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>

block/src/vhdx/mod.rs

@@ -2,6 +2,15 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+use std::collections::btree_map::BTreeMap;
+use std::fs::File;
+use std::io::{Read, Seek, SeekFrom, Write};
+
+use byteorder::{BigEndian, ByteOrder};
+use remain::sorted;
+use thiserror::Error;
+use uuid::Uuid;
+
 use crate::vhdx::{
     vhdx_bat::{BatEntry, VhdxBatError},
     vhdx_header::{RegionInfo, RegionTableEntry, VhdxHeader, VhdxHeaderError},
@@ -9,13 +18,6 @@ use crate::vhdx::{
     vhdx_metadata::{DiskSpec, VhdxMetadataError},
 };
 use crate::BlockBackend;
-use byteorder::{BigEndian, ByteOrder};
-use remain::sorted;
-use std::collections::btree_map::BTreeMap;
-use std::fs::File;
-use std::io::{Read, Seek, SeekFrom, Write};
-use thiserror::Error;
-use uuid::Uuid;
 
 macro_rules! div_round_up {
     ($n:expr,$d:expr) => {

block/src/vhdx/vhdx_bat.rs

@@ -2,14 +2,16 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::vhdx::{vhdx_header::RegionTableEntry, vhdx_metadata::DiskSpec};
-use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
-use remain::sorted;
 use std::fs::File;
 use std::io::{self, Seek, SeekFrom};
 use std::mem::size_of;
+
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
+use remain::sorted;
 use thiserror::Error;
 
+use crate::vhdx::{vhdx_header::RegionTableEntry, vhdx_metadata::DiskSpec};
+
 // Payload BAT Entry States
 pub const PAYLOAD_BLOCK_NOT_PRESENT: u64 = 0;
 pub const PAYLOAD_BLOCK_UNDEFINED: u64 = 1;

block/src/vhdx/vhdx_header.rs

@@ -4,12 +4,13 @@
 
 extern crate log;
 
-use byteorder::{ByteOrder, LittleEndian, ReadBytesExt};
-use remain::sorted;
 use std::collections::btree_map::BTreeMap;
 use std::fs::File;
 use std::io::{self, Read, Seek, SeekFrom, Write};
 use std::mem::size_of;
+
+use byteorder::{ByteOrder, LittleEndian, ReadBytesExt};
+use remain::sorted;
 use thiserror::Error;
 use uuid::Uuid;
 

block/src/vhdx/vhdx_io.rs

@@ -2,14 +2,16 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+use std::fs::File;
+use std::io::{self, Read, Seek, SeekFrom, Write};
+
+use remain::sorted;
+use thiserror::Error;
+
 use crate::vhdx::{
     vhdx_bat::{self, BatEntry, VhdxBatError},
     vhdx_metadata::{self, DiskSpec},
 };
-use remain::sorted;
-use std::fs::File;
-use std::io::{self, Read, Seek, SeekFrom, Write};
-use thiserror::Error;
 
 const SECTOR_SIZE: u64 = 512;
 

block/src/vhdx/vhdx_metadata.rs

@@ -2,15 +2,17 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::vhdx::vhdx_header::RegionTableEntry;
-use byteorder::{LittleEndian, ReadBytesExt};
-use remain::sorted;
 use std::fs::File;
 use std::io::{self, Read, Seek, SeekFrom};
 use std::mem::size_of;
+
+use byteorder::{LittleEndian, ReadBytesExt};
+use remain::sorted;
 use thiserror::Error;
 use uuid::Uuid;
 
+use crate::vhdx::vhdx_header::RegionTableEntry;
+
 const METADATA_SIGN: u64 = 0x6174_6164_6174_656D;
 const METADATA_ENTRY_SIZE: usize = 32;
 const METADATA_MAX_ENTRIES: u16 = 2047;