From patchwork Sat Jul 18 10:31:59 2009 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Andi Kleen X-Patchwork-Id: 29960 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@bilbo.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id BD93CB7087 for ; Sat, 18 Jul 2009 20:32:17 +1000 (EST) Received: by ozlabs.org (Postfix) id 9FC96DDD0C; Sat, 18 Jul 2009 20:32:17 +1000 (EST) Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.176.167]) by ozlabs.org (Postfix) with ESMTP id B5AC4DDD04 for ; Sat, 18 Jul 2009 20:32:16 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757929AbZGRKcF (ORCPT ); Sat, 18 Jul 2009 06:32:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756745AbZGRKcF (ORCPT ); Sat, 18 Jul 2009 06:32:05 -0400 Received: from one.firstfloor.org ([213.235.205.2]:40700 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753447AbZGRKcE (ORCPT ); Sat, 18 Jul 2009 06:32:04 -0400 Received: from basil.firstfloor.org (p5B3C88D5.dip0.t-ipconnect.de [91.60.136.213]) by one.firstfloor.org (Postfix) with ESMTP id DAAE31A98002; Sat, 18 Jul 2009 12:31:59 +0200 (CEST) Received: by basil.firstfloor.org (Postfix, from userid 1000) id 74804B1E95; Sat, 18 Jul 2009 12:31:59 +0200 (CEST) Date: Sat, 18 Jul 2009 12:31:59 +0200 From: Andi Kleen To: Ilpo =?iso-8859-1?Q?J=E4rvinen?= Cc: Andi Kleen , Netdev , David Miller Subject: [PATCH] TCP: Add comments to (near) all functions in tcp_output.c v2 Message-ID: <20090718103159.GB2682@basil.fritz.box> References: <20090717204004.GA516@basil.fritz.box> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Here's a updated version incorporating feedback. -Andi --- TCP: Add comments to (near) all functions in tcp_output.c v2 While looking for something else I spent some time adding one liner comments to the tcp_output.c functions that didn't have any. That makes the comments more consistent. I hope I documented everything right. No code changes. v2: Incorporated feedback from Ilpo. Signed-off-by: Andi Kleen Acked-by: Ilpo Järvinen --- net/ipv4/tcp_output.c | 51 +++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 46 insertions(+), 5 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Index: linux-2.6.31-rc3-ak/net/ipv4/tcp_output.c =================================================================== --- linux-2.6.31-rc3-ak.orig/net/ipv4/tcp_output.c +++ linux-2.6.31-rc3-ak/net/ipv4/tcp_output.c @@ -59,6 +59,8 @@ int sysctl_tcp_base_mss __read_mostly = /* By default, RFC2861 behavior. */ int sysctl_tcp_slow_start_after_idle __read_mostly = 1; +/* Account for new data that has been sent to the network. + */ static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); @@ -142,6 +144,8 @@ static void tcp_cwnd_restart(struct sock tp->snd_cwnd_used = 0; } +/* Congestion state accounting after a packet has been sent. + */ static void tcp_event_data_sent(struct tcp_sock *tp, struct sk_buff *skb, struct sock *sk) { @@ -276,6 +280,8 @@ static u16 tcp_select_window(struct sock return new_win; } +/* Packet ECN state for a SYN-ACK + */ static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb) { TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_CWR; @@ -283,6 +289,8 @@ static inline void TCP_ECN_send_synack(s TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_ECE; } +/* Packet ECN state for a SYN. + */ static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); @@ -301,6 +309,9 @@ TCP_ECN_make_synack(struct request_sock th->ece = 1; } +/* Set up ECN state for a packet on a ESTABLISHED socket that is about to + * be sent. + */ static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb, int tcp_header_len) { @@ -362,7 +373,9 @@ struct tcp_out_options { __u32 tsval, tsecr; /* need to include OPTION_TS */ }; -/* Beware: Something in the Internet is very sensitive to the ordering of +/* Write previously computed TCP options to the packet. + * + * Beware: Something in the Internet is very sensitive to the ordering of * TCP options, we learned this through the hard way, so be careful here. * Luckily we can at least blame others for their non-compliance but from * inter-operatibility perspective it seems that we're somewhat stuck with @@ -445,6 +458,9 @@ static void tcp_options_write(__be32 *pt } } +/* Compute TCP options for SYN packets. This is not the final + * network wire format yet. + */ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb, struct tcp_out_options *opts, struct tcp_md5sig_key **md5) { @@ -493,6 +509,8 @@ static unsigned tcp_syn_options(struct s return size; } +/* Set up TCP options for SYN-ACKs. + */ static unsigned tcp_synack_options(struct sock *sk, struct request_sock *req, unsigned mss, struct sk_buff *skb, @@ -541,6 +559,9 @@ static unsigned tcp_synack_options(struc return size; } +/* Compute TCP options for ESTABLISHED sockets. This is not the + * final wire format yet. + */ static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb, struct tcp_out_options *opts, struct tcp_md5sig_key **md5) { @@ -705,7 +726,7 @@ static int tcp_transmit_skb(struct sock return net_xmit_eval(err); } -/* This routine just queue's the buffer +/* This routine just queues the buffer * * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, * otherwise socket can stall. @@ -909,6 +930,8 @@ static void __pskb_trim_head(struct sk_b skb->len = skb->data_len; } +/* Remove acked data from a packet in the transmit queue. + */ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) { if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) @@ -937,7 +960,9 @@ int tcp_trim_head(struct sock *sk, struc return 0; } -/* Not accounting for SACKs here. */ +/* Calculate MSS + * Not accounting for SACKs here. + */ int tcp_mtu_to_mss(struct sock *sk, int pmtu) { struct tcp_sock *tp = tcp_sk(sk); @@ -1143,7 +1168,8 @@ static inline unsigned int tcp_cwnd_test return 0; } -/* This must be invoked the first time we consider transmitting +/* Intialize TSO state of a skb. + * This must be invoked the first time we consider transmitting * SKB onto the wire. */ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, @@ -1242,6 +1268,8 @@ static unsigned int tcp_snd_test(struct return cwnd_quota; } +/* Test if sending is allowed right now. + */ int tcp_may_send_now(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); @@ -1378,6 +1406,10 @@ send_now: } /* Create a new MTU probe if we are ready. + * MTU probe is regularly attempting to increase the path MTU by + * deliberately sending larger packets. This discovers routing + * changes resulting in larger path MTUs. + * * Returns 0 if we should wait to probe (no cwnd available), * 1 if a probe was sent, * -1 otherwise @@ -1808,6 +1840,9 @@ static int tcp_can_collapse(struct sock return 1; } +/* Collapse packets in the retransmit queue to make to create + * less packets on the wire. This is only done on retransmission. + */ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, int space) { @@ -1957,6 +1992,9 @@ int tcp_retransmit_skb(struct sock *sk, return err; } +/* Check if we forward retransmits are possible in the current + * window/congestion state. + */ static int tcp_can_forward_retransmit(struct sock *sk) { const struct inet_connection_sock *icsk = inet_csk(sk); @@ -2145,7 +2183,8 @@ void tcp_send_active_reset(struct sock * TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); } -/* WARNING: This routine must only be called when we have already sent +/* Send a crossed SYN-ACK during socket establishment. + * WARNING: This routine must only be called when we have already sent * a SYN packet that crossed the incoming SYN that caused this routine * to get called. If this assumption fails then the initial rcv_wnd * and rcv_wscale values will not be correct. @@ -2493,6 +2532,8 @@ static int tcp_xmit_probe_skb(struct soc return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC); } +/* Initiate keepalive or window probe from timer. + */ int tcp_write_wakeup(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk);