genetlink: Add per family bind/unbind callbacks

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 <kuba@kernel.org>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240212161615.161935-2-stanislaw.gruszka@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index e614691..ecadba8 100644 (file)
--- 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 8c7af02..50ec599 100644 (file)
--- 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 +1846,39 @@ 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) {
+               int i;
+
+               if (family->n_mcgrps == 0)
+                       continue;
+
+               i = group - family->mcgrp_offset;
+               if (i < 0 || i >= family->n_mcgrps)
+                       continue;
+
+               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,
        };