netdev - Re: [PATCH v4 bpf-next 3/9] libbpf: add ability to attach/detach BPF program to perf event

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Message-ID: <CAPhsuW460zkY6JzNUOsFQqVsezG1++nb1pKo-azwusrTJZumDg@mail.gmail.com>
Date:   Sat, 29 Jun 2019 01:48:12 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Stanislav Fomichev <sdf@...ichev.me>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH v4 bpf-next 3/9] libbpf: add ability to attach/detach BPF
 program to perf event

On Fri, Jun 28, 2019 at 8:49 PM Andrii Nakryiko <andriin@...com> wrote:
>
> bpf_program__attach_perf_event allows to attach BPF program to existing
> perf event hook, providing most generic and most low-level way to attach BPF
> programs. It returns struct bpf_link, which should be passed to
> bpf_link__destroy to detach and free resources, associated with a link.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Acked-by: Song Liu <songliubraving@...com>

With one nit below.

> ---
>  tools/lib/bpf/libbpf.c   | 61 ++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.h   |  3 ++
>  tools/lib/bpf/libbpf.map |  1 +
>  3 files changed, 65 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 455795e6f8af..98c155ec3bfa 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -32,6 +32,7 @@
>  #include <linux/limits.h>
>  #include <linux/perf_event.h>
>  #include <linux/ring_buffer.h>
> +#include <sys/ioctl.h>
>  #include <sys/stat.h>
>  #include <sys/types.h>
>  #include <sys/vfs.h>
> @@ -3958,6 +3959,66 @@ int bpf_link__destroy(struct bpf_link *link)
>         return err;
>  }
>
> +struct bpf_link_fd {
> +       struct bpf_link link; /* has to be at the top of struct */
> +       int fd; /* hook FD */
> +};
> +
> +static int bpf_link__destroy_perf_event(struct bpf_link *link)
> +{
> +       struct bpf_link_fd *l = (void *)link;
> +       int err;
> +
> +       if (l->fd < 0)
> +               return 0;
> +
> +       err = ioctl(l->fd, PERF_EVENT_IOC_DISABLE, 0);
> +       if (err)
> +               err = -errno;
> +
> +       close(l->fd);
> +       return err;
> +}
> +
> +struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
> +                                               int pfd)
> +{
> +       char errmsg[STRERR_BUFSIZE];
> +       struct bpf_link_fd *link;
> +       int prog_fd, err;
> +
> +       prog_fd = bpf_program__fd(prog);
> +       if (prog_fd < 0) {
> +               pr_warning("program '%s': can't attach before loaded\n",
> +                          bpf_program__title(prog, false));

This warning message is not very easy to follow.

> +               return ERR_PTR(-EINVAL);
> +       }
> +
> +       link = malloc(sizeof(*link));
> +       if (!link)
> +               return ERR_PTR(-ENOMEM);
> +       link->link.destroy = &bpf_link__destroy_perf_event;
> +       link->fd = pfd;
> +
> +       if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) {
> +               err = -errno;
> +               free(link);
> +               pr_warning("program '%s': failed to attach to pfd %d: %s\n",
> +                          bpf_program__title(prog, false), pfd,
> +                          libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> +               return ERR_PTR(err);
> +       }
> +       if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
> +               err = -errno;
> +               free(link);
> +               pr_warning("program '%s': failed to enable pfd %d: %s\n",
> +                          bpf_program__title(prog, false), pfd,
> +                          libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> +               return ERR_PTR(err);
> +       }
> +       return (struct bpf_link *)link;
> +}
> +
>  enum bpf_perf_event_ret
>  bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
>                            void **copy_mem, size_t *copy_size,
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 5082a5ebb0c2..1bf66c4a9330 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -169,6 +169,9 @@ struct bpf_link;
>
>  LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
>
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_perf_event(struct bpf_program *prog, int pfd);
> +
>  struct bpf_insn;
>
>  /*
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 3cde850fc8da..756f5aa802e9 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -169,6 +169,7 @@ LIBBPF_0.0.4 {
>         global:
>                 bpf_link__destroy;
>                 bpf_object__load_xattr;
> +               bpf_program__attach_perf_event;
>                 btf_dump__dump_type;
>                 btf_dump__free;
>                 btf_dump__new;
> --
> 2.17.1
>