net/tcp: add Rust implementation of CUBIC

CUBIC is the default CCA since 2.6.18.

Missing features compared to the C implementation:
- configuration via module parameters,
- exporting callbacks to BPF programs as kfuncs.

Changes compared to the C implementation:
- uses only SI units for time, i.e., no jiffies and `BICTCP_HZ`,

Signed-off-by: Valentin Obst <kernel@valentinobst.de>

net/ipv4/Kconfig

@@ -527,6 +527,15 @@ config TCP_CONG_CUBIC
 	  among other techniques.
 	  See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
 
+config TCP_CONG_CUBIC_RUST
+	tristate "CUBIC TCP (Rust rewrite)"
+	depends on RUST_TCP_ABSTRACTIONS
+	help
+	  Rust rewrite of the original implementation of TCP CUBIC congestion
+	  control.
+
+	  If unsure, say N.
+
 config TCP_CONG_WESTWOOD
 	tristate "TCP Westwood+"
 	default m
@@ -720,6 +729,9 @@ choice
 	config DEFAULT_CUBIC
 		bool "Cubic" if TCP_CONG_CUBIC=y
 
+	config DEFAULT_CUBIC_RUST
+		bool "Cubic (Rust)" if TCP_CONG_CUBIC_RUST=y
+
 	config DEFAULT_HTCP
 		bool "Htcp" if TCP_CONG_HTCP=y
 
@@ -760,6 +772,7 @@ config DEFAULT_TCP_CONG
 	default "bic" if DEFAULT_BIC
 	default "bic_rust" if DEFAULT_BIC_RUST
 	default "cubic" if DEFAULT_CUBIC
+	default "cubic_rust" if DEFAULT_CUBIC_RUST
 	default "htcp" if DEFAULT_HTCP
 	default "hybla" if DEFAULT_HYBLA
 	default "vegas" if DEFAULT_VEGAS

net/ipv4/Makefile

@@ -49,6 +49,7 @@ obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_BIC_RUST) += tcp_bic_rust.o
 obj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o
 obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
+obj-$(CONFIG_TCP_CONG_CUBIC_RUST) += tcp_cubic_rust.o
 obj-$(CONFIG_TCP_CONG_DCTCP) += tcp_dctcp.o
 obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o
 obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o