netdev - [RFC net-next 2/9] genetlink: reorg struct genl

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Date:   Wed, 30 Sep 2020 17:05:11 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     netdev@...r.kernel.org
Cc:     andrew@...n.ch, johannes@...solutions.net, jiri@...nulli.us,
        mkubecek@...e.cz, dsahern@...nel.org, pablo@...filter.org,
        Jakub Kicinski <kuba@...nel.org>
Subject: [RFC net-next 2/9] genetlink: reorg struct genl_family

There are holes and oversized members in struct genl_family.

Before: /* size: 104, cachelines: 2, members: 16 */
After:  /* size:  88, cachelines: 2, members: 16 */

The command field in struct genlmsghdr is a u8, so no point
in the operation count being 32 bit. Also operation 0 is
usually undefined, so we only need 255 entries.

netnsok and parallel_ops are only ever initialized to true.

We can grow the fields as needed, compiler should warn us
if someone tries to assign larger constants.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 include/net/genetlink.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index a3484fd736d6..0033c76ff094 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -48,8 +48,11 @@ struct genl_family {
 	char			name[GENL_NAMSIZ];
 	unsigned int		version;
 	unsigned int		maxattr;
-	bool			netnsok;
-	bool			parallel_ops;
+	unsigned int		mcgrp_offset;	/* private */
+	u8			netnsok:1;
+	u8			parallel_ops:1;
+	u8			n_ops;
+	u8			n_mcgrps;
 	const struct nla_policy *policy;
 	int			(*pre_doit)(const struct genl_ops *ops,
 					    struct sk_buff *skb,
@@ -59,9 +62,6 @@ struct genl_family {
 					     struct genl_info *info);
 	const struct genl_ops *	ops;
 	const struct genl_multicast_group *mcgrps;
-	unsigned int		n_ops;
-	unsigned int		n_mcgrps;
-	unsigned int		mcgrp_offset;	/* private */
 	struct module		*module;
 };
 
-- 
2.26.2