netdev - Re: [PATCH bpf-next v2 03/20] bpf: support bpf tracing/iter programs for BPF_LINK

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Date:   Tue, 5 May 2020 14:30:51 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...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 v2 03/20] bpf: support bpf tracing/iter programs
 for BPF_LINK_CREATE

On Sun, May 3, 2020 at 11:26 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.
>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---

LGTM. See small nit about __GFP_NOWARN.

Acked-by: Andrii Nakryiko <andriin@...com>


>  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(+)
>

[...]

> +int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> +       struct bpf_link_primer link_primer;
> +       struct bpf_iter_target_info *tinfo;
> +       struct bpf_iter_link *link;
> +       bool existed = false;
> +       u32 prog_btf_id;
> +       int err;
> +
> +       if (attr->link_create.target_fd || attr->link_create.flags)
> +               return -EINVAL;
> +
> +       prog_btf_id = prog->aux->attach_btf_id;
> +       mutex_lock(&targets_mutex);
> +       list_for_each_entry(tinfo, &targets, list) {
> +               if (tinfo->btf_id == prog_btf_id) {
> +                       existed = true;
> +                       break;
> +               }
> +       }
> +       mutex_unlock(&targets_mutex);
> +       if (!existed)
> +               return -ENOENT;
> +
> +       link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);

nit: all existing link implementation don't specify __GFP_NOWARN,
wonder if bpf_iter_link should be special?

> +       if (!link)
> +               return -ENOMEM;
> +
> +       bpf_link_init(&link->link, BPF_LINK_TYPE_ITER, &bpf_iter_link_lops, prog);
> +       link->tinfo = tinfo;
> +
> +       err  = bpf_link_prime(&link->link, &link_primer);
> +       if (err) {
> +               kfree(link);
> +               return err;
> +       }
> +
> +       return bpf_link_settle(&link_primer);
> +}

[...]