lib: Replace rdrbuff with a proper slab allocatorbe

This is a first step towards the Secure Shared Memory (SSM)
infrastructure for Ouroboros, which will allow proper resource
separation for non-privileged processes.

This replaces the rdrbuff (random-deletion ring buffer) PoC allocator
with a sharded slab allocator for the packet buffer pool to avoid the
head-of-line blocking behaviour of the rdrb and reduce lock contention
in multi-process scenarios. Each size class contains multiple
independent shards, allowing parallel allocations without blocking.

- Configurable shard count per size class (default: 4, set via
  SSM_POOL_SHARDS in CMake). The configured number of blocks are
  spread over the number of shards. As an example:

  	 SSM_POOL_512_BLOCKS = 768 blocks total
	 These 768 blocks are shared among 4 shards
	       (not 768 × 4 = 3072 blocks)

- Lazy block distribution: all blocks initially reside in shard 0
  and naturally migrate to process-local shards upon first
  allocation and subsequent free operations

- Fallback with work stealing: processes attempt allocation from
  their local shard (pid % SSM_POOL_SHARDS) first, then steal
  from other shards if local is exhausted, eliminating
  fragmentation while maintaining low contention

- Round-robin condvar signaling: blocking allocations cycle
  through all shard condition variables to ensure fairness

- Blocks freed to allocator's shard: uses allocator_pid to
  determine target shard, enabling natural load balancing as
  process allocation patterns stabilize over time

Maintains existing robust mutex semantics including EOWNERDEAD
handling for dead process recovery. Internal structures exposed in
ssm.h for testing purposes. Adds some tests (pool_test,
pool_sharding_test.c. etc) verifying lazy distribution, migration,
fallback stealing, and multiprocess behavior.

Updates the ring buffer (rbuff) to use relaxed/acquire/release
ordering on atomic indices. The ring buffer requires the (robust)
mutex to ensure cross-structure synchronization between pool buffer
writes and ring buffer index publication.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 22 insertions, 22 deletions

diff --git a/src/lib/frct.c b/src/lib/frct.c
index 08c5ea80..76736931 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -237,21 +237,21 @@ static void __send_frct_pkt(int      fd,
                             uint32_t ackno,
                             uint32_t rwe)
 {
-        struct shm_du_buff * sdb;
+        struct ssm_pk_buff * spb;
         struct frct_pci *    pci;
         ssize_t              idx;
         struct flow *        f;
 
         /* Raw calls needed to bypass frcti. */
 #ifdef RXM_BLOCKING
-        idx = shm_rdrbuff_alloc_b(ai.rdrb, sizeof(*pci), NULL, &sdb, NULL);
+        idx = ssm_pool_alloc_b(ai.gspp, sizeof(*pci), NULL, &spb, NULL);
 #else
-        idx = shm_rdrbuff_alloc(ai.rdrb, sizeof(*pci), NULL, &sdb);
+        idx = ssm_pool_alloc(ai.gspp, sizeof(*pci), NULL, &spb);
 #endif
         if (idx < 0)
                 return;
 
-        pci = (struct frct_pci *) shm_du_buff_head(sdb);
+        pci = (struct frct_pci *) ssm_pk_buff_head(spb);
         memset(pci, 0, sizeof(*pci));
 
         *((uint32_t *) pci) = hton32(rwe);
@@ -261,22 +261,22 @@ static void __send_frct_pkt(int      fd,
 
         f = &ai.flows[fd];
 
-        if (sdb_encrypt(f, sdb) < 0)
+        if (spb_encrypt(f, spb) < 0)
                 goto fail;
 
 #ifdef RXM_BLOCKING
-        if (shm_rbuff_write_b(f->tx_rb, idx, NULL))
+        if (ssm_rbuff_write_b(f->tx_rb, idx, NULL))
 #else
-        if (shm_rbuff_write(f->tx_rb, idx))
+        if (ssm_rbuff_write(f->tx_rb, idx))
 #endif
                 goto fail;
 
-        shm_flow_set_notify(f->set, f->info.id, FLOW_PKT);
+        ssm_flow_set_notify(f->set, f->info.id, FLOW_PKT);
 
         return;
 
  fail:
-        ipcp_sdb_release(sdb);
+        ipcp_spb_release(spb);
         return;
 }
 
@@ -479,11 +479,11 @@ static void frcti_setflags(struct frcti * frcti,
 #define frcti_queued_pdu(frcti)                         \
         (frcti == NULL ? idx : __frcti_queued_pdu(frcti))
 
-#define frcti_snd(frcti, sdb)                           \
-        (frcti == NULL ? 0 : __frcti_snd(frcti, sdb))
+#define frcti_snd(frcti, spb)                           \
+        (frcti == NULL ? 0 : __frcti_snd(frcti, spb))
 
-#define frcti_rcv(frcti, sdb)                           \
-        (frcti == NULL ? 0 : __frcti_rcv(frcti, sdb))
+#define frcti_rcv(frcti, spb)                           \
+        (frcti == NULL ? 0 : __frcti_rcv(frcti, spb))
 
 #define frcti_dealloc(frcti)                            \
         (frcti == NULL ? 0 : __frcti_dealloc(frcti))
@@ -683,7 +683,7 @@ static time_t __frcti_dealloc(struct frcti * frcti)
 }
 
 static int __frcti_snd(struct frcti *       frcti,
-                       struct shm_du_buff * sdb)
+                       struct ssm_pk_buff * spb)
 {
         struct frct_pci * pci;
         struct timespec   now;
@@ -693,14 +693,14 @@ static int __frcti_snd(struct frcti *       frcti,
         bool              rtx;
 
         assert(frcti);
-        assert(shm_du_buff_len(sdb) != 0);
+        assert(ssm_pk_buff_len(spb) != 0);
 
         snd_cr = &frcti->snd_cr;
         rcv_cr = &frcti->rcv_cr;
 
         timerwheel_move();
 
-        pci = (struct frct_pci *) shm_du_buff_head_alloc(sdb, FRCT_PCILEN);
+        pci = (struct frct_pci *) ssm_pk_buff_head_alloc(spb, FRCT_PCILEN);
         if (pci == NULL)
                 return -ENOMEM;
 
@@ -759,7 +759,7 @@ static int __frcti_snd(struct frcti *       frcti,
         pthread_rwlock_unlock(&frcti->lock);
 
         if (rtx)
-                timerwheel_rxm(frcti, seqno, sdb);
+                timerwheel_rxm(frcti, seqno, spb);
 
         return 0;
 }
@@ -793,7 +793,7 @@ static void rtt_estimator(struct frcti * frcti,
 
 /* Always queues the next application packet on the RQ. */
 static void __frcti_rcv(struct frcti *       frcti,
-                        struct shm_du_buff * sdb)
+                        struct ssm_pk_buff * spb)
 {
         ssize_t           idx;
         size_t            pos;
@@ -813,9 +813,9 @@ static void __frcti_rcv(struct frcti *       frcti,
 
         clock_gettime(PTHREAD_COND_CLOCK, &now);
 
-        pci = (struct frct_pci *) shm_du_buff_head_release(sdb, FRCT_PCILEN);
+        pci = (struct frct_pci *) ssm_pk_buff_head_release(spb, FRCT_PCILEN);
 
-        idx = shm_du_buff_get_idx(sdb);
+        idx = ssm_pk_buff_get_idx(spb);
         seqno = ntoh32(pci->seqno);
         pos = seqno & (RQ_SIZE - 1);
 
@@ -841,7 +841,7 @@ static void __frcti_rcv(struct frcti *       frcti,
 
                 __send_frct_pkt(fd, FRCT_FC, 0, rwe);
 
-                shm_rdrbuff_remove(ai.rdrb, idx);
+                ssm_pool_remove(ai.gspp, idx);
                 return;
         }
 
@@ -928,7 +928,7 @@ static void __frcti_rcv(struct frcti *       frcti,
 
  drop_packet:
         pthread_rwlock_unlock(&frcti->lock);
-        shm_rdrbuff_remove(ai.rdrb, idx);
+        ssm_pool_remove(ai.gspp, idx);
         send_frct_pkt(frcti);
         return;
 }