Support the Android Sparse disk format

Android defines its own "sparse disk" format, which its images are
usually published in. Cuttlefish has special-cased this to build raw
images in the android build system, but it still causes a performance
hit when downloading and extracting the image zip files. Experimentally,
running bsdtar on the zip file of raw images is about 50 seconds slower
than bsdtar on the equivalent zip file of android sparse images.

These disks can only be opened as read-only, as the Android Sparse
format is designed around writing once then interpreting the contents
while flashing a physical device through e.g. fastboot.

TEST=Run with aosp/1184800 on cuttlefish, unit tests
BUG=b:145841395
Change-Id: I13337b042e92841bd3cba88dc8b231fde88c091e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1956487
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Cody Schuffelen <schuffelen@google.com>

2 files changed, 527 insertions, 0 deletions

diff --git a/disk/src/android_sparse.rs b/disk/src/android_sparse.rs
new file mode 100644
index 0000000..07e5714
--- /dev/null
+++ b/disk/src/android_sparse.rs
@@ -0,0 +1,515 @@
+// Copyright 2019 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 file.
+
+// https://android.googlesource.com/platform/system/core/+/7b444f0/libsparse/sparse_format.h
+
+use std::collections::BTreeMap;
+use std::fmt::{self, Display};
+use std::fs::File;
+use std::io::{self, ErrorKind, Read, Seek, SeekFrom};
+use std::mem;
+use std::os::unix::io::{AsRawFd, RawFd};
+
+use crate::DiskGetLen;
+use data_model::{DataInit, Le16, Le32, VolatileSlice};
+use remain::sorted;
+use sys_util::{
+    FileAllocate, FileReadWriteAtVolatile, FileSetLen, FileSync, PunchHole, WriteZeroesAt,
+};
+
+#[sorted]
+#[derive(Debug)]
+pub enum Error {
+    InvalidMagicHeader,
+    InvalidSpecification(String),
+    ReadSpecificationError(io::Error),
+}
+
+impl Display for Error {
+    #[remain::check]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::Error::*;
+
+        #[sorted]
+        match self {
+            InvalidMagicHeader => write!(f, "invalid magic header for android sparse format"),
+            InvalidSpecification(s) => write!(f, "invalid specification: \"{}\"", s),
+            ReadSpecificationError(e) => write!(f, "failed to read specification: \"{}\"", e),
+        }
+    }
+}
+
+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)]
+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 */
+    image_checksum: Le32, /* CRC32 checksum of the original data, counting "don't care" */
+                          /* as 0. Standard 802.3 polynomial, use a Public Domain */
+                          /* table implementation */
+}
+
+unsafe impl DataInit for SparseHeader {}
+
+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)]
+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 */
+}
+
+unsafe impl DataInit for ChunkHeader {}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+enum Chunk {
+    Raw(u64), // Offset into the file
+    Fill(Vec<u8>),
+    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>(
+    mut input: &mut T,
+    chunk_hdr_size: u64,
+    blk_sz: u64,
+) -> Result<Option<ChunkWithSize>> {
+    let current_offset = input
+        .seek(SeekFrom::Current(0))
+        .map_err(Error::ReadSpecificationError)?;
+    let chunk_header =
+        ChunkHeader::from_reader(&mut input).map_err(Error::ReadSpecificationError)?;
+    let chunk = match chunk_header.chunk_type.to_native() {
+        CHUNK_TYPE_RAW => {
+            input
+                .seek(SeekFrom::Current(
+                    chunk_header.total_sz.to_native() as i64 - chunk_hdr_size as i64,
+                ))
+                .map_err(Error::ReadSpecificationError)?;
+            Chunk::Raw(current_offset + chunk_hdr_size as u64)
+        }
+        CHUNK_TYPE_FILL => {
+            if chunk_header.total_sz == chunk_hdr_size as u32 {
+                return Err(Error::InvalidSpecification(format!(
+                    "Fill chunk did not have any data to fill"
+                )));
+            }
+            let fill_size = chunk_header.total_sz.to_native() as u64 - chunk_hdr_size as u64;
+            let mut fill_bytes = vec![0u8; fill_size as usize];
+            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 {:x}",
+                unknown_type
+            )))
+        }
+    };
+    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 sparse_header =
+            SparseHeader::from_reader(&mut file).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>()
+        {
+            return Err(Error::InvalidSpecification(format!(
+                "Chunk header size does not fit chunk header struct, expected >={}, was {}",
+                sparse_header.chunk_hdr_size.to_native(),
+                mem::size_of::<ChunkHeader>()
+            )));
+        }
+        let header_size = sparse_header.chunk_hdr_size.to_native() as u64;
+        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, header_size, 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 = image.get_len().map_err(Error::ReadSpecificationError)?;
+        if calculated_len != size {
+            return Err(Error::InvalidSpecification(format!(
+                "Header promised size {}, chunks added up to {}",
+                size, 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 FileSync for AndroidSparse {
+    fn fsync(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl PunchHole for AndroidSparse {
+    fn punch_hole(&mut self, _offset: u64, _length: u64) -> io::Result<()> {
+        Err(io::Error::new(
+            ErrorKind::PermissionDenied,
+            "unsupported operation",
+        ))
+    }
+}
+
+impl WriteZeroesAt for AndroidSparse {
+    fn write_zeroes_at(&mut self, _offset: u64, _length: usize) -> io::Result<usize> {
+        Err(io::Error::new(
+            ErrorKind::PermissionDenied,
+            "unsupported operation",
+        ))
+    }
+}
+
+impl AsRawFd for AndroidSparse {
+    fn as_raw_fd(&self) -> RawFd {
+        self.file.as_raw_fd()
+    }
+}
+
+impl FileAllocate for AndroidSparse {
+    fn allocate(&mut self, _offset: u64, _length: u64) -> io::Result<()> {
+        Err(io::Error::new(
+            ErrorKind::PermissionDenied,
+            "unsupported operation",
+        ))
+    }
+}
+
+// Performs reads up to the chunk boundary.
+impl FileReadWriteAtVolatile for AndroidSparse {
+    fn read_at_volatile(&mut 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(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() > chunk_size {
+            slice
+                .sub_slice(0, chunk_size - chunk_offset)
+                .map_err(|e| io::Error::new(ErrorKind::InvalidData, format!("{:?}", e)))?
+        } else {
+            slice
+        };
+        match chunk {
+            Chunk::DontCare => {
+                subslice.write_bytes(0);
+                Ok(subslice.size() as usize)
+            }
+            Chunk::Raw(file_offset) => self
+                .file
+                .read_at_volatile(subslice, *file_offset + chunk_offset),
+            Chunk::Fill(fill_bytes) => {
+                let filled_memory: Vec<u8> = fill_bytes
+                    .iter()
+                    .cloned()
+                    .cycle()
+                    .skip(chunk_offset as usize)
+                    .take(subslice.size() as usize)
+                    .collect();
+                subslice.copy_from(&filled_memory);
+                Ok(subslice.size() as usize)
+            }
+        }
+    }
+    fn write_at_volatile(&mut self, _slice: VolatileSlice, _offset: u64) -> io::Result<usize> {
+        Err(io::Error::new(
+            ErrorKind::PermissionDenied,
+            "unsupported operation",
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use data_model::VolatileMemory;
+    use std::io::{Cursor, Write};
+    use sys_util::SharedMemory;
+
+    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_slice();
+        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, CHUNK_SIZE as u64, 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_slice();
+        let mut chunk_cursor = Cursor::new(header_bytes);
+        let chunk = parse_chunk(&mut chunk_cursor, CHUNK_SIZE as u64, 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_slice();
+        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, CHUNK_SIZE as u64, 123)
+            .expect("Failed to parse")
+            .expect("Failed to determine chunk type");
+        let expected_chunk = ChunkWithSize {
+            chunk: Chunk::Fill(vec![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_slice();
+        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, CHUNK_SIZE as u64, 123).expect("Failed to parse");
+        assert_eq!(None, chunk);
+    }
+
+    fn test_image(chunks: Vec<ChunkWithSize>) -> AndroidSparse {
+        let file: File = SharedMemory::anon().unwrap().into();
+        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 mut image = test_image(chunks);
+        let mut input_memory = [55u8; 100];
+        let input_volatile_memory = &mut input_memory[..];
+        image
+            .read_exact_at_volatile(input_volatile_memory.get_slice(0, 100).unwrap(), 0)
+            .expect("Could not read");
+        let input_vec: Vec<u8> = input_memory.into_iter().cloned().collect();
+        assert_eq!(input_vec, vec![0u8; 100]);
+    }
+
+    #[test]
+    fn read_fill_simple() {
+        let chunks = vec![ChunkWithSize {
+            chunk: Chunk::Fill(vec![10, 20]),
+            expanded_size: 8,
+        }];
+        let mut image = test_image(chunks);
+        let mut input_memory = [55u8; 8];
+        let input_volatile_memory = &mut input_memory[..];
+        image
+            .read_exact_at_volatile(input_volatile_memory.get_slice(0, 8).unwrap(), 0)
+            .expect("Could not read");
+        let input_vec: Vec<u8> = input_memory.into_iter().cloned().collect();
+        assert_eq!(input_vec, vec![10, 20, 10, 20, 10, 20, 10, 20]);
+    }
+
+    #[test]
+    fn read_fill_edges() {
+        let chunks = vec![ChunkWithSize {
+            chunk: Chunk::Fill(vec![10, 20, 30]),
+            expanded_size: 8,
+        }];
+        let mut image = test_image(chunks);
+        let mut input_memory = [55u8; 6];
+        let input_volatile_memory = &mut input_memory[..];
+        image
+            .read_exact_at_volatile(input_volatile_memory.get_slice(0, 6).unwrap(), 1)
+            .expect("Could not read");
+        let input_vec: Vec<u8> = input_memory.into_iter().cloned().collect();
+        assert_eq!(input_vec, vec![20, 30, 10, 20, 30, 10]);
+    }
+
+    #[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];
+        let input_volatile_memory = &mut input_memory[..];
+        image
+            .read_exact_at_volatile(input_volatile_memory.get_slice(0, 5).unwrap(), 0)
+            .expect("Could not read");
+        let input_vec: Vec<u8> = input_memory.into_iter().cloned().collect();
+        assert_eq!(input_vec, vec![104, 101, 108, 108, 111]);
+    }
+
+    #[test]
+    fn read_two_fills() {
+        let chunks = vec![
+            ChunkWithSize {
+                chunk: Chunk::Fill(vec![10, 20]),
+                expanded_size: 4,
+            },
+            ChunkWithSize {
+                chunk: Chunk::Fill(vec![30, 40]),
+                expanded_size: 4,
+            },
+        ];
+        let mut image = test_image(chunks);
+        let mut input_memory = [55u8; 8];
+        let input_volatile_memory = &mut input_memory[..];
+        image
+            .read_exact_at_volatile(input_volatile_memory.get_slice(0, 8).unwrap(), 0)
+            .expect("Could not read");
+        let input_vec: Vec<u8> = input_memory.into_iter().cloned().collect();
+        assert_eq!(input_vec, vec![10, 20, 10, 20, 30, 40, 30, 40]);
+    }
+}
diff --git a/disk/src/disk.rs b/disk/src/disk.rs
index 2f9ad72..e00e843 100644
--- a/disk/src/disk.rs
+++ b/disk/src/disk.rs
@@ -22,11 +22,15 @@ mod composite;
 #[cfg(feature = "composite-disk")]
 use composite::{CompositeDiskFile, CDISK_MAGIC, CDISK_MAGIC_LEN};
 
+mod android_sparse;
+use android_sparse::{AndroidSparse, SPARSE_HEADER_MAGIC};
+
 #[sorted]
 #[derive(Debug)]
 pub enum Error {
     BlockDeviceNew(sys_util::Error),
     ConversionNotSupported,
+    CreateAndroidSparseDisk(android_sparse::Error),
     #[cfg(feature = "composite-disk")]
     CreateCompositeDisk(composite::Error),
     QcowError(qcow::Error),
@@ -95,6 +99,7 @@ impl Display for Error {
         match self {
             BlockDeviceNew(e) => write!(f, "failed to create block device: {}", e),
             ConversionNotSupported => write!(f, "requested file conversion not supported"),
+            CreateAndroidSparseDisk(e) => write!(f, "failure in android sparse disk: {}", e),
             #[cfg(feature = "composite-disk")]
             CreateCompositeDisk(e) => write!(f, "failure in composite disk: {}", e),
             QcowError(e) => write!(f, "failure in qcow: {}", e),
@@ -114,6 +119,7 @@ pub enum ImageType {
     Raw,
     Qcow2,
     CompositeDisk,
+    AndroidSparse,
 }
 
 fn convert_copy<R, W>(reader: &mut R, writer: &mut W, offset: u64, size: u64) -> Result<()>
@@ -248,6 +254,8 @@ pub fn detect_image_type(file: &File) -> Result<ImageType> {
     }
     let image_type = if magic == QCOW_MAGIC {
         ImageType::Qcow2
+    } else if magic == SPARSE_HEADER_MAGIC.to_be() {
+        ImageType::AndroidSparse
     } else {
         ImageType::Raw
     };
@@ -272,5 +280,9 @@ pub fn create_disk_file(raw_image: File) -> Result<Box<dyn DiskFile>> {
         }
         #[cfg(not(feature = "composite-disk"))]
         ImageType::CompositeDisk => return Err(Error::UnknownType),
+        ImageType::AndroidSparse => {
+            Box::new(AndroidSparse::from_file(raw_image).map_err(Error::CreateAndroidSparseDisk)?)
+                as Box<dyn DiskFile>
+        }
     })
 }