From f6318d86523d1a994a127aadace0d304f2a8b22a Mon Sep 17 00:00:00 2001
From: Herbert Wolverson <herberticus@gmail.com>
Date: Tue, 21 Mar 2023 17:46:51 +0000
Subject: [PATCH] Change 'map ip' to add or insert, rather than just insert.
 This allows for speedy changes without a remove, making it an atomic
 operation. So you can add a new queue, change the IP/net, and wait a few
 seconds before deleting the old one to avoid packet loss during reloads.

---
 src/rust/lqos_sys/src/bpf_map.rs        | 32 +++++++++++++++++++++++++
 src/rust/lqos_sys/src/ip_mapping/mod.rs |  2 +-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/rust/lqos_sys/src/bpf_map.rs b/src/rust/lqos_sys/src/bpf_map.rs
index 675db85f..be461b79 100644
--- a/src/rust/lqos_sys/src/bpf_map.rs
+++ b/src/rust/lqos_sys/src/bpf_map.rs
@@ -130,6 +130,38 @@ where
     }
   }
 
+  /// Inserts an entry into a BPF map, or updates an existing entry with
+  /// the same key.
+  /// 
+  /// Use this sparingly, because it briefly pauses XDP access to the
+  /// underlying map (through internal locking we can't reach from
+  /// userland).
+  ///
+  /// ## Arguments
+  ///
+  /// * `key` - the key to insert.
+  /// * `value` - the value to insert.
+  ///
+  /// Returns Ok if insertion succeeded, a generic error (no details yet)
+  /// if it fails.
+  pub(crate) fn insert_or_update(&mut self, key: &mut K, value: &mut V) -> Result<()> {
+    let key_ptr: *mut K = key;
+    let val_ptr: *mut V = value;
+    let err = unsafe {
+      bpf_map_update_elem(
+        self.fd,
+        key_ptr as *mut c_void,
+        val_ptr as *mut c_void,
+        BPF_NOEXIST.into(),
+      )
+    };
+    if err != 0 {
+      Err(Error::msg(format!("Unable to insert into map ({err})")))
+    } else {
+      Ok(())
+    }
+  }
+
   /// Deletes an entry from the underlying eBPF map.
   /// Use this sparingly, it locks the underlying map in the
   /// kernel. This can cause *long* delays under heavy load.
diff --git a/src/rust/lqos_sys/src/ip_mapping/mod.rs b/src/rust/lqos_sys/src/ip_mapping/mod.rs
index 83c4ab9d..80ecb3b9 100644
--- a/src/rust/lqos_sys/src/ip_mapping/mod.rs
+++ b/src/rust/lqos_sys/src/ip_mapping/mod.rs
@@ -34,7 +34,7 @@ pub fn add_ip_to_tc(
   let mut key = IpHashKey { prefixlen: ip_to_add.prefix, address: address.0 };
   let mut value =
     IpHashData { cpu: ip_to_add.cpu, tc_handle: ip_to_add.handle() };
-  bpf_map.insert(&mut key, &mut value)?;
+  bpf_map.insert_or_update(&mut key, &mut value)?;
   Ok(())
 }