Re: [PATCH bpf-next v4] bpftool: Dump map id instead of value for map_of_maps types

Yonghong Song
2023-04-27T14:44:32Z

On 4/27/23 5:03 AM, Xueming Feng wrote:
> When using `bpftool map dump` with map_of_maps, it is usually
> more convenient to show the inner map id instead of raw value.
>
> We are changing the plain print behavior to show inner_map_id
> instead of hex value, this would help with quick look up of
> inner map with `bpftool map dump id <inner_map_id>`.
> To avoid disrupting scripted behavior, we will add a new
> `inner_map_id` field to json output instead of replacing value.
>
> plain print:
> ```
> $ bpftool map dump id 138
>
> Without Patch:
> key:
> fc 00 00 00 00 00 00 00 00 00 00 00 00 00 00 05
> 27 16 06 00
> value:
> 8b 00 00 00
> Found 1 element
>
> With Patch:
> key:
> fc 00 00 00 00 00 00 00 00 00 00 00 00 00 00 05
> 27 16 06 00
> inner_map_id:
> 139
> Found 1 element
> ```
>
> json print:
> ```
> $ bpftool -p map dump id 567
>
> Without Patch:
> [{
> "key": ["0xc0","0x00","0x02","0x05","0x27","0x16","0x06","0x00"
> ],
> "value": ["0x38","0x02","0x00","0x00"
> ]
> }
> ]
>
> With Patch:
> [{
> "key": ["0xc0","0x00","0x02","0x05","0x27","0x16","0x06","0x00"
> ],
> "value": ["0x38","0x02","0x00","0x00"
> ],
> "inner_map_id": 568
> }
> ]
> ```
>
> Signed-off-by: Xueming Feng <kuro@kuroa.me>

You can carry my Ack from v3 since there is no big changes.
Anyway, Ack again.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
>
> Changes in v4:
> - Remove unnecessary parenthesis ('{}').
>
> Changes in v3:
> - In plain print, use printf() directly since inner map id is always a 32bit int.
> - Remove unused print_uint() function.
> - Rename `id` to `inner_map_id` in plain print output for clearness.
> - Add a new `inner_map_id` field to json output.
> - Add example output to commit message.
>
> Changes in v2:
> - Fix commit message grammar.
> - Change `print_uint` to only print to stdout, make `arg` const,
> and rename `n` to `arg_size`.
> - Make `print_uint` able to take any size of argument up to `unsigned long`,
> and print it as unsigned decimal.
>
> tools/bpf/bpftool/map.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index aaeb8939e137..ae9e822aa3fe 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -139,6 +139,9 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key,
> print_hex_data_json(key, info->key_size);
> jsonw_name(json_wtr, "value");
> print_hex_data_json(value, info->value_size);
> + if (map_is_map_of_maps(info->type))
> + jsonw_uint_field(json_wtr, "inner_map_id",
> + *(unsigned int *)value);
> if (btf) {
> struct btf_dumper d = {
> .btf = btf,
> @@ -259,8 +262,13 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
> }
>
> if (info->value_size) {
> - printf("value:%c", break_names ? '\n' : ' ');
> - fprint_hex(stdout, value, info->value_size, " ");
> + if (map_is_map_of_maps(info->type)) {
> + printf("inner_map_id:%c", break_names ? '\n' : ' ');
> + printf("%u ", *(unsigned int *)value);
> + } else {
> + printf("value:%c", break_names ? '\n' : ' ');
> + fprint_hex(stdout, value, info->value_size, " ");
> + }
> }
>
> printf("\n");