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 <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>

2 files changed, 4 insertions, 47 deletions

diff --git a/include/ouroboros/shm_du_buff.h b/include/ouroboros/shm_du_buff.h
index 31090cd3..066898df 100644
--- a/include/ouroboros/shm_du_buff.h
+++ b/include/ouroboros/shm_du_buff.h
@@ -49,4 +49,8 @@ uint8_t * shm_du_buff_tail_release(struct shm_du_buff * sdb,
 void      shm_du_buff_truncate(struct shm_du_buff * sdb,
                                size_t               len);
 
+int       shm_du_buff_wait_ack(struct shm_du_buff * sdb);
+
+int       shm_du_buff_ack(struct shm_du_buff * sdb);
+
 #endif /* OUROBOROS_SHM_DU_BUFF_H */
diff --git a/include/ouroboros/timerwheel.h b/include/ouroboros/timerwheel.h
deleted file mode 100644
index 231e8103..00000000
--- a/include/ouroboros/timerwheel.h
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- * Ouroboros - Copyright (C) 2016 - 2018
- *
- * Ring buffer for incoming SDUs
- *
- *    Dimitri Staessens <[email protected]>
- *    Sander Vrijders   <[email protected]>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public License
- * version 2.1 as published by the Free Software Foundation.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., http://www.fsf.org/about/contact/.
- */
-
-#ifndef OUROBOROS_LIB_TIMERWHEEL_H
-#define OUROBOROS_LIB_TIMERWHEEL_H
-
-struct timerwheel;
-
-struct timerwheel * timerwheel_create(time_t resolution,
-                                      time_t max_delay);
-
-void                timerwheel_destroy(struct timerwheel * tw);
-
-struct tw_f *       timerwheel_start(struct timerwheel * tw,
-                                     void (* func)(void *),
-                                     void *              arg,
-                                     time_t              delay); /* ms */
-
-int                 timerwheel_restart(struct timerwheel * tw,
-                                       struct tw_f *       f,
-                                       time_t              delay); /* ms */
-
-void                timerwheel_stop(struct timerwheel * tw,
-                                    struct tw_f *       f);
-
-void                timerwheel_move(struct timerwheel * tw);
-
-#endif /* OUROBOROS_LIB_TIMERWHEEL_H */