsact_egress");
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int do_show(int argc, char **argv)
+{
+	int i, sock, ret, filter_idx = -1;
+	struct bpf_netdev_t dev_array;
+	unsigned int nl_pid;
+	char err_buf[256];
+
+	if (argc == 2) {
+		if (strcmp(argv[0], "dev") != 0)
+			usage();
+		filter_idx = if_nametoindex(argv[1]);
+		if (filter_idx == 0) {
+			fprintf(stderr, "invalid dev name %s\n", argv[1]);
+			return -1;
+		}
+	} else if (argc != 0) {
+		usage();
+	}
+
+	sock = bpf_netlink_open(&nl_pid);
+	if (sock < 0) {
+		fprintf(stderr, "failed to open netlink sock\n");
+		return -1;
+	}
+
+	dev_array.ifindex_array = NULL;
+	dev_array.used_len = 0;
+	dev_array.array_len = 0;
+	dev_array.filter_idx = filter_idx;
+
+	if (json_output)
+		jsonw_start_array(json_wtr);
+	NET_START_OBJECT;
+	NET_START_ARRAY("xdp", "\n");
+	ret = nl_get_link(sock, nl_pid, dump_link_nlmsg, &dev_array);
+	NET_END_ARRAY("\n");
+
+	if (!ret) {
+		NET_START_ARRAY("tc_filters", "\n");
+		for (i = 0; i < dev_array.used_len; i++) {
+			ret = show_dev_tc_bpf(sock, nl_pid,
+					      dev_array.ifindex_array[i]);
+			if (ret)
+				break;
+		}
+		NET_END_ARRAY("\n");
+	}
+	NET_END_OBJECT;
+	if (json_output)
+		jsonw_end_array(json_wtr);
+
+	if (ret) {
+		if (json_output)
+			jsonw_null(json_wtr);
+		libbpf_strerror(ret, err_buf, sizeof(err_buf));
+		fprintf(stderr, "Error: %s\n", err_buf);
+	}
+	free(dev_array.ifindex_array);
+	close(sock);
+	return ret;
+}
+
+static int do_help(int argc, char **argv)
+{
+	if (json_output) {
+		jsonw_null(json_wtr);
+		return 0;
+	}
+
+	fprintf(stderr,
+		"Usage: %s %s { show | list } [dev <devname>]\n"
+		"       %s %s help\n",
+		bin_name, argv[-2], bin_name, argv[-2]);
+
+	return 0;
+}
+
+static const struct cmd cmds[] = {
+	{ "show",	do_show },
+	{ "list",	do_show },
+	{ "help",	do_help },
+	{ 0 }
+};
+
+int do_net(int argc, char **argv)
+{
+	return cmd_select(cmds, argc, argv, do_help);
+}

tools/bpf/bpftool/netlink_dumper.c

+// SPDX-License-Identifier: GPL-2.0+
+// Copyright (C) 2018 Facebook
+
+#include <stdlib.h>
+#include <string.h>
+#include <libbpf.h>
+#include <linux/rtnetlink.h>
+#include <linux/tc_act/tc_bpf.h>
+
+#include <nlattr.h>
+#include "main.h"
+#include "netlink_dumper.h"
+
+static void xdp_dump_prog_id(struct nlattr **tb, int attr,
+			     const char *type)
+{
+	if (!tb[attr])
+		return;
+
+	NET_DUMP_UINT(type, nla_getattr_u32(tb[attr]))
+}
+
+static int do_xdp_dump_one(struct nlattr *attr, unsigned int ifindex,
+			   const char *name)
+{
+	struct nlattr *tb[IFLA_XDP_MAX + 1];
+	unsigned char mode;
+
+	if (nla_parse_nested(tb, IFLA_XDP_MAX, attr, NULL) < 0)
+		return -1;
+
+	if (!tb[IFLA_XDP_ATTACHED])
+		return 0;
+
+	mode = nla_getattr_u8(tb[IFLA_XDP_ATTACHED]);
+	if (mode == XDP_ATTACHED_NONE)
+		return 0;
+
+	NET_START_OBJECT;
+	NET_DUMP_UINT("ifindex", ifindex);
+
+	if (name)
+		NET_DUMP_STR("devname", name);
+
+	if (tb[IFLA_XDP_PROG_ID])
+		NET_DUMP_UINT("prog_id", nla_getattr_u32(tb[IFLA_XDP_PROG_ID]));
+
+	if (mode == XDP_ATTACHED_MULTI) {
+		xdp_dump_prog_id(tb, IFLA_XDP_SKB_PROG_ID, "generic_prog_id");
+		xdp_dump_prog_id(tb, IFLA_XDP_DRV_PROG_ID, "drv_prog_id");
+		xdp_dump_prog_id(tb, IFLA_XDP_HW_PROG_ID, "offload_prog_id");
+	}
+
+	NET_END_OBJECT_FINAL;
+	return 0;
+}
+
+int do_xdp_dump(struct ifinfomsg *ifinfo, struct nlattr **tb)
+{
+	if (!tb[IFLA_XDP])
+		return 0;
+
+	return do_xdp_dump_one(tb[IFLA_XDP], ifinfo->ifi_index,
+			       nla_getattr_str(tb[IFLA_IFNAME]));
+}
+
+static char *hexstring_n2a(const unsigned char *str, int len,
+			   char *buf, int blen)
+{
+	char *ptr = buf;
+	int i;
+
+	for (i = 0; i < len; i++) {
+		if (blen < 3)
+			break;
+		sprintf(ptr, "%02x", str[i]);
+		ptr += 2;
+		blen -= 2;
+	}
+	return buf;
+}
+
+static int do_bpf_dump_one_act(struct nlattr *attr)
+{
+	struct nlattr *tb[TCA_ACT_BPF_MAX + 1];
+	char buf[256];
+
+	if (nla_parse_nested(tb, TCA_ACT_BPF_MAX, attr, NULL) < 0)
+		return -LIBBPF_ERRNO__NLPARSE;
+
+	if (!tb[TCA_ACT_BPF_PARMS])
+		return -LIBBPF_ERRNO__NLPARSE;
+
+	NET_START_OBJECT_NESTED2;
+	if (tb[TCA_ACT_BPF_NAME])
+		NET_DUMP_STR("name", nla_getattr_str(tb[TCA_ACT_BPF_NAME]));
+	if (tb[TCA_ACT_BPF_ID])
+		NET_DUMP_UINT("bpf_id", nla_getattr_u32(tb[TCA_ACT_BPF_ID]));
+	if (tb[TCA_ACT_BPF_TAG])
+		NET_DUMP_STR("tag", hexstring_n2a(nla_data(tb[TCA_ACT_BPF_TAG]),
+						  nla_len(tb[TCA_ACT_BPF_TAG]),
+						  buf, sizeof(buf)));
+	NET_END_OBJECT_NESTED;
+	return 0;
+}
+
+static int do_dump_one_act(struct nlattr *attr)
+{
+	struct nlattr *tb[TCA_ACT_MAX + 1];
+
+	if (!attr)
+		return 0;
+
+	if (nla_parse_nested(tb, TCA_ACT_MAX, attr, NULL) < 0)
+		return -LIBBPF_ERRNO__NLPARSE;
+
+	if (tb[TCA_ACT_KIND] && strcmp(nla_data(tb[TCA_ACT_KIND]), "bpf") == 0)
+		return do_bpf_dump_one_act(tb[TCA_ACT_OPTIONS]);
+
+	return 0;
+}
+
+static int do_bpf_act_dump(struct nlattr *attr)
+{
+	struct nlattr *tb[TCA_ACT_MAX_PRIO + 1];
+	int act, ret;
+
+	if (nla_parse_nested(tb, TCA_ACT_MAX_PRIO, attr, NULL) < 0)
+		return -LIBBPF_ERRNO__NLPARSE;
+
+	NET_START_ARRAY("act", "");
+	for (act = 0; act <= TCA_ACT_MAX_PRIO; act++) {
+		ret = do_dump_one_act(tb[act]);
+		if (ret)
+			break;
+	}
+	NET_END_ARRAY(" ");
+
+	return ret;
+}
+
+static int do_bpf_filter_dump(struct nlattr *attr)
+{
+	struct nlattr *tb[TCA_BPF_MAX + 1];
+	char buf[256];
+	int ret;
+
+	if (nla_parse_nested(tb, TCA_BPF_MAX, attr, NULL) < 0)
+		return -LIBBPF_ERRNO__NLPARSE;
+
+	if (tb[TCA_BPF_NAME])
+		NET_DUMP_STR("name", nla_getattr_str(tb[TCA_BPF_NAME]));
+	if (tb[TCA_BPF_ID])
+		NET_DUMP_UINT("prog_id", nla_getattr_u32(tb[TCA_BPF_ID]));
+	if (tb[TCA_BPF_TAG])
+		NET_DUMP_STR("tag", hexstring_n2a(nla_data(tb[TCA_BPF_TAG]),
+						  nla_len(tb[TCA_BPF_TAG]),
+						  buf, sizeof(buf)));
+	if (tb[TCA_BPF_ACT]) {
+		ret = do_bpf_act_dump(tb[TCA_BPF_ACT]);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+int do_filter_dump(struct tcmsg *info, struct nlattr **tb, const char *kind)
+{
+	int ret = 0;
+
+	if (tb[TCA_OPTIONS] && strcmp(nla_data(tb[TCA_KIND]), "bpf") == 0) {
+		NET_START_OBJECT;
+		NET_DUMP_UINT("ifindex", info->tcm_ifindex);
+		NET_DUMP_STR("kind", kind);
+		ret = do_bpf_filter_dump(tb[TCA_OPTIONS]);
+		NET_END_OBJECT_FINAL;
+	}
+
+	return ret;
+}

tools/bpf/bpftool/netlink_dumper.h

+// SPDX-License-Identifier: GPL-2.0+
+// Copyright (C) 2018 Facebook
+
+#ifndef _NETLINK_DUMPER_H_
+#define _NETLINK_DUMPER_H_
+
+#define NET_START_OBJECT				\
+{							\
+	if (json_output)				\
+		jsonw_start_object(json_wtr);		\
+}
+
+#define NET_START_OBJECT_NESTED(name)			\
+{							\
+	if (json_output) {				\
+		jsonw_name(json_wtr, name);		\
+		jsonw_start_object(json_wtr);		\
+	} else {					\
+		fprintf(stderr, "%s {", name);		\
+	}						\
+}
+
+#define NET_START_OBJECT_NESTED2			\
+{							\
+	if (json_output)				\
+		jsonw_start_object(json_wtr);		\
+	else						\
+		fprintf(stderr, "{");			\
+}
+
+#define NET_END_OBJECT_NESTED				\
+{							\
+	if (json_output)				\
+		jsonw_end_object(json_wtr);		\
+	else						\
+		fprintf(stderr, "}");			\
+}
+
+#define NET_END_OBJECT					\
+{							\
+	if (json_output)				\
+		jsonw_end_object(json_wtr);		\
+}
+
+#define NET_END_OBJECT_FINAL				\
+{							\
+	if (json_output)				\
+		jsonw_end_object(json_wtr);		\
+	else						\
+		fprintf(stderr, "\n");			\
+}
+
+#define NET_START_ARRAY(name, newline)			\
+{							\
+	if (json_output) {				\
+		jsonw_name(json_wtr, name);		\
+		jsonw_start_array(json_wtr);		\
+	} else {					\
+		fprintf(stderr, "%s [%s", name, newline);\
+	}						\
+}
+
+#define NET_END_ARRAY(endstr)				\
+{							\
+	if (json_output)				\
+		jsonw_end_array(json_wtr);		\
+	else						\
+		fprintf(stderr, "]%s", endstr);		\
+}
+
+#define NET_DUMP_UINT(name, val)			\
+{							\
+	if (json_output)				\
+		jsonw_uint_field(json_wtr, name, val);	\
+	else						\
+		fprintf(stderr, "%s %d ", name, val);	\
+}
+
+#define NET_DUMP_LLUINT(name, val)			\
+{							\
+	if (json_output)				\
+		jsonw_lluint_field(json_wtr, name, val);\
+	else						\
+		fprintf(stderr, "%s %lld ", name, val);	\
+}
+
+#define NET_DUMP_STR(name, str)				\
+{							\
+	if (json_output)				\
+		jsonw_string_field(json_wtr, name, str);\
+	else						\
+		fprintf(stderr, "%s %s ", name, str);	\
+}
+
+#define NET_DUMP_STR_ONLY(str)				\
+{							\
+	if (json_output)				\
+		jsonw_string(json_wtr, str);		\
+	else						\
+		fprintf(stderr, "%s ", str);		\
+}
+
+#endif