net: move net_hdr operations to the backends

We're going to incorporate a new backend that doesn't require us to
write the header on each frame, so move this functionality from the
worker to each backend.

Signed-off-by: Sergio Lopez <[email protected]>

Author: slp

src/devices/src/virtio/net/unixgram.rs

@@ -8,6 +8,7 @@ use std::os::fd::{AsRawFd, RawFd};
 use std::path::PathBuf;
 
 use super::backend::{ConnectError, NetBackend, ReadError, WriteError};
+use super::write_virtio_net_hdr;
 
 const VFKIT_MAGIC: [u8; 4] = *b"VFKT";
 
@@ -94,7 +95,8 @@ impl Unixgram {
 impl NetBackend for Unixgram {
     /// Try to read a frame the proxy. If no bytes are available reports ReadError::NothingRead
     fn read_frame(&mut self, buf: &mut [u8]) -> Result<usize, ReadError> {
-        let frame_length = match recv(self.fd, buf, MsgFlags::empty()) {
+        let hdr_len = write_virtio_net_hdr(buf);
+        let frame_length = match recv(self.fd, &mut buf[hdr_len..], MsgFlags::empty()) {
             Ok(f) => f,
             #[allow(unreachable_patterns)]
             Err(nix::Error::EAGAIN | nix::Error::EWOULDBLOCK) => {
@@ -105,7 +107,7 @@ impl NetBackend for Unixgram {
             }
         };
         debug!("Read eth frame from proxy: {frame_length} bytes");
-        Ok(frame_length)
+        Ok(hdr_len + frame_length)
     }
 
     /// Try to write a frame to the proxy.

src/devices/src/virtio/net/unixstream.rs

@@ -10,6 +10,7 @@ use std::{
 use crate::virtio::net::backend::ConnectError;
 
 use super::backend::{NetBackend, ReadError, WriteError};
+use super::write_virtio_net_hdr;
 
 /// Each frame the network proxy is prepended by a 4 byte "header".
 /// It is interpreted as a big-endian u32 integer and is the length of the following ethernet frame.
@@ -158,11 +159,13 @@ impl NetBackend for Unixstream {
             };
         }
 
+        let hdr_len = write_virtio_net_hdr(buf);
+        let buf = &mut buf[hdr_len..];
         let frame_length = self.expecting_frame_length as usize;
         self.read_loop(&mut buf[..frame_length], false)?;
         self.expecting_frame_length = 0;
         log::trace!("Read eth frame from network proxy: {frame_length} bytes");
-        Ok(frame_length)
+        Ok(hdr_len + frame_length)
     }
 
     /// Try to write a frame to the proxy.

src/devices/src/virtio/net/worker.rs

@@ -7,7 +7,7 @@ use crate::Error as DeviceError;
 
 use super::backend::{NetBackend, ReadError, WriteError};
 use super::device::{FrontendError, RxError, TxError, VirtioNetBackend};
-use super::{vnet_hdr_len, write_virtio_net_hdr};
+use super::vnet_hdr_len;
 
 use std::os::fd::AsRawFd;
 use std::sync::atomic::AtomicUsize;
@@ -456,10 +456,7 @@ impl NetWorker {
 
     /// Fills self.rx_frame_buf with an ethernet frame from backend and prepends virtio_net_hdr to it
     fn read_into_rx_frame_buf_from_backend(&mut self) -> result::Result<(), ReadError> {
-        let mut len = 0;
-        len += write_virtio_net_hdr(&mut self.rx_frame_buf);
-        len += self.backend.read_frame(&mut self.rx_frame_buf[len..])?;
-        self.rx_frame_buf_len = len;
+        self.rx_frame_buf_len = self.backend.read_frame(&mut self.rx_frame_buf)?;
         Ok(())
     }
 }