From 81daa87f8b3ac25de22d4854313507a1258dbe6d Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Sun, 14 Jun 2026 18:52:54 -0700
Subject: [PATCH] rdma-engine: ranged RDMA READ (offset+size) in rdma-client

Match the real read API shape (file_id + offset + size): rdma-client
takes optional [offset] [size] and RDMA-READs only that sub-range from
the remote MR (remote_addr + offset). Verified over rxe0: reading
[3 MiB, 4 MiB) of an 8 MiB target file yields bytes whose md5 matches
the source slice.
---
 .../rdma-engine/src/bin/rdma_client.rs        | 25 +++++++++++++++----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/seaweedfs-rdma-sidecar/rdma-engine/src/bin/rdma_client.rs b/seaweedfs-rdma-sidecar/rdma-engine/src/bin/rdma_client.rs
index ce70ac506..6cb2efd94 100644
--- a/seaweedfs-rdma-sidecar/rdma-engine/src/bin/rdma_client.rs
+++ b/seaweedfs-rdma-sidecar/rdma-engine/src/bin/rdma_client.rs
@@ -3,7 +3,10 @@
 //! space), and write it out. md5 of the output vs the target's source file
 //! proves a real cross-process RDMA read of real data.
 //!
-//!   cargo run --features real-rdma --bin rdma-client -- <target_ip> <port> <out_file>
+//!   cargo run --features real-rdma --bin rdma-client -- <target_ip> <port> <out_file> [offset] [size]
+//!
+//! With [offset]/[size] it RDMA-READs only that byte range (the real read API
+//! shape: file_id + offset + size); without them it reads the whole MR.
 
 use std::fs;
 
@@ -12,12 +15,13 @@ use rdma_engine::rdma_real::RealRdmaContext;
 fn main() {
     let args: Vec<String> = std::env::args().collect();
     if args.len() < 4 {
-        eprintln!("usage: rdma-client <target_ip> <port> <out_file>");
+        eprintln!("usage: rdma-client <target_ip> <port> <out_file> [offset] [size]");
         std::process::exit(2);
     }
     let ip = args[1].clone();
     let port: u16 = args[2].parse().expect("port");
     let out = &args[3];
+    let offset: u64 = args.get(4).and_then(|s| s.parse().ok()).unwrap_or(0);
 
     let (ctx, raddr, rkey, rlen) = match RealRdmaContext::connect(&ip, port) {
         Ok(v) => v,
@@ -26,11 +30,22 @@ fn main() {
             std::process::exit(1);
         }
     };
-    eprintln!("client: connected to {ip}:{port}, remote MR len={rlen} rkey=0x{rkey:x}");
+    // Default to the rest of the MR from `offset`.
+    let size: usize = args
+        .get(5)
+        .and_then(|s| s.parse().ok())
+        .unwrap_or(rlen - offset.min(rlen as u64) as usize);
+    eprintln!(
+        "client: connected to {ip}:{port}, remote MR len={rlen} rkey=0x{rkey:x}; reading [{offset}, {})",
+        offset as usize + size
+    );
+    assert!(offset as usize + size <= rlen, "range exceeds remote MR");
 
-    let mut dest = vec![0u8; rlen];
+    let mut dest = vec![0u8; size];
     let (_mi, mr) = ctx.register_memory(&mut dest).expect("register dest");
-    ctx.post_read(&mut dest, mr, raddr, rkey, 1).expect("post_read");
+    // RDMA-READ the sub-range: remote source is the MR base + offset.
+    ctx.post_read(&mut dest, mr, raddr + offset, rkey, 1)
+        .expect("post_read");
     let wc = ctx.poll_completion().expect("poll completion");
     ctx.finish();
     eprintln!(