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

Yonghong Song
2020-05-13T16:57:39Z

On 5/11/20 8:15 PM, Andrii Nakryiko wrote:
> On Fri, May 8, 2020 at 6:36 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 5/8/20 11:24 AM, Andrii Nakryiko wrote:
>>> On Wed, May 6, 2020 at 10:41 PM Yonghong Song <yhs@fb.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@fb.com>
>>>> Signed-off-by: Yonghong Song <yhs@fb.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
>
> Not all, e.g., bpf_iter target is invisible right now. It's good to
> have this added in a follow up, but certainly not a blocker.

Indeed, bpf_iter target is not visible now. We can add it to program
or to link. Adding to link is a reasonable idea as link itself is
the concept to merge program and target.

Will have a follow up patch for this later.

>
>
>> 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.
>
> yep
>
>>
>>>
>>>
>>> [...]
>>>