output.c

一种在UDP协议中实现了拥赛控制和重传机制的协议

/* SCTP kernel reference Implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 *
 * This file is part of the SCTP kernel reference Implementation
 *
 * These functions handle output processing.
 *
 * The SCTP reference implementation is free software;
 * you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * The SCTP reference implementation is distributed in the hope that it
 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
 *                 ************************
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[e-mail]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[e-mail]>
 *    Karl Knutson          <[e-mail]>
 *    Jon Grimm             <[e-mail]>
 *    Sridhar Samudrala     <[e-mail]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/time.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/init.h>
#include <net/inet_ecn.h>
#include <net/icmp.h>

#ifndef TEST_FRAME
#include <net/tcp.h>
#endif /* TEST_FRAME (not defined) */

#include <linux/socket.h> /* for sa_family_t */
#include <net/sock.h>

#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

/* Forward declarations for private helpers. */
static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
					   struct sctp_chunk *chunk);

/* Config a packet.
 * This appears to be a followup set of initializations.
 */
struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
				       __u32 vtag, int ecn_capable)
{
	struct sctp_chunk *chunk = NULL;

	SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __FUNCTION__,
			  packet, vtag);

	packet->vtag = vtag;
	packet->has_cookie_echo = 0;
	packet->has_sack = 0;
	packet->ipfragok = 0;

	if (ecn_capable && sctp_packet_empty(packet)) {
		chunk = sctp_get_ecne_prepend(packet->transport->asoc);

		/* If there a is a prepend chunk stick it on the list before
	 	 * any other chunks get appended.
	 	 */
		if (chunk)
			sctp_packet_append_chunk(packet, chunk);
	}

	return packet;
}

/* Initialize the packet structure. */
struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
				     struct sctp_transport *transport,
				     __u16 sport, __u16 dport)
{
	struct sctp_association *asoc = transport->asoc;
	size_t overhead;

	SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __FUNCTION__,
			  packet, transport);

	packet->transport = transport;
	packet->source_port = sport;
	packet->destination_port = dport;
	skb_queue_head_init(&packet->chunks);
	if (asoc) {
		struct sctp_sock *sp = sctp_sk(asoc->base.sk);	
		overhead = sp->pf->af->net_header_len; 
	} else {
		overhead = sizeof(struct ipv6hdr);
	}
	overhead += sizeof(struct sctphdr);
	packet->overhead = overhead;
	packet->size = overhead;
	packet->vtag = 0;
	packet->has_cookie_echo = 0;
	packet->has_sack = 0;
	packet->ipfragok = 0;
	packet->malloced = 0;
	return packet;
}

/* Free a packet.  */
void sctp_packet_free(struct sctp_packet *packet)
{
	struct sctp_chunk *chunk;

	SCTP_DEBUG_PRINTK("%s: packet:%p\n", __FUNCTION__, packet);

        while ((chunk = (struct sctp_chunk *)__skb_dequeue(&packet->chunks)) != NULL)
		sctp_chunk_free(chunk);

	if (packet->malloced)
		kfree(packet);
}

/* This routine tries to append the chunk to the offered packet. If adding
 * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 * is not present in the packet, it transmits the input packet.
 * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 * as it can fit in the packet, but any more data that does not fit in this
 * packet can be sent only after receiving the COOKIE_ACK.
 */
sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
				       struct sctp_chunk *chunk)
{
	sctp_xmit_t retval;
	int error = 0;

	SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __FUNCTION__,
			  packet, chunk);

	switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
	case SCTP_XMIT_PMTU_FULL:
		if (!packet->has_cookie_echo) {
			error = sctp_packet_transmit(packet);
			if (error < 0)
				chunk->skb->sk->sk_err = -error;

			/* If we have an empty packet, then we can NOT ever
			 * return PMTU_FULL.
			 */
			retval = sctp_packet_append_chunk(packet, chunk);
		}
		break;

	case SCTP_XMIT_RWND_FULL:
	case SCTP_XMIT_OK:
	case SCTP_XMIT_NAGLE_DELAY:
		break;
	};

	return retval;
}

/* Try to bundle a SACK with the packet. */
static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
					   struct sctp_chunk *chunk)
{
	sctp_xmit_t retval = SCTP_XMIT_OK;

	/* If sending DATA and haven't aleady bundled a SACK, try to
	 * bundle one in to the packet.
	 */
	if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
	    !pkt->has_cookie_echo) {
		struct sctp_association *asoc;
		asoc = pkt->transport->asoc;

		if (asoc->a_rwnd > asoc->rwnd) {
			struct sctp_chunk *sack;
			asoc->a_rwnd = asoc->rwnd;
			sack = sctp_make_sack(asoc);
			if (sack) {
				struct timer_list *timer;
				retval = sctp_packet_append_chunk(pkt, sack);
				asoc->peer.sack_needed = 0;
				timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
				if (timer_pending(timer) && del_timer(timer))
					sctp_association_put(asoc);
			}
		}
	}
	return retval;
}

/* Append a chunk to the offered packet reporting back any inability to do
 * so.
 */
sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
				     struct sctp_chunk *chunk)
{
	sctp_xmit_t retval = SCTP_XMIT_OK;
	__u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
	size_t psize;
	size_t pmtu;
	int too_big;

	SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __FUNCTION__, packet,
			  chunk);

	retval = sctp_packet_bundle_sack(packet, chunk);
	psize = packet->size;

	if (retval != SCTP_XMIT_OK)
		goto finish;

	pmtu  = ((packet->transport->asoc) ?
		 (packet->transport->asoc->pmtu) :
		 (packet->transport->pmtu));

	too_big = (psize + chunk_len > pmtu);

	/* Decide if we need to fragment or resubmit later. */
	if (too_big) {
		/* Both control chunks and data chunks with TSNs are
		 * non-fragmentable.
		 */
		if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk)) {
			/* We no longer do re-fragmentation.
			 * Just fragment at the IP layer, if we
			 * actually hit this condition
			 */
			packet->ipfragok = 1;
			goto append;

		} else {
			retval = SCTP_XMIT_PMTU_FULL;
			goto finish;
		}
	}

append:
	/* We believe that this chunk is OK to add to the packet (as
	 * long as we have the cwnd for it).
	 */

	/* DATA is a special case since we must examine both rwnd and cwnd
	 * before we send DATA.
	 */
	if (sctp_chunk_is_data(chunk)) {
		retval = sctp_packet_append_data(packet, chunk);
		/* Disallow SACK bundling after DATA. */
		packet->has_sack = 1;
		if (SCTP_XMIT_OK != retval)
			goto finish;
	} else if (SCTP_CID_COOKIE_ECHO == chunk->chunk_hdr->type)
		packet->has_cookie_echo = 1;
	else if (SCTP_CID_SACK == chunk->chunk_hdr->type)
		packet->has_sack = 1;

	/* It is OK to send this chunk.  */
	__skb_queue_tail(&packet->chunks, (struct sk_buff *)chunk);
	packet->size += chunk_len;
	chunk->transport = packet->transport;
finish:
	return retval;
}

/* All packets are sent to the network through this function from
 * sctp_outq_tail().
 *
 * The return value is a normal kernel error return value.
 */
int sctp_packet_transmit(struct sctp_packet *packet)
{
	struct sctp_transport *tp = packet->transport;
	struct sctp_association *asoc = tp->asoc;
	struct sctphdr *sh;
	__u32 crc32;
	struct sk_buff *nskb;
	struct sctp_chunk *chunk;
	struct sock *sk;
	int err = 0;
	int padding;		/* How much padding do we need?  */
	__u8 has_data = 0;
	struct dst_entry *dst;

	SCTP_DEBUG_PRINTK("%s: packet:%p\n", __FUNCTION__, packet);

	/* Do NOT generate a chunkless packet. */
	chunk = (struct sctp_chunk *)skb_peek(&packet->chunks);
	if (unlikely(!chunk))
		return err;

	/* Set up convenience variables... */
	sk = chunk->skb->sk;

	/* Allocate the new skb.  */
	nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
	if (!nskb)
		goto nomem;

	/* Make sure the outbound skb has enough header room reserved. */
	skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);

	/* Set the owning socket so that we know where to get the
	 * destination IP address.