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Commit 67edfef7 authored by Andi Kleen's avatar Andi Kleen Committed by David S. Miller
Browse files

TCP: Add comments to (near) all functions in tcp_output.c v3 



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.
v3: Change style of one liner comments, add a few more comments.

Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
Acked-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 40d4e3df

net/ipv4/tcp_output.c

+44 −14
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ int sysctl_tcp_base_mss __read_mostly = 512; 
/* 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 +143,7 @@ static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst) 
	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)

{
@@ -161,6 +163,7 @@ static void tcp_event_data_sent(struct tcp_sock *tp, 
		icsk->icsk_ack.pingpong = 1;

}



/* Account for an ACK we sent. */

static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)

{

	tcp_dec_quickack_mode(sk, pkts);
@@ -276,6 +279,7 @@ static u16 tcp_select_window(struct sock *sk) 
	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 +287,7 @@ static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb) 
		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 +306,9 @@ TCP_ECN_make_synack(struct request_sock *req, struct tcphdr *th) 
		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 +370,9 @@ 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 +455,9 @@ static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp, 
	}

}



/* 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 +506,7 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb, 
	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 +555,9 @@ static unsigned tcp_synack_options(struct sock *sk, 
	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 +722,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, 
	return net_xmit_eval(err);

}



/* This routine just queue's the buffer

/* This routine just queues the buffer for sending.

 *

 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,

 * otherwise socket can stall.
@@ -722,6 +739,7 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) 
	sk_mem_charge(sk, skb->truesize);

}



/* Initialize TSO segments for a packet. */

static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,

				 unsigned int mss_now)

{
@@ -909,6 +927,7 @@ static void __pskb_trim_head(struct sk_buff *skb, int len) 
	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 +956,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) 
	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);
@@ -981,6 +1000,7 @@ int tcp_mss_to_mtu(struct sock *sk, int mss) 
	return mtu;

}



/* MTU probing init per socket */

void tcp_mtup_init(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);
@@ -1143,7 +1163,8 @@ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, 
	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,
@@ -1158,6 +1179,7 @@ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, 
	return tso_segs;

}



/* Minshall's variant of the Nagle send check. */

static inline int tcp_minshall_check(const struct tcp_sock *tp)

{

	return after(tp->snd_sml, tp->snd_una) &&
@@ -1242,6 +1264,7 @@ static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb, 
	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 +1401,10 @@ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb) 
}



/* 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
@@ -1790,6 +1817,7 @@ static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) 
	sk_wmem_free_skb(sk, next_skb);

}



/* Check if coalescing SKBs is legal. */

static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)

{

	if (tcp_skb_pcount(skb) > 1)
@@ -1808,6 +1836,9 @@ static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb) 
	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 +1988,9 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) 
	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 +2179,8 @@ void tcp_send_active_reset(struct sock *sk, gfp_t priority) 
	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.
@@ -2180,9 +2215,7 @@ int tcp_send_synack(struct sock *sk) 
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);

}



/*

 * Prepare a SYN-ACK.

 */

/* Prepare a SYN-ACK. */

struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,

				struct request_sock *req)

{
@@ -2269,9 +2302,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst, 
	return skb;

}



/*

 * Do all connect socket setups that can be done AF independent.

 */

/* Do all connect socket setups that can be done AF independent. */

static void tcp_connect_init(struct sock *sk)

{

	struct dst_entry *dst = __sk_dst_get(sk);
@@ -2330,9 +2361,7 @@ static void tcp_connect_init(struct sock *sk) 
	tcp_clear_retrans(tp);

}



/*

 * Build a SYN and send it off.

 */

/* Build a SYN and send it off. */

int tcp_connect(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);
@@ -2493,6 +2522,7 @@ static int tcp_xmit_probe_skb(struct sock *sk, int urgent) 
	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);