sm_make_chunk.c

在linux环境下的流控制传输协议（sctp）的源代码

struct sctp_chunk *sctp_make_abort_no_data(
	const struct sctp_association *asoc,
	const struct sctp_chunk *chunk, __u32 tsn)
{
	struct sctp_chunk *retval;
	__be32 payload;

	retval = sctp_make_abort(asoc, chunk, sizeof(sctp_errhdr_t)
				 + sizeof(tsn));

	if (!retval)
		goto no_mem;

	/* Put the tsn back into network byte order.  */
	payload = htonl(tsn);
	sctp_init_cause(retval, SCTP_ERROR_NO_DATA, sizeof(payload));
	sctp_addto_chunk(retval, sizeof(payload), (const void *)&payload);

	/* RFC 2960 6.4 Multi-homed SCTP Endpoints
	 *
	 * An endpoint SHOULD transmit reply chunks (e.g., SACK,
	 * HEARTBEAT ACK, * etc.) to the same destination transport
	 * address from which it * received the DATA or control chunk
	 * to which it is replying.
	 *
	 * [ABORT back to where the offender came from.]
	 */
	if (chunk)
		retval->transport = chunk->transport;

no_mem:
	return retval;
}

/* Helper to create ABORT with a SCTP_ERROR_USER_ABORT error.  */
struct sctp_chunk *sctp_make_abort_user(const struct sctp_association *asoc,
					const struct msghdr *msg,
					size_t paylen)
{
	struct sctp_chunk *retval;
	void *payload = NULL;
	int err;

	retval = sctp_make_abort(asoc, NULL, sizeof(sctp_errhdr_t) + paylen);
	if (!retval)
		goto err_chunk;

	if (paylen) {
		/* Put the msg_iov together into payload.  */
		payload = kmalloc(paylen, GFP_KERNEL);
		if (!payload)
			goto err_payload;

		err = memcpy_fromiovec(payload, msg->msg_iov, paylen);
		if (err < 0)
			goto err_copy;
	}

	sctp_init_cause(retval, SCTP_ERROR_USER_ABORT, paylen);
	sctp_addto_chunk(retval, paylen, payload);

	if (paylen)
		kfree(payload);

	return retval;

err_copy:
	kfree(payload);
err_payload:
	sctp_chunk_free(retval);
	retval = NULL;
err_chunk:
	return retval;
}

/* Append bytes to the end of a parameter.  Will panic if chunk is not big
 * enough.
 */
static void *sctp_addto_param(struct sctp_chunk *chunk, int len,
			      const void *data)
{
	void *target;
	int chunklen = ntohs(chunk->chunk_hdr->length);

	target = skb_put(chunk->skb, len);

	memcpy(target, data, len);

	/* Adjust the chunk length field.  */
	chunk->chunk_hdr->length = htons(chunklen + len);
	chunk->chunk_end = skb_tail_pointer(chunk->skb);

	return target;
}

/* Make an ABORT chunk with a PROTOCOL VIOLATION cause code. */
struct sctp_chunk *sctp_make_abort_violation(
	const struct sctp_association *asoc,
	const struct sctp_chunk *chunk,
	const __u8   *payload,
	const size_t paylen)
{
	struct sctp_chunk  *retval;
	struct sctp_paramhdr phdr;

	retval = sctp_make_abort(asoc, chunk, sizeof(sctp_errhdr_t) + paylen
					+ sizeof(sctp_paramhdr_t));
	if (!retval)
		goto end;

	sctp_init_cause(retval, SCTP_ERROR_PROTO_VIOLATION, paylen
					+ sizeof(sctp_paramhdr_t));

	phdr.type = htons(chunk->chunk_hdr->type);
	phdr.length = chunk->chunk_hdr->length;
	sctp_addto_chunk(retval, paylen, payload);
	sctp_addto_param(retval, sizeof(sctp_paramhdr_t), &phdr);

end:
	return retval;
}

/* Make a HEARTBEAT chunk.  */
struct sctp_chunk *sctp_make_heartbeat(const struct sctp_association *asoc,
				  const struct sctp_transport *transport,
				  const void *payload, const size_t paylen)
{
	struct sctp_chunk *retval = sctp_make_chunk(asoc, SCTP_CID_HEARTBEAT,
						    0, paylen);

	if (!retval)
		goto nodata;

	/* Cast away the 'const', as this is just telling the chunk
	 * what transport it belongs to.
	 */
	retval->transport = (struct sctp_transport *) transport;
	retval->subh.hbs_hdr = sctp_addto_chunk(retval, paylen, payload);

nodata:
	return retval;
}

struct sctp_chunk *sctp_make_heartbeat_ack(const struct sctp_association *asoc,
				      const struct sctp_chunk *chunk,
				      const void *payload, const size_t paylen)
{
	struct sctp_chunk *retval;

	retval  = sctp_make_chunk(asoc, SCTP_CID_HEARTBEAT_ACK, 0, paylen);
	if (!retval)
		goto nodata;

	retval->subh.hbs_hdr = sctp_addto_chunk(retval, paylen, payload);

	/* RFC 2960 6.4 Multi-homed SCTP Endpoints
	 *
	 * An endpoint SHOULD transmit reply chunks (e.g., SACK,
	 * HEARTBEAT ACK, * etc.) to the same destination transport
	 * address from which it * received the DATA or control chunk
	 * to which it is replying.
	 *
	 * [HBACK back to where the HEARTBEAT came from.]
	 */
	if (chunk)
		retval->transport = chunk->transport;

nodata:
	return retval;
}

/* Create an Operation Error chunk with the specified space reserved.
 * This routine can be used for containing multiple causes in the chunk.
 */
static struct sctp_chunk *sctp_make_op_error_space(
	const struct sctp_association *asoc,
	const struct sctp_chunk *chunk,
	size_t size)
{
	struct sctp_chunk *retval;

	retval = sctp_make_chunk(asoc, SCTP_CID_ERROR, 0,
				 sizeof(sctp_errhdr_t) + size);
	if (!retval)
		goto nodata;

	/* RFC 2960 6.4 Multi-homed SCTP Endpoints
	 *
	 * An endpoint SHOULD transmit reply chunks (e.g., SACK,
	 * HEARTBEAT ACK, etc.) to the same destination transport
	 * address from which it received the DATA or control chunk
	 * to which it is replying.
	 *
	 */
	if (chunk)
		retval->transport = chunk->transport;

nodata:
	return retval;
}

/* Create an Operation Error chunk.  */
struct sctp_chunk *sctp_make_op_error(const struct sctp_association *asoc,
				 const struct sctp_chunk *chunk,
				 __be16 cause_code, const void *payload,
				 size_t paylen)
{
	struct sctp_chunk *retval;

	retval = sctp_make_op_error_space(asoc, chunk, paylen);
	if (!retval)
		goto nodata;

	sctp_init_cause(retval, cause_code, paylen);
	sctp_addto_chunk(retval, paylen, payload);

nodata:
	return retval;
}

struct sctp_chunk *sctp_make_auth(const struct sctp_association *asoc)
{
	struct sctp_chunk *retval;
	struct sctp_hmac *hmac_desc;
	struct sctp_authhdr auth_hdr;
	__u8 *hmac;

	/* Get the first hmac that the peer told us to use */
	hmac_desc = sctp_auth_asoc_get_hmac(asoc);
	if (unlikely(!hmac_desc))
		return NULL;

	retval = sctp_make_chunk(asoc, SCTP_CID_AUTH, 0,
			hmac_desc->hmac_len + sizeof(sctp_authhdr_t));
	if (!retval)
		return NULL;

	auth_hdr.hmac_id = htons(hmac_desc->hmac_id);
	auth_hdr.shkey_id = htons(asoc->active_key_id);

	retval->subh.auth_hdr = sctp_addto_chunk(retval, sizeof(sctp_authhdr_t),
						&auth_hdr);

	hmac = skb_put(retval->skb, hmac_desc->hmac_len);
	memset(hmac, 0, hmac_desc->hmac_len);

	/* Adjust the chunk header to include the empty MAC */
	retval->chunk_hdr->length =
		htons(ntohs(retval->chunk_hdr->length) + hmac_desc->hmac_len);
	retval->chunk_end = skb_tail_pointer(retval->skb);

	return retval;
}


/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* Turn an skb into a chunk.
 * FIXME: Eventually move the structure directly inside the skb->cb[].
 */
struct sctp_chunk *sctp_chunkify(struct sk_buff *skb,
			    const struct sctp_association *asoc,
			    struct sock *sk)
{
	struct sctp_chunk *retval;

	retval = kmem_cache_zalloc(sctp_chunk_cachep, GFP_ATOMIC);

	if (!retval)
		goto nodata;

	if (!sk) {
		SCTP_DEBUG_PRINTK("chunkifying skb %p w/o an sk\n", skb);
	}

	INIT_LIST_HEAD(&retval->list);
	retval->skb		= skb;
	retval->asoc		= (struct sctp_association *)asoc;
	retval->resent  	= 0;
	retval->has_tsn		= 0;
	retval->has_ssn         = 0;
	retval->rtt_in_progress	= 0;
	retval->sent_at		= 0;
	retval->singleton	= 1;
	retval->end_of_packet	= 0;
	retval->ecn_ce_done	= 0;
	retval->pdiscard	= 0;

	/* sctpimpguide-05.txt Section 2.8.2
	 * M1) Each time a new DATA chunk is transmitted
	 * set the 'TSN.Missing.Report' count for that TSN to 0. The
	 * 'TSN.Missing.Report' count will be used to determine missing chunks
	 * and when to fast retransmit.
	 */
	retval->tsn_missing_report = 0;
	retval->tsn_gap_acked = 0;
	retval->fast_retransmit = 0;

	/* If this is a fragmented message, track all fragments
	 * of the message (for SEND_FAILED).
	 */
	retval->msg = NULL;

	/* Polish the bead hole.  */
	INIT_LIST_HEAD(&retval->transmitted_list);
	INIT_LIST_HEAD(&retval->frag_list);
	SCTP_DBG_OBJCNT_INC(chunk);
	atomic_set(&retval->refcnt, 1);

nodata:
	return retval;
}

/* Set chunk->source and dest based on the IP header in chunk->skb.  */
void sctp_init_addrs(struct sctp_chunk *chunk, union sctp_addr *src,
		     union sctp_addr *dest)
{
	memcpy(&chunk->source, src, sizeof(union sctp_addr));
	memcpy(&chunk->dest, dest, sizeof(union sctp_addr));
}

/* Extract the source address from a chunk.  */
const union sctp_addr *sctp_source(const struct sctp_chunk *chunk)
{
	/* If we have a known transport, use that.  */
	if (chunk->transport) {
		return &chunk->transport->ipaddr;
	} else {
		/* Otherwise, extract it from the IP header.  */
		return &chunk->source;
	}
}

/* Create a new chunk, setting the type and flags headers from the
 * arguments, reserving enough space for a 'paylen' byte payload.
 */
SCTP_STATIC
struct sctp_chunk *sctp_make_chunk(const struct sctp_association *asoc,
				   __u8 type, __u8 flags, int paylen)
{
	struct sctp_chunk *retval;
	sctp_chunkhdr_t *chunk_hdr;
	struct sk_buff *skb;
	struct sock *sk;

	/* No need to allocate LL here, as this is only a chunk. */
	skb = alloc_skb(WORD_ROUND(sizeof(sctp_chunkhdr_t) + paylen),
			GFP_ATOMIC);
	if (!skb)
		goto nodata;

	/* Make room for the chunk header.  */
	chunk_hdr = (sctp_chunkhdr_t *)skb_put(skb, sizeof(sctp_chunkhdr_t));
	chunk_hdr->type	  = type;
	chunk_hdr->flags  = flags;
	chunk_hdr->length = htons(sizeof(sctp_chunkhdr_t));

	sk = asoc ? asoc->base.sk : NULL;
	retval = sctp_chunkify(skb, asoc, sk);
	if (!retval) {
		kfree_skb(skb);
		goto nodata;
	}

	retval->chunk_hdr = chunk_hdr;
	retval->chunk_end = ((__u8 *)chunk_hdr) + sizeof(struct sctp_chunkhdr);

	/* Determine if the chunk needs to be authenticated */
	if (sctp_auth_send_cid(type, asoc))
		retval->auth = 1;

	/* Set the skb to the belonging sock for accounting.  */
	skb->sk = sk;

	return retval;
nodata:
	return NULL;
}


/* Release the memory occupied by a chunk.  */
static void sctp_chunk_destroy(struct sctp_chunk *chunk)
{
	BUG_ON(!list_empty(&chunk->list));
	list_del_init(&chunk->transmitted_list);

	/* Free the chunk skb data and the SCTP_chunk stub itself. */
	dev_kfree_skb(chunk->skb);

	SCTP_DBG_OBJCNT_DEC(chunk);
	kmem_cache_free(sctp_chunk_cachep, chunk);
}

/* Possibly, free the chunk.  */
void sctp_chunk_free(struct sctp_chunk *chunk)
{
	/* Release our reference on the message tracker. */
	if (chunk->msg)
		sctp_datamsg_put(chunk->msg);

	sctp_chunk_put(chunk);
}

/* Grab a reference to the chunk. */
void sctp_chunk_hold(struct sctp_chunk *ch)
{
	atomic_inc(&ch->refcnt);
}

/* Release a reference to the chunk. */
void sctp_chunk_put(struct sctp_chunk *ch)
{
	if (atomic_dec_and_test(&ch->refcnt))
		sctp_chunk_destroy(ch);
}

/* Append bytes to the end of a chunk.  Will panic if chunk is not big
 * enough.
 */
void *sctp_addto_chunk(struct sctp_chunk *chunk, int len, const void *data)
{
	void *target;
	void *padding;
	int chunklen = ntohs(chunk->chunk_hdr->length);
	int padlen = WORD_ROUND(chunklen) - chunklen;

	padding = skb_put(chunk->skb, padlen);
	target = skb_put(chunk->skb, len);

	memset(padding, 0, padlen);
	memcpy(target, data, len);

	/* Adjust the chunk length field.  */
	chunk->chunk_hdr->length = htons(chunklen + padlen + len);
	chunk->chunk_end = skb_tail_pointer(chunk->skb);

	return target;
}

/* Append bytes from user space to the end of a chunk.  Will panic if
 * chunk is not big enough.
 * Returns a kernel err value.
 */
int sctp_user_addto_chunk(struct sctp_chunk *chunk, int off, int len,