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>

devices/src/legacy/cmos.rs

@@ -4,18 +4,18 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use libc::{clock_gettime, gmtime_r, timespec, tm, CLOCK_REALTIME};
 use std::cmp::min;
 use std::mem;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Barrier};
 use std::thread;
-use vm_device::BusDevice;
-use vmm_sys_util::eventfd::EventFd;
 
 // https://github.com/rust-lang/libc/issues/1848
 #[cfg_attr(target_env = "musl", allow(deprecated))]
 use libc::time_t;
+use libc::{clock_gettime, gmtime_r, timespec, tm, CLOCK_REALTIME};
+use vm_device::BusDevice;
+use vmm_sys_util::eventfd::EventFd;
 
 const INDEX_MASK: u8 = 0x7f;
 const INDEX_OFFSET: u64 = 0x0;

devices/src/legacy/debug_port.rs

@@ -5,6 +5,7 @@
 
 use std::fmt;
 use std::time::Instant;
+
 use vm_device::BusDevice;
 
 /// Debug I/O port, see:

devices/src/legacy/fwdebug.rs

@@ -8,6 +8,7 @@
 //
 
 use std::sync::{Arc, Barrier};
+
 use vm_device::BusDevice;
 
 /// Provides firmware debug output via I/O port controls

devices/src/legacy/gpio_pl061.rs

@@ -7,16 +7,18 @@
 //! This module implements an ARM PrimeCell General Purpose Input/Output(PL061) to support gracefully poweroff microvm from external.
 //!
 
-use crate::{read_le_u32, write_le_u32};
-use serde::{Deserialize, Serialize};
 use std::io;
 use std::result;
 use std::sync::{Arc, Barrier};
+
+use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use vm_device::interrupt::InterruptSourceGroup;
 use vm_device::BusDevice;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 
+use crate::{read_le_u32, write_le_u32};
+
 const OFS_DATA: u64 = 0x400; // Data Register
 const GPIODIR: u64 = 0x400; // Direction Register
 const GPIOIS: u64 = 0x404; // Interrupt Sense Register
@@ -323,10 +325,11 @@ impl Migratable for Gpio {}
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use vm_device::interrupt::{InterruptIndex, InterruptSourceConfig};
     use vmm_sys_util::eventfd::EventFd;
 
+    use super::*;
+
     const GPIO_NAME: &str = "gpio";
     const LEGACY_GPIO_MAPPED_IO_START: u64 = 0x0902_0000;
 

devices/src/legacy/i8042.rs

@@ -9,6 +9,7 @@ use std::sync::{
     Arc, Barrier,
 };
 use std::thread;
+
 use vm_device::BusDevice;
 use vmm_sys_util::eventfd::EventFd;
 

devices/src/legacy/mod.rs

@@ -24,14 +24,13 @@ pub use self::cmos::Cmos;
 pub use self::debug_port::DebugPort;
 #[cfg(target_arch = "x86_64")]
 pub use self::fwdebug::FwDebugDevice;
-pub use self::i8042::I8042Device;
-pub use self::serial::Serial;
-
 #[cfg(target_arch = "aarch64")]
 pub use self::gpio_pl061::Error as GpioDeviceError;
 #[cfg(target_arch = "aarch64")]
 pub use self::gpio_pl061::Gpio;
+pub use self::i8042::I8042Device;
 #[cfg(target_arch = "aarch64")]
 pub use self::rtc_pl031::Rtc;
+pub use self::serial::Serial;
 #[cfg(target_arch = "aarch64")]
 pub use self::uart_pl011::Pl011;

devices/src/legacy/rtc_pl031.rs

@@ -8,14 +8,16 @@
 //! This is achieved by generating an interrupt signal after counting for a programmed number of cycles of
 //! a real-time clock input.
 //!
-use crate::{read_le_u32, write_le_u32};
 use std::sync::{Arc, Barrier};
 use std::time::Instant;
 use std::{io, result};
+
 use thiserror::Error;
 use vm_device::interrupt::InterruptSourceGroup;
 use vm_device::BusDevice;
 
+use crate::{read_le_u32, write_le_u32};
+
 // As you can see in https://static.docs.arm.com/ddi0224/c/real_time_clock_pl031_r1p3_technical_reference_manual_DDI0224C.pdf
 // at section 3.2 Summary of RTC registers, the total size occupied by this device is 0x000 -> 0xFFC + 4 = 0x1000.
 // From 0x0 to 0x1C we have following registers:
@@ -228,13 +230,14 @@ impl BusDevice for Rtc {
 
 #[cfg(test)]
 mod tests {
+    use vm_device::interrupt::{InterruptIndex, InterruptSourceConfig};
+    use vmm_sys_util::eventfd::EventFd;
+
     use super::*;
     use crate::{
         read_be_u16, read_be_u32, read_le_i32, read_le_u16, read_le_u64, write_be_u16,
         write_be_u32, write_le_i32, write_le_u16, write_le_u64,
     };
-    use vm_device::interrupt::{InterruptIndex, InterruptSourceConfig};
-    use vmm_sys_util::eventfd::EventFd;
 
     const LEGACY_RTC_MAPPED_IO_START: u64 = 0x0901_0000;
 

devices/src/legacy/serial.rs

@@ -5,10 +5,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE-BSD-3-Clause file.
 
-use serde::{Deserialize, Serialize};
 use std::collections::VecDeque;
 use std::sync::{Arc, Barrier};
 use std::{io, result};
+
+use serde::{Deserialize, Serialize};
 use vm_device::interrupt::InterruptSourceGroup;
 use vm_device::BusDevice;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
@@ -340,11 +341,13 @@ impl Migratable for Serial {}
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use std::sync::Mutex;
+
     use vm_device::interrupt::{InterruptIndex, InterruptSourceConfig};
     use vmm_sys_util::eventfd::EventFd;
 
+    use super::*;
+
     const SERIAL_NAME: &str = "serial";
 
     struct TestInterrupt {

devices/src/legacy/uart_pl011.rs

@@ -6,17 +6,19 @@
 //! This module implements an ARM PrimeCell UART(PL011).
 //!
 
-use crate::{read_le_u32, write_le_u32};
-use serde::{Deserialize, Serialize};
 use std::collections::VecDeque;
 use std::sync::{Arc, Barrier};
 use std::time::Instant;
 use std::{io, result};
+
+use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use vm_device::interrupt::InterruptSourceGroup;
 use vm_device::BusDevice;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 
+use crate::{read_le_u32, write_le_u32};
+
 /* Registers */
 const UARTDR: u64 = 0;
 const UARTRSR_UARTECR: u64 = 1;
@@ -452,11 +454,13 @@ impl Migratable for Pl011 {}
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use std::sync::Mutex;
+
     use vm_device::interrupt::{InterruptIndex, InterruptSourceConfig};
     use vmm_sys_util::eventfd::EventFd;
 
+    use super::*;
+
     const SERIAL_NAME: &str = "serial";
 
     struct TestInterrupt {