misc: Adapt consistent import style formatting

Historically the Cloud Hypervisor coding style has been to ensure that
all imports are ordered and placed in a single group. Unfortunately
cargo fmt has no support for ensuring that all imports are in a single
group so if whitespace lines were added as part of the import statements
then they would only be odered correctly in the group.

By adopting "group_imports="StdExternalCrate" we can enforce a style
where imports are placed in at most three groups for std, external
crates and the crate itself. Choosing a style enforceable by the tooling
reduces the reviewer burden.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

net_util/src/ctrl_queue.rs

@@ -2,10 +2,9 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use crate::GuestMemoryMmap;
-use crate::Tap;
-use libc::c_uint;
 use std::sync::Arc;
+
+use libc::c_uint;
 use virtio_bindings::virtio_net::{
     VIRTIO_NET_CTRL_GUEST_OFFLOADS, VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, VIRTIO_NET_CTRL_MQ,
     VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN,
@@ -17,6 +16,9 @@ use virtio_queue::{Queue, QueueT};
 use vm_memory::{ByteValued, Bytes, GuestMemoryError};
 use vm_virtio::{AccessPlatform, Translatable};
 
+use crate::GuestMemoryMmap;
+use crate::Tap;
+
 #[derive(Debug)]
 pub enum Error {
     /// Read queue failed.

net_util/src/lib.rs

@@ -14,13 +14,13 @@ mod open_tap;
 mod queue_pair;
 mod tap;
 
-use serde::{Deserialize, Serialize};
 use std::io::Error as IoError;
 use std::os::raw::c_uint;
 use std::os::unix::io::{FromRawFd, RawFd};
 use std::{io, mem, net};
-use thiserror::Error;
 
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
 use virtio_bindings::virtio_net::{
     virtio_net_hdr_v1, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN,
     VIRTIO_NET_F_GUEST_CSUM, VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_TSO4,

net_util/src/open_tap.rs

@@ -2,12 +2,14 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use super::{vnet_hdr_len, MacAddr, Tap, TapError};
 use std::net::Ipv4Addr;
 use std::path::Path;
 use std::{fs, io};
+
 use thiserror::Error;
 
+use super::{vnet_hdr_len, MacAddr, Tap, TapError};
+
 #[derive(Error, Debug)]
 pub enum Error {
     #[error("Failed to convert an hexadecimal string into an integer: {0}")]

net_util/src/queue_pair.rs

@@ -2,19 +2,21 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use super::{register_listener, unregister_listener, vnet_hdr_len, Tap};
-use rate_limiter::{RateLimiter, TokenType};
 use std::io;
 use std::num::Wrapping;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
+
+use rate_limiter::{RateLimiter, TokenType};
 use thiserror::Error;
 use virtio_queue::{Queue, QueueOwnedT, QueueT};
 use vm_memory::bitmap::Bitmap;
 use vm_memory::{Bytes, GuestMemory};
 use vm_virtio::{AccessPlatform, Translatable};
 
+use super::{register_listener, unregister_listener, vnet_hdr_len, Tap};
+
 #[derive(Clone)]
 pub struct TxVirtio {
     pub counter_bytes: Wrapping<u64>,

net_util/src/tap.rs

@@ -5,19 +5,21 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the THIRD-PARTY file.
 
-use super::{
-    create_inet_socket, create_sockaddr, create_unix_socket, vnet_hdr_len, Error as NetUtilError,
-    MacAddr,
-};
-use crate::mac::MAC_ADDR_LEN;
 use std::fs::File;
 use std::io::{Error as IoError, Read, Result as IoResult, Write};
 use std::net;
 use std::os::raw::*;
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
+
 use thiserror::Error;
 use vmm_sys_util::ioctl::{ioctl_with_mut_ref, ioctl_with_ref, ioctl_with_val};
 
+use super::{
+    create_inet_socket, create_sockaddr, create_unix_socket, vnet_hdr_len, Error as NetUtilError,
+    MacAddr,
+};
+use crate::mac::MAC_ADDR_LEN;
+
 #[derive(Error, Debug)]
 pub enum Error {
     #[error("Couldn't open /dev/net/tun: {0}")]
@@ -428,7 +430,6 @@ mod tests {
     use std::time::Duration;
 
     use once_cell::sync::Lazy;
-
     use pnet::packet::ethernet::{EtherTypes, EthernetPacket, MutableEthernetPacket};
     use pnet::packet::ip::IpNextHeaderProtocols;
     use pnet::packet::ipv4::{Ipv4Packet, MutableIpv4Packet};