[PATCH RFC net-next 2/9] bpf: add bpf_ktime_get_real_ns() kfunc

[Jason Xing <kerneljasonxing@gmail.com>]

Introduce a new BPF kfunc bpf_ktime_get_real_ns() that returns the
current CLOCK_REALTIME time. This allows BPF programs to perform
accurate delay calculations without clock domain mismatch issue.

Previously BPF programs only had access to monotonic, boot and
TAI clocks (bpf_ktime_get_ns/boot_ns/tai_ns), none of which can be
subtracted from a realtime start time.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
https://lore.kernel.org/all/20260518082344.96647-2-kerneljasonxing@gmail.com/
---
 kernel/bpf/helpers.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b3cc5c8fc875..7a0db620a273 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2335,6 +2335,11 @@ void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
 
 __bpf_kfunc_start_defs();
 
+__bpf_kfunc u64 bpf_ktime_get_real_ns(void)
+{
+	return ktime_to_ns(ktime_get_real());
+}
+
 /**
  * bpf_obj_new() - allocate an object described by program BTF
  * @local_type_id__k: type ID in program BTF
@@ -4972,6 +4977,7 @@ BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_dynptr_from_file)
 BTF_ID_FLAGS(func, bpf_dynptr_file_discard, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_timer_cancel_async)
+BTF_ID_FLAGS(func, bpf_ktime_get_real_ns)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
-- 
2.43.7