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block: Ensure probing reads are block size aligned

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This is necessary for O_DIRECT based use of raw block devices which may
require access at a larger block size than that of a sector (512 bytes.)

Fixes: #5722

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
This commit is contained in:
Rob Bradford
2023-09-03 12:00:30 +01:00
committed by Bo Chen
parent 9ca2c336f2
commit 01097aa130
2 changed files with 45 additions and 39 deletions
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31
block/src/lib.rs
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@@ -731,24 +731,33 @@ pub enum ImageType {
const QCOW_MAGIC: u32 = 0x5146_49fb;
const VHDX_SIGN: u64 = 0x656C_6966_7864_6876;
/// Read a block into memory aligned by the source block size (needed for O_DIRECT)
pub fn read_aligned_block_size(f: &mut File) -> std::io::Result<Vec<u8>> {
let blocksize = DiskTopology::probe(f)?.logical_block_size as usize;
// SAFETY: We are allocating memory that is naturally aligned (size = alignment) and we meet
// requirements for safety from Vec::from_raw_parts() as we are using the global allocator
// and transferring ownership of the memory.
let mut data = unsafe {
Vec::from_raw_parts(
alloc_zeroed(Layout::from_size_align_unchecked(blocksize, blocksize)),
blocksize,
blocksize,
)
};
f.read_exact(&mut data)?;
Ok(data)
}
/// Determine image type through file parsing.
pub fn detect_image_type(f: &mut File) -> std::io::Result<ImageType> {
// We must create a buffer aligned on 512 bytes with a size being a
// multiple of 512 bytes as the file might be opened with O_DIRECT flag.
#[repr(align(512))]
struct Sector {
data: [u8; 512],
}
let mut s = Sector { data: [0; 512] };
f.read_exact(&mut s.data)?;
let block = read_aligned_block_size(f)?;
// Check 4 first bytes to get the header value and determine the image type
let image_type = if u32::from_be_bytes(s.data[0..4].try_into().unwrap()) == QCOW_MAGIC {
let image_type = if u32::from_be_bytes(block[0..4].try_into().unwrap()) == QCOW_MAGIC {
ImageType::Qcow2
} else if vhd::is_fixed_vhd(f)? {
ImageType::FixedVhd
} else if u64::from_le_bytes(s.data[0..8].try_into().unwrap()) == VHDX_SIGN {
} else if u64::from_le_bytes(block[0..8].try_into().unwrap()) == VHDX_SIGN {
ImageType::Vhdx
} else {
ImageType::Raw