samples/rust: add minimal CCA

Add an example that uses the `module_cca` macro and the `Algorithm`
trait to implement a minimal CCA.

IMPORTANT: This CCA is not compliant with the relevant RFCs and must not
be used outside of test environments.

Author: Valentin Obst

samples/rust/Kconfig

@@ -30,6 +30,16 @@ config SAMPLE_RUST_PRINT
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_CCA
+	tristate "Congestion control algorithm"
+	help
+	  This option builds the Rust congestion control algorithm sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_cca.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help

samples/rust/Makefile

@@ -2,5 +2,6 @@
 
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
+obj-$(CONFIG_SAMPLE_RUST_CCA)			+= rust_cca.o
 
 subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs

samples/rust/rust_cca.rs

@@ -0,0 +1,35 @@
+//! Congestion control algorithm example.
+use core::num::NonZeroU32;
+use kernel::net::tcp::cong::*;
+use kernel::prelude::*;
+use kernel::{c_str, module_cca};
+
+struct MyCca {}
+
+#[vtable]
+impl Algorithm for MyCca {
+    type Data = ();
+
+    const NAME: &'static CStr = c_str!("my_cca");
+
+    fn undo_cwnd(sk: &mut Sock<'_, Self>) -> u32 {
+        reno::undo_cwnd(sk)
+    }
+
+    fn ssthresh(_sk: &mut Sock<'_, Self>) -> u32 {
+        2
+    }
+
+    fn cong_avoid(sk: &mut Sock<'_, Self>, _ack: u32, acked: u32) {
+        sk.tcp_sk_mut()
+            .cong_avoid_ai(NonZeroU32::new(1).unwrap(), acked)
+    }
+}
+
+module_cca! {
+    type: MyCca,
+    name: "my_cca",
+    author: "Rust for Linux Contributors",
+    description: "Sample congestion control algorithm implemented in Rust.",
+    license: "GPL v2",
+}