[RFC net-next 05/15] netlink: add macro for checking dump ctx size

[Jakub Kicinski <kuba@kernel.org>]

We encourage casting struct netlink_callback::ctx to a local
struct (in a comment above the field). Provide a convenience
macro for checking if the local struct fits into the ctx.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: pablo@netfilter.org
CC: kadlec@netfilter.org
CC: fw@strlen.de
CC: johannes@sipsolutions.net
CC: ecree.xilinx@gmail.com
CC: netfilter-devel@vger.kernel.org
CC: coreteam@netfilter.org
---
 include/linux/netlink.h              | 4 ++++
 net/netfilter/nf_conntrack_netlink.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index d81bde5a5844..38f6334f408c 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -263,6 +263,10 @@ struct netlink_callback {
 	};
 };
 
+#define NL_ASSET_DUMP_CTX_FITS(type_name)				\
+	BUILD_BUG_ON(sizeof(type_name) >				\
+		     sizeof_field(struct netlink_callback, ctx))
+
 struct netlink_notify {
 	struct net *net;
 	u32 portid;
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 1286ae7d4609..90672e293e57 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3866,7 +3866,7 @@ static int __init ctnetlink_init(void)
 {
 	int ret;
 
-	BUILD_BUG_ON(sizeof(struct ctnetlink_list_dump_ctx) > sizeof_field(struct netlink_callback, ctx));
+	NL_ASSET_DUMP_CTX_FITS(struct ctnetlink_list_dump_ctx);
 
 	ret = nfnetlink_subsys_register(&ctnl_subsys);
 	if (ret < 0) {
-- 
2.38.1