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Date: Mon, 27 Jul 2020 16:52:31 -0700
From: Song Liu <song@...nel.org>
To: bimmy.pujari@...el.com
Cc: bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
mchehab@...nel.org, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>, maze@...gle.com,
ashkan.nikravesh@...el.com
Subject: Re: [PATCH] bpf: Add bpf_ktime_get_real_ns
On Mon, Jul 27, 2020 at 4:35 PM <bimmy.pujari@...el.com> wrote:
>
> From: Ashkan Nikravesh <ashkan.nikravesh@...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>
Looks good. Except I am not sure whether we want to call it real_ns or
epoch_timestamp_ns, or epoch_ns.
Please add a selftest for this function.
Also, when resending the patch, please specify which tree it applies to,
like "PATCH bpf-next" or "PATCH bpf".
Thanks,
Song
> ---
> drivers/media/rc/bpf-lirc.c | 2 ++
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 7 +++++++
> kernel/bpf/core.c | 1 +
> kernel/bpf/helpers.c | 14 ++++++++++++++
> kernel/trace/bpf_trace.c | 2 ++
> tools/include/uapi/linux/bpf.h | 7 +++++++
> 7 files changed, 34 insertions(+)
>
> diff --git a/drivers/media/rc/bpf-lirc.c b/drivers/media/rc/bpf-lirc.c
> index 5bb144435c16..1cae0cfdcbaf 100644
> --- a/drivers/media/rc/bpf-lirc.c
> +++ b/drivers/media/rc/bpf-lirc.c
> @@ -103,6 +103,8 @@ lirc_mode2_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_map_peek_elem_proto;
> case BPF_FUNC_ktime_get_ns:
> return &bpf_ktime_get_ns_proto;
> + case BPF_FUNC_ktime_get_real_ns:
> + return &bpf_ktime_get_real_ns_proto;
> case BPF_FUNC_ktime_get_boot_ns:
> return &bpf_ktime_get_boot_ns_proto;
> case BPF_FUNC_tail_call:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 72221aea1c60..9c00ad932f08 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1639,6 +1639,7 @@ 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 54d0c886e3ba..7742c10fbc95 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3377,6 +3377,12 @@ union bpf_attr {
> * A non-negative value equal to or less than *size* 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), \
> @@ -3521,6 +3527,7 @@ union bpf_attr {
> FN(skc_to_tcp_request_sock), \
> FN(skc_to_udp6_sock), \
> FN(get_task_stack), \
> + 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 7be02e555ab9..0f25f3413208 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2211,6 +2211,7 @@ const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
> 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_real_ns_proto __weak;
> const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;
>
> const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index be43ab3e619f..b726fd077698 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -155,6 +155,18 @@ const struct bpf_func_proto bpf_ktime_get_ns_proto = {
> .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 = true,
> + .ret_type = RET_INTEGER,
> +};
> +
> BPF_CALL_0(bpf_ktime_get_boot_ns)
> {
> /* NMI safe access to clock boottime */
> @@ -633,6 +645,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
> return &bpf_tail_call_proto;
> case BPF_FUNC_ktime_get_ns:
> return &bpf_ktime_get_ns_proto;
> + case BPF_FUNC_ktime_get_real_ns:
> + return &bpf_ktime_get_real_ns_proto;
> case BPF_FUNC_ktime_get_boot_ns:
> return &bpf_ktime_get_boot_ns_proto;
> case BPF_FUNC_ringbuf_output:
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 3cc0dcb60ca2..4e048dfb527b 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1116,6 +1116,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_map_peek_elem_proto;
> case BPF_FUNC_ktime_get_ns:
> return &bpf_ktime_get_ns_proto;
> + case BPF_FUNC_ktime_get_real_ns:
> + return &bpf_ktime_get_real_ns_proto;
> case BPF_FUNC_ktime_get_boot_ns:
> return &bpf_ktime_get_boot_ns_proto;
> case BPF_FUNC_tail_call:
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 54d0c886e3ba..9ca51f82dd35 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3377,6 +3377,12 @@ union bpf_attr {
> * A non-negative value equal to or less than *size* 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), \
> @@ -3521,6 +3527,7 @@ union bpf_attr {
> FN(skc_to_tcp_request_sock), \
> FN(skc_to_udp6_sock), \
> FN(get_task_stack), \
> + FN(ktime_get_real_ns), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> --
> 2.17.1
>
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