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, 1 insertions, 11 deletions

diff --git a/src/lib/config.h.in b/src/lib/config.h.in
index 465068cb..b2b17669 100644
--- a/src/lib/config.h.in
+++ b/src/lib/config.h.in
@@ -26,23 +26,16 @@
 #ifdef HAVE_OPENSSL
 #cmakedefine HAVE_OPENSSL_PQC
 #define HAVE_ENCRYPTION
-#define PROC_SECMEM_MAX          @PROC_SECMEM_MAX@
 #define SECMEM_GUARD             @SECMEM_GUARD@
 #endif
+#define PROC_SECMEM_MAX          @PROC_SECMEM_MAX@
 
 #define SYS_MAX_FLOWS            @SYS_MAX_FLOWS@
 
-#cmakedefine                     SHM_RDRB_MULTI_BLOCK
 #cmakedefine                     QOS_DISABLE_CRC
 #cmakedefine                     HAVE_OPENSSL_RNG
 
-#define SHM_RBUFF_PREFIX         "@SHM_RBUFF_PREFIX@"
 #define SHM_LOCKFILE_NAME        "@SHM_LOCKFILE_NAME@"
-#define SHM_FLOW_SET_PREFIX      "@SHM_FLOW_SET_PREFIX@"
-#define SHM_RDRB_NAME            "@SHM_RDRB_NAME@"
-#define SHM_RDRB_BLOCK_SIZE       @SHM_RDRB_BLOCK_SIZE@
-#define SHM_BUFFER_SIZE           @SHM_BUFFER_SIZE@
-#define SHM_RBUFF_SIZE            @SHM_RBUFF_SIZE@
 #define FLOW_ALLOC_TIMEOUT        @FLOW_ALLOC_TIMEOUT@
 
 #define TPM_DEBUG_REPORT_INTERVAL @TPM_DEBUG_REPORT_INTERVAL@
@@ -70,9 +63,6 @@
 #define PROG_RES_FDS        @PROG_RES_FDS@
 #define PROG_MAX_FQUEUES    @PROG_MAX_FQUEUES@
 
-#define DU_BUFF_HEADSPACE   @DU_BUFF_HEADSPACE@
-#define DU_BUFF_TAILSPACE   @DU_BUFF_TAILSPACE@
-
 /* Default Delta-t parameters */
 #cmakedefine                FRCT_LINUX_RTT_ESTIMATOR
 #define DELT_A              (@DELTA_T_ACK@)                  /* ns */