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

[Quentin Monnet]

On 30/08/2022 00:18, Hao Luo wrote:
> 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 "";

I wonder if that one should be "unknown", in case another option is
added in the future, so we can spot it and address it?

> +	}
> +}
> +
>  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)

Looks good to me, thank you!

Reviewed-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>