feat(net): TCP segmentation offload

Author: cagatay-y

Cargo.lock

@@ -150,7 +150,7 @@ smp = ["acpi"]
 #! ### Network Features
 
 ## Enables TCP support.
-tcp = ["net", "smoltcp", "smoltcp/socket-tcp"]
+tcp = ["net", "smoltcp", "smoltcp/socket-tcp", "smoltcp/segmentation-offload"]
 
 ## Enables UDP support.
 udp = ["net", "smoltcp", "smoltcp/socket-udp"]
@@ -417,6 +417,7 @@ exclude = [
 
 [patch.crates-io]
 safe-mmio = { git = "https://github.com/hermit-os/safe-mmio", branch = "be" }
+smoltcp = { git = "https://github.com/cagatay-y/smoltcp", branch = "segmentation-offload" }
 
 [profile.profiling]
 inherits = "release"

Cargo.toml

@@ -17,11 +17,12 @@ cfg_select! {
 use alloc::boxed::Box;
 use alloc::vec::Vec;
 use core::mem::{ManuallyDrop, MaybeUninit};
+use core::num::NonZeroUsize;
 use core::str::FromStr;
 use core::{mem, slice};
 
 use smallvec::SmallVec;
-use smoltcp::phy::{Checksum, ChecksumCapabilities, DeviceCapabilities};
+use smoltcp::phy::{Checksum, ChecksumCapabilities, DeviceCapabilities, PacketMeta};
 use smoltcp::wire::{ETHERNET_HEADER_LEN, EthernetFrame, Ipv4Packet, Ipv6Packet};
 use virtio::DeviceConfigSpace;
 use virtio::net::{ConfigVolatileFieldAccess, Hdr, HdrF};
@@ -180,12 +181,23 @@ pub struct TxQueues {
 	buf_size: u32,
 }
 
+#[expect(
+	clippy::decimal_literal_representation,
+	reason = "In the VIRTIO specification the size limit is provided in decimal."
+)]
+const MAX_BUFFER_SIZE: usize = 65550;
+
 impl TxQueues {
 	pub fn new(vqs: Vec<VirtQueue>, dev_cfg: &NetDevCfg) -> Self {
-		Self {
-			vqs,
-			buf_size: determine_mtu(dev_cfg).into(),
-		}
+		let buf_size = if dev_cfg
+			.features
+			.intersects(virtio::net::F::HOST_TSO4 | virtio::net::F::HOST_TSO6)
+		{
+			MAX_BUFFER_SIZE.try_into().unwrap()
+		} else {
+			determine_mtu(dev_cfg).into()
+		};
+		Self { vqs, buf_size }
 	}
 
 	#[allow(dead_code)]
@@ -253,6 +265,7 @@ pub struct TxToken<'a> {
 	send_vqs: &'a mut TxQueues,
 	checksums: ChecksumCapabilities,
 	send_capacity: &'a mut u32,
+	meta: PacketMeta,
 }
 
 impl Drop for TxToken<'_> {
@@ -291,6 +304,17 @@ impl smoltcp::phy::TxToken for TxToken<'_> {
 			header.csum_offset = csum_offset.into();
 		}
 
+		if let Some(gso_size) = token.meta.segmentation_offload_size {
+			header.gso_type = match EthernetFrame::new_unchecked(&packet).ethertype() {
+				smoltcp::wire::EthernetProtocol::Ipv4 => virtio::net::HdrGso::Tcpv4.into(),
+				smoltcp::wire::EthernetProtocol::Ipv6 => virtio::net::HdrGso::Tcpv6.into(),
+				_ => unreachable!(
+					"We don't advertise segmentation offload support for any other protocol."
+				),
+			};
+			header.gso_size = gso_size.get().into();
+		}
+
 		let buff_tkn = AvailBufferToken::new(
 			SmallVec::from_buf([BufferElem::Sized(header), BufferElem::Vector(packet)]),
 			SmallVec::new(),
@@ -303,6 +327,10 @@ impl smoltcp::phy::TxToken for TxToken<'_> {
 
 		result
 	}
+
+	fn set_meta(&mut self, meta: PacketMeta) {
+		self.meta = meta;
+	}
 }
 
 pub struct RxToken<'a> {
@@ -436,6 +464,16 @@ impl smoltcp::phy::Device for VirtioNetDriver {
 		device_capabilities.max_burst_size =
 			Some(usize::try_from(self.inner.send_capacity).unwrap() / usize::from(BUFF_PER_PACKET));
 		device_capabilities.checksum = self.checksums.clone();
+		device_capabilities.segmentation.tcpv4 = self
+			.dev_cfg
+			.features
+			.contains(virtio::net::F::HOST_TSO4)
+			.then_some(NonZeroUsize::new(MAX_BUFFER_SIZE).unwrap());
+		device_capabilities.segmentation.tcpv6 = self
+			.dev_cfg
+			.features
+			.contains(virtio::net::F::HOST_TSO6)
+			.then_some(NonZeroUsize::new(MAX_BUFFER_SIZE).unwrap());
 		device_capabilities
 	}
 
@@ -463,6 +501,7 @@ impl smoltcp::phy::Device for VirtioNetDriver {
 				send_vqs: &mut self.inner.send_vqs,
 				checksums: self.checksums.clone(),
 				send_capacity: &mut self.inner.send_capacity,
+				meta: PacketMeta::default(),
 			},
 		))
 	}
@@ -479,6 +518,7 @@ impl smoltcp::phy::Device for VirtioNetDriver {
 			send_vqs: &mut self.inner.send_vqs,
 			checksums: self.checksums.clone(),
 			send_capacity: &mut self.inner.send_capacity,
+			meta: PacketMeta::default(),
 		})
 	}
 }
@@ -673,7 +713,9 @@ impl VirtioNetDriver<Uninit> {
 			// Multiqueue support
 			| virtio::net::F::MQ
 			// Checksum calculation can partially be offloaded to the device
-			| virtio::net::F::CSUM;
+			| virtio::net::F::CSUM
+			| virtio::net::F::HOST_TSO4
+			| virtio::net::F::HOST_TSO6;
 
 		// Currently the driver does NOT support the features below.
 		// In order to provide functionality for these, the driver