Re: [PATCH bpf-next v1 05/19] bpf: support bpf tracing/iter programs for BPF_LINK_CREATE

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Mon, Apr 27, 2020 at 1:13 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 anonymous bpf iterator (and its underlying bpf_link) will be
> used to create file based bpf iterator as well.
>
> The benefit to use of bpf_iter_link:
>   - 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.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  include/linux/bpf.h   |  2 ++
>  kernel/bpf/bpf_iter.c | 54 +++++++++++++++++++++++++++++++++++++++++++
>  kernel/bpf/syscall.c  | 15 ++++++++++++
>  3 files changed, 71 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4ac8d61f7c3e..60ecb73d8f6d 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1034,6 +1034,7 @@ extern const struct file_operations bpf_prog_fops;
>  extern const struct bpf_prog_ops bpf_offload_prog_ops;
>  extern const struct bpf_verifier_ops tc_cls_act_analyzer_ops;
>  extern const struct bpf_verifier_ops xdp_analyzer_ops;
> +extern const struct bpf_link_ops bpf_iter_link_lops;

show_fdinfo implementation for bpf_link has changed, so thankfully
this won't be necessary after you rebase on latest master :)

>
>  struct bpf_prog *bpf_prog_get(u32 ufd);
>  struct bpf_prog *bpf_prog_get_type_dev(u32 ufd, enum bpf_prog_type type,
> @@ -1129,6 +1130,7 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
>  struct bpf_prog *bpf_iter_get_prog(struct seq_file *seq, u32 priv_data_size,
>                                    u64 *session_id, u64 *seq_num, bool is_last);
>  int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
> +int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
>
>  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/bpf_iter.c b/kernel/bpf/bpf_iter.c
> index 284c95587803..9532e7bcb8e1 100644
> --- a/kernel/bpf/bpf_iter.c
> +++ b/kernel/bpf/bpf_iter.c
> @@ -14,6 +14,11 @@ struct bpf_iter_target_info {
>         u32 target_feature;
>  };
>
> +struct bpf_iter_link {
> +       struct bpf_link link;
> +       struct bpf_iter_target_info *tinfo;
> +};
> +
>  static struct list_head targets;
>  static struct mutex targets_mutex;
>  static bool bpf_iter_inited = false;
> @@ -67,3 +72,52 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
>
>         return ret;
>  }
> +
> +static void bpf_iter_link_release(struct bpf_link *link)
> +{
> +}
> +
> +static void bpf_iter_link_dealloc(struct bpf_link *link)
> +{

Here you need to kfree() link struct. See bpf_raw_tp_link_dealloc() for example.


> +}
> +
> +const struct bpf_link_ops bpf_iter_link_lops = {
> +       .release = bpf_iter_link_release,
> +       .dealloc = bpf_iter_link_dealloc,
> +};
> +

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