From d829f5084e913a2d15b5b26d497e245a65d58acf Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Sat, 29 Mar 2025 15:08:13 +0000
Subject: [PATCH] socket::sockopt AttachReusePortCbpf for Linux addition.

Set a BPF program to the socket to set how packets are handled
within the reuseport group.
---
 changelog/2621.added.md   |  1 +
 src/sys/socket/sockopt.rs | 12 ++++++++++++
 test/sys/test_sockopt.rs  | 25 +++++++++++++++++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 changelog/2621.added.md

diff --git a/changelog/2621.added.md b/changelog/2621.added.md
new file mode 100644
index 0000000000..ad8b8c415e
--- /dev/null
+++ b/changelog/2621.added.md
@@ -0,0 +1 @@
+Added `socket::sockopt::AttachReusePortCbpf` for Linux
diff --git a/src/sys/socket/sockopt.rs b/src/sys/socket/sockopt.rs
index f30844881d..5dcf199d23 100644
--- a/src/sys/socket/sockopt.rs
+++ b/src/sys/socket/sockopt.rs
@@ -1269,6 +1269,18 @@ sockopt_impl!(
     libc::SO_EXCLBIND,
     bool
 );
+#[cfg(target_os = "linux")]
+sockopt_impl!(
+    /// To be used with `ReusePort`,
+    /// we can then attach a BPF (classic)
+    /// to set how the packets are assigned
+    /// to the socket (e.g. cpu distribution).
+    AttachReusePortCbpf,
+    SetOnly,
+    libc::SOL_SOCKET,
+    libc::SO_ATTACH_REUSEPORT_CBPF,
+    libc::sock_fprog
+);
 
 #[allow(missing_docs)]
 // Not documented by Linux!
diff --git a/test/sys/test_sockopt.rs b/test/sys/test_sockopt.rs
index 27e08411b5..afd5aff7ea 100644
--- a/test/sys/test_sockopt.rs
+++ b/test/sys/test_sockopt.rs
@@ -1194,3 +1194,28 @@ fn test_solfilter() {
     assert_eq!(Err(Errno::ENOENT), setsockopt(&s, attach, data));
     assert_eq!(Err(Errno::ENOENT), setsockopt(&s, detach, data));
 }
+
+#[cfg(target_os = "linux")]
+#[test]
+pub fn test_so_attach_reuseport_cbpf() {
+    let fd = socket(
+        AddressFamily::Inet6,
+        SockType::Datagram,
+        SockFlag::empty(),
+        None,
+    )
+    .unwrap();
+    setsockopt(&fd, sockopt::ReusePort, &true).unwrap();
+    setsockopt(&fd, sockopt::ReuseAddr, &true).unwrap();
+    let mut flt: [libc::sock_filter; 2] = unsafe { std::mem::zeroed() };
+    flt[0].code = (libc::BPF_LD | libc::BPF_W | libc::BPF_ABS) as u16;
+    flt[0].k = (libc::SKF_AD_OFF + libc::SKF_AD_CPU) as u32;
+    flt[1].code = (libc::BPF_RET | 0x10) as u16;
+    let fp = libc::sock_fprog {
+        len: flt.len() as u16,
+        filter: flt.as_mut_ptr(),
+    };
+    setsockopt(&fd, sockopt::AttachReusePortCbpf, &fp).unwrap_or_else(|e| {
+        assert_eq!(e, nix::errno::Errno::ENOPROTOOPT);
+    });
+}