netdev - [PATCH net-next 1/4] flow_dissector: add meaningful comments

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Message-Id: <20191021200948.23775-2-mcroce@redhat.com>
Date:   Mon, 21 Oct 2019 22:09:45 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller " <davem@...emloft.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Paul Blakey <paulb@...lanox.com>, linux-kernel@...r.kernel.org
Subject: [PATCH net-next 1/4] flow_dissector: add meaningful comments

Documents two piece of code which can't be understood at a glance.

Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 include/net/flow_dissector.h | 1 +
 net/core/flow_dissector.c    | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index 90bd210be060..7747af3cc500 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -282,6 +282,7 @@ struct flow_keys {
 	struct flow_dissector_key_vlan cvlan;
 	struct flow_dissector_key_keyid keyid;
 	struct flow_dissector_key_ports ports;
+	/* 'addrs' must be the last member */
 	struct flow_dissector_key_addrs addrs;
 };
 
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 7c09d87d3269..affde70dad47 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1374,6 +1374,9 @@ static inline size_t flow_keys_hash_length(const struct flow_keys *flow)
 {
 	size_t diff = FLOW_KEYS_HASH_OFFSET + sizeof(flow->addrs);
 	BUILD_BUG_ON((sizeof(*flow) - FLOW_KEYS_HASH_OFFSET) % sizeof(u32));
+	/* flow.addrs MUST be the last member in struct flow_keys because
+	 * different L3 protocols have different address length
+	 */
 	BUILD_BUG_ON(offsetof(typeof(*flow), addrs) !=
 		     sizeof(*flow) - sizeof(flow->addrs));
 
@@ -1421,6 +1424,9 @@ __be32 flow_get_u32_dst(const struct flow_keys *flow)
 }
 EXPORT_SYMBOL(flow_get_u32_dst);
 
+/* Sort the source and destination IP (and the ports if the IP are the same),
+ * to have consistent hash within the two directions
+ */
 static inline void __flow_hash_consistentify(struct flow_keys *keys)
 {
 	int addr_diff, i;
-- 
2.21.0