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>

arch/src/x86_64/mod.rs

@@ -12,22 +12,24 @@ pub mod layout;
 mod mpspec;
 mod mptable;
 pub mod regs;
-use crate::GuestMemoryMmap;
-use crate::InitramfsConfig;
-use crate::RegionType;
+use std::collections::BTreeMap;
+use std::mem;
+
 use hypervisor::arch::x86::{CpuIdEntry, CPUID_FLAG_VALID_INDEX};
 use hypervisor::{CpuVendor, HypervisorCpuError, HypervisorError};
 use linux_loader::loader::bootparam::{boot_params, setup_header};
 use linux_loader::loader::elf::start_info::{
     hvm_memmap_table_entry, hvm_modlist_entry, hvm_start_info,
 };
-use std::collections::BTreeMap;
-use std::mem;
 use thiserror::Error;
 use vm_memory::{
     Address, Bytes, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic,
     GuestMemoryRegion, GuestUsize,
 };
+
+use crate::GuestMemoryMmap;
+use crate::InitramfsConfig;
+use crate::RegionType;
 mod smbios;
 use std::arch::x86_64;
 #[cfg(feature = "tdx")]
@@ -1551,9 +1553,10 @@ fn update_cpuid_sgx(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use linux_loader::loader::bootparam::boot_e820_entry;
 
+    use super::*;
+
     #[test]
     fn regions_base_addr() {
         let regions = arch_memory_regions();

arch/src/x86_64/mptable.rs

@@ -5,16 +5,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE-BSD-3-Clause file.
 
-use crate::layout::{APIC_START, HIGH_RAM_START, IOAPIC_START};
-use crate::x86_64::{get_x2apic_id, mpspec};
-use crate::GuestMemoryMmap;
-use libc::c_uchar;
 use std::mem;
 use std::result;
 use std::slice;
+
+use libc::c_uchar;
 use thiserror::Error;
 use vm_memory::{Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError};
 
+use crate::layout::{APIC_START, HIGH_RAM_START, IOAPIC_START};
+use crate::x86_64::{get_x2apic_id, mpspec};
+use crate::GuestMemoryMmap;
+
 // This is a workaround to the Rust enforcement specifying that any implementation of a foreign
 // trait (in this case `ByteValued`) where:
 // *    the type that is implementing the trait is foreign or
@@ -304,12 +306,13 @@ pub fn setup_mptable(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
-    use crate::layout::MPTABLE_START;
     use vm_memory::{
         bitmap::BitmapSlice, GuestUsize, VolatileMemoryError, VolatileSlice, WriteVolatile,
     };
 
+    use super::*;
+    use crate::layout::MPTABLE_START;
+
     fn table_entry_size(type_: u8) -> usize {
         match type_ as u32 {
             mpspec::MP_PROCESSOR => mem::size_of::<MpcCpuWrapper>(),

arch/src/x86_64/regs.rs

@@ -6,17 +6,19 @@
 // Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE-BSD-3-Clause file.
+use std::sync::Arc;
+use std::{mem, result};
+
+use hypervisor::arch::x86::gdt::{gdt_entry, segment_from_gdt};
+use hypervisor::arch::x86::regs::CR0_PE;
+use hypervisor::arch::x86::{FpuState, SpecialRegisters};
+use thiserror::Error;
+use vm_memory::{Address, Bytes, GuestMemory, GuestMemoryError};
+
 use crate::layout::{
     BOOT_GDT_START, BOOT_IDT_START, BOOT_STACK_POINTER, PVH_INFO_START, ZERO_PAGE_START,
 };
 use crate::{EntryPoint, GuestMemoryMmap};
-use hypervisor::arch::x86::gdt::{gdt_entry, segment_from_gdt};
-use hypervisor::arch::x86::regs::CR0_PE;
-use hypervisor::arch::x86::{FpuState, SpecialRegisters};
-use std::sync::Arc;
-use std::{mem, result};
-use thiserror::Error;
-use vm_memory::{Address, Bytes, GuestMemory, GuestMemoryError};
 
 #[derive(Debug, Error)]
 pub enum Error {
@@ -186,9 +188,10 @@ pub fn configure_segments_and_sregs(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use vm_memory::GuestAddress;
 
+    use super::*;
+
     fn create_guest_mem() -> GuestMemoryMmap {
         GuestMemoryMmap::from_ranges(&[(GuestAddress(0), 0x10000)]).unwrap()
     }

arch/src/x86_64/smbios.rs

@@ -6,16 +6,18 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use crate::layout::SMBIOS_START;
-use crate::GuestMemoryMmap;
 use std::mem;
 use std::result;
 use std::slice;
+
 use thiserror::Error;
 use uuid::Uuid;
 use vm_memory::ByteValued;
 use vm_memory::{Address, Bytes, GuestAddress};
 
+use crate::layout::SMBIOS_START;
+use crate::GuestMemoryMmap;
+
 #[derive(Debug, Error)]
 pub enum Error {
     /// There was too little guest memory to store the entire SMBIOS table.

arch/src/x86_64/tdx/mod.rs

@@ -1,14 +1,16 @@
 // Copyright © 2021 Intel Corporation
 //
 // SPDX-License-Identifier: Apache-2.0
-use crate::GuestMemoryMmap;
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom};
 use std::str::FromStr;
+
 use thiserror::Error;
 use uuid::Uuid;
 use vm_memory::{ByteValued, Bytes, GuestAddress, GuestMemoryError};
 
+use crate::GuestMemoryMmap;
+
 #[derive(Error, Debug)]
 pub enum TdvfError {
     #[error("Failed read TDVF descriptor: {0}")]