android_sparse.rs

// Copyright 2019 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// https://android.googlesource.com/platform/system/core/+/7b444f0/libsparse/sparse_format.h

use std::collections::BTreeMap;
use std::fs::File;
use std::io;
use std::io::ErrorKind;
use std::io::Read;
use std::io::Seek;
use std::io::SeekFrom;
use std::mem;
use std::sync::Arc;

use async_trait::async_trait;
use base::AsRawDescriptor;
use base::FileAllocate;
use base::FileReadWriteAtVolatile;
use base::FileSetLen;
use base::RawDescriptor;
use base::VolatileSlice;
use cros_async::BackingMemory;
use cros_async::Executor;
use cros_async::IoSource;
use data_model::Le16;
use data_model::Le32;
use remain::sorted;
use thiserror::Error;
use zerocopy::FromBytes;
use zerocopy::FromZeros;
use zerocopy::Immutable;
use zerocopy::IntoBytes;
use zerocopy::KnownLayout;

use crate::AsyncDisk;
use crate::DiskFile;
use crate::DiskGetLen;
use crate::Error as DiskError;
use crate::Result as DiskResult;
use crate::ToAsyncDisk;

#[sorted]
#[derive(Error, Debug)]
pub enum Error {
    #[error("invalid magic header for android sparse format")]
    InvalidMagicHeader,
    #[error("invalid specification: \"{0}\"")]
    InvalidSpecification(String),
    #[error("failed to read specification: \"{0}\"")]
    ReadSpecificationError(io::Error),
}

pub type Result<T> = std::result::Result<T, Error>;

pub const SPARSE_HEADER_MAGIC: u32 = 0xed26ff3a;
const MAJOR_VERSION: u16 = 1;

#[repr(C)]
#[derive(Clone, Copy, Debug, FromBytes, Immutable, IntoBytes, KnownLayout)]
struct SparseHeader {
    magic: Le32,          // SPARSE_HEADER_MAGIC
    major_version: Le16,  // (0x1) - reject images with higher major versions
    minor_version: Le16,  // (0x0) - allow images with higer minor versions
    file_hdr_sz: Le16,    // 28 bytes for first revision of the file format
    chunk_hdr_size: Le16, // 12 bytes for first revision of the file format
    blk_sz: Le32,         // block size in bytes, must be a multiple of 4 (4096)
    total_blks: Le32,     // total blocks in the non-sparse output image
    total_chunks: Le32,   // total chunks in the sparse input image
    // CRC32 checksum of the original data, counting "don't care" as 0. Standard 802.3 polynomial,
    // use a Public Domain table implementation
    image_checksum: Le32,
}

const CHUNK_TYPE_RAW: u16 = 0xCAC1;
const CHUNK_TYPE_FILL: u16 = 0xCAC2;
const CHUNK_TYPE_DONT_CARE: u16 = 0xCAC3;
const CHUNK_TYPE_CRC32: u16 = 0xCAC4;

#[repr(C)]
#[derive(Clone, Copy, Debug, FromBytes, Immutable, IntoBytes, KnownLayout)]
struct ChunkHeader {
    chunk_type: Le16, /* 0xCAC1 -> raw; 0xCAC2 -> fill; 0xCAC3 -> don't care */
    reserved1: u16,
    chunk_sz: Le32, /* in blocks in output image */
    total_sz: Le32, /* in bytes of chunk input file including chunk header and data */
}

#[derive(Clone, Debug, PartialEq, Eq)]
enum Chunk {
    Raw(u64), // Offset into the file
    Fill([u8; 4]),
    DontCare,
}

#[derive(Clone, Debug, PartialEq, Eq)]
struct ChunkWithSize {
    chunk: Chunk,
    expanded_size: u64,
}

/* Following a Raw or Fill or CRC32 chunk is data.
 *  For a Raw chunk, it's the data in chunk_sz * blk_sz.
 *  For a Fill chunk, it's 4 bytes of the fill data.
 *  For a CRC32 chunk, it's 4 bytes of CRC32
 */
#[derive(Debug)]
pub struct AndroidSparse {
    file: File,
    total_size: u64,
    chunks: BTreeMap<u64, ChunkWithSize>,
}

fn parse_chunk<T: Read + Seek>(input: &mut T, blk_sz: u64) -> Result<Option<ChunkWithSize>> {
    const HEADER_SIZE: usize = mem::size_of::<ChunkHeader>();
    let current_offset = input
        .stream_position()
        .map_err(Error::ReadSpecificationError)?;
    let mut chunk_header = ChunkHeader::new_zeroed();
    input
        .read_exact(chunk_header.as_mut_bytes())
        .map_err(Error::ReadSpecificationError)?;
    let chunk_body_size = (chunk_header.total_sz.to_native() as usize)
        .checked_sub(HEADER_SIZE)
        .ok_or(Error::InvalidSpecification(format!(
            "chunk total_sz {} smaller than header size {}",
            chunk_header.total_sz.to_native(),
            HEADER_SIZE
        )))?;
    let chunk = match chunk_header.chunk_type.to_native() {
        CHUNK_TYPE_RAW => {
            input
                .seek(SeekFrom::Current(chunk_body_size as i64))
                .map_err(Error::ReadSpecificationError)?;
            Chunk::Raw(current_offset + HEADER_SIZE as u64)
        }
        CHUNK_TYPE_FILL => {
            let mut fill_bytes = [0u8; 4];
            if chunk_body_size != fill_bytes.len() {
                return Err(Error::InvalidSpecification(format!(
                    "Fill chunk had bad size. Expected {}, was {}",
                    fill_bytes.len(),
                    chunk_body_size
                )));
            }
            input
                .read_exact(&mut fill_bytes)
                .map_err(Error::ReadSpecificationError)?;
            Chunk::Fill(fill_bytes)
        }
        CHUNK_TYPE_DONT_CARE => Chunk::DontCare,
        CHUNK_TYPE_CRC32 => return Ok(None), // TODO(schuffelen): Validate crc32s in input
        unknown_type => {
            return Err(Error::InvalidSpecification(format!(
                "Chunk had invalid type, was {unknown_type:x}"
            )))
        }
    };
    let expanded_size = chunk_header.chunk_sz.to_native() as u64 * blk_sz;
    Ok(Some(ChunkWithSize {
        chunk,
        expanded_size,
    }))
}

impl AndroidSparse {
    pub fn from_file(mut file: File) -> Result<AndroidSparse> {
        file.seek(SeekFrom::Start(0))
            .map_err(Error::ReadSpecificationError)?;
        let mut sparse_header = SparseHeader::new_zeroed();
        file.read_exact(sparse_header.as_mut_bytes())
            .map_err(Error::ReadSpecificationError)?;
        if sparse_header.magic != SPARSE_HEADER_MAGIC {
            return Err(Error::InvalidSpecification(format!(
                "Header did not match magic constant. Expected {:x}, was {:x}",
                SPARSE_HEADER_MAGIC,
                sparse_header.magic.to_native()
            )));
        } else if sparse_header.major_version != MAJOR_VERSION {
            return Err(Error::InvalidSpecification(format!(
                "Header major version did not match. Expected {}, was {}",
                MAJOR_VERSION,
                sparse_header.major_version.to_native(),
            )));
        } else if sparse_header.chunk_hdr_size.to_native() as usize != mem::size_of::<ChunkHeader>()
        {
            // The canonical parser for this format allows `chunk_hdr_size >= sizeof(ChunkHeader)`,
            // but we've chosen to be stricter for simplicity.
            return Err(Error::InvalidSpecification(format!(
                "Chunk header size does not match chunk header struct, expected {}, was {}",
                sparse_header.chunk_hdr_size.to_native(),
                mem::size_of::<ChunkHeader>()
            )));
        }
        let block_size = sparse_header.blk_sz.to_native() as u64;
        let chunks = (0..sparse_header.total_chunks.to_native())
            .filter_map(|_| parse_chunk(&mut file, block_size).transpose())
            .collect::<Result<Vec<ChunkWithSize>>>()?;
        let total_size =
            sparse_header.total_blks.to_native() as u64 * sparse_header.blk_sz.to_native() as u64;
        AndroidSparse::from_parts(file, total_size, chunks)
    }

    fn from_parts(file: File, size: u64, chunks: Vec<ChunkWithSize>) -> Result<AndroidSparse> {
        let mut chunks_map: BTreeMap<u64, ChunkWithSize> = BTreeMap::new();
        let mut expanded_location: u64 = 0;
        for chunk_with_size in chunks {
            let size = chunk_with_size.expanded_size;
            if chunks_map
                .insert(expanded_location, chunk_with_size)
                .is_some()
            {
                return Err(Error::InvalidSpecification(format!(
                    "Two chunks were at {expanded_location}"
                )));
            }
            expanded_location += size;
        }
        let image = AndroidSparse {
            file,
            total_size: size,
            chunks: chunks_map,
        };
        let calculated_len: u64 = image.chunks.iter().map(|x| x.1.expanded_size).sum();
        if calculated_len != size {
            return Err(Error::InvalidSpecification(format!(
                "Header promised size {size}, chunks added up to {calculated_len}"
            )));
        }
        Ok(image)
    }
}

impl DiskGetLen for AndroidSparse {
    fn get_len(&self) -> io::Result<u64> {
        Ok(self.total_size)
    }
}

impl FileSetLen for AndroidSparse {
    fn set_len(&self, _len: u64) -> io::Result<()> {
        Err(io::Error::new(
            ErrorKind::PermissionDenied,
            "unsupported operation",
        ))
    }
}

impl AsRawDescriptor for AndroidSparse {
    fn as_raw_descriptor(&self) -> RawDescriptor {
        self.file.as_raw_descriptor()
    }
}

// Performs reads up to the chunk boundary.
impl FileReadWriteAtVolatile for AndroidSparse {
    fn read_at_volatile(&self, slice: VolatileSlice, offset: u64) -> io::Result<usize> {
        let found_chunk = self.chunks.range(..=offset).next_back();
        let (
            chunk_start,
            ChunkWithSize {
                chunk,
                expanded_size,
            },
        ) = found_chunk.ok_or_else(|| {
            io::Error::new(
                ErrorKind::UnexpectedEof,
                format!("no chunk for offset {offset}"),
            )
        })?;
        let chunk_offset = offset - chunk_start;
        let chunk_size = *expanded_size;
        let subslice = if chunk_offset + (slice.size() as u64) > chunk_size {
            slice
                .sub_slice(0, (chunk_size - chunk_offset) as usize)
                .map_err(|e| io::Error::new(ErrorKind::InvalidData, format!("{e:?}")))?
        } else {
            slice
        };
        match chunk {
            Chunk::DontCare => {
                subslice.write_bytes(0);
                Ok(subslice.size())
            }
            Chunk::Raw(file_offset) => self
                .file
                .read_at_volatile(subslice, *file_offset + chunk_offset),
            Chunk::Fill(fill_bytes) => {
                let chunk_offset_mod = chunk_offset % fill_bytes.len() as u64;
                let filled_memory: Vec<u8> = fill_bytes
                    .iter()
                    .cloned()
                    .cycle()
                    .skip(chunk_offset_mod as usize)
                    .take(subslice.size())
                    .collect();
                subslice.copy_from(&filled_memory);
                Ok(subslice.size())
            }
        }
    }
    fn write_at_volatile(&self, _slice: VolatileSlice, _offset: u64) -> io::Result<usize> {
        Err(io::Error::new(
            ErrorKind::PermissionDenied,
            "unsupported operation",
        ))
    }
}

// TODO(b/271381851): implement `try_clone`. It allows virtio-blk to run multiple workers.
impl DiskFile for AndroidSparse {}

/// An Android Sparse disk that implements `AsyncDisk` for access.
pub struct AsyncAndroidSparse {
    inner: IoSource<File>,
    total_size: u64,
    chunks: BTreeMap<u64, ChunkWithSize>,
}

impl ToAsyncDisk for AndroidSparse {
    fn to_async_disk(self: Box<Self>, ex: &Executor) -> DiskResult<Box<dyn AsyncDisk>> {
        Ok(Box::new(AsyncAndroidSparse {
            inner: ex.async_from(self.file).map_err(DiskError::ToAsync)?,
            total_size: self.total_size,
            chunks: self.chunks,
        }))
    }
}

impl DiskGetLen for AsyncAndroidSparse {
    fn get_len(&self) -> io::Result<u64> {
        Ok(self.total_size)
    }
}

impl FileSetLen for AsyncAndroidSparse {
    fn set_len(&self, _len: u64) -> io::Result<()> {
        Err(io::Error::new(
            ErrorKind::PermissionDenied,
            "unsupported operation",
        ))
    }
}

impl FileAllocate for AsyncAndroidSparse {
    fn allocate(&self, _offset: u64, _length: u64) -> io::Result<()> {
        Err(io::Error::new(
            ErrorKind::PermissionDenied,
            "unsupported operation",
        ))
    }
}

#[async_trait(?Send)]
impl AsyncDisk for AsyncAndroidSparse {
    async fn flush(&self) -> crate::Result<()> {
        // android sparse is read-only, nothing to flush.
        Ok(())
    }

    async fn fsync(&self) -> DiskResult<()> {
        // Do nothing because it's read-only.
        Ok(())
    }

    async fn fdatasync(&self) -> DiskResult<()> {
        // Do nothing because it's read-only.
        Ok(())
    }

    /// Reads data from `file_offset` to the end of the current chunk and write them into memory
    /// `mem` at `mem_offsets`.
    async fn read_to_mem<'a>(
        &'a self,
        file_offset: u64,
        mem: Arc<dyn BackingMemory + Send + Sync>,
        mem_offsets: cros_async::MemRegionIter<'a>,
    ) -> DiskResult<usize> {
        let found_chunk = self.chunks.range(..=file_offset).next_back();
        let (
            chunk_start,
            ChunkWithSize {
                chunk,
                expanded_size,
            },
        ) = found_chunk.ok_or(DiskError::ReadingData(io::Error::new(
            ErrorKind::UnexpectedEof,
            format!("no chunk for offset {file_offset}"),
        )))?;
        let chunk_offset = file_offset - chunk_start;
        let chunk_size = *expanded_size;

        // Truncate `mem_offsets` to the remaining size of the current chunk.
        let mem_offsets = mem_offsets.take_bytes((chunk_size - chunk_offset) as usize);
        let mem_size = mem_offsets.clone().map(|x| x.len).sum();
        match chunk {
            Chunk::DontCare => {
                for region in mem_offsets {
                    mem.get_volatile_slice(region)
                        .map_err(DiskError::GuestMemory)?
                        .write_bytes(0);
                }
                Ok(mem_size)
            }
            Chunk::Raw(offset) => self
                .inner
                .read_to_mem(Some(offset + chunk_offset), mem, mem_offsets)
                .await
                .map_err(DiskError::ReadToMem),
            Chunk::Fill(fill_bytes) => {
                let chunk_offset_mod = chunk_offset % fill_bytes.len() as u64;
                let filled_memory: Vec<u8> = fill_bytes
                    .iter()
                    .cloned()
                    .cycle()
                    .skip(chunk_offset_mod as usize)
                    .take(mem_size)
                    .collect();

                let mut filled_count = 0;
                for region in mem_offsets {
                    let buf = &filled_memory[filled_count..filled_count + region.len];
                    mem.get_volatile_slice(region)
                        .map_err(DiskError::GuestMemory)?
                        .copy_from(buf);
                    filled_count += region.len;
                }
                Ok(mem_size)
            }
        }
    }

    async fn write_from_mem<'a>(
        &'a self,
        _file_offset: u64,
        _mem: Arc<dyn BackingMemory + Send + Sync>,
        _mem_offsets: cros_async::MemRegionIter<'a>,
    ) -> DiskResult<usize> {
        Err(DiskError::UnsupportedOperation)
    }

    async fn punch_hole(&self, _file_offset: u64, _length: u64) -> DiskResult<()> {
        Err(DiskError::UnsupportedOperation)
    }

    async fn write_zeroes_at(&self, _file_offset: u64, _length: u64) -> DiskResult<()> {
        Err(DiskError::UnsupportedOperation)
    }
}

#[cfg(test)]
mod tests {
    use std::io::Cursor;
    use std::io::Write;

    use super::*;

    const CHUNK_SIZE: usize = mem::size_of::<ChunkHeader>();

    #[test]
    fn parse_raw() {
        let chunk_raw = ChunkHeader {
            chunk_type: CHUNK_TYPE_RAW.into(),
            reserved1: 0,
            chunk_sz: 1.into(),
            total_sz: (CHUNK_SIZE as u32 + 123).into(),
        };
        let header_bytes = chunk_raw.as_bytes();
        let mut chunk_bytes: Vec<u8> = Vec::new();
        chunk_bytes.extend_from_slice(header_bytes);
        chunk_bytes.extend_from_slice(&[0u8; 123]);
        let mut chunk_cursor = Cursor::new(chunk_bytes);
        let chunk = parse_chunk(&mut chunk_cursor, 123)
            .expect("Failed to parse")
            .expect("Failed to determine chunk type");
        let expected_chunk = ChunkWithSize {
            chunk: Chunk::Raw(CHUNK_SIZE as u64),
            expanded_size: 123,
        };
        assert_eq!(expected_chunk, chunk);
    }

    #[test]
    fn parse_dont_care() {
        let chunk_raw = ChunkHeader {
            chunk_type: CHUNK_TYPE_DONT_CARE.into(),
            reserved1: 0,
            chunk_sz: 100.into(),
            total_sz: (CHUNK_SIZE as u32).into(),
        };
        let header_bytes = chunk_raw.as_bytes();
        let mut chunk_cursor = Cursor::new(header_bytes);
        let chunk = parse_chunk(&mut chunk_cursor, 123)
            .expect("Failed to parse")
            .expect("Failed to determine chunk type");
        let expected_chunk = ChunkWithSize {
            chunk: Chunk::DontCare,
            expanded_size: 12300,
        };
        assert_eq!(expected_chunk, chunk);
    }

    #[test]
    fn parse_fill() {
        let chunk_raw = ChunkHeader {
            chunk_type: CHUNK_TYPE_FILL.into(),
            reserved1: 0,
            chunk_sz: 100.into(),
            total_sz: (CHUNK_SIZE as u32 + 4).into(),
        };
        let header_bytes = chunk_raw.as_bytes();
        let mut chunk_bytes: Vec<u8> = Vec::new();
        chunk_bytes.extend_from_slice(header_bytes);
        chunk_bytes.extend_from_slice(&[123u8; 4]);
        let mut chunk_cursor = Cursor::new(chunk_bytes);
        let chunk = parse_chunk(&mut chunk_cursor, 123)
            .expect("Failed to parse")
            .expect("Failed to determine chunk type");
        let expected_chunk = ChunkWithSize {
            chunk: Chunk::Fill([123, 123, 123, 123]),
            expanded_size: 12300,
        };
        assert_eq!(expected_chunk, chunk);
    }

    #[test]
    fn parse_crc32() {
        let chunk_raw = ChunkHeader {
            chunk_type: CHUNK_TYPE_CRC32.into(),
            reserved1: 0,
            chunk_sz: 0.into(),
            total_sz: (CHUNK_SIZE as u32 + 4).into(),
        };
        let header_bytes = chunk_raw.as_bytes();
        let mut chunk_bytes: Vec<u8> = Vec::new();
        chunk_bytes.extend_from_slice(header_bytes);
        chunk_bytes.extend_from_slice(&[123u8; 4]);
        let mut chunk_cursor = Cursor::new(chunk_bytes);
        let chunk = parse_chunk(&mut chunk_cursor, 123).expect("Failed to parse");
        assert_eq!(None, chunk);
    }

    fn test_image(chunks: Vec<ChunkWithSize>) -> AndroidSparse {
        let file = tempfile::tempfile().expect("failed to create tempfile");
        let size = chunks.iter().map(|x| x.expanded_size).sum();
        AndroidSparse::from_parts(file, size, chunks).expect("Could not create image")
    }

    #[test]
    fn read_dontcare() {
        let chunks = vec![ChunkWithSize {
            chunk: Chunk::DontCare,
            expanded_size: 100,
        }];
        let image = test_image(chunks);
        let mut input_memory = [55u8; 100];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 0)
            .expect("Could not read");
        let expected = [0u8; 100];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    #[test]
    fn read_fill_simple() {
        let chunks = vec![ChunkWithSize {
            chunk: Chunk::Fill([10, 20, 10, 20]),
            expanded_size: 8,
        }];
        let image = test_image(chunks);
        let mut input_memory = [55u8; 8];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 0)
            .expect("Could not read");
        let expected = [10, 20, 10, 20, 10, 20, 10, 20];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    #[test]
    fn read_fill_edges() {
        let chunks = vec![ChunkWithSize {
            chunk: Chunk::Fill([10, 20, 30, 40]),
            expanded_size: 8,
        }];
        let image = test_image(chunks);
        let mut input_memory = [55u8; 6];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 1)
            .expect("Could not read");
        let expected = [20, 30, 40, 10, 20, 30];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    #[test]
    fn read_fill_offset_edges() {
        let chunks = vec![
            ChunkWithSize {
                chunk: Chunk::DontCare,
                expanded_size: 20,
            },
            ChunkWithSize {
                chunk: Chunk::Fill([10, 20, 30, 40]),
                expanded_size: 100,
            },
        ];
        let image = test_image(chunks);
        let mut input_memory = [55u8; 7];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 39)
            .expect("Could not read");
        let expected = [40, 10, 20, 30, 40, 10, 20];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    #[test]
    fn read_raw() {
        let chunks = vec![ChunkWithSize {
            chunk: Chunk::Raw(0),
            expanded_size: 100,
        }];
        let mut image = test_image(chunks);
        write!(image.file, "hello").expect("Failed to write into internal file");
        let mut input_memory = [55u8; 5];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 0)
            .expect("Could not read");
        let expected = [104, 101, 108, 108, 111];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    #[test]
    fn read_two_fills() {
        let chunks = vec![
            ChunkWithSize {
                chunk: Chunk::Fill([10, 20, 10, 20]),
                expanded_size: 4,
            },
            ChunkWithSize {
                chunk: Chunk::Fill([30, 40, 30, 40]),
                expanded_size: 4,
            },
        ];
        let image = test_image(chunks);
        let mut input_memory = [55u8; 8];
        image
            .read_exact_at_volatile(VolatileSlice::new(&mut input_memory[..]), 0)
            .expect("Could not read");
        let expected = [10, 20, 10, 20, 30, 40, 30, 40];
        assert_eq!(&expected[..], &input_memory[..]);
    }

    /**
     * Tests for Async.
     */
    use cros_async::MemRegion;
    use cros_async::MemRegionIter;
    use vm_memory::GuestAddress;
    use vm_memory::GuestMemory;

    fn test_async_image(
        chunks: Vec<ChunkWithSize>,
        ex: &Executor,
    ) -> DiskResult<Box<dyn AsyncDisk>> {
        Box::new(test_image(chunks)).to_async_disk(ex)
    }

    /// Reads `len` bytes of data from `image` at 'offset'.
    async fn read_exact_at(image: &dyn AsyncDisk, offset: usize, len: usize) -> Vec<u8> {
        let guest_mem = Arc::new(GuestMemory::new(&[(GuestAddress(0), 4096)]).unwrap());
        // Fill in guest_mem with dirty data.
        guest_mem
            .write_all_at_addr(&vec![55u8; len], GuestAddress(0))
            .unwrap();

        let mut count = 0usize;
        while count < len {
            let result = image
                .read_to_mem(
                    (offset + count) as u64,
                    guest_mem.clone(),
                    MemRegionIter::new(&[MemRegion {
                        offset: count as u64,
                        len: len - count,
                    }]),
                )
                .await;
            count += result.unwrap();
        }

        let mut buf = vec![0; len];
        guest_mem.read_at_addr(&mut buf, GuestAddress(0)).unwrap();
        buf
    }

    #[test]
    fn async_read_dontcare() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::DontCare,
                expanded_size: 100,
            }];
            let image = test_async_image(chunks, &ex).unwrap();
            let buf = read_exact_at(&*image, 0, 100).await;
            assert!(buf.iter().all(|x| *x == 0));
        })
        .unwrap();
    }

    #[test]
    fn async_read_dontcare_with_offsets() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::DontCare,
                expanded_size: 10,
            }];
            let image = test_async_image(chunks, &ex).unwrap();
            // Prepare guest_mem with dirty data.
            let guest_mem = Arc::new(GuestMemory::new(&[(GuestAddress(0), 4096)]).unwrap());
            guest_mem
                .write_all_at_addr(&[55u8; 20], GuestAddress(0))
                .unwrap();

            // Pass multiple `MemRegion` to `read_to_mem`.
            image
                .read_to_mem(
                    0,
                    guest_mem.clone(),
                    MemRegionIter::new(&[
                        MemRegion { offset: 1, len: 3 },
                        MemRegion { offset: 6, len: 2 },
                    ]),
                )
                .await
                .unwrap();
            let mut buf = vec![0; 10];
            guest_mem.read_at_addr(&mut buf, GuestAddress(0)).unwrap();
            let expected = [55, 0, 0, 0, 55, 55, 0, 0, 55, 55];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_fill_simple() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::Fill([10, 20, 10, 20]),
                expanded_size: 8,
            }];
            let image = test_async_image(chunks, &ex).unwrap();
            let buf = read_exact_at(&*image, 0, 8).await;
            let expected = [10, 20, 10, 20, 10, 20, 10, 20];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_fill_simple_with_offset() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::Fill([10, 20, 10, 20]),
                expanded_size: 8,
            }];
            let image = test_async_image(chunks, &ex).unwrap();
            // Prepare guest_mem with dirty data.
            let guest_mem = Arc::new(GuestMemory::new(&[(GuestAddress(0), 4096)]).unwrap());
            guest_mem
                .write_all_at_addr(&[55u8; 20], GuestAddress(0))
                .unwrap();

            // Pass multiple `MemRegion` to `read_to_mem`.
            image
                .read_to_mem(
                    0,
                    guest_mem.clone(),
                    MemRegionIter::new(&[
                        MemRegion { offset: 1, len: 3 },
                        MemRegion { offset: 6, len: 2 },
                    ]),
                )
                .await
                .unwrap();
            let mut buf = vec![0; 10];
            guest_mem.read_at_addr(&mut buf, GuestAddress(0)).unwrap();
            let expected = [55, 10, 20, 10, 55, 55, 20, 10, 55, 55];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_fill_edges() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::Fill([10, 20, 30, 40]),
                expanded_size: 8,
            }];
            let image = test_async_image(chunks, &ex).unwrap();
            let buf = read_exact_at(&*image, 1, 6).await;
            let expected = [20, 30, 40, 10, 20, 30];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_fill_offset_edges() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![
                ChunkWithSize {
                    chunk: Chunk::DontCare,
                    expanded_size: 20,
                },
                ChunkWithSize {
                    chunk: Chunk::Fill([10, 20, 30, 40]),
                    expanded_size: 100,
                },
            ];
            let image = test_async_image(chunks, &ex).unwrap();
            let buf = read_exact_at(&*image, 39, 7).await;
            let expected = [40, 10, 20, 30, 40, 10, 20];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_raw() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::Raw(0),
                expanded_size: 100,
            }];
            let mut image = Box::new(test_image(chunks));
            write!(image.file, "hello").unwrap();
            let async_image = image.to_async_disk(&ex).unwrap();
            let buf = read_exact_at(&*async_image, 0, 5).await;
            let expected = [104, 101, 108, 108, 111];
            assert_eq!(&expected[..], &buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_fill_raw_with_offset() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![ChunkWithSize {
                chunk: Chunk::Raw(0),
                expanded_size: 100,
            }];
            let mut image = Box::new(test_image(chunks));
            write!(image.file, "hello").unwrap();
            let async_image = image.to_async_disk(&ex).unwrap();
            // Prepare guest_mem with dirty data.
            let guest_mem = Arc::new(GuestMemory::new(&[(GuestAddress(0), 4096)]).unwrap());
            guest_mem
                .write_all_at_addr(&[55u8; 20], GuestAddress(0))
                .unwrap();

            // Pass multiple `MemRegion` to `read_to_mem`.
            async_image
                .read_to_mem(
                    0,
                    guest_mem.clone(),
                    MemRegionIter::new(&[
                        MemRegion { offset: 1, len: 3 },
                        MemRegion { offset: 6, len: 2 },
                    ]),
                )
                .await
                .unwrap();
            let mut buf = vec![0; 10];
            guest_mem.read_at_addr(&mut buf, GuestAddress(0)).unwrap();
            let expected = [55, 104, 101, 108, 55, 55, 108, 111, 55, 55];
            assert_eq!(expected[..], buf[..]);
        })
        .unwrap();
    }

    #[test]
    fn async_read_two_fills() {
        let ex = Executor::new().unwrap();
        ex.run_until(async {
            let chunks = vec![
                ChunkWithSize {
                    chunk: Chunk::Fill([10, 20, 10, 20]),
                    expanded_size: 4,
                },
                ChunkWithSize {
                    chunk: Chunk::Fill([30, 40, 30, 40]),
                    expanded_size: 4,
                },
            ];
            let image = test_async_image(chunks, &ex).unwrap();
            let buf = read_exact_at(&*image, 0, 8).await;
            let expected = [10, 20, 10, 20, 30, 40, 30, 40];
            assert_eq!(&expected[..], &buf[..]);
        })
        .unwrap();
    }
}