genetlink: introduce pre_doit/post_doit hooks

Each family may have some amount of boilerplate
locking code that applies to most, or even all,
commands.

This allows a family to handle such things in
a more generic way, by allowing it to
 a) include private flags in each operation
 b) specify a pre_doit hook that is called,
    before an operation's doit() callback and
    may return an error directly,
 c) specify a post_doit hook that can undo
    locking or similar things done by pre_doit,
    and finally
 d) include two private pointers in each info
    struct passed between all these operations
    including doit(). (It's two because I'll
    need two in nl80211 -- can be extended.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 26ed3e8587c2..1781d99145e2 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -547,8 +547,20 @@ static int genl_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	info.userhdr = nlmsg_data(nlh) + GENL_HDRLEN;
 	info.attrs = family->attrbuf;
 	genl_info_net_set(&info, net);
+	memset(&info.user_ptr, 0, sizeof(info.user_ptr));
 
-	return ops->doit(skb, &info);
+	if (family->pre_doit) {
+		err = family->pre_doit(ops, skb, &info);
+		if (err)
+			return err;
+	}
+
+	err = ops->doit(skb, &info);
+
+	if (family->post_doit)
+		family->post_doit(ops, skb, &info);
+
+	return err;
 }
 
 static void genl_rcv(struct sk_buff *skb)