[PATCH bpf-next v1] bpftool: Add support for querying cgroup_iter link

From: Hao Luo
Date: Mon Aug 29 2022 - 19:18:40 EST


Support dumping info of a cgroup_iter link. This includes
showing the cgroup's id and the order for walking the cgroup
hierarchy. Example output is as follows:

> bpftool link show
1: iter prog 2 target_name bpf_map
2: iter prog 3 target_name bpf_prog
3: iter prog 12 target_name cgroup cgroup_id 72 order self_only

> bpftool -p link show
[{
"id": 1,
"type": "iter",
"prog_id": 2,
"target_name": "bpf_map"
},{
"id": 2,
"type": "iter",
"prog_id": 3,
"target_name": "bpf_prog"
},{
"id": 3,
"type": "iter",
"prog_id": 12,
"target_name": "cgroup",
"cgroup_id": 72,
"order": "self_only"
}
]

Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
---
tools/bpf/bpftool/link.c | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)

diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index 7a20931c3250..9e8d14d0114d 100644
--- a/tools/bpf/bpftool/link.c
+++ b/tools/bpf/bpftool/link.c
@@ -83,6 +83,29 @@ static bool is_iter_map_target(const char *target_name)
strcmp(target_name, "bpf_sk_storage_map") == 0;
}

+static bool is_iter_cgroup_target(const char *target_name)
+{
+ return strcmp(target_name, "cgroup") == 0;
+}
+
+static const char *cgroup_order_string(__u32 order)
+{
+ switch (order) {
+ case BPF_CGROUP_ITER_ORDER_UNSPEC:
+ return "order_unspec";
+ case BPF_CGROUP_ITER_SELF_ONLY:
+ return "self_only";
+ case BPF_CGROUP_ITER_DESCENDANTS_PRE:
+ return "descendants_pre";
+ case BPF_CGROUP_ITER_DESCENDANTS_POST:
+ return "descendants_post";
+ case BPF_CGROUP_ITER_ANCESTORS_UP:
+ return "ancestors_up";
+ default: /* won't happen */
+ return "";
+ }
+}
+
static void show_iter_json(struct bpf_link_info *info, json_writer_t *wtr)
{
const char *target_name = u64_to_ptr(info->iter.target_name);
@@ -91,6 +114,12 @@ static void show_iter_json(struct bpf_link_info *info, json_writer_t *wtr)

if (is_iter_map_target(target_name))
jsonw_uint_field(wtr, "map_id", info->iter.map.map_id);
+
+ if (is_iter_cgroup_target(target_name)) {
+ jsonw_lluint_field(wtr, "cgroup_id", info->iter.cgroup.cgroup_id);
+ jsonw_string_field(wtr, "order",
+ cgroup_order_string(info->iter.cgroup.order));
+ }
}

static int get_prog_info(int prog_id, struct bpf_prog_info *info)
@@ -208,6 +237,12 @@ static void show_iter_plain(struct bpf_link_info *info)

if (is_iter_map_target(target_name))
printf("map_id %u ", info->iter.map.map_id);
+
+ if (is_iter_cgroup_target(target_name)) {
+ printf("cgroup_id %llu ", info->iter.cgroup.cgroup_id);
+ printf("order %s ",
+ cgroup_order_string(info->iter.cgroup.order));
+ }
}

static int show_link_close_plain(int fd, struct bpf_link_info *info)
--
2.37.2.672.g94769d06f0-goog