bpftool: Implement link show support for tcx

Add support to dump tcx link information to bpftool. This adds a
common helper show_link_ifindex_{plain,json}() which can be reused
also for other link types. The plain text and json device output is
the same format as in bpftool net dump.

Below shows an example link dump output along with a cgroup link
for comparison:

  # bpftool link
  [...]
  10: cgroup  prog 1977
        cgroup_id 1  attach_type cgroup_inet6_post_bind
  [...]
  13: tcx  prog 2053
        ifindex enp5s0(3)  attach_type tcx_ingress
  14: tcx  prog 2080
        ifindex enp5s0(3)  attach_type tcx_egress
  [...]

Equivalent json output:

  # bpftool link --json
  [...]
  {
    "id": 10,
    "type": "cgroup",
    "prog_id": 1977,
    "cgroup_id": 1,
    "attach_type": "cgroup_inet6_post_bind"
  },
  [...]
  {
    "id": 13,
    "type": "tcx",
    "prog_id": 2053,
    "devname": "enp5s0",
    "ifindex": 3,
    "attach_type": "tcx_ingress"
  },
  {
    "id": 14,
    "type": "tcx",
    "prog_id": 2080,
    "devname": "enp5s0",
    "ifindex": 3,
    "attach_type": "tcx_egress"
  }
  [...]
Suggested-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230816095651.10014-1-daniel@iogearbox.netSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/bpf/bpftool/link.c

@@ -150,6 +150,18 @@ static void show_link_attach_type_json(__u32 attach_type, json_writer_t *wtr)
 		jsonw_uint_field(wtr, "attach_type", attach_type);
 }
 
+static void show_link_ifindex_json(__u32 ifindex, json_writer_t *wtr)
+{
+	char devname[IF_NAMESIZE] = "(unknown)";
+
+	if (ifindex)
+		if_indextoname(ifindex, devname);
+	else
+		snprintf(devname, sizeof(devname), "(detached)");
+	jsonw_string_field(wtr, "devname", devname);
+	jsonw_uint_field(wtr, "ifindex", ifindex);
+}
+
 static bool is_iter_map_target(const char *target_name)
 {
 	return strcmp(target_name, "bpf_map_elem") == 0 ||
@@ -433,6 +445,10 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
 	case BPF_LINK_TYPE_NETFILTER:
 		netfilter_dump_json(info, json_wtr);
 		break;
+	case BPF_LINK_TYPE_TCX:
+		show_link_ifindex_json(info->tcx.ifindex, json_wtr);
+		show_link_attach_type_json(info->tcx.attach_type, json_wtr);
+		break;
 	case BPF_LINK_TYPE_STRUCT_OPS:
 		jsonw_uint_field(json_wtr, "map_id",
 				 info->struct_ops.map_id);
@@ -509,6 +525,22 @@ static void show_link_attach_type_plain(__u32 attach_type)
 		printf("attach_type %u  ", attach_type);
 }
 
+static void show_link_ifindex_plain(__u32 ifindex)
+{
+	char devname[IF_NAMESIZE * 2] = "(unknown)";
+	char tmpname[IF_NAMESIZE];
+	char *ret = NULL;
+
+	if (ifindex)
+		ret = if_indextoname(ifindex, tmpname);
+	else
+		snprintf(devname, sizeof(devname), "(detached)");
+	if (ret)
+		snprintf(devname, sizeof(devname), "%s(%d)",
+			 tmpname, ifindex);
+	printf("ifindex %s  ", devname);
+}
+
 static void show_iter_plain(struct bpf_link_info *info)
 {
 	const char *target_name = u64_to_ptr(info->iter.target_name);
@@ -745,6 +777,11 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
 	case BPF_LINK_TYPE_NETFILTER:
 		netfilter_dump_plain(info);
 		break;
+	case BPF_LINK_TYPE_TCX:
+		printf("\n\t");
+		show_link_ifindex_plain(info->tcx.ifindex);
+		show_link_attach_type_plain(info->tcx.attach_type);
+		break;
 	case BPF_LINK_TYPE_KPROBE_MULTI:
 		show_kprobe_multi_plain(info);
 		break;