netdev - Re: [PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs for BPF_LINK

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Date:   Fri, 8 May 2020 18:36:10 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs
 for BPF_LINK_CREATE



On 5/8/20 11:24 AM, Andrii Nakryiko wrote:
> On Wed, May 6, 2020 at 10:41 PM Yonghong Song <yhs@...com> wrote:
>>
>> Given a bpf program, the step to create an anonymous bpf iterator is:
>>    - create a bpf_iter_link, which combines bpf program and the target.
>>      In the future, there could be more information recorded in the link.
>>      A link_fd will be returned to the user space.
>>    - create an anonymous bpf iterator with the given link_fd.
>>
>> The bpf_iter_link can be pinned to bpffs mount file system to
>> create a file based bpf iterator as well.
>>
>> The benefit to use of bpf_iter_link:
>>    - using bpf link simplifies design and implementation as bpf link
>>      is used for other tracing bpf programs.
>>    - for file based bpf iterator, bpf_iter_link provides a standard
>>      way to replace underlying bpf programs.
>>    - for both anonymous and free based iterators, bpf link query
>>      capability can be leveraged.
>>
>> The patch added support of tracing/iter programs for BPF_LINK_CREATE.
>> A new link type BPF_LINK_TYPE_ITER is added to facilitate link
>> querying. Currently, only prog_id is needed, so there is no
>> additional in-kernel show_fdinfo() and fill_link_info() hook
>> is needed for BPF_LINK_TYPE_ITER link.
>>
>> Acked-by: Andrii Nakryiko <andriin@...com>
>> Signed-off-by: Yonghong Song <yhs@...com>
>> ---
> 
> still looks good, but I realized show_fdinfo and fill_link_info is
> missing, see request for a follow-up below :)
> 
> 
>>   include/linux/bpf.h            |  1 +
>>   include/linux/bpf_types.h      |  1 +
>>   include/uapi/linux/bpf.h       |  1 +
>>   kernel/bpf/bpf_iter.c          | 62 ++++++++++++++++++++++++++++++++++
>>   kernel/bpf/syscall.c           | 14 ++++++++
>>   tools/include/uapi/linux/bpf.h |  1 +
>>   6 files changed, 80 insertions(+)
>>
> 
> [...]
> 
>> +static const struct bpf_link_ops bpf_iter_link_lops = {
>> +       .release = bpf_iter_link_release,
>> +       .dealloc = bpf_iter_link_dealloc,
>> +};
> 
> Link infra supports .show_fdinfo and .fill_link_info methods, there is
> no need to block on this, but it would be great to implement them from
> BPF_LINK_TYPE_ITER as well in the same release as a follow-up. Thanks!

The reason I did not implement is due to we do not have additional 
information beyond prog_id to present. The prog_id itself gives all
information about this link. I looked at tracing program 
show_fdinfo/fill_link_info, the additional attach_type is printed.
But attach_type is obvious for BPF_LINK_TYPE_ITER which does not
need print.

In the future when we add more stuff to parameterize the bpf_iter,
will need to implement these two callbacks as well as bpftool.

> 
> 
> [...]
>