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Test MRG_RXBUF #1795

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Test MRG_RXBUF #1795

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0ff6f3d
virtio-net: allow specifying the buffer size
cagatay-y Jun 27, 2025
cdde3c1
test(virtio-net): have a CI test with small receive buffers
cagatay-y Sep 26, 2025
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5 changes: 5 additions & 0 deletions .github/workflows/ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -233,6 +233,11 @@ jobs:
if: matrix.arch == 'x86_64'
- run: cargo xtask ci rs --arch ${{ matrix.arch }} --profile ${{ matrix.profile }} --package httpd --features ci,hermit/dhcpv4,hermit/virtio-net qemu ${{ matrix.flags }} --devices virtio-net-pci
if: matrix.arch != 'riscv64'
- run: cargo xtask ci rs --arch ${{ matrix.arch }} --profile ${{ matrix.profile }} --package httpd --features ci,hermit/dhcpv4,hermit/virtio-net qemu ${{ matrix.flags }} --devices virtio-net-pci
if: matrix.arch != 'riscv64'
env:
# The buffer is sized to be smaller than the packets received during DHCPv4 address acquisition and thus exercise the buffer merging code path.
HERMIT_MRG_RXBUF_SIZE: 200
- run: cargo xtask ci rs --arch ${{ matrix.arch }} --profile ${{ matrix.profile }} --package httpd --features ci,hermit/virtio-net qemu --sudo --devices virtio-net-pci --tap
if: matrix.arch != 'riscv64'
- run: cargo xtask ci rs --arch ${{ matrix.arch }} --profile ${{ matrix.profile }} --package httpd --features ci,hermit/dhcpv4,hermit/virtio-net qemu ${{ matrix.flags }} --devices virtio-net-pci --no-default-virtio-features
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18 changes: 14 additions & 4 deletions src/drivers/net/virtio/mod.rs
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Expand Up @@ -13,6 +13,7 @@ cfg_if::cfg_if! {
use alloc::boxed::Box;
use alloc::vec::Vec;
use core::mem::{ManuallyDrop, MaybeUninit, transmute};
use core::str::FromStr;

use smallvec::SmallVec;
use smoltcp::phy::{Checksum, ChecksumCapabilities, DeviceCapabilities};
Expand Down Expand Up @@ -59,15 +60,24 @@ fn determine_mtu(dev_cfg: &NetDevCfg) -> u16 {
}
}

fn determine_buf_size(dev_cfg: &NetDevCfg) -> u32 {
fn determine_rx_buf_size(dev_cfg: &NetDevCfg) -> u32 {
// See Virtio specification v1.1 - 5.1.6.3.1 and 5.1.4.2

// Our desired minimum buffer size - we want it to be at least the MTU generally
let mut min_buf_size = determine_mtu(dev_cfg).into();

// If VIRTIO_NET_F_MRG_RXBUF is negotiated, each buffer MUST be at least the size of the struct virtio_net_hdr.
// We just use MTU in that case, but otherwise...
if !dev_cfg.features.contains(virtio::net::F::MRG_RXBUF) {
if dev_cfg.features.contains(virtio::net::F::MRG_RXBUF)
&& let Some(my_mrg_rxbuf_size) = hermit_var!("HERMIT_MRG_RXBUF_SIZE")
{
let my_mrg_rxbuf_size = u32::from_str(&my_mrg_rxbuf_size).unwrap();
assert!(
my_mrg_rxbuf_size > 0,
"VIRTIO does not allow buffer elements of size 0."
);
min_buf_size = my_mrg_rxbuf_size;
} else {
// If [...] are negotiated, the driver SHOULD populate the receive queue(s) with buffers of at least 65562 bytes.
if dev_cfg.features.contains(virtio::net::F::GUEST_TSO4)
|| dev_cfg.features.contains(virtio::net::F::GUEST_TSO6)
Expand All @@ -92,7 +102,7 @@ impl RxQueues {
pub fn new(vqs: Vec<VirtQueue>, dev_cfg: &NetDevCfg) -> Self {
Self {
vqs,
buf_size: determine_buf_size(dev_cfg),
buf_size: determine_rx_buf_size(dev_cfg),
}
}

Expand Down Expand Up @@ -167,7 +177,7 @@ impl TxQueues {
pub fn new(vqs: Vec<VirtQueue>, dev_cfg: &NetDevCfg) -> Self {
Self {
vqs,
buf_size: determine_buf_size(dev_cfg),
buf_size: determine_mtu(dev_cfg).into(),
}
}

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