netdev - Re: [PATCH net-next 01/14] tcp: Add clean acked data hook

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Date:   Wed, 21 Mar 2018 13:21:21 +0200
From:   Boris Pismenny <borisp@...lanox.com>
To:     Rao Shoaib <rao.shoaib@...cle.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Dave Watson <davejwatson@...com>,
        Ilya Lesokhin <ilyal@...lanox.com>,
        Aviad Yehezkel <aviadye@...lanox.com>
Subject: Re: [PATCH net-next 01/14] tcp: Add clean acked data hook



On 3/20/2018 10:36 PM, Rao Shoaib wrote:
> 
> 
> On 03/19/2018 07:44 PM, Saeed Mahameed wrote:
>> From: Ilya Lesokhin <ilyal@...lanox.com>
>>
>> Called when a TCP segment is acknowledged.
>> Could be used by application protocols who hold additional
>> metadata associated with the stream data.
>>
>> This is required by TLS device offload to release
>> metadata associated with acknowledged TLS records.
>>
>> Signed-off-by: Ilya Lesokhin <ilyal@...lanox.com>
>> Signed-off-by: Boris Pismenny <borisp@...lanox.com>
>> Signed-off-by: Aviad Yehezkel <aviadye@...lanox.com>
>> Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
>> ---
>>   include/net/inet_connection_sock.h | 2 ++
>>   net/ipv4/tcp_input.c               | 2 ++
>>   2 files changed, 4 insertions(+)
>>
>> diff --git a/include/net/inet_connection_sock.h 
>> b/include/net/inet_connection_sock.h
>> index b68fea022a82..2ab6667275df 100644
>> --- a/include/net/inet_connection_sock.h
>> +++ b/include/net/inet_connection_sock.h
>> @@ -77,6 +77,7 @@ struct inet_connection_sock_af_ops {
>>    * @icsk_af_ops           Operations which are AF_INET{4,6} specific
>>    * @icsk_ulp_ops       Pluggable ULP control hook
>>    * @icsk_ulp_data       ULP private data
>> + * @icsk_clean_acked       Clean acked data hook
>>    * @icsk_listen_portaddr_node    hash to the portaddr listener 
>> hashtable
>>    * @icsk_ca_state:       Congestion control state
>>    * @icsk_retransmits:       Number of unrecovered [RTO] timeouts
>> @@ -102,6 +103,7 @@ struct inet_connection_sock {
>>       const struct inet_connection_sock_af_ops *icsk_af_ops;
>>       const struct tcp_ulp_ops  *icsk_ulp_ops;
>>       void              *icsk_ulp_data;
>> +    void (*icsk_clean_acked)(struct sock *sk, u32 acked_seq);
>>       struct hlist_node         icsk_listen_portaddr_node;
>>       unsigned int          (*icsk_sync_mss)(struct sock *sk, u32 pmtu);
>>       __u8              icsk_ca_state:6,
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index 451ef3012636..9854ecae7245 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -3542,6 +3542,8 @@ static int tcp_ack(struct sock *sk, const struct 
>> sk_buff *skb, int flag)
>>       if (after(ack, prior_snd_una)) {
>>           flag |= FLAG_SND_UNA_ADVANCED;
>>           icsk->icsk_retransmits = 0;
>> +        if (icsk->icsk_clean_acked)
>> +            icsk->icsk_clean_acked(sk, ack);
>>       }
>>       prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : 
>> tp->snd_una;
> Per Dave we are not allowed to use function pointers any more, so why 
> extend their use. I implemented a similar callback for my changes but in 
> my use case I need to call the meta data update function even when the 
> packet does not ack any new data or has no payload. Is it possible to 
> move this to say tcp_data_queue() ?

Sometimes function pointers are unavoidable. For example, when a module 
must change the functionality of a function. I think it is preferable to 
advance the kernel

This function is used to free memory based on new acknowledged data. It 
is unrelated to whether data was received or not. So it is not possible 
to move this call to tcp_data_queue.

Just in case, I'll add a static key here to reduce the impact on the 
fast-path as once suggested by EricD on netdev2.2.

> 
> Thanks,
> 
> Shoaib
> 
> 

Best,
Boris.