Re: [PATCH bpf-next v2 1/3] bpf: Parameterize task iterators.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Aug 1, 2022 at 4:27 PM Kui-Feng Lee <kuifeng@fb.com> wrote:
>
> Allow creating an iterator that loops through resources of one task/thread.
>
> People could only create iterators to loop through all resources of
> files, vma, and tasks in the system, even though they were interested
> in only the resources of a specific task or process.  Passing the
> additional parameters, people can now create an iterator to go
> through all resources or only the resources of a task.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
> ---
>  include/linux/bpf.h            |  4 ++
>  include/uapi/linux/bpf.h       | 23 +++++++++
>  kernel/bpf/task_iter.c         | 93 ++++++++++++++++++++++++++--------
>  tools/include/uapi/linux/bpf.h | 23 +++++++++
>  4 files changed, 121 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 11950029284f..3c26dbfc9cef 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1718,6 +1718,10 @@ int bpf_obj_get_user(const char __user *pathname, int flags);
>
>  struct bpf_iter_aux_info {
>         struct bpf_map *map;
> +       struct {
> +               u32     tid;
> +               u8      type;
> +       } task;
>  };
>
>  typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index ffcbf79a556b..ed5ba501609f 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -87,10 +87,33 @@ struct bpf_cgroup_storage_key {
>         __u32   attach_type;            /* program attach type (enum bpf_attach_type) */
>  };
>
> +enum bpf_task_iter_type {
> +       BPF_TASK_ITER_ALL = 0,
> +       BPF_TASK_ITER_TID,
> +};
> +
>  union bpf_iter_link_info {
>         struct {
>                 __u32   map_fd;
>         } map;
> +       /*
> +        * Parameters of task iterators.
> +        */
> +       struct {
> +               __u32   pid_fd;
> +               /*
> +                * The type of the iterator.
> +                *
> +                * It can be one of enum bpf_task_iter_type.
> +                *
> +                * BPF_TASK_ITER_ALL (default)
> +                *      The iterator iterates over resources of everyprocess.
> +                *
> +                * BPF_TASK_ITER_TID
> +                *      You should also set *pid_fd* to iterate over one task.
> +                */
> +               __u8    type;   /* BPF_TASK_ITER_* */

__u8 might be a pain for future extensibility.
big vs little endian will be another potential issue.

Maybe use enum bpf_task_iter_type type; here and
move the comment to enum def ?
Or rename it to '__u32 flags;' ?