dccp ccid-2: Separate option parsing from CCID processing

This patch replaces an almost identical replication of code: large parts
of dccp_parse_options() re-appeared as ccid2_ackvector() in ccid2.c.

Apart from the duplication, this caused two more problems:
 1. CCIDs should not need to be concerned with parsing header options;
 2. one can not assume that Ack Vectors appear as a contiguous area within an
    skb, it is legal to insert other options and/or padding in between. The
    current code would throw an error and stop reading in such a case.

The patch provides a new data structure and associated list housekeeping.

Only small changes were necessary to integrate with CCID-2: data structure
initialisation, adapt list traversal routine, and add call to the provided
cleanup routine.

The latter also lead to fixing the following BUG: CCID-2 so far ignored
Ack Vectors on all packets other than Ack/DataAck, which is incorrect,
since Ack Vectors can be present on any packet that has an Ack field.

Details:
--------
 * received Ack Vectors are parsed by dccp_parse_options() alone, which passes
   the result on to the CCID-specific routine ccid_hc_tx_parse_options();
 * CCIDs interested in using/decoding Ack Vector information will add code
   to fetch parsed Ack Vectors via this interface;
 * a data structure, `struct dccp_ackvec_parsed' is provided as interface;
 * this structure arranges Ack Vectors of the same skb into a FIFO order;
 * a doubly-linked list is used to keep the required FIFO code small.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

2 files changed, 44 insertions, 93 deletions

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 813d5cd40e8b..bbf16b35734d 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -317,68 +317,6 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
 #endif
 }
 
-/* XXX Lame code duplication!
- * returns -1 if none was found.
- * else returns the next offset to use in the function call.
- */
-static int ccid2_ackvector(struct sock *sk, struct sk_buff *skb, int offset,
-                           unsigned char **vec, unsigned char *veclen)
-{
-        const struct dccp_hdr *dh = dccp_hdr(skb);
-        unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
-        unsigned char *opt_ptr;
-        const unsigned char *opt_end = (unsigned char *)dh +
-                                        (dh->dccph_doff * 4);
-        unsigned char opt, len;
-        unsigned char *value;
-
-        BUG_ON(offset < 0);
-        options += offset;
-        opt_ptr = options;
-        if (opt_ptr >= opt_end)
-                return -1;
-
-        while (opt_ptr != opt_end) {
-                opt   = *opt_ptr++;
-                len   = 0;
-                value = NULL;
-
-                /* Check if this isn't a single byte option */
-                if (opt > DCCPO_MAX_RESERVED) {
-                        if (opt_ptr == opt_end)
-                                goto out_invalid_option;
-
-                        len = *opt_ptr++;
-                        if (len < 3)
-                                goto out_invalid_option;
-                        /*
-                         * Remove the type and len fields, leaving
-                         * just the value size
-                         */
-                        len     -= 2;
-                        value   = opt_ptr;
-                        opt_ptr += len;
-
-                        if (opt_ptr > opt_end)
-                                goto out_invalid_option;
-                }
-
-                switch (opt) {
-                case DCCPO_ACK_VECTOR_0:
-                case DCCPO_ACK_VECTOR_1:
-                        *vec    = value;
-                        *veclen = len;
-                        return offset + (opt_ptr - options);
-                }
-        }
-
-        return -1;
-
-out_invalid_option:
-        DCCP_BUG("Invalid option - this should not happen (previous parsing)!");
-        return -1;
-}
-
 static void ccid2_hc_tx_kill_rto_timer(struct sock *sk)
 {
         struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
@@ -499,15 +437,27 @@ static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
                 ccid2_change_l_ack_ratio(sk, hctx->cwnd);
 }
 
+static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
+                                     u8 option, u8 *optval, u8 optlen)
+{
+        struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
+
+        switch (option) {
+        case DCCPO_ACK_VECTOR_0:
+        case DCCPO_ACK_VECTOR_1:
+                return dccp_ackvec_parsed_add(&hctx->av_chunks, optval, optlen,
+                                              option - DCCPO_ACK_VECTOR_0);
+        }
+        return 0;
+}
+
 static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
         struct dccp_sock *dp = dccp_sk(sk);
         struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
+        struct dccp_ackvec_parsed *avp;
         u64 ackno, seqno;
         struct ccid2_seq *seqp;
-        unsigned char *vector;
-        unsigned char veclen;
-        int offset = 0;
         int done = 0;
         unsigned int maxincr = 0;
 
@@ -542,17 +492,12 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
         }
 
         /* check forward path congestion */
-        /* still didn't send out new data packets */
-        if (hctx->seqh == hctx->seqt)
+        if (dccp_packet_without_ack(skb))
                 return;
 
-        switch (DCCP_SKB_CB(skb)->dccpd_type) {
-        case DCCP_PKT_ACK:
-        case DCCP_PKT_DATAACK:
-                break;
-        default:
-                return;
-        }
+        /* still didn't send out new data packets */
+        if (hctx->seqh == hctx->seqt)
+                goto done;
 
         ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
         if (after48(ackno, hctx->high_ack))
@@ -576,15 +521,16 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                 maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);
 
         /* go through all ack vectors */
-        while ((offset = ccid2_ackvector(sk, skb, offset,
-                                         &vector, &veclen)) != -1) {
+        list_for_each_entry(avp, &hctx->av_chunks, node) {
                 /* go through this ack vector */
-                while (veclen--) {
-                        u64 ackno_end_rl = SUB48(ackno, dccp_ackvec_runlen(vector));
+                for (; avp->len--; avp->vec++) {
+                        u64 ackno_end_rl = SUB48(ackno,
+                                                 dccp_ackvec_runlen(avp->vec));
 
-                        ccid2_pr_debug("ackvec start:%llu end:%llu\n",
+                        ccid2_pr_debug("ackvec %llu |%u,%u|\n",
                                        (unsigned long long)ackno,
-                                       (unsigned long long)ackno_end_rl);
+                                       dccp_ackvec_state(avp->vec) >> 6,
+                                       dccp_ackvec_runlen(avp->vec));
                         /* if the seqno we are analyzing is larger than the
                          * current ackno, then move towards the tail of our
                          * seqnos.
@@ -603,7 +549,7 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                          * run length
                          */
                         while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
-                                const u8 state = dccp_ackvec_state(vector);
+                                const u8 state = dccp_ackvec_state(avp->vec);
 
                                 /* new packet received or marked */
                                 if (state != DCCPAV_NOT_RECEIVED &&
@@ -630,7 +576,6 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                                 break;
 
                         ackno = SUB48(ackno_end_rl, 1);
-                        vector++;
                 }
                 if (done)
                         break;
@@ -694,6 +639,8 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
         }
 
         ccid2_hc_tx_check_sanity(hctx);
+done:
+        dccp_ackvec_parsed_cleanup(&hctx->av_chunks);
 }
 
 static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
@@ -727,6 +674,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
         hctx->rpdupack  = -1;
         hctx->last_cong = jiffies;
         setup_timer(&hctx->rtotimer, ccid2_hc_tx_rto_expire, (unsigned long)sk);
+        INIT_LIST_HEAD(&hctx->av_chunks);
 
         ccid2_hc_tx_check_sanity(hctx);
         return 0;
@@ -762,17 +710,18 @@ static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
 }
 
 static struct ccid_operations ccid2 = {
-        .ccid_id                = DCCPC_CCID2,
-        .ccid_name              = "TCP-like",
-        .ccid_owner             = THIS_MODULE,
-        .ccid_hc_tx_obj_size    = sizeof(struct ccid2_hc_tx_sock),
-        .ccid_hc_tx_init        = ccid2_hc_tx_init,
-        .ccid_hc_tx_exit        = ccid2_hc_tx_exit,
-        .ccid_hc_tx_send_packet = ccid2_hc_tx_send_packet,
-        .ccid_hc_tx_packet_sent = ccid2_hc_tx_packet_sent,
-        .ccid_hc_tx_packet_recv = ccid2_hc_tx_packet_recv,
-        .ccid_hc_rx_obj_size    = sizeof(struct ccid2_hc_rx_sock),
-        .ccid_hc_rx_packet_recv = ccid2_hc_rx_packet_recv,
+        .ccid_id                  = DCCPC_CCID2,
+        .ccid_name                = "TCP-like",
+        .ccid_owner               = THIS_MODULE,
+        .ccid_hc_tx_obj_size      = sizeof(struct ccid2_hc_tx_sock),
+        .ccid_hc_tx_init          = ccid2_hc_tx_init,
+        .ccid_hc_tx_exit          = ccid2_hc_tx_exit,
+        .ccid_hc_tx_send_packet   = ccid2_hc_tx_send_packet,
+        .ccid_hc_tx_packet_sent   = ccid2_hc_tx_packet_sent,
+        .ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
+        .ccid_hc_tx_packet_recv   = ccid2_hc_tx_packet_recv,
+        .ccid_hc_rx_obj_size      = sizeof(struct ccid2_hc_rx_sock),
+        .ccid_hc_rx_packet_recv   = ccid2_hc_rx_packet_recv,
 };
 
 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
index d7815804bceb..907deed255b4 100644
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -47,6 +47,7 @@ struct ccid2_seq {
  * @lastrtt: time RTT was last measured
  * @rpseq: last consecutive seqno
  * @rpdupack: dupacks since rpseq
+ * @av_chunks: list of Ack Vectors received on current skb
  */
 struct ccid2_hc_tx_sock {
         u32                     cwnd;
@@ -66,6 +67,7 @@ struct ccid2_hc_tx_sock {
         int                     rpdupack;
         unsigned long           last_cong;
         u64                     high_ack;
+        struct list_head        av_chunks;
 };
 
 struct ccid2_hc_rx_sock {