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, 18 deletions

diff --git a/cmake/lib/lib.cmake b/cmake/lib/lib.cmake
index bb24d1b9..86b4418c 100644
--- a/cmake/lib/lib.cmake
+++ b/cmake/lib/lib.cmake
@@ -2,10 +2,6 @@ set(LIB_SOURCE_DIR "${CMAKE_SOURCE_DIR}/src/lib")
 set(LIB_BINARY_DIR "${CMAKE_BINARY_DIR}/src/lib")
 
 # Library configuration variables
-set(SHM_BUFFER_SIZE 16384 CACHE STRING
-    "Number of blocks in packet buffer, must be a power of 2")
-set(SHM_RBUFF_SIZE 1024 CACHE STRING
-    "Number of blocks in rbuff buffer, must be a power of 2")
 set(SYS_MAX_FLOWS 10240 CACHE STRING
   "Maximum number of total flows for this system")
 set(PROG_MAX_FLOWS 4096 CACHE STRING
@@ -14,10 +10,6 @@ set(PROG_RES_FDS 64 CACHE STRING
   "Number of reserved flow descriptors per application")
 set(PROG_MAX_FQUEUES 32 CACHE STRING
   "Maximum number of flow sets per application")
-set(DU_BUFF_HEADSPACE 256 CACHE STRING
-  "Bytes of headspace to reserve for future headers")
-set(DU_BUFF_TAILSPACE 32 CACHE STRING
-  "Bytes of tailspace to reserve for future tails")
 
 if (NOT APPLE)
   set(PTHREAD_COND_CLOCK "CLOCK_MONOTONIC" CACHE STRING
@@ -31,18 +23,9 @@ set(SOCKET_TIMEOUT 500 CACHE STRING
   "Default timeout for responses from IPCPs (ms)")
 set(SHM_PREFIX "ouroboros" CACHE STRING
   "String to prepend to POSIX shared memory filenames")
-set(SHM_RBUFF_PREFIX "/${SHM_PREFIX}.rbuff." CACHE INTERNAL
-  "Prefix for rbuff POSIX shared memory filenames")
 set(SHM_LOCKFILE_NAME "/${SHM_PREFIX}.lockfile" CACHE INTERNAL
   "Filename for the POSIX shared memory lockfile")
-set(SHM_FLOW_SET_PREFIX "/${SHM_PREFIX}.set." CACHE INTERNAL
-  "Prefix for the POSIX shared memory flow set")
-set(SHM_RDRB_NAME "/${SHM_PREFIX}.rdrb" CACHE INTERNAL
-  "Name for the main POSIX shared memory buffer")
-set(SHM_RDRB_BLOCK_SIZE "sysconf(_SC_PAGESIZE)" CACHE STRING
-  "Packet buffer block size, multiple of pagesize for performance")
-set(SHM_RDRB_MULTI_BLOCK TRUE CACHE BOOL
-  "Packet buffer multiblock packet support")
+
 set(QOS_DISABLE_CRC TRUE CACHE BOOL
   "Ignores ber setting on all QoS cubes")
 set(DELTA_T_MPL 60 CACHE STRING