SlopRing
Submission/completion ring ABI
SlopRing is SlopOS's io_uring-style async edge. The kernel side remains synchronous; userland batches work in a shared SQ/CQ ring and drives futures through the SlopOS runtime.
The source ABI defines exact numeric syscall assignments, opcode values, feature bits, limits, and struct layout. This page describes the public behavior and the names to look for in generated or source ABI reference.
Syscalls
| Name | Purpose |
|---|---|
ring_setup | Create a ring, map the shared region, and return a ring fd |
ring_enter | Submit SQEs, harvest CQEs, and optionally block for completions |
ring_register | Register or unregister fixed buffers and provided-buffer rings |
Layout
| Struct | Role |
|---|---|
RingParams | Header and offsets for the single shared mapping |
Sqe | Submission queue entry |
Cqe | Completion queue entry |
BufIovec | One registered fixed buffer |
RegisterBufRingCmd | Provided-buffer ring registration |
IouringBuf | One provided-buffer descriptor |
The region is one mapping with header, SQ control words, CQ control words, SQE array, and CQE array. SQ and CQ use split-ownership head/tail counters. The kernel snapshots SQE bytes through volatile user-frame accessors and never takes a Rust reference directly into user-writable ring memory.
Feature names
| Feature | Meaning |
|---|---|
SLOPRING_FEAT_SINGLE_MMAP | One shared region for all ring state |
SLOPRING_FEAT_MULTISHOT | Multishot accept, receive, and poll behavior |
SLOPRING_FEAT_REG_BUFFERS | Fixed and provided buffer registration |
Opcode names
| Opcode name | Summary |
|---|---|
OP_NOP | Complete immediately |
OP_READ | File or socket read path |
OP_WRITE | File or socket write path |
OP_RECVMSG | Receive a message, including AF_UNIX paths |
OP_SEND | Send buffer contents |
OP_ACCEPT | Accept a socket connection |
OP_POLL_ADD | Register and probe fd readiness |
OP_TIMEOUT | Harvest wait deadline |
OP_CANCEL | Cancel in-flight ops by user_data |
OP_RECVFROM | Receive a datagram and source address |
OP_OPENAT | Open a path and install an fd |
OP_CLOSE | Close an fd |
OP_SEND_ZC | Zero-copy send from a registered fixed buffer |
OP_CONNECT | Async, non-blocking socket connect |
Fixed buffers
ring_register can pin a fixed-buffer set once and let later SQEs select a
buffer by index. SQEs use SLOPRING_SQE_FIXED_BUFFER and Sqe.buf_index.
Unregistering fails while any in-flight operation holds a registered buffer.
Provided buffers
Provided-buffer rings let userland publish a group of receive buffers. Receive
SQEs use SLOPRING_SQE_BUFFER_SELECT and Sqe.buf_group; completions set
SLOPRING_CQE_F_BUFFER and carry the selected buffer id in Cqe.flags.
Zero-copy send
OP_SEND_ZC requires a registered fixed buffer. It posts a result CQE first and
later posts a terminal notification CQE with SLOPRING_CQE_F_NOTIF when the
buffer is reusable.
The network stack has separate one-shot and TCP retransmit-safe models. TCP keeps the registered buffer pinned across retransmit and releases it only after ACK or teardown.
Connect
OP_CONNECT submits a socket connect and completes with success or a negated
errno. It does not install a new fd and does not select a buffer. The probe can
defer while a TCP handshake is in progress and is re-driven during harvest.