lib: Simplify delta-t logic

This revises the delta-t implementation to align with Watson's timer
specifications. FRCT will never deliver out-of-order packets. A raw
flow (without delta-t state machine) will be able to provide such a
service.

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

3 files changed, 56 insertions, 58 deletions

diff --git a/doc/man/fccntl.3 b/doc/man/fccntl.3
index bec506ec..543a6bb6 100644
--- a/doc/man/fccntl.3
+++ b/doc/man/fccntl.3
@@ -83,8 +83,6 @@ argument. Supported flags are:
 
 \fIFRCTFERRCHCK\fR  - enable checksum (CRC32).
 
-\fIFRCTFORDERING\fR - enable packet in-order delivery.
-
 \fIFRCTFPARTIAL\fR  - enable partial delivery.
 
 .RE
diff --git a/include/ouroboros/fccntl.h b/include/ouroboros/fccntl.h
index 5c3fc064..bc7c7206 100644
--- a/include/ouroboros/fccntl.h
+++ b/include/ouroboros/fccntl.h
@@ -48,8 +48,7 @@
 #define FRCTFRESCNTRL 00000001 /* Feedback from receiver */
 #define FRCTFRTX      00000002 /* Reliable flow          */
 #define FRCTFERRCHCK  00000004 /* Check for errors       */
-#define FRCTFORDERING 00000010 /* Ordered delivery       */
-#define FRCTFPARTIAL  00000020 /* Allow partial delivery */
+#define FRCTFPARTIAL  00000010 /* Allow partial delivery */
 
 /* Flow operations */
 #define FLOWSRCVTIMEO 00000001 /* Set read timeout       */
diff --git a/src/lib/frct.c b/src/lib/frct.c
index 2eb79fb4..395fa2d8 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -56,7 +56,7 @@ struct frcti {
         struct frct_cr   snd_cr;
         struct frct_cr   rcv_cr;
 
-        size_t           rq[RQ_SIZE];
+        ssize_t          rq[RQ_SIZE];
 
         struct timespec  rtt;
 
@@ -107,20 +107,25 @@ static void frct_fini(void)
 
 static struct frcti * frcti_create(int fd)
 {
-        struct frcti * frcti;
-        time_t         delta_t;
-        ssize_t        idx;
+        struct frcti *  frcti;
+        time_t          delta_t;
+        ssize_t         idx;
+        struct timespec now;
 
         frcti = malloc(sizeof(*frcti));
         if (frcti == NULL)
                 goto fail_malloc;
 
+        memset(frcti, 0, sizeof(*frcti));
+
         if (pthread_rwlock_init(&frcti->lock, NULL))
                 goto fail_lock;
 
         for (idx = 0; idx < RQ_SIZE; ++idx)
                 frcti->rq[idx] = -1;
 
+        clock_gettime(CLOCK_REALTIME_COARSE, &now);
+
         frcti->mpl = DELT_MPL;
         frcti->a   = DELT_A;
         frcti->r   = DELT_R;
@@ -128,23 +133,12 @@ static struct frcti * frcti_create(int fd)
 
         delta_t = (frcti->mpl + frcti->a + frcti->r) / 1000;
 
-        frcti->snd_cr.drf    = true;
         frcti->snd_cr.conf   = true;
-#ifdef OUROBOROS_CONFIG_DEBUG
-        frcti->snd_cr.seqno  = 0;
-#else
-        random_buffer(&frcti->snd_cr.seqno, sizeof(frcti->snd_cr.seqno));
-#endif
-        frcti->snd_cr.lwe    = 0;
-        frcti->snd_cr.rwe    = 0;
-        frcti->snd_cr.cflags = 0;
         frcti->snd_cr.inact  = 3 * delta_t + 1;
+        frcti->snd_cr.act    = now.tv_sec - (frcti->snd_cr.inact + 1);
 
-        frcti->rcv_cr.drf    = true;
-        frcti->rcv_cr.lwe    = 0;
-        frcti->rcv_cr.rwe    = 0;
-        frcti->rcv_cr.cflags = 0;
         frcti->rcv_cr.inact  = 2 * delta_t + 1;
+        frcti->rcv_cr.act    = now.tv_sec - (frcti->rcv_cr.inact + 1);
 
         return frcti;
 
@@ -226,10 +220,8 @@ static ssize_t __frcti_queued_pdu(struct frcti * frcti)
 
                 sdb = shm_rdrbuff_get(ai.rdrb, idx);
                 pci = (struct frct_pci *) shm_du_buff_head(sdb) - 1;
-                if (pci->flags & FRCT_CFG) {
-                        assert(pci->flags & FRCT_DRF);
+                if (pci->flags & FRCT_CFG)
                         frcti->rcv_cr.cflags = pci->cflags;
-                }
 
                 ++frcti->rcv_cr.lwe;
                 frcti->rq[pos] = -1;
@@ -286,23 +278,8 @@ static int __frcti_snd(struct frcti *       frcti,
 
         pthread_rwlock_wrlock(&frcti->lock);
 
-        /* Check if sender is inactive. */
-        if (!snd_cr->drf && now.tv_sec - snd_cr->act > snd_cr->inact)
-                snd_cr->drf = true;
-
         pci->flags |= FRCT_DATA;
 
-        /* Set the DRF in the first packet of a new run of SDUs. */
-        if (snd_cr->drf) {
-                pci->flags |= FRCT_DRF;
-                if (snd_cr->conf) {
-                        pci->flags |= FRCT_CFG;
-                        pci->cflags = snd_cr->cflags;
-                }
-        }
-
-        pci->seqno = hton32(snd_cr->seqno++);
-
         if (snd_cr->cflags & FRCTFERRCHCK) {
                 uint8_t * tail = shm_du_buff_tail_alloc(sdb, FRCT_CRCLEN);
                 if (tail == NULL) {
@@ -315,9 +292,33 @@ static int __frcti_snd(struct frcti *       frcti,
                 pci->flags |= FRCT_CRC;
         }
 
-        snd_cr->act = now.tv_sec;
+        /* Set DRF if there are no unacknowledged packets. */
+        if (snd_cr->seqno == snd_cr->lwe)
+                pci->flags |= FRCT_DRF;
+
+        if (snd_cr->conf) {
+                /* FIXME: This packet must be acked! */
+                pci->flags |= FRCT_CFG;
+                pci->cflags = snd_cr->cflags;
+        }
+
+        /* Choose a new sequence number if sender inactivity expired. */
+        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
+                frcti->snd_cr.seqno = 0;
+#else
+                random_buffer(&snd_cr->seqno, sizeof(snd_cr->seqno));
+#endif
+                frcti->snd_cr.lwe = frcti->snd_cr.seqno;
+        }
+
+        pci->seqno = hton32(snd_cr->seqno++);
+        if (!(snd_cr->cflags & FRCTFRTX))
+                snd_cr->lwe++;
 
-        snd_cr->drf  = false;
+        snd_cr->act  = now.tv_sec;
         snd_cr->conf = false;
 
         pthread_rwlock_unlock(&frcti->lock);
@@ -354,13 +355,10 @@ static int __frcti_rcv(struct frcti *       frcti,
                         goto drop_packet;
         }
 
-        /* Check if receiver inactivity is true. */
-        if (!rcv_cr->drf && now.tv_sec - rcv_cr->act > rcv_cr->inact)
-                rcv_cr->drf = true;
-
         seqno = ntoh32(pci->seqno);
 
-        if (rcv_cr->drf) {
+        /* Check if receiver inactivity is true. */
+        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;
@@ -368,24 +366,27 @@ static int __frcti_rcv(struct frcti *       frcti,
                         goto drop_packet;
         }
 
-        /* Queue the PDU if needed. */
-        if (rcv_cr->cflags & FRCTFORDERING) {
-                if (seqno < rcv_cr->lwe || seqno > rcv_cr->lwe + RQ_SIZE)
+        if (seqno == rcv_cr->lwe) {
+                ++rcv_cr->lwe;
+                /* Check for online reconfiguration. */
+                if (pci->flags & FRCT_CFG)
+                        rcv_cr->cflags = pci->cflags;
+        } else { /* Out of order. */
+                if (seqno < rcv_cr->lwe) /* Duplicate. */
                         goto drop_packet;
 
-                if (seqno == rcv_cr->lwe) {
-                        ++rcv_cr->lwe;
-                        /* Check for online reconfiguration. */
-                        if (pci->flags & FRCT_CFG) {
-                                assert(pci->flags & FRCT_DRF);
-                                rcv_cr->cflags = pci->cflags;
-                        }
+                if (rcv_cr->cflags & FRCTFRTX) {
+                        size_t pos = seqno & (RQ_SIZE - 1);
+                        if (seqno > rcv_cr->lwe + RQ_SIZE || /* Out of range. */
+                            frcti->rq[pos] != -1) /* Duplicate in rq. */
+                                goto drop_packet;
+                        /* Queue. */
+                        frcti->rq[pos] = idx;
                 } else {
-                        frcti->rq[seqno & (RQ_SIZE - 1)] = idx;
+                        rcv_cr->lwe = seqno;
                 }
         }
 
-        rcv_cr->drf = false;
         rcv_cr->act = now.tv_sec;
 
         if (!(pci->flags & FRCT_DATA))