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From:   Pedro Tammela <pctammela@gmail.com>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Joe Stringer <joe@cilium.io>,
        Quentin Monnet <quentin@isovalent.com>,
        netdev@vger.kernel.org (open list:BPF (Safe dynamic programs and tools)),
        bpf@vger.kernel.org (open list:BPF (Safe dynamic programs and tools)),
        linux-kernel@vger.kernel.org (open list)
Cc:     Pedro Tammela <pctammela@mojatatu.com>
Subject: [PATCH bpf-next v2] libbpf: clarify flags in ringbuf helpers
Date:   Mon, 12 Apr 2021 16:24:32 -0300
Message-Id: <20210412192434.944343-1-pctammela@mojatatu.com>
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In 'bpf_ringbuf_reserve()' we require the flag to '0' at the moment.

For 'bpf_ringbuf_{discard,submit,output}' a flag of '0' might send a
notification to the process if needed.

Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
---
 include/uapi/linux/bpf.h       | 16 ++++++++++++++++
 tools/include/uapi/linux/bpf.h | 16 ++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 49371eba98ba..24593fd72f9d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4061,12 +4061,20 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		An adaptive notification is a notification sent whenever the user-space
+ * 		process has caught up and consumed all available payloads. In case the user-space
+ * 		process is still processing a previous payload, then no notification is needed
+ * 		as it will process the newly added payload automatically.
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  *
  * void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)
  * 	Description
  * 		Reserve *size* bytes of payload in a ring buffer *ringbuf*.
+ * 		*flags* must be 0.
  * 	Return
  * 		Valid pointer with *size* bytes of memory available; NULL,
  * 		otherwise.
@@ -4078,6 +4086,10 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		See 'bpf_ringbuf_output()' for the definition of adaptive notification.
  * 	Return
  * 		Nothing. Always succeeds.
  *
@@ -4088,6 +4100,10 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		See 'bpf_ringbuf_output()' for the definition of adaptive notification.
  * 	Return
  * 		Nothing. Always succeeds.
  *
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 69902603012c..8debc8280f3e 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4061,12 +4061,20 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		An adaptive notification is a notification sent whenever the user-space
+ * 		process has caught up and consumed all available payloads. In case the user-space
+ * 		process is still processing a previous payload, then no notification is needed
+ * 		as it will process the newly added payload automatically.
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  *
  * void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)
  * 	Description
  * 		Reserve *size* bytes of payload in a ring buffer *ringbuf*.
+ * 		*flags* must be 0.
  * 	Return
  * 		Valid pointer with *size* bytes of memory available; NULL,
  * 		otherwise.
@@ -4078,6 +4086,10 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		See 'bpf_ringbuf_output()' for the definition of adaptive notification.
  * 	Return
  * 		Nothing. Always succeeds.
  *
@@ -4088,6 +4100,10 @@ union bpf_attr {
  * 		of new data availability is sent.
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
+ * 		If **0** is specified in *flags*, an adaptive notification
+ * 		of new data availability is sent.
+ *
+ * 		See 'bpf_ringbuf_output()' for the definition of adaptive notification.
  * 	Return
  * 		Nothing. Always succeeds.
  *
-- 
2.25.1