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Message-ID: <CANP3RGf-rDPkf2=YoLEn=jcHyFEDcrNrQO27RdZRCoa_xi8-4Q@mail.gmail.com>
Date: Wed, 23 Sep 2020 18:19:48 -0700
From: Maciej Żenczykowski <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 v2 1/2] bpf: Add bpf_ktime_get_real_ns
On Wed, Sep 23, 2020 at 5:03 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..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 fc5c901c7542..3179fcc4ef53 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1756,6 +1756,7 @@ extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
> 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_real_ns_proto;
> extern const struct bpf_func_proto bpf_ktime_get_boot_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;
> 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..af38af5ffc8b 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2207,6 +2207,7 @@ 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 5cc7425ee476..776ff58f969d 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -155,6 +155,17 @@ 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,
imho should be false, this is normally accessible to userspace code
via syscall, no reason why it should be gpl only for bpf
> + .ret_type = RET_INTEGER,
> +};
> BPF_CALL_0(bpf_ktime_get_boot_ns)
> {
> /* NMI safe access to clock boottime */
> @@ -655,6 +666,8 @@ 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 36508f46a8db..18b644fff0be 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1165,6 +1165,8 @@ 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;
should probably be here to stay alpha sorted more or less (also
applies to other places)
> case BPF_FUNC_tail_call:
> 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
>
Maciej Żenczykowski, Kernel Networking Developer @ Google
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