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Date:   Wed, 23 Sep 2020 19:41:48 -0700
From:   Maciej ┼╗enczykowski <maze@...gle.com>
To:     bimmy.pujari@...el.com
Cc:     bpf <bpf@...r.kernel.org>, Linux NetDev <netdev@...r.kernel.org>,
        mchehab@...nel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, ashkan.nikravesh@...el.com
Subject: Re: [PATCH bpf-next v3 1/2] bpf: Add bpf_ktime_get_real_ns

On Wed, Sep 23, 2020 at 7:26 PM <bimmy.pujari@...el.com> wrote:
>
> From: Bimmy Pujari <bimmy.pujari@...el.com>
>
> The existing bpf helper functions to get timestamp return the time
> elapsed since system boot. This timestamp is not particularly useful
> where epoch timestamp is required or more than one server is involved
> and time sync is required. Instead, you want to use CLOCK_REALTIME,
> which provides epoch timestamp.
> Hence add bfp_ktime_get_real_ns() based around CLOCK_REALTIME.
>
> Signed-off-by: Ashkan Nikravesh <ashkan.nikravesh@...el.com>
> Signed-off-by: Bimmy Pujari <bimmy.pujari@...el.com>
> ---
>  drivers/media/rc/bpf-lirc.c    |  2 ++
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       |  8 ++++++++
>  kernel/bpf/core.c              |  1 +
>  kernel/bpf/helpers.c           | 13 +++++++++++++
>  kernel/trace/bpf_trace.c       |  2 ++
>  tools/include/uapi/linux/bpf.h |  8 ++++++++
>  7 files changed, 35 insertions(+)
>
> diff --git a/drivers/media/rc/bpf-lirc.c b/drivers/media/rc/bpf-lirc.c
> index 5bb144435c16..649015fef3c1 100644
> --- a/drivers/media/rc/bpf-lirc.c
> +++ b/drivers/media/rc/bpf-lirc.c
> @@ -105,6 +105,8 @@ lirc_mode2_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_ktime_get_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_tail_call:
>                 return &bpf_tail_call_proto;
>         case BPF_FUNC_get_prandom_u32:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index fc5c901c7542..18c4fdce65c8 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1757,6 +1757,7 @@ extern const struct bpf_func_proto bpf_get_numa_node_id_proto;
>  extern const struct bpf_func_proto bpf_tail_call_proto;
>  extern const struct bpf_func_proto bpf_ktime_get_ns_proto;
>  extern const struct bpf_func_proto bpf_ktime_get_boot_ns_proto;
> +extern const struct bpf_func_proto bpf_ktime_get_real_ns_proto;
>  extern const struct bpf_func_proto bpf_get_current_pid_tgid_proto;
>  extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
>  extern const struct bpf_func_proto bpf_get_current_comm_proto;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a22812561064..198e69a6508d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3586,6 +3586,13 @@ union bpf_attr {
>   *             the data in *dst*. This is a wrapper of **copy_from_user**\ ().
>   *     Return
>   *             0 on success, or a negative error in case of failure.
> + *
> + * u64 bpf_ktime_get_real_ns(void)
> + *     Description
> + *             Return the real time in nanoseconds.
> + *             See: **clock_gettime**\ (**CLOCK_REALTIME**)
> + *     Return
> + *             Current *ktime*.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3737,6 +3744,7 @@ union bpf_attr {
>         FN(inode_storage_delete),       \
>         FN(d_path),                     \
>         FN(copy_from_user),             \
> +       FN(ktime_get_real_ns),          \
>         /* */
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index c4811b139caa..0dbbda9b743b 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2208,6 +2208,7 @@ const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
>  const struct bpf_func_proto bpf_get_numa_node_id_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_ns_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;
> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto __weak;
>
>  const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;
>  const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 5cc7425ee476..300db9269996 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -166,6 +166,17 @@ const struct bpf_func_proto bpf_ktime_get_boot_ns_proto = {
>         .gpl_only       = false,
>         .ret_type       = RET_INTEGER,
>  };
> +BPF_CALL_0(bpf_ktime_get_real_ns)
> +{
> +       /* NMI safe access to clock realtime */
> +       return ktime_get_real_fast_ns();
> +}
> +
> +const struct bpf_func_proto bpf_ktime_get_real_ns_proto = {
> +       .func           = bpf_ktime_get_real_ns,
> +       .gpl_only       = false,
> +       .ret_type       = RET_INTEGER,
> +};
>
>  BPF_CALL_0(bpf_get_current_pid_tgid)
>  {
> @@ -657,6 +668,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
>                 return &bpf_ktime_get_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_ringbuf_output:
>                 return &bpf_ringbuf_output_proto;
>         case BPF_FUNC_ringbuf_reserve:
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 36508f46a8db..8ea2a0e50041 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1167,6 +1167,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_ktime_get_ns_proto;
>         case BPF_FUNC_ktime_get_boot_ns:
>                 return &bpf_ktime_get_boot_ns_proto;
> +       case BPF_FUNC_ktime_get_real_ns:
> +               return &bpf_ktime_get_real_ns_proto;
>         case BPF_FUNC_tail_call:
>                 return &bpf_tail_call_proto;
>         case BPF_FUNC_get_current_pid_tgid:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index a22812561064..198e69a6508d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3586,6 +3586,13 @@ union bpf_attr {
>   *             the data in *dst*. This is a wrapper of **copy_from_user**\ ().
>   *     Return
>   *             0 on success, or a negative error in case of failure.
> + *
> + * u64 bpf_ktime_get_real_ns(void)
> + *     Description
> + *             Return the real time in nanoseconds.
> + *             See: **clock_gettime**\ (**CLOCK_REALTIME**)
> + *     Return
> + *             Current *ktime*.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3737,6 +3744,7 @@ union bpf_attr {
>         FN(inode_storage_delete),       \
>         FN(d_path),                     \
>         FN(copy_from_user),             \
> +       FN(ktime_get_real_ns),          \
>         /* */
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> --
> 2.17.1

Reviewed-by: Maciej ┼╗enczykowski <maze@...gle.com>

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