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//! RDMA transport for high-performance shard migration base copy.
//!
//! Feature-gated behind `rdma`. When RDMA hardware is unavailable,
//! the QUIC transport provides a correctness-equivalent fallback path
//! using the same `VShardEnvelope` wire format.
//!
//! RDMA advantages for base copy:
//! - Zero-copy: DMA directly from source NVMe → target memory
//! - Kernel bypass: no syscall overhead on the data path
//! - Low latency: ~1µs per transfer vs ~50µs for QUIC
//!
//! The RDMA transport is only used for Phase 1 (base copy) of shard
//! migration. All other communication uses QUIC/TCP.
use std::net::SocketAddr;
use serde::{Deserialize, Serialize};
use tracing::{debug, info};
use crate::error::{ClusterError, Result};
/// RDMA transport configuration.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RdmaConfig {
/// RDMA device name (e.g., "mlx5_0").
pub device: String,
/// Port number on the RDMA device.
pub port: u8,
/// GID index for RoCEv2.
pub gid_index: i32,
/// Maximum transfer size per RDMA SEND operation.
pub max_send_size: usize,
/// Number of pre-allocated memory regions for zero-copy.
pub num_memory_regions: usize,
/// Queue pair depth (outstanding operations).
pub qp_depth: u32,
}
impl Default for RdmaConfig {
fn default() -> Self {
Self {
device: "mlx5_0".into(),
port: 1,
gid_index: 0,
max_send_size: 4 * 1024 * 1024, // 4 MiB per SEND
num_memory_regions: 16,
qp_depth: 64,
}
}
}
/// RDMA connection state for a peer.
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum RdmaState {
/// RDMA device not available — fall back to QUIC.
Unavailable,
/// RDMA device found but connection not established.
Disconnected,
/// Queue pair created, ready to send.
Connected,
/// Connection failed — fall back to QUIC.
Failed,
}
/// RDMA transport handle.
///
/// Wraps the RDMA device interaction. When RDMA hardware is not available
/// (no ibverbs, no device), `state()` returns `Unavailable` and all
/// operations fall through to the QUIC transport.
pub struct RdmaTransport {
config: RdmaConfig,
state: RdmaState,
/// Bytes transferred via RDMA.
bytes_transferred: u64,
/// Number of RDMA SEND operations completed.
sends_completed: u64,
}
impl RdmaTransport {
/// Create an RDMA transport. Probes for hardware availability.
///
/// If RDMA hardware is not present, returns a transport in
/// `Unavailable` state — all operations will return
/// `Err(Unavailable)` and the caller should use QUIC instead.
pub fn new(config: RdmaConfig) -> Self {
let state = if Self::probe_rdma_device(&config.device) {
info!(device = %config.device, "RDMA device found");
RdmaState::Disconnected
} else {
debug!(device = %config.device, "RDMA device not available, using QUIC fallback");
RdmaState::Unavailable
};
Self {
config,
state,
bytes_transferred: 0,
sends_completed: 0,
}
}
/// Check if RDMA hardware is available and usable.
pub fn is_available(&self) -> bool {
!matches!(self.state, RdmaState::Unavailable | RdmaState::Failed)
}
/// Current RDMA state.
pub fn state(&self) -> RdmaState {
self.state
}
/// Send a segment via RDMA for migration base copy.
///
/// Returns `Err` with `Unavailable` if RDMA is not available —
/// caller should fall back to QUIC `send_migration_segment()`.
pub fn send_segment(&mut self, _peer: SocketAddr, vshard_id: u16, data: &[u8]) -> Result<()> {
if !self.is_available() {
return Err(ClusterError::Transport {
detail: "RDMA not available — use QUIC fallback".into(),
});
}
if data.len() > self.config.max_send_size {
// Fragment into multiple RDMA SENDs.
let chunks = data.len().div_ceil(self.config.max_send_size);
debug!(
vshard_id,
chunks,
total_bytes = data.len(),
"RDMA: fragmenting large segment"
);
for chunk_idx in 0..chunks {
let start = chunk_idx * self.config.max_send_size;
let end = (start + self.config.max_send_size).min(data.len());
let chunk = &data[start..end];
self.bytes_transferred += chunk.len() as u64;
self.sends_completed += 1;
// Actual RDMA SEND would happen here via ibverbs.
// For now, this is a structural placeholder that tracks
// metrics and validates the data path.
}
} else {
self.bytes_transferred += data.len() as u64;
self.sends_completed += 1;
}
Ok(())
}
/// Total bytes transferred via RDMA.
pub fn bytes_transferred(&self) -> u64 {
self.bytes_transferred
}
/// Number of RDMA SEND operations completed.
pub fn sends_completed(&self) -> u64 {
self.sends_completed
}
/// Probe for RDMA device availability.
///
/// Checks if `/sys/class/infiniband/{device}` exists, which indicates
/// an RDMA-capable NIC is present (Mellanox ConnectX, etc.).
fn probe_rdma_device(device: &str) -> bool {
let path = format!("/sys/class/infiniband/{device}");
std::path::Path::new(&path).exists()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn rdma_unavailable_on_non_rdma_hardware() {
let transport = RdmaTransport::new(RdmaConfig {
device: "nonexistent_device_xyz".into(),
..Default::default()
});
assert_eq!(transport.state(), RdmaState::Unavailable);
assert!(!transport.is_available());
}
#[test]
fn send_fails_when_unavailable() {
let mut transport = RdmaTransport::new(RdmaConfig {
device: "nonexistent".into(),
..Default::default()
});
let result = transport.send_segment("127.0.0.1:9000".parse().unwrap(), 1, b"data");
assert!(result.is_err());
}
#[test]
fn config_defaults() {
let config = RdmaConfig::default();
assert_eq!(config.device, "mlx5_0");
assert_eq!(config.max_send_size, 4 * 1024 * 1024);
assert_eq!(config.qp_depth, 64);
}
}