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block: vhd: Read the VHD footer positionally

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Read the trailing footer sector with query_device_size and
read_exact_at instead of seeking to the end of the AlignedFile and
reading through its cursor.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
This commit is contained in:
Anatol Belski
2026-07-04 09:02:48 +02:00
committed by Rob Bradford
parent c257cdd695
commit 26080f264a
1 changed files with 9 additions and 5 deletions
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14
block/src/formats/vhd/internal/footer.rs
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@@ -3,9 +3,10 @@
// SPDX-License-Identifier: Apache-2.0
use std::fs::File;
use std::io::{self, Read, Seek, SeekFrom};
use std::io;
use std::os::unix::fs::FileExt;
use crate::AlignedFile;
use crate::{AlignedFile, query_device_size};
// Production code uses: cookie, file_format_version, data_offset,
// current_size, disk_type. The remaining fields are parsed for VHD
@@ -32,10 +33,13 @@ pub struct VhdFooter {
impl VhdFooter {
pub fn new(file: &mut File) -> io::Result<VhdFooter> {
let mut aligned = AlignedFile::new(file.try_clone()?, true);
aligned.seek(SeekFrom::End(-512))?;
let aligned = AlignedFile::new(file.try_clone()?, true);
let size = query_device_size(file)?.0;
let footer_offset = size.checked_sub(512).ok_or_else(|| {
io::Error::new(io::ErrorKind::InvalidInput, "file too small for VHD footer")
})?;
let mut sector = [0u8; 512];
aligned.read_exact(&mut sector)?;
aligned.read_exact_at(&mut sector, footer_offset)?;
Ok(VhdFooter {
cookie: u64::from_be_bytes(sector[0..8].try_into().unwrap()),