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mod wire;
use {
anyhow::{anyhow, Error},
std::convert::TryInto,
std::io::{Read, Seek},
std::mem,
zerocopy::FromBytes,
};
const QCOW_MAGIC: u32 = 0x514649fb;
#[inline]
const fn cluster_size(cluster_bits: u32) -> u64 {
1 << cluster_bits
}
#[inline]
const fn cluster_mask(cluster_bits: u32) -> u64 {
cluster_size(cluster_bits) - 1
}
#[inline]
const fn l2_bits(cluster_bits: u32) -> u32 {
assert!(cluster_bits > 3);
cluster_bits - 3
}
#[inline]
const fn l2_size(cluster_bits: u32) -> u64 {
1 << l2_bits(cluster_bits)
}
#[inline]
const fn l2_mask(cluster_bits: u32) -> u64 {
l2_size(cluster_bits) - 1
}
#[inline]
fn required_l1_size(disk_size: u64, cluster_bits: u32) -> u32 {
let l1_entry_size = cluster_size(cluster_bits) * l2_size(cluster_bits);
let disk_size = disk_size + l1_entry_size - 1;
(disk_size / l1_entry_size).try_into().unwrap()
}
fn read_header(file: &mut std::fs::File) -> Result<wire::Header, Error> {
const HEADER_SIZE: usize = mem::size_of::<wire::Header>();
let mut buf = vec![0u8; HEADER_SIZE];
file.seek(std::io::SeekFrom::Start(0))?;
file.read_exact(&mut buf)?;
Ok(wire::Header::read_from(buf.as_slice()).expect("read_from failed unexpectedly"))
}
fn load_tranlsation_table<Entry: FromBytes + Sized>(
file: &mut std::fs::File,
num_entries: u64,
table_offset: u64,
) -> Result<Vec<Entry>, Error> {
let entry_size = std::mem::size_of::<Entry>() as u64;
assert!(entry_size == 8);
let bytes_to_read = num_entries * entry_size;
let mut table = vec![0u8; bytes_to_read as usize];
file.seek(std::io::SeekFrom::Start(table_offset))?;
file.read_exact(&mut table)?;
Ok(table
.chunks_exact(entry_size as usize)
.map(Entry::read_from)
.map(Option::unwrap)
.collect::<Vec<Entry>>())
}
#[derive(Debug, Clone)]
pub enum Mapping {
Mapped {
physical_offset: u64,
length: u64,
},
Unmapped { length: u64 },
}
impl Mapping {
pub fn len(&self) -> u64 {
match self {
Mapping::Mapped { length, .. } => *length,
Mapping::Unmapped { length } => *length,
}
}
}
pub struct Translation<'a> {
translation: &'a TranslationTable,
linear_range: std::ops::Range<u64>,
}
impl<'a> Iterator for Translation<'a> {
type Item = Mapping;
fn next(&mut self) -> Option<Self::Item> {
if self.linear_range.is_empty() {
return None;
}
let translation = self.translation.translate_range(&self.linear_range);
if let Some(translation) = translation.as_ref() {
self.linear_range.start += translation.len();
}
translation
}
}
pub struct TranslationTable {
cluster_bits: u32,
linear_size: u64,
l1: Vec<Option<Vec<wire::L2Entry>>>,
}
impl TranslationTable {
pub fn load(file: &mut std::fs::File) -> Result<Self, Error> {
let mut header = read_header(file)?;
if header.magic.get() != QCOW_MAGIC {
return Err(anyhow!("File has bad magic"));
}
let version = header.version.get();
if version != 2 && version != 3 {
return Err(anyhow!("QCOW file has unsupported version {}", version));
}
if version == 2 {
header.incompatible_features.set(0);
header.compatible_features.set(0);
header.autoclear_features.set(0);
header.refcount_order.set(4);
header.header_length.set(72);
}
let backing_file_size = header.backing_file_size.get();
if backing_file_size != 0 {
return Err(anyhow!("QCOW file has backing file, which is not supported"));
}
let cluster_bits = header.cluster_bits.get();
if cluster_bits < 9 || cluster_bits > 22 {
return Err(anyhow!("cluster_bits is out of the supported range."));
}
let size = header.size.get();
if size == 0 {
return Err(anyhow!("QCOW file has 0 size"));
}
if header.crypt_method.get() != wire::QCOW_CRYPT_NONE {
return Err(anyhow!("QCOW encryption is not supported"));
}
let l1_size = header.l1_size.get();
if l1_size < required_l1_size(size, cluster_bits) {
return Err(anyhow!("QCOW L1 table is not large enough to address the entire disk"));
}
let l1_entries = load_tranlsation_table::<wire::L1Entry>(
file,
header.l1_size.get().into(),
header.l1_table_offset.get(),
)?;
let l1 = l1_entries
.into_iter()
.map(move |entry| {
let entry: Option<Vec<wire::L2Entry>> = if let Some(offset) = entry.offset() {
let l2 = load_tranlsation_table::<wire::L2Entry>(
file,
l2_size(cluster_bits),
offset,
)?;
if l2.iter().find(|e| e.compressed()).is_some() {
return Err(anyhow!("QCOW contains compressed sectors"));
}
Some(l2)
} else {
None
};
Ok::<Option<Vec<wire::L2Entry>>, Error>(entry)
})
.collect::<Result<Vec<Option<Vec<wire::L2Entry>>>, Error>>()?;
Ok(Self { cluster_bits, linear_size: size, l1 })
}
pub fn linear_size(&self) -> u64 {
self.linear_size
}
pub fn translate<'a>(&'a self, linear_range: std::ops::Range<u64>) -> Translation<'a> {
Translation { linear_range: linear_range.clone(), translation: self }
}
fn translate_range(&self, linear_range: &std::ops::Range<u64>) -> Option<Mapping> {
if linear_range.start >= self.linear_size() {
return None;
}
let offset = linear_range.start;
let cluster_offset = offset & cluster_mask(self.cluster_bits);
let offset = offset >> self.cluster_bits;
let l2_index = offset & l2_mask(self.cluster_bits);
let l1_index = (offset >> l2_bits(self.cluster_bits)) as u32;
let maybe_physical_cluster = self.l1[l1_index as usize]
.as_ref()
.map(|l2_table| &l2_table[l2_index as usize])
.and_then(|entry| entry.offset());
let length = std::cmp::min(
linear_range.end - linear_range.start,
cluster_size(self.cluster_bits) - cluster_offset,
);
let transation = match maybe_physical_cluster {
Some(physical_cluster) => {
Mapping::Mapped { physical_offset: physical_cluster + cluster_offset, length }
}
None => Mapping::Unmapped { length },
};
Some(transation)
}
}
#[cfg(test)]
struct QcowFileReadOnly {
file: std::cell::RefCell<std::fs::File>,
translation: TranslationTable,
}
#[cfg(test)]
impl QcowFileReadOnly {
pub fn new(mut file: std::fs::File) -> Result<Self, Error> {
Ok(Self {
translation: TranslationTable::load(&mut file)?,
file: std::cell::RefCell::new(file),
})
}
pub fn size(&self) -> u64 {
self.translation.linear_size()
}
pub fn read_at(&self, length: u64, offset: u64) -> Result<Vec<u8>, Error> {
self.translation
.translate(std::ops::Range { start: offset, end: offset + length })
.try_fold(Vec::new(), |mut result, translation| -> Result<Vec<u8>, Error> {
let result_len = result.len();
result.resize(result_len + translation.len() as usize, 0);
match translation {
Mapping::Mapped { physical_offset, .. } => {
self.file.borrow_mut().seek(std::io::SeekFrom::Start(physical_offset))?;
self.file.borrow_mut().read_exact(&mut result[result_len..])?;
}
Mapping::Unmapped { .. } => {}
}
Ok(result)
})
}
}
#[cfg(test)]
mod test {
use {super::*, std::fs::File};
fn open_qcow_file(path: &str) -> QcowFileReadOnly {
let test_image = File::open(path).expect("Failed to open file");
QcowFileReadOnly::new(test_image).expect("Failed to create QcowFileReadOnly")
}
fn check_range(file: &QcowFileReadOnly, start: u64, length: u64, value: u8) {
let bytes = file.read_at(length, start).expect("Failed to read from file");
assert_eq!(bytes.len() as u64, length);
for byte in bytes {
assert_eq!(byte, value);
}
}
#[test]
fn test_empty_1gb() {
const SIZE: u64 = 1 * 1024 * 1024 * 1024;
let qcow = open_qcow_file("/pkg/data/empty_1gb.qcow2");
assert_eq!(SIZE, qcow.size());
check_range(&qcow, 0, 1024, 0);
check_range(&qcow, SIZE - 1024, 1024, 0);
}
#[test]
fn test_read_basic() {
const SIZE: u64 = 1 * 1024 * 1024 * 1024;
let qcow = open_qcow_file("/pkg/data/sparse.qcow2");
assert_eq!(SIZE, qcow.size());
{
const REGION_START: u64 = 0;
check_range(&qcow, REGION_START, 1024, 0xaa);
check_range(&qcow, REGION_START + 1024, 1024, 0);
}
{
const REGION_START: u64 = 512 * 1024 * 1024;
check_range(&qcow, REGION_START - 1024, 1024, 0);
check_range(&qcow, REGION_START, 1024, 0xcc);
check_range(&qcow, REGION_START + 1024, 1024, 0);
}
{
const REGION_START: u64 = 1 * 1024 * 1024 * 1024 - 1024;
check_range(&qcow, REGION_START - 1024, 1024, 0);
check_range(&qcow, REGION_START, 1024, 0xbb);
}
}
#[test]
fn test_read_across_translations() {
const SIZE: u64 = 1 * 1024 * 1024 * 1024;
let qcow = open_qcow_file("/pkg/data/sparse.qcow2");
assert_eq!(SIZE, qcow.size());
let bytes = qcow.read_at(4096, 0).expect("Failed to read the last byte from file");
assert_eq!(bytes[0..1024], vec![0xaa; 1024]);
assert_eq!(bytes[1024..2048], vec![0; 1024]);
assert_eq!(bytes[2048..3072], vec![0xab; 1024]);
assert_eq!(bytes[3072..4096], vec![0; 1024]);
}
#[test]
fn test_read_short() {
const SIZE: u64 = 1 * 1024 * 1024 * 1024;
let qcow = open_qcow_file("/pkg/data/sparse.qcow2");
assert_eq!(SIZE, qcow.size());
let bytes = qcow.read_at(1, SIZE - 1).expect("Failed to read the last byte from file");
assert_eq!(1, bytes.len());
assert_eq!(0xbb, bytes[0]);
let bytes =
qcow.read_at(10, SIZE - 1).expect("Failed to read 1 byte past the end of the file");
assert_eq!(1, bytes.len());
let bytes =
qcow.read_at(100, SIZE).expect("Failed to read entire buffer past the end of the file");
assert_eq!(0, bytes.len());
let bytes =
qcow.read_at(100, 2 * SIZE).expect("Failed to read far past the end of the file");
assert_eq!(0, bytes.len());
}
}