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Date:   Thu, 20 Aug 2020 23:44:45 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next v2 2/3] bpf: implement link_query callbacks in
 map element iterators



On 8/20/20 11:33 PM, Andrii Nakryiko wrote:
> On Thu, Aug 20, 2020 at 3:50 PM Yonghong Song <yhs@...com> wrote:
>>
>> For bpf_map_elem and bpf_sk_local_storage bpf iterators,
>> additional map_id should be shown for fdinfo and
>> userspace query. For example, the following is for
>> a bpf_map_elem iterator.
>>    $ cat /proc/1753/fdinfo/9
>>    pos:    0
>>    flags:  02000000
>>    mnt_id: 14
>>    link_type:      iter
>>    link_id:        34
>>    prog_tag:       104be6d3fe45e6aa
>>    prog_id:        173
>>    target_name:    bpf_map_elem
>>    map_id:         127
>>
>> Signed-off-by: Yonghong Song <yhs@...com>
>> ---
>>   include/linux/bpf.h       |  4 ++++
>>   kernel/bpf/map_iter.c     | 15 +++++++++++++++
>>   net/core/bpf_sk_storage.c |  2 ++
>>   3 files changed, 21 insertions(+)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 529e9b183eeb..30c144af894a 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1256,6 +1256,10 @@ int bpf_iter_new_fd(struct bpf_link *link);
>>   bool bpf_link_is_iter(struct bpf_link *link);
>>   struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop);
>>   int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
>> +void bpf_iter_map_show_fdinfo(const struct bpf_iter_aux_info *aux,
>> +                             struct seq_file *seq);
>> +int bpf_iter_map_fill_link_info(const struct bpf_iter_aux_info *aux,
>> +                               struct bpf_link_info *info);
>>
>>   int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
>>   int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
>> diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
>> index af86048e5afd..714e74556aa2 100644
>> --- a/kernel/bpf/map_iter.c
>> +++ b/kernel/bpf/map_iter.c
>> @@ -149,6 +149,19 @@ static void bpf_iter_detach_map(struct bpf_iter_aux_info *aux)
>>          bpf_map_put_with_uref(aux->map);
>>   }
>>
>> +void bpf_iter_map_show_fdinfo(const struct bpf_iter_aux_info *aux,
>> +                             struct seq_file *seq)
>> +{
>> +       seq_printf(seq, "map_id:\t\t%u\n", aux->map->id);
> 
> nit: I think it's a bad idea to have two tabs here to align everything
> visually, might make parsing unnecessarily harder

You are 100% correct. This is on purpose to please visual alignment.
I debate with myself to add extra '\t'. But yes, it is bad for tool 
parsing. I will fix it in the next revision.

> 
>> +}
>> +
>> +int bpf_iter_map_fill_link_info(const struct bpf_iter_aux_info *aux,
>> +                               struct bpf_link_info *info)
>> +{
>> +       info->iter.map.map_id = aux->map->id;
>> +       return 0;
>> +}
>> +
>>   DEFINE_BPF_ITER_FUNC(bpf_map_elem, struct bpf_iter_meta *meta,
>>                       struct bpf_map *map, void *key, void *value)
>>
>> @@ -156,6 +169,8 @@ static const struct bpf_iter_reg bpf_map_elem_reg_info = {
>>          .target                 = "bpf_map_elem",
>>          .attach_target          = bpf_iter_attach_map,
>>          .detach_target          = bpf_iter_detach_map,
>> +       .show_fdinfo            = bpf_iter_map_show_fdinfo,
>> +       .fill_link_info         = bpf_iter_map_fill_link_info,
>>          .ctx_arg_info_size      = 2,
>>          .ctx_arg_info           = {
>>                  { offsetof(struct bpf_iter__bpf_map_elem, key),
>> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
>> index b988f48153a4..281200dc0a01 100644
>> --- a/net/core/bpf_sk_storage.c
>> +++ b/net/core/bpf_sk_storage.c
>> @@ -1437,6 +1437,8 @@ static struct bpf_iter_reg bpf_sk_storage_map_reg_info = {
>>          .target                 = "bpf_sk_storage_map",
>>          .attach_target          = bpf_iter_attach_map,
>>          .detach_target          = bpf_iter_detach_map,
>> +       .show_fdinfo            = bpf_iter_map_show_fdinfo,
>> +       .fill_link_info         = bpf_iter_map_fill_link_info,
>>          .ctx_arg_info_size      = 2,
>>          .ctx_arg_info           = {
>>                  { offsetof(struct bpf_iter__bpf_sk_storage_map, sk),
>> --
>> 2.24.1
>>

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