net_util, virtio-devices, vhost_user_net: Relocate {Rx,Tx}Virtio

By moving the code for opening the two RX and TX queues into a shared
location we are starting to remove the requirement for the
vhost-user-net backend to depend on the virtio-devices crate which in of
itself depends on many other crates that are not necessary for the
backend to function.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

net_util/src/queue_pair.rs

@@ -0,0 +1,189 @@
+// Copyright (c) 2020 Intel Corporation. All rights reserved.
+//
+// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
+
+use super::Tap;
+use std::cmp;
+use std::io::Write;
+use std::num::Wrapping;
+use vm_memory::{Bytes, GuestAddress, GuestMemoryMmap};
+use vm_virtio::{DescriptorChain, Queue};
+use virtio_bindings::bindings::virtio_net::virtio_net_hdr_v1
+
+/// The maximum buffer size when segmentation offload is enabled. This
+/// includes the 12-byte virtio net header.
+/// http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html#x1-1740003
+const MAX_BUFFER_SIZE: usize = 65562;
+
+#[derive(Clone)]
+pub struct TxVirtio {
+    pub iovec: Vec<(GuestAddress, usize)>,
+    pub frame_buf: [u8; MAX_BUFFER_SIZE],
+    pub counter_bytes: Wrapping<u64>,
+    pub counter_frames: Wrapping<u64>,
+}
+
+impl Default for TxVirtio {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl TxVirtio {
+    pub fn new() -> Self {
+        TxVirtio {
+            iovec: Vec::new(),
+            frame_buf: [0u8; MAX_BUFFER_SIZE],
+            counter_bytes: Wrapping(0),
+            counter_frames: Wrapping(0),
+        }
+    }
+
+    pub fn process_desc_chain(&mut self, mem: &GuestMemoryMmap, tap: &mut Tap, queue: &mut Queue) {
+        while let Some(avail_desc) = queue.iter(&mem).next() {
+            let head_index = avail_desc.index;
+            let mut read_count = 0;
+            let mut next_desc = Some(avail_desc);
+
+            self.iovec.clear();
+            while let Some(desc) = next_desc {
+                if desc.is_write_only() {
+                    break;
+                }
+                self.iovec.push((desc.addr, desc.len as usize));
+                read_count += desc.len as usize;
+                next_desc = desc.next_descriptor();
+            }
+
+            read_count = 0;
+            // Copy buffer from across multiple descriptors.
+            // TODO(performance - Issue #420): change this to use `writev()` instead of `write()`
+            // and get rid of the intermediate buffer.
+            for (desc_addr, desc_len) in self.iovec.drain(..) {
+                let limit = cmp::min((read_count + desc_len) as usize, self.frame_buf.len());
+
+                let read_result =
+                    mem.read_slice(&mut self.frame_buf[read_count..limit as usize], desc_addr);
+                match read_result {
+                    Ok(_) => {
+                        // Increment by number of bytes actually read
+                        read_count += limit - read_count;
+                    }
+                    Err(e) => {
+                        println!("Failed to read slice: {:?}", e);
+                        break;
+                    }
+                }
+            }
+
+            let write_result = tap.write(&self.frame_buf[..read_count]);
+            match write_result {
+                Ok(_) => {}
+                Err(e) => {
+                    println!("net: tx: error failed to write to tap: {}", e);
+                }
+            };
+
+            self.counter_bytes += Wrapping((read_count - vnet_hdr_len()) as u64);
+            self.counter_frames += Wrapping(1);
+
+            queue.add_used(&mem, head_index, 0);
+            queue.update_avail_event(&mem);
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct RxVirtio {
+    pub deferred_frame: bool,
+    pub deferred_irqs: bool,
+    pub bytes_read: usize,
+    pub frame_buf: [u8; MAX_BUFFER_SIZE],
+    pub counter_bytes: Wrapping<u64>,
+    pub counter_frames: Wrapping<u64>,
+}
+
+impl Default for RxVirtio {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl RxVirtio {
+    pub fn new() -> Self {
+        RxVirtio {
+            deferred_frame: false,
+            deferred_irqs: false,
+            bytes_read: 0,
+            frame_buf: [0u8; MAX_BUFFER_SIZE],
+            counter_bytes: Wrapping(0),
+            counter_frames: Wrapping(0),
+        }
+    }
+
+    pub fn process_desc_chain(
+        &mut self,
+        mem: &GuestMemoryMmap,
+        mut next_desc: Option<DescriptorChain>,
+        queue: &mut Queue,
+    ) -> bool {
+        let head_index = next_desc.as_ref().unwrap().index;
+        let mut write_count = 0;
+
+        // Copy from frame into buffer, which may span multiple descriptors.
+        loop {
+            match next_desc {
+                Some(desc) => {
+                    if !desc.is_write_only() {
+                        break;
+                    }
+                    let limit = cmp::min(write_count + desc.len as usize, self.bytes_read);
+                    let source_slice = &self.frame_buf[write_count..limit];
+                    let write_result = mem.write_slice(source_slice, desc.addr);
+
+                    match write_result {
+                        Ok(_) => {
+                            write_count = limit;
+                        }
+                        Err(e) => {
+                            error!("Failed to write slice: {:?}", e);
+                            break;
+                        }
+                    };
+
+                    if write_count >= self.bytes_read {
+                        break;
+                    }
+                    next_desc = desc.next_descriptor();
+                }
+                None => {
+                    warn!("Receiving buffer is too small to hold frame of current size");
+                    break;
+                }
+            }
+        }
+
+        self.counter_bytes += Wrapping((write_count - vnet_hdr_len()) as u64);
+        self.counter_frames += Wrapping(1);
+
+        queue.add_used(&mem, head_index, write_count as u32);
+        queue.update_avail_event(&mem);
+
+        // Mark that we have at least one pending packet and we need to interrupt the guest.
+        self.deferred_irqs = true;
+
+        // Update the frame_buf buffer.
+        if write_count < self.bytes_read {
+            self.frame_buf.copy_within(write_count..self.bytes_read, 0);
+            self.bytes_read -= write_count;
+            false
+        } else {
+            self.bytes_read = 0;
+            true
+        }
+    }
+}
+
+fn vnet_hdr_len() -> usize {
+    std::mem::size_of::<virtio_net_hdr_v1>()
+}