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

On 03/21/2018 04:21 AM, Boris Pismenny wrote:

On 3/20/2018 10:36 PM, Rao Shoaib wrote:

quoted

On 03/19/2018 07:44 PM, Saeed Mahameed wrote:

quoted

From: Ilya Lesokhin <redacted>

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 <redacted>
Signed-off-by: Boris Pismenny <redacted>
Signed-off-by: Aviad Yehezkel <redacted>
Signed-off-by: Saeed Mahameed <redacted>
---
  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

I agree, in fact I was using function pointers for the exact reason, to 
change the functionality of a function. I asked Dave about the use and 
he said No (Also note that the relevant CPU optimizations have been 
turned off on selected NIC's due to the latest security issues -- On AMD 
CPU's the optimizations are not turned off). So it is Dave's decision -- 
I am hoping that he would reconsider and allow me to use pointers as 
well as pointers solve the problem nicely and are used extensively.

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.

After reviewing my changes I believe I can work with the change. So go 
ahead.

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.

Regards,

Shoaib

quoted

Thanks,

Shoaib

Best,
Boris.