lib: Support for rudimentary retransmission

This adds rudimentary support for sending and processing
acknowledgments and doing retransmission.

It replaces the generic timerwheel with a specific one for
retransmission. This is currently a fixed wheel allowing
retransmissions to be scheduled up to about 32 seconds into the
future. It currently has an 8ms resolution. This could be made
configurable in the future. Failures of the flow (i.e. rtx not
working) are indicated by the rxmwheel_move() function returning a fd.
This is currently not yet handled (maybe just setting the state of the
flow to FLOWDOWN is a better solution).

The shm_rdrbuff tracks the number of users of a du_buff. One user is
the full stack, each retransmission will increment the refs counter
(which effectively acts as a semaphore). The refs counter is
decremented when a packet is acked. The du_buff is only allowed to be
removed if there is only one user left (the "stack").

When a packet is retransmitted, it is copied in the rdrbuff. This is
to ensure integrity of the packet when multiple layers do
retransmission and it is passed down the stack again.

Signed-off-by: Dimitri Staessens <dimitri.staessens@ugent.be>
Signed-off-by: Sander Vrijders <sander.vrijders@ugent.be>

1 files changed, 38 insertions, 35 deletions

diff --git a/src/lib/frct.c b/src/lib/frct.c
index 296d5b2c..0f3173c5 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -42,8 +42,9 @@ struct frct_cr {
         bool     conf;
         uint8_t  cflags;
 
-        time_t   act;
-        time_t   inact;
+        time_t   rto;     /* ms */
+        time_t   act;     /* s */
+        time_t   inact;   /* s */
 };
 
 struct frcti {
@@ -57,16 +58,9 @@ struct frcti {
         struct frct_cr   rcv_cr;
 
         ssize_t          rq[RQ_SIZE];
-
-        struct timespec  rtt;
-
         pthread_rwlock_t lock;
 };
 
-struct {
-        struct timerwheel * tw;
-} frct;
-
 enum frct_flags {
         FRCT_DATA = 0x01, /* PDU carries data */
         FRCT_DRF  = 0x02, /* Data run flag    */
@@ -89,21 +83,7 @@ struct frct_pci {
         uint32_t ackno;
 } __attribute__((packed));
 
-static int frct_init(void)
-{
-        frct.tw = timerwheel_create(TW_RESOLUTION, TW_RESOLUTION * TW_ELEMENTS);
-        if (frct.tw == NULL)
-                return -1;
-
-        return 0;
-}
-
-static void frct_fini(void)
-{
-        assert(frct.tw);
-
-        timerwheel_destroy(frct.tw);
-}
+#include <rxmwheel.c>
 
 static struct frcti * frcti_create(int       fd,
                                    qoscube_t qc)
@@ -140,6 +120,8 @@ static struct frcti * frcti_create(int       fd,
         frcti->snd_cr.conf   = true;
         frcti->snd_cr.inact  = 3 * delta_t + 1;
         frcti->snd_cr.act    = now.tv_sec - (frcti->snd_cr.inact + 1);
+        /* Initial rto. FIXME: recalc using Karn algorithm. */
+        frcti->snd_cr.rto    = 120;
 
         frcti->rcv_cr.inact  = 2 * delta_t + 1;
         frcti->rcv_cr.act    = now.tv_sec - (frcti->rcv_cr.inact + 1);
@@ -159,6 +141,8 @@ static void frcti_destroy(struct frcti * frcti)
          * make sure everything is acked.
          */
 
+        rxmwheel_clear(frcti->fd);
+
         pthread_rwlock_destroy(&frcti->lock);
 
         free(frcti);
@@ -254,7 +238,7 @@ static void frct_add_crc(uint8_t * head,
 
 static struct frct_pci * frcti_alloc_head(struct shm_du_buff * sdb)
 {
-        struct frct_pci * pci = NULL;
+        struct frct_pci * pci;
 
         pci = (struct frct_pci *) shm_du_buff_head_alloc(sdb, FRCT_PCILEN);
         if (pci != NULL)
@@ -269,10 +253,14 @@ static int __frcti_snd(struct frcti *       frcti,
         struct frct_pci * pci;
         struct timespec   now;
         struct frct_cr *  snd_cr;
+        struct frct_cr *  rcv_cr;
 
         assert(frcti);
 
         snd_cr = &frcti->snd_cr;
+        rcv_cr = &frcti->rcv_cr;
+
+        rxmwheel_move();
 
         pci = frcti_alloc_head(sdb);
         if (pci == NULL)
@@ -310,7 +298,7 @@ static int __frcti_snd(struct frcti *       frcti,
         if (now.tv_sec - snd_cr->act > snd_cr->inact) {
                 /* There are no unacknowledged packets. */
                 assert(snd_cr->seqno == snd_cr->lwe);
-#ifdef OUROBOROS_CONFIG_DEBUG
+#ifdef CONFIG_OUROBOROS_DEBUG
                 frcti->snd_cr.seqno = 0;
 #else
                 random_buffer(&snd_cr->seqno, sizeof(snd_cr->seqno));
@@ -318,13 +306,16 @@ static int __frcti_snd(struct frcti *       frcti,
                 frcti->snd_cr.lwe = frcti->snd_cr.seqno;
         }
 
-        pci->seqno = hton32(snd_cr->seqno++);
-        if (!(snd_cr->cflags & FRCTFRTX))
-                snd_cr->lwe++;
-        else
-                /* TODO: update on ACK */
+        pci->seqno = hton32(snd_cr->seqno);
+        if (!(snd_cr->cflags & FRCTFRTX)) {
                 snd_cr->lwe++;
+        } else if (now.tv_sec - rcv_cr->act <= rcv_cr->inact) {
+                rxmwheel_add(frcti, snd_cr->seqno, sdb);
+                pci->flags |= FRCT_ACK;
+                pci->ackno = hton32(rcv_cr->lwe);
+        }
 
+        snd_cr->seqno++;
         snd_cr->act  = now.tv_sec;
         snd_cr->conf = false;
 
@@ -340,6 +331,7 @@ static int __frcti_rcv(struct frcti *       frcti,
         ssize_t           idx;
         struct frct_pci * pci;
         struct timespec   now;
+        struct frct_cr *  snd_cr;
         struct frct_cr *  rcv_cr;
         uint32_t          seqno;
         int               ret = 0;
@@ -347,6 +339,7 @@ static int __frcti_rcv(struct frcti *       frcti,
         assert(frcti);
 
         rcv_cr = &frcti->rcv_cr;
+        snd_cr = &frcti->snd_cr;
 
         pci = (struct frct_pci *) shm_du_buff_head_release(sdb, FRCT_PCILEN);
 
@@ -369,18 +362,18 @@ static int __frcti_rcv(struct frcti *       frcti,
         if (now.tv_sec - rcv_cr->act > rcv_cr->inact) {
                 /* Inactive receiver, check for DRF. */
                 if (pci->flags & FRCT_DRF) /* New run. */
-                        rcv_cr->lwe = seqno;
+                        rcv_cr->lwe = seqno - 1;
                 else
                         goto drop_packet;
         }
 
-        if (seqno == rcv_cr->lwe) {
-                ++rcv_cr->lwe;
+        if (seqno == rcv_cr->lwe + 1) {
+                rcv_cr->lwe = seqno;
                 /* Check for online reconfiguration. */
                 if (pci->flags & FRCT_CFG)
                         rcv_cr->cflags = pci->cflags;
         } else { /* Out of order. */
-                if ((int32_t)(seqno - rcv_cr->lwe) < 0) /* Duplicate. */
+                if ((int32_t)(seqno - rcv_cr->lwe) <= 0) /* Duplicate. */
                         goto drop_packet;
 
                 if (rcv_cr->cflags & FRCTFRTX) {
@@ -396,6 +389,13 @@ static int __frcti_rcv(struct frcti *       frcti,
                 }
         }
 
+        if (rcv_cr->cflags & FRCTFRTX && pci->flags & FRCT_ACK) {
+                uint32_t ackno = ntoh32(pci->ackno);
+                /* Check for duplicate (old) acks. */
+                if ((int32_t)(ackno - snd_cr->lwe) >= 0)
+                        snd_cr->lwe = ackno;
+        }
+
         rcv_cr->act = now.tv_sec;
 
         if (!(pci->flags & FRCT_DATA))
@@ -403,10 +403,13 @@ static int __frcti_rcv(struct frcti *       frcti,
 
         pthread_rwlock_unlock(&frcti->lock);
 
+        rxmwheel_move();
+
         return ret;
 
  drop_packet:
         shm_rdrbuff_remove(ai.rdrb, idx);
         pthread_rwlock_unlock(&frcti->lock);
+        rxmwheel_move();
         return -EAGAIN;
 }