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/ipcpd/unicast/dt.c b/src/ipcpd/unicast/dt.c
index e2679ffe..9435350f 100644
--- a/src/ipcpd/unicast/dt.c
+++ b/src/ipcpd/unicast/dt.c
@@ -68,7 +68,7 @@
 #endif
 
 struct comp_info {
-        void (* post_packet)(void * comp, struct shm_du_buff * sdb);
+        void (* post_packet)(void * comp, struct ssm_pk_buff * spb);
         void * comp;
         char * name;
 };
@@ -135,11 +135,11 @@ static void dt_pci_des(uint8_t *       head,
         memcpy(&dt_pci->eid, head + dt_pci_info.eid_o, dt_pci_info.eid_size);
 }
 
-static void dt_pci_shrink(struct shm_du_buff * sdb)
+static void dt_pci_shrink(struct ssm_pk_buff * spb)
 {
-        assert(sdb);
+        assert(spb);
 
-        shm_du_buff_head_release(sdb, dt_pci_info.head_size);
+        ssm_pk_buff_head_release(spb, dt_pci_info.head_size);
 }
 
 struct {
@@ -429,7 +429,7 @@ static void handle_event(void *       self,
 
 static void packet_handler(int                  fd,
                            qoscube_t            qc,
-                           struct shm_du_buff * sdb)
+                           struct ssm_pk_buff * spb)
 {
         struct dt_pci dt_pci;
         int           ret;
@@ -437,7 +437,7 @@ static void packet_handler(int                  fd,
         uint8_t *     head;
         size_t        len;
 
-        len = shm_du_buff_len(sdb);
+        len = ssm_pk_buff_len(spb);
 
 #ifndef IPCP_FLOW_STATS
         (void)        fd;
@@ -451,13 +451,13 @@ static void packet_handler(int                  fd,
 #endif
         memset(&dt_pci, 0, sizeof(dt_pci));
 
-        head = shm_du_buff_head(sdb);
+        head = ssm_pk_buff_head(spb);
 
         dt_pci_des(head, &dt_pci);
         if (dt_pci.dst_addr != dt.addr) {
                 if (dt_pci.ttl == 0) {
                         log_dbg("TTL was zero.");
-                        ipcp_sdb_release(sdb);
+                        ipcp_spb_release(spb);
 #ifdef IPCP_FLOW_STATS
                         pthread_mutex_lock(&dt.stat[fd].lock);
 
@@ -474,7 +474,7 @@ static void packet_handler(int                  fd,
                 if (ofd < 0) {
                         log_dbg("No next hop for %" PRIu64 ".",
                                 dt_pci.dst_addr);
-                        ipcp_sdb_release(sdb);
+                        ipcp_spb_release(spb);
 #ifdef IPCP_FLOW_STATS
                         pthread_mutex_lock(&dt.stat[fd].lock);
 
@@ -488,12 +488,12 @@ static void packet_handler(int                  fd,
 
                 (void) ca_calc_ecn(ofd, head + dt_pci_info.ecn_o, qc, len);
 
-                ret = ipcp_flow_write(ofd, sdb);
+                ret = ipcp_flow_write(ofd, spb);
                 if (ret < 0) {
                         log_dbg("Failed to write packet to fd %d.", ofd);
                         if (ret == -EFLOWDOWN)
                                 notifier_event(NOTIFY_DT_FLOW_DOWN, &ofd);
-                        ipcp_sdb_release(sdb);
+                        ipcp_spb_release(spb);
 #ifdef IPCP_FLOW_STATS
                         pthread_mutex_lock(&dt.stat[ofd].lock);
 
@@ -513,17 +513,17 @@ static void packet_handler(int                  fd,
                 pthread_mutex_unlock(&dt.stat[ofd].lock);
 #endif
         } else {
-                dt_pci_shrink(sdb);
+                dt_pci_shrink(spb);
                 if (dt_pci.eid >= PROG_RES_FDS) {
                         uint8_t ecn = *(head + dt_pci_info.ecn_o);
-                        fa_np1_rcv(dt_pci.eid, ecn, sdb);
+                        fa_np1_rcv(dt_pci.eid, ecn, spb);
                         return;
                 }
 
                 if (dt.comps[dt_pci.eid].post_packet == NULL) {
                         log_err("No registered component on eid %" PRIu64 ".",
                                 dt_pci.eid);
-                        ipcp_sdb_release(sdb);
+                        ipcp_spb_release(spb);
                         return;
                 }
 #ifdef IPCP_FLOW_STATS
@@ -541,7 +541,7 @@ static void packet_handler(int                  fd,
                 pthread_mutex_unlock(&dt.stat[dt_pci.eid].lock);
 #endif
                 dt.comps[dt_pci.eid].post_packet(dt.comps[dt_pci.eid].comp,
-                                                 sdb);
+                                                 spb);
         }
 }
 
@@ -758,7 +758,7 @@ void dt_stop(void)
 }
 
 int dt_reg_comp(void * comp,
-                void (* func)(void * func, struct shm_du_buff *),
+                void (* func)(void * func, struct ssm_pk_buff *),
                 char * name)
 {
         int eid;
@@ -809,7 +809,7 @@ void dt_unreg_comp(int eid)
 int dt_write_packet(uint64_t             dst_addr,
                     qoscube_t            qc,
                     uint64_t             eid,
-                    struct shm_du_buff * sdb)
+                    struct ssm_pk_buff * spb)
 {
         struct dt_pci dt_pci;
         int           fd;
@@ -817,10 +817,10 @@ int dt_write_packet(uint64_t             dst_addr,
         uint8_t *     head;
         size_t        len;
 
-        assert(sdb);
+        assert(spb);
         assert(dst_addr != dt.addr);
 
-        len = shm_du_buff_len(sdb);
+        len = ssm_pk_buff_len(spb);
 
 #ifdef IPCP_FLOW_STATS
         if (eid < PROG_RES_FDS) {
@@ -849,13 +849,13 @@ int dt_write_packet(uint64_t             dst_addr,
                 return -EPERM;
         }
 
-        head = shm_du_buff_head_alloc(sdb, dt_pci_info.head_size);
+        head = ssm_pk_buff_head_alloc(spb, dt_pci_info.head_size);
         if (head == NULL) {
                 log_dbg("Failed to allocate DT header.");
                 goto fail_write;
         }
 
-        len = shm_du_buff_len(sdb);
+        len = ssm_pk_buff_len(spb);
 
         dt_pci.dst_addr = dst_addr;
         dt_pci.qc       = qc;
@@ -866,7 +866,7 @@ int dt_write_packet(uint64_t             dst_addr,
 
         dt_pci_ser(head, &dt_pci);
 
-        ret = ipcp_flow_write(fd, sdb);
+        ret = ipcp_flow_write(fd, spb);
         if (ret < 0) {
                 log_dbg("Failed to write packet to fd %d.", fd);
                 if (ret == -EFLOWDOWN)