From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: [PATCH] TCP: Add comments to (near) all functions in tcp_output.c v2 Date: Sat, 18 Jul 2009 12:31:59 +0200 Message-ID: <20090718103159.GB2682@basil.fritz.box> References: <20090717204004.GA516@basil.fritz.box> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andi Kleen , Netdev , David Miller To: Ilpo =?iso-8859-1?Q?J=E4rvinen?= Return-path: 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 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: 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 J=E4rvinen --- net/ipv4/tcp_output.c | 51 +++++++++++++++++++++++++++++++++++++++++= ++++----- 1 file changed, 46 insertions(+), 5 deletions(-) Index: linux-2.6.31-rc3-ak/net/ipv4/tcp_output.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- 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 =3D /* By default, RFC2861 behavior. */ int sysctl_tcp_slow_start_after_idle __read_mostly =3D 1; =20 +/* Account for new data that has been sent to the network. + */ static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *s= kb) { struct tcp_sock *tp =3D tcp_sk(sk); @@ -142,6 +144,8 @@ static void tcp_cwnd_restart(struct sock tp->snd_cwnd_used =3D 0; } =20 +/* 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; } =20 +/* 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 &=3D ~TCPCB_FLAG_CWR; @@ -283,6 +289,8 @@ static inline void TCP_ECN_send_synack(s TCP_SKB_CB(skb)->flags &=3D ~TCPCB_FLAG_ECE; } =20 +/* Packet ECN state for a SYN. + */ static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *s= kb) { struct tcp_sock *tp =3D tcp_sk(sk); @@ -301,6 +309,9 @@ TCP_ECN_make_synack(struct request_sock th->ece =3D 1; } =20 +/* 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 */ }; =20 -/* 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 he= re. * Luckily we can at least blame others for their non-compliance but f= rom * inter-operatibility perspective it seems that we're somewhat stuck = with @@ -445,6 +458,9 @@ static void tcp_options_write(__be32 *pt } } =20 +/* 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; } =20 +/* 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; } =20 +/* Compute TCP options for ESTABLISHED sockets. This is not the + * final wire format yet. + */ static unsigned tcp_established_options(struct sock *sk, struct sk_buf= f *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); } =20 -/* 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_f= rames, * otherwise socket can stall. @@ -909,6 +930,8 @@ static void __pskb_trim_head(struct sk_b skb->len =3D skb->data_len; } =20 +/* 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; } =20 -/* 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 =3D tcp_sk(sk); @@ -1143,7 +1168,8 @@ static inline unsigned int tcp_cwnd_test return 0; } =20 -/* 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; } =20 +/* Test if sending is allowed right now. + */ int tcp_may_send_now(struct sock *sk) { struct tcp_sock *tp =3D tcp_sk(sk); @@ -1378,6 +1406,10 @@ send_now: } =20 /* 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; } =20 +/* 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; } =20 +/* 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 =3D inet_csk(sk); @@ -2145,7 +2183,8 @@ void tcp_send_active_reset(struct sock * TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); } =20 -/* 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); } =20 +/* Initiate keepalive or window probe from timer. + */ int tcp_write_wakeup(struct sock *sk) { struct tcp_sock *tp =3D tcp_sk(sk);