Commit b3d14bff authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp ccid-2: Implementation of circular Ack Vector buffer with overflow handling 

This completes the implementation of a circular buffer for Ack Vectors, by
extending the current (linear array-based) implementation.  The changes are:

 (a) An `overflow' flag to deal with the case of overflow. As before, dynamic
     growth of the buffer will not be supported; but code will be added to deal
     robustly with overflowing Ack Vector buffers.

 (b) A `tail_seqno' field. When naively implementing the algorithm of Appendix A
     in RFC 4340, problems arise whenever subsequent Ack Vector records overlap,
     which can bring the entire run length calculation completely out of synch.
     (This is documented on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/\


                                             ack_vectors/tracking_tail_ackno/ .)
 (c) The buffer length is now computed dynamically (i.e. current fill level),
     as the span between head to tail.

As a result, dccp_ackvec_pending() is now simpler - the #ifdef is no longer
necessary since buf_empty is always true when IP_DCCP_ACKVEC is not configured.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 7d870936

net/dccp/ackvec.c

+30 −1
Original line number Diff line number Diff line
@@ -29,7 +29,7 @@ struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority) 
	struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);



	if (av != NULL) {

		av->av_buf_head	= DCCPAV_MAX_ACKVEC_LEN - 1;

		av->av_buf_head	= av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;

		INIT_LIST_HEAD(&av->av_records);

	}

	return av;
@@ -71,6 +71,14 @@ int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum) 
	avr->avr_ack_ackno  = av->av_buf_ackno;

	avr->avr_ack_nonce  = nonce_sum;

	avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);

	/*

	 * When the buffer overflows, we keep no more than one record. This is

	 * the simplest way of disambiguating sender-Acks dating from before the

	 * overflow from sender-Acks which refer to after the overflow; a simple

	 * solution is preferable here since we are handling an exception.

	 */

	if (av->av_overflow)

		dccp_ackvec_purge_records(av);

	/*

	 * Since GSS is incremented for each packet, the list is automatically

	 * arranged in descending order of @ack_seqno.
@@ -84,6 +92,27 @@ int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum) 
	return 0;

}



/*

 * Buffer index and length computation using modulo-buffersize arithmetic.

 * Note that, as pointers move from right to left, head is `before' tail.

 */

static inline u16 __ackvec_idx_add(const u16 a, const u16 b)

{

	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;

}



static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)

{

	return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);

}



u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)

{

	if (unlikely(av->av_overflow))

		return DCCPAV_MAX_ACKVEC_LEN;

	return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);

}



/*

 * If several packets are missing, the HC-Receiver may prefer to enter multiple

 * bytes with run length 0, rather than a single byte with a larger run length;

net/dccp/ackvec.h

+8 −2
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
 * the maximum size of a single Ack Vector. Setting %DCCPAV_NUM_ACKVECS to 1

 * will be sufficient for most cases of low Ack Ratios, using a value of 2 gives

 * more headroom if Ack Ratio is higher or when the sender acknowledges slowly.

 * The maximum value is bounded by the u16 types for indices and functions.

 */

#define DCCPAV_NUM_ACKVECS	2

#define DCCPAV_MAX_ACKVEC_LEN	(DCCP_SINGLE_OPT_MAXLEN * DCCPAV_NUM_ACKVECS)
@@ -55,8 +56,10 @@ static inline u8 dccp_ackvec_state(const u8 *cell) 
 * @av_buf_head:   head index; begin of live portion in @av_buf

 * @av_buf_tail:   tail index; first index _after_ the live portion in @av_buf

 * @av_buf_ackno:  highest seqno of acknowledgeable packet recorded in @av_buf

 * @av_tail_ackno: lowest  seqno of acknowledgeable packet recorded in @av_buf

 * @av_buf_nonce:  ECN nonce sums, each covering subsequent segments of up to

 *		   %DCCP_SINGLE_OPT_MAXLEN cells in the live portion of @av_buf

 * @av_overflow:   if 1 then buf_head == buf_tail indicates buffer wraparound

 * @av_records:	   list of %dccp_ackvec_record (Ack Vectors sent previously)

 * @av_veclen:	   length of the live portion of @av_buf

 */
@@ -65,7 +68,9 @@ struct dccp_ackvec { 
	u16			av_buf_head;

	u16			av_buf_tail;

	u64			av_buf_ackno:48;

	u64			av_tail_ackno:48;

	bool			av_buf_nonce[DCCPAV_NUM_ACKVECS];

	u8			av_overflow:1;

	struct list_head	av_records;

	u16			av_vec_len;

};
@@ -112,9 +117,10 @@ extern int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb, 
			     const u8 *value, const u8 len);



extern int  dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum);

extern u16  dccp_ackvec_buflen(const struct dccp_ackvec *av);



static inline int dccp_ackvec_pending(const struct dccp_ackvec *av)

static inline bool dccp_ackvec_is_empty(const struct dccp_ackvec *av)

{

	return av->av_vec_len;

	return av->av_overflow == 0 && av->av_buf_head == av->av_buf_tail;

}

#endif /* _ACKVEC_H */

net/dccp/dccp.h

+7 −4
Original line number Diff line number Diff line
@@ -457,12 +457,15 @@ static inline void dccp_update_gss(struct sock *sk, u64 seq) 
	dp->dccps_awh = dp->dccps_gss;

}



static inline int dccp_ackvec_pending(const struct sock *sk)

{

	return dccp_sk(sk)->dccps_hc_rx_ackvec != NULL &&

	       !dccp_ackvec_is_empty(dccp_sk(sk)->dccps_hc_rx_ackvec);

}



static inline int dccp_ack_pending(const struct sock *sk)

{

	const struct dccp_sock *dp = dccp_sk(sk);

	return (dp->dccps_hc_rx_ackvec != NULL &&

		dccp_ackvec_pending(dp->dccps_hc_rx_ackvec)) ||

	       inet_csk_ack_scheduled(sk);

	return dccp_ackvec_pending(sk) || inet_csk_ack_scheduled(sk);

}



extern int  dccp_feat_finalise_settings(struct dccp_sock *dp);

net/dccp/options.c

+5 −5
Original line number Diff line number Diff line
@@ -429,9 +429,10 @@ static int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb) 
{

	struct dccp_sock *dp = dccp_sk(sk);

	struct dccp_ackvec *av = dp->dccps_hc_rx_ackvec;

	const u16 buflen = dccp_ackvec_buflen(av);

	/* Figure out how many options do we need to represent the ackvec */

	const u8 nr_opts = DIV_ROUND_UP(av->av_vec_len, DCCP_SINGLE_OPT_MAXLEN);

	u16 len = av->av_vec_len + 2 * nr_opts;

	const u8 nr_opts = DIV_ROUND_UP(buflen, DCCP_SINGLE_OPT_MAXLEN);

	u16 len = buflen + 2 * nr_opts;

	u8 i, nonce = 0;

	const unsigned char *tail, *from;

	unsigned char *to;
@@ -442,7 +443,7 @@ static int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb) 
	DCCP_SKB_CB(skb)->dccpd_opt_len += len;



	to   = skb_push(skb, len);

	len  = av->av_vec_len;

	len  = buflen;

	from = av->av_buf + av->av_buf_head;

	tail = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;
@@ -580,8 +581,7 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb) 
			if (dccp_insert_option_timestamp(skb))

				return -1;



		} else if (dp->dccps_hc_rx_ackvec != NULL &&

			   dccp_ackvec_pending(dp->dccps_hc_rx_ackvec) &&

		} else if (dccp_ackvec_pending(sk) &&

			   dccp_insert_option_ackvec(sk, skb)) {

				return -1;

		}

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