[v2,1/3] genetlink: Add per family bind/unbind callbacks

Commit Message

Stanislaw Gruszka Feb. 6, 2024, 1:36 p.m. UTC

Add genetlink family bind()/unbind() callbacks when adding/removing
multicast group to/from netlink client socket via setsockopt() or
bind() syscall.

They can be used to track if consumers of netlink multicast messages
emerge or disappear. Thus, a client implementing callbacks, can now
send events only when there are active consumers, preventing unnecessary
work when none exist.

Suggested-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Stanislaw Gruszka <[e-mail]>
---
 include/net/genetlink.h |  4 ++++
 net/netlink/genetlink.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

Comments

Jakub Kicinski Feb. 7, 2024, 2:42 a.m. UTC | #1

On Tue,  6 Feb 2024 14:36:03 +0100 Stanislaw Gruszka wrote:
> +static void genl_unbind(struct net *net, int group)
> +{
> +	const struct genl_family *family;
> +	unsigned int id;
> +
> +	down_read(&cb_lock);
> +
> +	idr_for_each_entry(&genl_fam_idr, family, id) {
> +		const struct genl_multicast_group *grp;
> +		int i;
> +
> +		if (family->n_mcgrps == 0)
> +			continue;
> +
> +		i = group - family->mcgrp_offset;
> +		if (i < 0 || i >= family->n_mcgrps)
> +			continue;
> +
> +		grp = &family->mcgrps[i];
> +
> +		if (family->unbind)
> +			family->unbind(i);
> +
> +		break;

Compiler says:

net/netlink/genetlink.c:1857:52: warning: variable ‘grp’ set but not used [-Wunused-but-set-variable]
 1857 |                 const struct genl_multicast_group *grp;
      |                                                    ^~~

Patch

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index e61469129402..ecadba836ae5 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -41,6 +41,8 @@  struct genl_info;
  *	do additional, common, filtering and return an error
  * @post_doit: called after an operation's doit callback, it may
  *	undo operations done by pre_doit, for example release locks
+ * @bind: called when family multicast group is added to a netlink socket
+ * @unbind: called when family multicast group is removed from a netlink socket
  * @module: pointer to the owning module (set to THIS_MODULE)
  * @mcgrps: multicast groups used by this family
  * @n_mcgrps: number of multicast groups
@@ -84,6 +86,8 @@  struct genl_family {
 	void			(*post_doit)(const struct genl_split_ops *ops,
 					     struct sk_buff *skb,
 					     struct genl_info *info);
+	int			(*bind)(int mcgrp);
+	void			(*unbind)(int mcgrp);
 	const struct genl_ops *	ops;
 	const struct genl_small_ops *small_ops;
 	const struct genl_split_ops *split_ops;
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 8c7af02f8454..0d1551dadb63 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1836,6 +1836,9 @@  static int genl_bind(struct net *net, int group)
 		    !ns_capable(net->user_ns, CAP_SYS_ADMIN))
 			ret = -EPERM;
 
+		if (family->bind)
+			family->bind(i);
+
 		break;
 	}
 
@@ -1843,12 +1846,42 @@  static int genl_bind(struct net *net, int group)
 	return ret;
 }
 
+static void genl_unbind(struct net *net, int group)
+{
+	const struct genl_family *family;
+	unsigned int id;
+
+	down_read(&cb_lock);
+
+	idr_for_each_entry(&genl_fam_idr, family, id) {
+		const struct genl_multicast_group *grp;
+		int i;
+
+		if (family->n_mcgrps == 0)
+			continue;
+
+		i = group - family->mcgrp_offset;
+		if (i < 0 || i >= family->n_mcgrps)
+			continue;
+
+		grp = &family->mcgrps[i];
+
+		if (family->unbind)
+			family->unbind(i);
+
+		break;
+	}
+
+	up_read(&cb_lock);
+}
+
 static int __net_init genl_pernet_init(struct net *net)
 {
 	struct netlink_kernel_cfg cfg = {
 		.input		= genl_rcv,
 		.flags		= NL_CFG_F_NONROOT_RECV,
 		.bind		= genl_bind,
+		.unbind		= genl_unbind,
 		.release	= genl_release,
 	};