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block: vhd: Read footer via AlignedFile

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Read the trailing footer sector through an AlignedFile rather than
probing the device topology and reading a full logical block. The
AlignedFile bounce buffer serves the trailing sector of an O_DIRECT
fd whose offset is unaligned against the device block size, so the
read no longer fails with EINVAL on a 4k sector backing store.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
This commit is contained in:
Anatol Belski
2026-06-19 21:57:12 +02:00
committed by Rob Bradford
parent 2359003001
commit 693987b9e2
1 changed files with 6 additions and 12 deletions
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18
block/src/formats/vhd/internal/footer.rs
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@@ -3,9 +3,9 @@
// SPDX-License-Identifier: Apache-2.0
use std::fs::File;
use std::io::{self, Seek, SeekFrom};
use std::io::{self, Read, Seek, SeekFrom};
use crate::{DiskTopology, read_aligned_block_size};
use crate::AlignedFile;
// Production code uses: cookie, file_format_version, data_offset,
// current_size, disk_type. The remaining fields are parsed for VHD
@@ -32,16 +32,10 @@ pub struct VhdFooter {
impl VhdFooter {
pub fn new(file: &mut File) -> io::Result<VhdFooter> {
let blocksize = DiskTopology::probe(file)?.logical_block_size as usize;
// Place the cursor in the last block of the file
file.seek(SeekFrom::End(0 - (blocksize as i64)))?;
// Read in the last block
let data = read_aligned_block_size(file)?;
// We only care about the last sector
let offset = blocksize - 512;
let sector = &data[offset..];
let mut aligned = AlignedFile::new(file.try_clone()?, true);
aligned.seek(SeekFrom::End(-512))?;
let mut sector = [0u8; 512];
aligned.read_exact(&mut sector)?;
Ok(VhdFooter {
cookie: u64::from_be_bytes(sector[0..8].try_into().unwrap()),