From mboxrd@z Thu Jan 1 00:00:00 1970 From: Quentin Monnet Subject: Re: [PATCH bpf-next v3 4/8] bpf: add documentation for eBPF helpers (23-32) Date: Fri, 20 Apr 2018 19:54:37 +0100 Message-ID: References: <20180417143438.7018-1-quentin.monnet@netronome.com> <20180417143438.7018-5-quentin.monnet@netronome.com> <6f1b43c7-5d79-7419-1053-d0b29c1e2bb9@iogearbox.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <6f1b43c7-5d79-7419-1053-d0b29c1e2bb9@iogearbox.net> Content-Language: en-US Sender: netdev-owner@vger.kernel.org To: Daniel Borkmann , ast@kernel.org Cc: netdev@vger.kernel.org, oss-drivers@netronome.com, linux-doc@vger.kernel.org, linux-man@vger.kernel.org List-Id: linux-man@vger.kernel.org 2018-04-19 13:16 UTC+0200 ~ Daniel Borkmann > On 04/17/2018 04:34 PM, 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, all >> written by Daniel: >> >> - bpf_get_prandom_u32() >> - bpf_get_smp_processor_id() >> - bpf_get_cgroup_classid() >> - bpf_get_route_realm() >> - bpf_skb_load_bytes() >> - bpf_csum_diff() >> - bpf_skb_get_tunnel_opt() >> - bpf_skb_set_tunnel_opt() >> - bpf_skb_change_proto() >> - bpf_skb_change_type() >> >> v3: >> - bpf_get_prandom_u32(): Fix helper name :(. Add description, including >> a note on the internal random state. >> - bpf_get_smp_processor_id(): Add description, including a note on the >> processor id remaining stable during program run. >> - bpf_get_cgroup_classid(): State that CONFIG_CGROUP_NET_CLASSID is >> required to use the helper. Add a reference to related documentation. >> State that placing a task in net_cls controller disables cgroup-bpf. >> - bpf_get_route_realm(): State that CONFIG_CGROUP_NET_CLASSID is >> required to use this helper. >> - bpf_skb_load_bytes(): Fix comment on current use cases for the helper. >> >> Cc: Daniel Borkmann >> Signed-off-by: Quentin Monnet >> --- >> include/uapi/linux/bpf.h | 152 +++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 152 insertions(+) >> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index c59bf5b28164..d748f65a8f58 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h [...] >> @@ -615,6 +632,27 @@ union bpf_attr { >> * Return >> * 0 on success, or a negative error in case of failure. >> * >> + * u32 bpf_get_cgroup_classid(struct sk_buff *skb) >> + * Description >> + * Retrieve the classid for the current task, i.e. for the >> + * net_cls (network classifier) cgroup to which *skb* belongs. >> + * >> + * This helper is only available is the kernel was compiled with >> + * the **CONFIG_CGROUP_NET_CLASSID** configuration option set to >> + * "**y**" or to "**m**". >> + * >> + * Note that placing a task into the net_cls controller completely >> + * disables the execution of eBPF programs with the cgroup. > > I'm not sure I follow the above sentence, what do you mean by that? Please see comment below. > I would definitely also add here that this helper is limited to cgroups v1 > only, and that it works on clsact TC egress hook but not the ingress one. > >> + * Also note that, in the above description, the "network >> + * classifier" cgroup does not designate a generic classifier, but >> + * a particular mechanism that provides an interface to tag >> + * network packets with a specific class identifier. See also the > > The "generic classifier" part is a bit strange to parse. I would probably > leave the first part out and explain that this provides a means to tag > packets based on a user-provided ID for all traffic coming from the tasks > belonging to the related cgroup. In this paragraph and in the one above, I am trying to address Alexei comments to the RFC v2: please add that kernel should be configured with CONFIG_NET_CLS_CGROUP=y|m and mention Documentation/cgroup-v1/net_cls.txt Otherwise 'network classifier' is way too generic. I'd also mention that placing a task into net_cls controller disables all of cgroup-bpf. But I must admit I am struggling a bit on this helper. If I understand correctly, "network classifier" is too generic and could be confused with TC classifiers? Hence the attempt to avoid that in the second paragraph... As for "placing a task into net_cls controller disables all of cgroup-bpf", again if I understand correctly, I think it refers to cgroup_sk_alloc_disable() being called in write_classid() in file net/core/netclassid_cgroup.c. But I am not familiar with it and cannot find a nice way to explain that in the doc :/. >> + * related kernel documentation, available from the Linux sources >> + * in file *Documentation/cgroup-v1/net_cls.txt*. >> + * Return >> + * The classid, or 0 for the default unconfigured classid. >> + * >> * int bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci) >> * Description >> * Push a *vlan_tci* (VLAN tag control information) of protocol >> @@ -734,6 +772,16 @@ union bpf_attr { >> * are **TC_ACT_REDIRECT** on success or **TC_ACT_SHOT** on >> * error. >> * >> + * u32 bpf_get_route_realm(struct sk_buff *skb) >> + * Description >> + * Retrieve the realm or the route, that is to say the >> + * **tclassid** field of the destination for the *skb*. This >> + * helper is available only if the kernel was compiled with >> + * **CONFIG_IP_ROUTE_CLASSID** configuration option. > > Could mention that this is a similar user provided tag like in the net_cls > case with cgroups only that this applies to routes here (dst entries) which > hold this tag. > > Also, should say that this works with clsact TC egress hook or alternatively > conventional classful egress qdiscs, but not on TC ingress. In case of clsact > TC egress hook this has the advantage that the dst entry has not been dropped > yet in the xmit path. Therefore, the dst entry does not need to be artificially > held via netif_keep_dst() for a classful qdisc until the skb is freed. Here I am not sure to follow, the advantage is for clsact, but this is only for a classful qdisc that we can avoid holding the dst entry? How does holding the entry with netif_keep_dst() translate, from a user space point of view? Thanks a lot for the exhaustive review! Quentin