Date: Mon, 8 Apr 2024 21:24:17 +0200
From: Adrian Moreno <amorenoz@...hat.com>
To: Ilya Maximets <i.maximets@....org>, netdev@...r.kernel.org
Cc: jiri@...nulli.us, xiyou.wangcong@...il.com, cmi@...dia.com,
 yotam.gi@...il.com, aconole@...hat.com, echaudro@...hat.com, horms@...nel.org
Subject: Re: [RFC net-next v2 2/5] net: psample: add multicast filtering on
 group_id



On 4/8/24 15:18, Ilya Maximets wrote:
> [copying my previous reply since this version actually has netdev@ in Cc]
> 
> On 4/8/24 14:57, Adrian Moreno 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
>> SAMPLE_FILTER_SET 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 <amorenoz@...hat.com>
>> ---
>>   include/uapi/linux/psample.h |   1 +
>>   net/psample/psample.c        | 127 +++++++++++++++++++++++++++++++++--
>>   2 files changed, 122 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/uapi/linux/psample.h b/include/uapi/linux/psample.h
>> index e585db5bf2d2..5e0305b1520d 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_SAMPLE_FILTER_SET,
> Other commands are names as PSAMPLE_CMD_VERB_NOUN, so this new one
> should be PSAMPLE_CMD_SET_FILTER.  (The SAMPLE part seems unnecessary.)
> Some functions/structures need to be renamed accordingly.
> 

Sure, I'll rename it when I sent the next version.

>>   };
>>   
>>   enum psample_tunnel_key_attr {
>> diff --git a/net/psample/psample.c b/net/psample/psample.c
>> index a5d9b8446f77..a0cef63dfdec 100644
>> --- a/net/psample/psample.c
>> +++ b/net/psample/psample.c
>> @@ -98,13 +98,84 @@ 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;
>> +	bool group_num_valid;
>> +};
>> +
>> +struct psample_nl_sock_priv {
>> +	struct psample_obj_desc __rcu *flt;
> 
> Can we call it 'fileter' ?  I find it hard to read the code with
> this unnecessary abbreviation.  Same for the lock below.
> 

Sure.

>> +	spinlock_t flt_lock; /* Protects flt. */
>> +};
>> +
>> +static void psample_nl_sock_priv_init(void *priv)
>> +{
>> +	struct psample_nl_sock_priv *sk_priv = priv;
>> +
>> +	spin_lock_init(&sk_priv->flt_lock);
>> +}
>> +
>> +static void psample_nl_sock_priv_destroy(void *priv)
>> +{
>> +	struct psample_nl_sock_priv *sk_priv = priv;
>> +	struct psample_obj_desc *flt;
>> +
>> +	flt = rcu_dereference_protected(sk_priv->flt, true);
>> +	kfree_rcu(flt, rcu);
>> +}
>> +
>> +static int psample_nl_sample_filter_set_doit(struct sk_buff *skb,
>> +					     struct genl_info *info)
>> +{
>> +	struct psample_nl_sock_priv *sk_priv;
>> +	struct nlattr **attrs = info->attrs;
>> +	struct psample_obj_desc *flt;
>> +
>> +	flt = kzalloc(sizeof(*flt), GFP_KERNEL);
>> +
>> +	if (attrs[PSAMPLE_ATTR_SAMPLE_GROUP]) {
>> +		flt->group_num = nla_get_u32(attrs[PSAMPLE_ATTR_SAMPLE_GROUP]);
>> +		flt->group_num_valid = true;
>> +	}
>> +
>> +	if (!flt->group_num_valid) {
>> +		kfree(flt);
> 
> Might be better to not allocate it in the first place.
> 

Absolutely.

>> +		flt = NULL;
>> +	}
>> +
>> +	sk_priv = genl_sk_priv_get(&psample_nl_family, NETLINK_CB(skb).sk);
>> +	if (IS_ERR(sk_priv)) {
>> +		kfree(flt);
>> +		return PTR_ERR(sk_priv);
>> +	}
>> +
>> +	spin_lock(&sk_priv->flt_lock);
>> +	flt = rcu_replace_pointer(sk_priv->flt, flt,
>> +				  lockdep_is_held(&sk_priv->flt_lock));
>> +	spin_unlock(&sk_priv->flt_lock);
>> +	kfree_rcu(flt, rcu);
>> +	return 0;
>> +}
>> +
>> +static const struct nla_policy
>> +	psample_sample_filter_set_policy[PSAMPLE_ATTR_SAMPLE_GROUP + 1] = {
>> +	[PSAMPLE_ATTR_SAMPLE_GROUP] = { .type = NLA_U32, },
> 
> This indentation is confusing, though I'm not sure what's a better way.
> 

I now! I'll try to move it around see if it improves things.

>> +};
>> +
>> +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_SAMPLE_FILTER_SET,
>> +		.doit		= psample_nl_sample_filter_set_doit,
>> +		.policy		= psample_sample_filter_set_policy,
>> +		.flags		= 0,
>> +	},
>>   };
>>   
>>   static struct genl_family psample_nl_family __ro_after_init = {
>> @@ -114,10 +185,13 @@ 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 +434,42 @@ 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;
>> +	desc->group_num_valid = true;
>> +}
>> +
>> +static bool psample_obj_desc_match(struct psample_obj_desc *desc,
>> +				   struct psample_obj_desc *flt)
>> +{
>> +	if (desc->group_num_valid && flt->group_num_valid &&
>> +	    desc->group_num != flt->group_num)
>> +		return false;
>> +	return true;
> 
> This fucntion returns 'true' if one of the arguments is not valid.
> I'd not expect such behavior from a 'match' function.
> 
> I understand the intention that psample should sample everything
> to sockets that do not request filters, but that should not be part
> of the 'match' logic, or more appropriate function name should be
> chosen.  Also, if the group is not initialized, but the filter is,
> it should not match, logically.  The validity on filter and the
> current sample is not symmetric.
> 

The descriptor should always be initialized but I think double checking should 
be OK as in the context of this particular function, it might not be clear it is.

> And I'm not really sure if the 'group_num_valid' is actually needed.
> Can the NULL pointer be used as an indicator?  If so, then maybe
> the whole psample_obj_desc structure is not needed as it will
> contain a single field.

If we only filter on group_id, then yes. However, as I was writing this, I 
thought maybe opening the door to filtering on more fields such as the protocol 
in/out interfaces, etc. Now that I read this I understand the current code is 
confusing: I should have left a comment or mention it in the commit message.

> 
>> +}
>> +
>> +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 *flt;
>> +	int ret = 0;
>> +
>> +	rcu_read_lock();
>> +	sk_priv = __genl_sk_priv_get(&psample_nl_family, dsk);
>> +	if (!IS_ERR_OR_NULL(sk_priv)) {
>> +		flt = rcu_dereference(sk_priv->flt);
>> +		if (flt)
>> +			ret = !psample_obj_desc_match(desc, flt);
>> +	}
>> +	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 +480,7 @@ 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 +598,12 @@ 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:
> 

-- 
Adrián Moreno

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