On 11/24/25 11:35, Yureka Lilian wrote:
> The tokio-vhost & vhost-device-net crates which we also wrote and depend
> on are left external in the outlook of becoming a rust-vmm project soon.
> 
> Signed-off-by: Yureka Lilian <yureka@cyberchaos.dev>
> ---
>  pkgs/default.nix         |   2 +
>  tools/router/Cargo.lock  | 785 +++++++++++++++++++++++++++++++++++++++
>  tools/router/Cargo.toml  |  18 +
>  tools/router/default.nix |  18 +
>  tools/router/src/main.rs | 235 ++++++++++++
>  5 files changed, 1058 insertions(+)
>  create mode 100644 tools/router/Cargo.lock
>  create mode 100644 tools/router/Cargo.toml
>  create mode 100644 tools/router/default.nix
>  create mode 100644 tools/router/src/main.rs
> 
> diff --git a/pkgs/default.nix b/pkgs/default.nix
> index cc60228..7c1c9c3 100644
> --- a/pkgs/default.nix
> +++ b/pkgs/default.nix
> @@ -52,6 +52,8 @@ let
>      xdg-desktop-portal-spectrum-host =
>        self.callSpectrumPackage ../tools/xdg-desktop-portal-spectrum-host {};
>  
> +    spectrum-router = self.callSpectrumPackage ../tools/router {};
> +
>      # Packages from the overlay, so it's possible to build them from
>      # the CLI easily.
>      inherit (pkgs) cloud-hypervisor dbus;
> diff --git a/tools/router/Cargo.lock b/tools/router/Cargo.lock
> new file mode 100644
> index 0000000..04179af
> --- /dev/null
> +++ b/tools/router/Cargo.lock
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> + "libc",
> + "mio",
> + "pin-project-lite",
> + "socket2",
> + "tokio-macros",
> + "windows-sys 0.61.2",
> +]
> +
> +[[package]]
> +name = "tokio-eventfd"
> +version = "0.2.2"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "7e66bd133670ac39baa1aca5c3a86709f4595c08ca4464a1e1400b83d62c0639"
> +dependencies = [
> + "futures-lite",
> + "libc",
> + "tokio",
> +]
> +
> +[[package]]
> +name = "tokio-macros"
> +version = "2.6.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "af407857209536a95c8e56f8231ef2c2e2aff839b22e07a1ffcbc617e9db9fa5"
> +dependencies = [
> + "proc-macro2",
> + "quote",
> + "syn",
> +]
> +
> +[[package]]
> +name = "tokio-stream"
> +version = "0.1.17"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "eca58d7bba4a75707817a2c44174253f9236b2d5fbd055602e9d5c07c139a047"
> +dependencies = [
> + "futures-core",
> + "pin-project-lite",
> + "tokio",
> +]
> +
> +[[package]]
> +name = "tokio-vhost"
> +version = "0.1.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "21d64b3e4d573da90b2bb040d69a9c2d754e8a3ab9d9ecf04a268748c99f1cd3"
> +dependencies = [
> + "async-stream",
> + "bitvec",
> + "futures-util",
> + "libc",
> + "log",
> + "tokio",
> + "tokio-eventfd",
> + "virtio-queue",
> + "vm-memory",
> + "zerocopy",
> +]
> +
> +[[package]]
> +name = "unicode-ident"
> +version = "1.0.22"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "9312f7c4f6ff9069b165498234ce8be658059c6728633667c526e27dc2cf1df5"
> +
> +[[package]]
> +name = "utf8parse"
> +version = "0.2.2"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
> +
> +[[package]]
> +name = "vhost-device-net"
> +version = "0.1.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "ac05caccd6d484f672551a187f7110ff9d32edd6a39bb16bb04f53017b1e6fd0"
> +dependencies = [
> + "futures-util",
> + "log",
> + "tokio",
> + "tokio-vhost",
> + "vm-memory",
> +]
> +
> +[[package]]
> +name = "virtio-bindings"
> +version = "0.2.6"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "804f498a26d5a63be7bbb8bdcd3869c3f286c4c4a17108905276454da0caf8cb"
> +
> +[[package]]
> +name = "virtio-queue"
> +version = "0.16.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "fb0479158f863e59323771a1f684d843962f76960b86fecfec2bfa9c8f0f9180"
> +dependencies = [
> + "log",
> + "virtio-bindings",
> + "vm-memory",
> + "vmm-sys-util",
> +]
> +
> +[[package]]
> +name = "vm-memory"
> +version = "0.16.2"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "1fd5e56d48353c5f54ef50bd158a0452fc82f5383da840f7b8efc31695dd3b9d"
> +dependencies = [
> + "libc",
> + "thiserror",
> + "winapi",
> +]
> +
> +[[package]]
> +name = "vmm-sys-util"
> +version = "0.14.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "d21f366bf22bfba3e868349978766a965cbe628c323d58e026be80b8357ab789"
> +dependencies = [
> + "bitflags",
> + "libc",
> +]
> +
> +[[package]]
> +name = "wasi"
> +version = "0.11.1+wasi-snapshot-preview1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
> +
> +[[package]]
> +name = "winapi"
> +version = "0.3.9"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
> +dependencies = [
> + "winapi-i686-pc-windows-gnu",
> + "winapi-x86_64-pc-windows-gnu",
> +]
> +
> +[[package]]
> +name = "winapi-i686-pc-windows-gnu"
> +version = "0.4.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
> +
> +[[package]]
> +name = "winapi-x86_64-pc-windows-gnu"
> +version = "0.4.0"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
> +
> +[[package]]
> +name = "windows-link"
> +version = "0.2.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
> +
> +[[package]]
> +name = "windows-sys"
> +version = "0.60.2"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "f2f500e4d28234f72040990ec9d39e3a6b950f9f22d3dba18416c35882612bcb"
> +dependencies = [
> + "windows-targets",
> +]
> +
> +[[package]]
> +name = "windows-sys"
> +version = "0.61.2"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
> +dependencies = [
> + "windows-link",
> +]
> +
> +[[package]]
> +name = "windows-targets"
> +version = "0.53.5"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "4945f9f551b88e0d65f3db0bc25c33b8acea4d9e41163edf90dcd0b19f9069f3"
> +dependencies = [
> + "windows-link",
> + "windows_aarch64_gnullvm",
> + "windows_aarch64_msvc",
> + "windows_i686_gnu",
> + "windows_i686_gnullvm",
> + "windows_i686_msvc",
> + "windows_x86_64_gnu",
> + "windows_x86_64_gnullvm",
> + "windows_x86_64_msvc",
> +]
> +
> +[[package]]
> +name = "windows_aarch64_gnullvm"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "a9d8416fa8b42f5c947f8482c43e7d89e73a173cead56d044f6a56104a6d1b53"
> +
> +[[package]]
> +name = "windows_aarch64_msvc"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "b9d782e804c2f632e395708e99a94275910eb9100b2114651e04744e9b125006"
> +
> +[[package]]
> +name = "windows_i686_gnu"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "960e6da069d81e09becb0ca57a65220ddff016ff2d6af6a223cf372a506593a3"
> +
> +[[package]]
> +name = "windows_i686_gnullvm"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "fa7359d10048f68ab8b09fa71c3daccfb0e9b559aed648a8f95469c27057180c"
> +
> +[[package]]
> +name = "windows_i686_msvc"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "1e7ac75179f18232fe9c285163565a57ef8d3c89254a30685b57d83a38d326c2"
> +
> +[[package]]
> +name = "windows_x86_64_gnu"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "9c3842cdd74a865a8066ab39c8a7a473c0778a3f29370b5fd6b4b9aa7df4a499"
> +
> +[[package]]
> +name = "windows_x86_64_gnullvm"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "0ffa179e2d07eee8ad8f57493436566c7cc30ac536a3379fdf008f47f6bb7ae1"
> +
> +[[package]]
> +name = "windows_x86_64_msvc"
> +version = "0.53.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "d6bbff5f0aada427a1e5a6da5f1f98158182f26556f345ac9e04d36d0ebed650"
> +
> +[[package]]
> +name = "wyz"
> +version = "0.5.1"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "05f360fc0b24296329c78fda852a1e9ae82de9cf7b27dae4b7f62f118f77b9ed"
> +dependencies = [
> + "tap",
> +]
> +
> +[[package]]
> +name = "zerocopy"
> +version = "0.8.28"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "43fa6694ed34d6e57407afbccdeecfa268c470a7d2a5b0cf49ce9fcc345afb90"
> +dependencies = [
> + "zerocopy-derive",
> +]
> +
> +[[package]]
> +name = "zerocopy-derive"
> +version = "0.8.28"
> +source = "registry+https://github.com/rust-lang/crates.io-index"
> +checksum = "c640b22cd9817fae95be82f0d2f90b11f7605f6c319d16705c459b27ac2cbc26"
> +dependencies = [
> + "proc-macro2",
> + "quote",
> + "syn",
> +]
> diff --git a/tools/router/Cargo.toml b/tools/router/Cargo.toml
> new file mode 100644
> index 0000000..f9d8138
> --- /dev/null
> +++ b/tools/router/Cargo.toml
> @@ -0,0 +1,18 @@
> +# SPDX-License-Identifier: CC0-1.0
> +# SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev>
> +
> +[package]
> +name = "spectrum-router"
> +version = "0.1.0"
> +edition = "2024"
> +
> +[dependencies]
> +anyhow = "1.0.100"
> +clap = { version = "4.5.45", features = ["derive"] }
> +env_logger = "0.11.8"
> +log = { version = "0.4.27", features = ["release_max_level_debug"] }
> +vhost-device-net = "0.1.0"
> +tokio = { version = "1.48.0", features = ["macros", "rt"] }
> +futures-util = "0.3.31"
> +zerocopy = "0.8.27"
> +tokio-stream = "0.1.17"
> diff --git a/tools/router/default.nix b/tools/router/default.nix
> new file mode 100644
> index 0000000..e70f9ec
> --- /dev/null
> +++ b/tools/router/default.nix
> @@ -0,0 +1,18 @@
> +# SPDX-FileCopyrightText: 2024 Alyssa Ross <hi@alyssa.is>
> +# SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev>
> +# SPDX-License-Identifier: MIT
> +
> +import ../../lib/call-package.nix (
> +{ src, lib, rustPlatform }:
> +
> +rustPlatform.buildRustPackage {
> +  name = "spectrum-router";
> +
> +  src = lib.fileset.toSource {
> +    root = ../..;
> +    fileset = lib.fileset.intersection src ./.;
> +  };
> +  sourceRoot = "source/tools/router";
> +
> +  cargoLock.lockFile = ./Cargo.lock;
> +}) (_: {})
> diff --git a/tools/router/src/main.rs b/tools/router/src/main.rs
> new file mode 100644
> index 0000000..42fb8f7
> --- /dev/null
> +++ b/tools/router/src/main.rs
> @@ -0,0 +1,235 @@
> +// SPDX-License-Identifier: EUPL-1.2+
> +// SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev>
> +
> +use std::collections::HashMap;
> +use std::io;
> +use std::net::Ipv6Addr;
> +use std::path::PathBuf;
> +
> +use clap::Parser;

Nit: Would it make sense to use a lighter option parser, possibly even
C getopt?  This isn't going to be used interactively, so completions
aren't a concern.  Reducing the number of dependencies would be a
good idea.

> +use futures_util::SinkExt;
> +use futures_util::StreamExt;
> +use log::{debug, error, info, trace, warn};
> +use tokio::net::UnixListener;
> +use tokio_stream::StreamMap;
> +use vhost_device_net::VhostDeviceNet;
> +
> +use zerocopy::byteorder::network_endian::{U16, U32};
> +use zerocopy::*;
> +
> +type MacAddr = [u8; 6];
> +
> +#[derive(Debug, PartialEq, Eq, FromBytes, IntoBytes, KnownLayout, Immutable, Unaligned)]
> +#[repr(C)]
> +struct EtherFrame {
> +    //preamble_sfd: U64,
> +    dst_addr: MacAddr,
> +    src_addr: MacAddr,
> +    ether_type: U16,
> +    //data: [u8]
> +}
> +
> +impl AsRef<[u8]> for EtherFrame {
> +    fn as_ref(&self) -> &[u8] {
> +        self.as_bytes()
> +    }
> +}
> +
> +#[derive(Debug, PartialEq, Eq, FromBytes, IntoBytes, KnownLayout, Immutable, Unaligned)]
> +#[repr(C)]
> +struct VlanTag {
> +    tag_control_information: U16,
> +    ether_type: U16,
> +}
> +
> +impl AsRef<[u8]> for VlanTag {
> +    fn as_ref(&self) -> &[u8] {
> +        self.as_bytes()
> +    }
> +}
> +
> +#[derive(Debug, PartialEq, Eq, FromBytes, IntoBytes, KnownLayout, Immutable, Unaligned)]
> +#[repr(C)]
> +struct Ipv6Header {
> +    version_traffic_class_flow_label: U32,
> +    payload_length: U16,
> +    hext_header: u8,
> +    hop_limit: u8,
> +    src_addr: [u8; 16],
> +    dst_addr: [u8; 16],
> +    //data: [u8]
> +}
> +
> +impl AsRef<[u8]> for Ipv6Header {
> +    fn as_ref(&self) -> &[u8] {
> +        self.as_bytes()
> +    }
> +}
> +
> +#[derive(Parser, Debug)]
> +#[command()] //version = None, about = None, long_about = None)]
> +struct Args {
> +    #[arg(long)]
> +    driver_listen_path: PathBuf,
> +    #[arg(long)]
> +    app_listen_path: PathBuf,
> +    #[arg(long)]
> +    upstream_interface: u16,
> +}
> +
> +#[tokio::main(flavor = "current_thread")]
> +async fn main() -> anyhow::Result<()> {
> +    env_logger::init();
> +    let args = Args::parse();
> +
> +    run_router(args).await
> +}
> +
> +#[derive(Debug, Clone, PartialEq, Eq, Hash)]
> +enum InterfaceId {
> +    Driver,
> +    App(usize),
> +}
> +
> +async fn run_router(args: Args) -> anyhow::Result<()> {
> +    let driver_listener = UnixListener::bind(&args.driver_listen_path)?;
> +    let app_listener = UnixListener::bind(&args.app_listen_path)?;
> +
> +    let fib: HashMap<Ipv6Addr, (MacAddr, InterfaceId)> = Default::default();
> +
> +    let mut fib = fib.clone();
> +    let mut phys_mac = None;
> +
> +    let mut streams = StreamMap::new();

This won't scale to large numbers of streams.  See the documentation:

> In general, StreamMap works best with a “smallish” number of
> streams as all entries are scanned on insert, remove, and polling.

Also, would it be possible to provide a type signature here?  It's not
necessary, but it makes the code quite a bit easier to review,
especially when one doesn't have an IDE.

> +    let mut sinks = HashMap::<InterfaceId, _>::new();
> +
> +    let mut app_num = 0;
> +
> +    loop {
> +        tokio::select! {

tokio::select! isn't cancellation-safe in general.  Would it make
sense to use multiple tasks instead?

> +            driver_conn = driver_listener.accept() => {
> +                info!("driver connected");
> +                match driver_conn {
> +                    Ok((stream, _addr)) => {
> +                        let device = VhostDeviceNet::from_unix_stream(stream).await?;
> +                        streams.insert(InterfaceId::Driver, Box::pin(device.tx().await?));
> +                        sinks.insert(InterfaceId::Driver, Box::pin(device.rx::<Box<dyn io::Read + Send + Sync + 'static>>().await?));
> +                        phys_mac = None;
> +                    }
> +                    Err(e) => error!("driver connection failed: {}", e),
> +                }
> +            }
> +            app_conn = app_listener.accept() => {
> +                info!("app connected");
> +                match app_conn {
> +                    Ok((stream, _addr)) => {
> +                        let device = VhostDeviceNet::from_unix_stream(stream).await?;
> +                        streams.insert(InterfaceId::App(app_num), Box::pin(device.tx().await?));
> +                        sinks.insert(InterfaceId::App(app_num), Box::pin(device.rx().await?));
> +                        app_num = app_num.checked_add(1).unwrap();
> +                    }
> +                    Err(e) => error!("app connection failed: {}", e),
> +                }
> +            }
> +            next_res = streams.next(), if !streams.is_empty() => {
> +                let Some((key, Ok(buf))) = next_res else {
> +                    info!("incoming other");
> +                    continue;
> +                };
> +                match &key {
> +                    InterfaceId::Driver => {
> +                        use io::Read;
> +                        let mut ether_bytes = buf.take(size_of::<EtherFrame>() as u64);
> +                        let mut ether_frame = EtherFrame::read_from_io(&mut ether_bytes)?;
> +                        let remaining_buf = ether_bytes.into_inner();
> +
> +                        if ether_frame.ether_type != 0x8100 {
> +                            warn!("untagged packet from driver");

Anything that is logged by default should be rate-limited to avoid
filling the host disk or consuming too much CPU.

> +                            //eprintln!("{:x?}", ether_frame);
> +                            //let mut ipv6_bytes = remaining_buf.take(size_of::<Ipv6Header>() as u64);
> +                            //let ipv6_hdr = Ipv6Header::read_from_io(&mut ipv6_bytes)?;
> +                            //let remaining_buf = ipv6_bytes.into_inner();
> +                            //eprintln!("{:x?}", ipv6_hdr);

Would it be possible to make these into proper logs at debug level?

> +                            continue;
> +                        }
> +
> +                        let mut vlan_bytes = remaining_buf.take(size_of::<VlanTag>() as u64);
> +                        let vlan_tag = VlanTag::read_from_io(&mut vlan_bytes)?;
> +                        let remaining_buf = vlan_bytes.into_inner();
> +
> +                        let vlan_id = u16::from(vlan_tag.tag_control_information) & 0xfff;
> +                        if vlan_id != args.upstream_interface {
> +                            debug!("dropping packet with vlan {}", vlan_id);
> +                            continue;
> +                        }
> +                        if !phys_mac.is_some() {
> +                            debug!("set phys mac");
> +                            phys_mac = Some(ether_frame.dst_addr);
> +                        }
> +
> +                        if vlan_tag.ether_type != 0x86dd {
> +                            continue;
> +                        }

Could this use a named constant instead of a magic number?

> +                        let mut ipv6_bytes = remaining_buf.take(size_of::<Ipv6Header>() as u64);
> +                        let ipv6_hdr = Ipv6Header::read_from_io(&mut ipv6_bytes)?;
> +                        let remaining_buf = ipv6_bytes.into_inner();
> +                        trace!("{:x?}", ipv6_hdr);
> +                        let dst_addr = Ipv6Addr::from(ipv6_hdr.dst_addr);
> +
> +                        let Some((dst_mac, if_idx)) = fib.get(&dst_addr) else {
> +                            warn!("dropped incoming message to {} because no fib match", dst_addr);
> +                            continue;
> +                        };
> +                        ether_frame.dst_addr = *dst_mac;
> +                        ether_frame.ether_type = vlan_tag.ether_type;
> +
> +                        sinks.get_mut(if_idx).unwrap().send(Box::new(io::Cursor::new(ether_frame).chain(io::Cursor::new(ipv6_hdr)).chain(remaining_buf))).await.unwrap();
> +                    }
> +                    InterfaceId::App(_) => {
> +                        use io::Read;
> +                        let mut ether_bytes = buf.take(size_of::<EtherFrame>() as u64);
> +                        let mut ether_frame = EtherFrame::read_from_io(&mut ether_bytes)?;
> +                        let remaining_buf = ether_bytes.into_inner();
> +                        trace!("{:x?}", ether_frame);
> +                        if ether_frame.ether_type != 0x86dd {
> +                            continue;
> +                        }

Same here.

> +                        let mut ipv6_bytes = remaining_buf.take(size_of::<Ipv6Header>() as u64);
> +                        let ipv6_hdr = Ipv6Header::read_from_io(&mut ipv6_bytes)?;
> +                        let remaining_buf = ipv6_bytes.into_inner();
> +                        trace!("{:x?}", ipv6_hdr);
> +                        let src_addr = Ipv6Addr::from(ipv6_hdr.src_addr);
> +                        trace!("{:x?}", src_addr);
> +                        if !src_addr.is_unspecified() && !src_addr.is_multicast() && !fib.contains_key(&src_addr) {
> +                            debug!("adding fib entry for {}", src_addr);
> +                            fib.insert(src_addr, (ether_frame.src_addr.clone(), key));
> +                        }

Does this break Duplicate Address Detection?

> +                        let Some(phys_mac) = &phys_mac else {
> +                            warn!("dropped message because phys mac is unknown");
> +                            continue;
> +                        };
> +                        let vlan_tag = VlanTag {
> +                            ether_type: ether_frame.ether_type,
> +                            tag_control_information: args.upstream_interface.into(),
> +                        };
> +                        ether_frame.src_addr = phys_mac.clone();
> +                        ether_frame.ether_type = 0x8100.into();
> +
> +                        let Some(sink) = sinks.get_mut(&InterfaceId::Driver) else {
> +                            warn!("dropped message because driver is not ready");
> +                            continue;
> +                        };
> +
> +                        sink.send(Box::new(io::Cursor::new(ether_frame)
> +                            .chain(io::Cursor::new(vlan_tag))
> +                            .chain(io::Cursor::new(ipv6_hdr))
> +                            .chain(remaining_buf)))
> +                            .await?;
> +                    }
> +                }
> +            }
> +        }
> +    }
> +}

Some general notes that do not need to be addressed (yet):

- The overall design looks somewhat inefficient.  There are multiple
  copies and lots of heap allocations involved.  Some optimization
  opportunities:

  - memcpy() headers between VM memory and on-stack buffers.

  - memcpy() packet bodies from one VM directly to another VM.

  - Batch operations so that each individual operation fits in the
    L1 I-cache if it doesn't already.  This amortizes the cost of
    filling up the L1 I-cache across the entire batch.

  - Batch any needed table lookups.  For instance, if the FIB is a
    longest-prefix lookup tree, one can prefetch all of the cache
    lines that must be accessed before actually loading any of them.

  - If there are a bunch of packets in the buffer and the buffer
    just became empty, spin for a small amount of time before going
    to sleep.

  - The general-purpose Tokio datastructures you are using are probably
    suboptimal performance-wise.

  With proper optimization, I expect that you should be able to beat
  both pasta and the Linux kernel, possibly by a substantial margin.

  This should *not* block merging, but I think it *should* be done at
  some point.  If nothing else, it will improve battery life during
  heavy network I/O.

- Many people (like myself) do not have IPv6 connectivity at all.
  Therefore, this completely breaks networking for them.  I think
  that the old path should remain as an option until IPv4 support
  is implemented.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)