Subject: Re: [PATCH net-next 2/8] net: psample: add multicast filtering on group_id

From: Jiri Pirko <[email-masked]>
Date: Wed, 24 Apr 2024 16:54:13 +0200

Wed, Apr 24, 2024 at 03:50:49PM CEST, [email-masked] wrote:
>Packet samples can come from several places (e.g: different tc sample
>actions), typically using the sample group (PSAMPLE_ATTR_SAMPLE_GROUP)
>to differentiate them.
>
>Likewise, sample consumers that listen on the multicast group may only
>be interested on a single group. However, they are currently forced to
>receive all samples and discard the ones that are not relevant, causing
>unnecessary overhead.
>
>Allow users to filter on the desired group_id by adding a new command
>PSAMPLE_SET_FILTER that can be used to pass the desired group id.
>Store this filter on the per-socket private pointer and use it for
>filtering multicasted samples.
>
>Signed-off-by: Adrian Moreno <[email-masked]>
>---
> include/uapi/linux/psample.h |   1 +
> net/psample/psample.c        | 110 +++++++++++++++++++++++++++++++++--
> 2 files changed, 105 insertions(+), 6 deletions(-)
>
>diff --git a/include/uapi/linux/psample.h b/include/uapi/linux/psample.h
>index e585db5bf2d2..9d62983af0a4 100644
>--- a/include/uapi/linux/psample.h
>+++ b/include/uapi/linux/psample.h
>@@ -28,6 +28,7 @@ enum psample_command {
> 	PSAMPLE_CMD_GET_GROUP,
> 	PSAMPLE_CMD_NEW_GROUP,
> 	PSAMPLE_CMD_DEL_GROUP,
>+	PSAMPLE_CMD_SET_FILTER,
> };
> 
> enum psample_tunnel_key_attr {
>diff --git a/net/psample/psample.c b/net/psample/psample.c
>index a5d9b8446f77..f5f77515b969 100644
>--- a/net/psample/psample.c
>+++ b/net/psample/psample.c
>@@ -98,13 +98,77 @@ static int psample_nl_cmd_get_group_dumpit(struct sk_buff *msg,
> 	return msg->len;
> }
> 
>-static const struct genl_small_ops psample_nl_ops[] = {
>+struct psample_obj_desc {
>+	struct rcu_head rcu;
>+	u32 group_num;
>+};
>+
>+struct psample_nl_sock_priv {
>+	struct psample_obj_desc __rcu *filter;
>+	spinlock_t filter_lock; /* Protects filter. */
>+};
>+
>+static void psample_nl_sock_priv_init(void *priv)
>+{
>+	struct psample_nl_sock_priv *sk_priv = priv;
>+
>+	spin_lock_init(&sk_priv->filter_lock);
>+}
>+
>+static void psample_nl_sock_priv_destroy(void *priv)
>+{
>+	struct psample_nl_sock_priv *sk_priv = priv;
>+	struct psample_obj_desc *filter;
>+
>+	filter = rcu_dereference_protected(sk_priv->filter, true);
>+	kfree_rcu(filter, rcu);
>+}
>+
>+static int psample_nl_set_filter_doit(struct sk_buff *skb,
>+				      struct genl_info *info)
>+{
>+	struct psample_obj_desc *filter = NULL;
>+	struct psample_nl_sock_priv *sk_priv;
>+	struct nlattr **attrs = info->attrs;
>+
>+	if (attrs[PSAMPLE_ATTR_SAMPLE_GROUP]) {
>+		filter = kzalloc(sizeof(*filter), GFP_KERNEL);
>+		filter->group_num =
>+			nla_get_u32(attrs[PSAMPLE_ATTR_SAMPLE_GROUP]);
>+	}
>+
>+	sk_priv = genl_sk_priv_get(&psample_nl_family, NETLINK_CB(skb).sk);
>+	if (IS_ERR(sk_priv)) {
>+		kfree(filter);
>+		return PTR_ERR(sk_priv);
>+	}
>+
>+	spin_lock(&sk_priv->filter_lock);
>+	filter = rcu_replace_pointer(sk_priv->filter, filter,
>+				     lockdep_is_held(&sk_priv->filter_lock));
>+	spin_unlock(&sk_priv->filter_lock);
>+	kfree_rcu(filter, rcu);
>+	return 0;
>+}
>+
>+static const struct nla_policy
>+psample_set_filter_policy[PSAMPLE_ATTR_SAMPLE_GROUP + 1] = {
>+	[PSAMPLE_ATTR_SAMPLE_GROUP] = { .type = NLA_U32, },
>+};
>+
>+static const struct genl_ops psample_nl_ops[] = {
> 	{
> 		.cmd = PSAMPLE_CMD_GET_GROUP,
> 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
> 		.dumpit = psample_nl_cmd_get_group_dumpit,
> 		/* can be retrieved by unprivileged users */
>-	}
>+	},
>+	{
>+		.cmd		= PSAMPLE_CMD_SET_FILTER,
>+		.doit		= psample_nl_set_filter_doit,
>+		.policy		= psample_set_filter_policy,
>+		.flags		= 0,
>+	},

Sidenote:
Did you think about converting psample to split ops and to introcude
ynl spec file for it?

> };
> 
> static struct genl_family psample_nl_family __ro_after_init = {
>@@ -114,10 +178,13 @@ static struct genl_family psample_nl_family __ro_after_init = {
> 	.netnsok	= true,
> 	.module		= THIS_MODULE,
> 	.mcgrps		= psample_nl_mcgrps,
>-	.small_ops	= psample_nl_ops,
>-	.n_small_ops	= ARRAY_SIZE(psample_nl_ops),
>+	.ops		= psample_nl_ops,
>+	.n_ops		= ARRAY_SIZE(psample_nl_ops),
> 	.resv_start_op	= PSAMPLE_CMD_GET_GROUP + 1,
> 	.n_mcgrps	= ARRAY_SIZE(psample_nl_mcgrps),
>+	.sock_priv_size		= sizeof(struct psample_nl_sock_priv),
>+	.sock_priv_init		= psample_nl_sock_priv_init,
>+	.sock_priv_destroy	= psample_nl_sock_priv_destroy,
> };
> 
> static void psample_group_notify(struct psample_group *group,
>@@ -360,6 +427,32 @@ static int psample_tunnel_meta_len(struct ip_tunnel_info *tun_info)
> }
> #endif
> 
>+static inline void psample_nl_obj_desc_init(struct psample_obj_desc *desc,
>+					    u32 group_num)
>+{
>+	memset(desc, 0, sizeof(*desc));
>+	desc->group_num = group_num;
>+}
>+
>+static int psample_nl_sample_filter(struct sock *dsk, struct sk_buff *skb,
>+				    void *data)
>+{
>+	struct psample_obj_desc *desc = data;
>+	struct psample_nl_sock_priv *sk_priv;
>+	struct psample_obj_desc *filter;
>+	int ret = 0;
>+
>+	rcu_read_lock();
>+	sk_priv = __genl_sk_priv_get(&psample_nl_family, dsk);
>+	if (!IS_ERR_OR_NULL(sk_priv)) {
>+		filter = rcu_dereference(sk_priv->filter);
>+		if (filter && desc)
>+			ret = (filter->group_num != desc->group_num);
>+	}
>+	rcu_read_unlock();
>+	return ret;
>+}
>+
> void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
> 			   u32 sample_rate, const struct psample_metadata *md)
> {
>@@ -370,6 +463,7 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
> #ifdef CONFIG_INET
> 	struct ip_tunnel_info *tun_info;
> #endif
>+	struct psample_obj_desc desc;
> 	struct sk_buff *nl_skb;
> 	int data_len;
> 	int meta_len;
>@@ -487,8 +581,12 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
> #endif
> 
> 	genlmsg_end(nl_skb, data);
>-	genlmsg_multicast_netns(&psample_nl_family, group->net, nl_skb, 0,
>-				PSAMPLE_NL_MCGRP_SAMPLE, GFP_ATOMIC);
>+	psample_nl_obj_desc_init(&desc, group->group_num);
>+	genlmsg_multicast_netns_filtered(&psample_nl_family,
>+					 group->net, nl_skb, 0,
>+					 PSAMPLE_NL_MCGRP_SAMPLE,
>+					 GFP_ATOMIC, psample_nl_sample_filter,
>+					 &desc);
> 
> 	return;
> error:
>-- 
>2.44.0
>
>