On 4/17/18 7:34 AM, Quentin Monnet wrote:
Add documentation for eBPF helper functions to bpf.h user header file.
This documentation can be parsed with the Python script provided in
another commit of the patch series, in order to provide a RST document
that can later be converted into a man page.
The objective is to make the documentation easily understandable and
accessible to all eBPF developers, including beginners.
This patch contains descriptions for the following helper functions:
Helpers from Lawrence:
- bpf_setsockopt()
- bpf_getsockopt()
- bpf_sock_ops_cb_flags_set()
Helpers from Yonghong:
- bpf_perf_event_read_value()
- bpf_perf_prog_read_value()
Helper from Josef:
- bpf_override_return()
Helper from Andrey:
- bpf_bind()
v3:
- bpf_perf_event_read_value(): Fix time of selection for perf event type
in description. Remove occurences of "cores" to avoid confusion with
"CPU".
- bpf_bind(): Remove last paragraph of description, which was off topic.
Cc: Lawrence Brakmo <bra...@fb.com>
Cc: Yonghong Song <y...@fb.com>
Cc: Josef Bacik <jba...@fb.com>
Cc: Andrey Ignatov <r...@fb.com>
Signed-off-by: Quentin Monnet <quentin.mon...@netronome.com>
fix patch 7: Yonghong and Andrey
---
include/uapi/linux/bpf.h | 178 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 178 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index dd79a1c82adf..350459c583de 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1234,6 +1234,28 @@ union bpf_attr {
* Return
* 0
*
+ * int bpf_setsockopt(struct bpf_sock_ops_kern *bpf_socket, int level, int
optname, char *optval, int optlen)
+ * Description
+ * Emulate a call to **setsockopt()** on the socket associated to
+ * *bpf_socket*, which must be a full socket. The *level* at
+ * which the option resides and the name *optname* of the option
+ * must be specified, see **setsockopt(2)** for more information.
+ * The option value of length *optlen* is pointed by *optval*.
+ *
+ * This helper actually implements a subset of **setsockopt()**.
+ * It supports the following *level*\ s:
+ *
+ * * **SOL_SOCKET**, which supports the following *optname*\ s:
+ * **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**,
+ * **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**.
+ * * **IPPROTO_TCP**, which supports the following *optname*\ s:
+ * **TCP_CONGESTION**, **TCP_BPF_IW**,
+ * **TCP_BPF_SNDCWND_CLAMP**.
+ * * **IPPROTO_IP**, which supports *optname* **IP_TOS**.
+ * * **IPPROTO_IPV6**, which supports *optname* **IPV6_TCLASS**.
+ * Return
+ * 0 on success, or a negative error in case of failure.
+ *
* int bpf_skb_adjust_room(struct sk_buff *skb, u32 len_diff, u32 mode, u64
flags)
* Description
* Grow or shrink the room for data in the packet associated to
@@ -1281,6 +1303,162 @@ union bpf_attr {
* performed again.
* Return
* 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct
bpf_perf_event_value *buf, u32 buf_size)
+ * Description
+ * Read the value of a perf event counter, and store it into *buf*
+ * of size *buf_size*. This helper relies on a *map* of type
+ * **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the perf event
+ * counter is selected when *map* is updated with perf event file
+ * descriptors. The *map* is an array whose size is the number of
+ * available CPUs, and each cell contains a value relative to one
+ * CPU. The value to retrieve is indicated by *flags*, that
+ * contains the index of the CPU to look up, masked with
+ * **BPF_F_INDEX_MASK**. Alternatively, *flags* can be set to
+ * **BPF_F_CURRENT_CPU** to indicate that the value for the
+ * current CPU should be retrieved.
+ *
+ * This helper behaves in a way close to
+ * **bpf_perf_event_read**\ () helper, save that instead of
+ * just returning the value observed, it fills the *buf*
+ * structure. This allows for additional data to be retrieved: in
+ * particular, the enabled and running times (in *buf*\
+ * **->enabled** and *buf*\ **->running**, respectively) are
+ * copied.
+ *
+ * These values are interesting, because hardware PMU (Performance
+ * Monitoring Unit) counters are limited resources. When there are
+ * more PMU based perf events opened than available counters,
+ * kernel will multiplex these events so each event gets certain
+ * percentage (but not all) of the PMU time. In case that
+ * multiplexing happens, the number of samples or counter value
+ * will not reflect the case compared to when no multiplexing
+ * occurs. This makes comparison between different runs difficult.
+ * Typically, the counter value should be normalized before
+ * comparing to other experiments. The usual normalization is done
+ * as follows.
+ *
+ * ::
+ *
+ * normalized_counter = counter * t_enabled / t_running
+ *
+ * Where t_enabled is the time enabled for event and t_running is
+ * the time running for event since last normalization. The
+ * enabled and running times are accumulated since the perf event
+ * open. To achieve scaling factor between two invocations of an
+ * eBPF program, users can can use CPU id as the key (which is
+ * typical for perf array usage model) to remember the previous
+ * value and do the calculation inside the eBPF program.
+ * Return
+ * 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_perf_prog_read_value(struct bpf_perf_event_data_kern *ctx, struct
bpf_perf_event_value *buf, u32 buf_size)
+ * Description
+ * For en eBPF program attached to a perf event, retrieve the
+ * value of the event counter associated to *ctx* and store it in
+ * the structure pointed by *buf* and of size *buf_size*. Enabled
+ * and running times are also stored in the structure (see
+ * description of helper **bpf_perf_event_read_value**\ () for
+ * more details).
+ * Return
+ * 0 on success, or a negative error in case of failure.
Acked-by: Yonghong Song <y...@fb.com>
for the following two helpers:
- bpf_perf_event_read_value()
- bpf_perf_prog_read_value()
