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qcow: Add support for QCOW v2 header

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The QCOW2 format is documented here:
https://git.qemu.org/?p=qemu.git;a=blob;f=docs/interop/qcow2.txt;hb=HEAD

The only difference between v2 and v3 is the addition of some extra
fields into the header in v3 for which there are default values in v2.

This introduces a new unit test for the behaviour but it has been
manually verified by the converting the image from v3 to v2
with a command like:

qemu-img convert -O qcow2 -o compat=0.10 clear-29620-cloud.img clear-29620-cloud.img.v2

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2019-07-19 12:16:04 +01:00 committed by Samuel Ortiz
parent 6f65f3406e
commit 3f02ccaa8c
1 changed files with 99 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

129
qcow/src/qcow.rs
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@ -116,6 +116,7 @@ const MAX_CLUSTER_BITS: u32 = 30;
// Only support 2 byte refcounts, 2^refcount_order bits.
const DEFAULT_REFCOUNT_ORDER: u32 = 4;
const V2_BARE_HEADER_SIZE: u32 = 72;
const V3_BARE_HEADER_SIZE: u32 = 104;
// bits 0-8 and 56-63 are reserved.
@ -175,9 +176,11 @@ impl QcowHeader {
f.read_u64::<BigEndian>().map_err(Error::ReadingHeader)
}
let version = read_u32_from_file(f)?;
Ok(QcowHeader {
magic,
version: read_u32_from_file(f)?,
version,
backing_file_offset: read_u64_from_file(f)?,
backing_file_size: read_u32_from_file(f)?,
cluster_bits: read_u32_from_file(f)?,
@ -189,16 +192,36 @@ impl QcowHeader {
refcount_table_clusters: read_u32_from_file(f)?,
nb_snapshots: read_u32_from_file(f)?,
snapshots_offset: read_u64_from_file(f)?,
incompatible_features: read_u64_from_file(f)?,
compatible_features: read_u64_from_file(f)?,
autoclear_features: read_u64_from_file(f)?,
refcount_order: read_u32_from_file(f)?,
header_size: read_u32_from_file(f)?,
incompatible_features: if version == 2 {
0
} else {
read_u64_from_file(f)?
},
compatible_features: if version == 2 {
0
} else {
read_u64_from_file(f)?
},
autoclear_features: if version == 2 {
0
} else {
read_u64_from_file(f)?
},
refcount_order: if version == 2 {
DEFAULT_REFCOUNT_ORDER
} else {
read_u32_from_file(f)?
},
header_size: if version == 2 {
V2_BARE_HEADER_SIZE
} else {
read_u32_from_file(f)?
},
})
}
/// Create a header for the given `size`.
pub fn create_for_size(size: u64) -> QcowHeader {
pub fn create_for_size(version: u32, size: u64) -> QcowHeader {
let cluster_bits: u32 = DEFAULT_CLUSTER_BITS;
let cluster_size: u32 = 0x01 << cluster_bits;
// L2 blocks are always one cluster long. They contain cluster_size/sizeof(u64) addresses.
@ -209,7 +232,7 @@ impl QcowHeader {
let header_clusters = div_round_up_u32(size_of::<QcowHeader>() as u32, cluster_size);
QcowHeader {
magic: QCOW_MAGIC,
version: 3,
version,
backing_file_offset: 0,
backing_file_size: 0,
cluster_bits: DEFAULT_CLUSTER_BITS,
@ -240,7 +263,11 @@ impl QcowHeader {
compatible_features: 0,
autoclear_features: 0,
refcount_order: DEFAULT_REFCOUNT_ORDER,
header_size: V3_BARE_HEADER_SIZE,
header_size: if version == 2 {
V2_BARE_HEADER_SIZE
} else {
V3_BARE_HEADER_SIZE
},
}
}
@ -336,8 +363,8 @@ impl QcowFile {
pub fn from(mut file: File) -> Result<QcowFile> {
let header = QcowHeader::new(&mut file)?;
// Only v3 files are supported.
if header.version != 3 {
// Only v2 and v3 files are supported.
if header.version != 2 && header.version != 3 {
return Err(Error::UnsupportedVersion(header.version));
}
@ -461,8 +488,8 @@ impl QcowFile {
}
/// Creates a new QcowFile at the given path.
pub fn new(mut file: File, virtual_size: u64) -> Result<QcowFile> {
let header = QcowHeader::create_for_size(virtual_size);
pub fn new(mut file: File, version: u32, virtual_size: u64) -> Result<QcowFile> {
let header = QcowHeader::create_for_size(version, virtual_size);
file.seek(SeekFrom::Start(0)).map_err(Error::SeekingFile)?;
header.write_to(&mut file)?;
@ -1569,7 +1596,7 @@ where
match dst_type {
ImageType::Qcow2 => {
let mut dst_writer = QcowFile::new(dst_file, src_size)?;
let mut dst_writer = QcowFile::new(dst_file, 3, src_size)?;
convert_reader_writer(reader, &mut dst_writer, src_size)
}
ImageType::Raw => {
@ -1625,7 +1652,7 @@ mod tests {
use std::io::{Read, Seek, SeekFrom, Write};
use tempfile::tempfile;
fn valid_header() -> Vec<u8> {
fn valid_header_v3() -> Vec<u8> {
vec![
0x51u8, 0x46, 0x49, 0xfb, // magic
0x00, 0x00, 0x00, 0x03, // version
@ -1648,6 +1675,24 @@ mod tests {
]
}
fn valid_header_v2() -> Vec<u8> {
vec![
0x51u8, 0x46, 0x49, 0xfb, // magic
0x00, 0x00, 0x00, 0x02, // version
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // backing file offset
0x00, 0x00, 0x00, 0x00, // backing file size
0x00, 0x00, 0x00, 0x10, // cluster_bits
0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, // size
0x00, 0x00, 0x00, 0x00, // crypt method
0x00, 0x00, 0x01, 0x00, // L1 size
0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, // L1 table offset
0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, // refcount table offset
0x00, 0x00, 0x00, 0x03, // refcount table clusters
0x00, 0x00, 0x00, 0x00, // nb snapshots
0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, // snapshots offset
]
}
fn with_basic_file<F>(header: &[u8], mut testfn: F)
where
F: FnMut(File),
@ -1665,26 +1710,46 @@ mod tests {
F: FnMut(QcowFile),
{
let tmp = tempfile().unwrap();
let qcow_file = QcowFile::new(tmp, file_size).unwrap();
let qcow_file = QcowFile::new(tmp, 3, file_size).unwrap();
testfn(qcow_file); // File closed when the function exits.
}
#[test]
fn default_header() {
let header = QcowHeader::create_for_size(0x10_0000);
fn default_header_v2() {
let header = QcowHeader::create_for_size(2, 0x10_0000);
let mut disk_file: File = tempfile().unwrap();
header
.write_to(&mut disk_file)
.expect("Failed to write header to shm.");
.expect("Failed to write header to temporary file.");
disk_file.seek(SeekFrom::Start(0)).unwrap();
QcowFile::from(disk_file).expect("Failed to create Qcow from default Header");
}
#[test]
fn default_header_v3() {
let header = QcowHeader::create_for_size(3, 0x10_0000);
let mut disk_file: File = tempfile().unwrap();
header
.write_to(&mut disk_file)
.expect("Failed to write header to temporary file.");
disk_file.seek(SeekFrom::Start(0)).unwrap();
QcowFile::from(disk_file).expect("Failed to create Qcow from default Header");
}
#[test]
fn header_read() {
with_basic_file(&valid_header(), |mut disk_file: File| {
QcowHeader::new(&mut disk_file).expect("Failed to create Header.");
with_basic_file(&valid_header_v2(), |mut disk_file: File| {
let header = QcowHeader::new(&mut disk_file).expect("Failed to create Header.");
assert_eq!(header.version, 2);
assert_eq!(header.refcount_order, DEFAULT_REFCOUNT_ORDER);
assert_eq!(header.header_size, V2_BARE_HEADER_SIZE);
});
with_basic_file(&valid_header_v3(), |mut disk_file: File| {
let header = QcowHeader::new(&mut disk_file).expect("Failed to create Header.");
assert_eq!(header.version, 3);
assert_eq!(header.refcount_order, DEFAULT_REFCOUNT_ORDER);
assert_eq!(header.header_size, V3_BARE_HEADER_SIZE);
});
}
@ -1698,7 +1763,7 @@ mod tests {
#[test]
fn invalid_refcount_order() {
let mut header = valid_header();
let mut header = valid_header_v3();
header[99] = 2;
with_basic_file(&header, |disk_file: File| {
QcowFile::from(disk_file).expect_err("Invalid refcount order worked.");
@ -1707,7 +1772,7 @@ mod tests {
#[test]
fn write_read_start() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
q.write(b"test first bytes")
.expect("Failed to write test string.");
@ -1720,7 +1785,7 @@ mod tests {
#[test]
fn offset_write_read() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
let b = [0x55u8; 0x1000];
q.seek(SeekFrom::Start(0xfff2000)).expect("Failed to seek.");
@ -1734,7 +1799,7 @@ mod tests {
#[test]
fn write_zeroes_read() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
// Write some test data.
let b = [0x55u8; 0x1000];
@ -1760,7 +1825,7 @@ mod tests {
// Choose a size that is larger than a cluster.
// valid_header uses cluster_bits = 12, which corresponds to a cluster size of 4096.
const CHUNK_SIZE: usize = 4096 * 2 + 512;
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
// Write some test data.
let b = [0x55u8; CHUNK_SIZE];
@ -1781,7 +1846,11 @@ mod tests {
#[test]
fn test_header() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v2(), |disk_file: File| {
let q = QcowFile::from(disk_file).unwrap();
assert_eq!(q.virtual_size(), 0x20_0000_0000);
});
with_basic_file(&valid_header_v3(), |disk_file: File| {
let q = QcowFile::from(disk_file).unwrap();
assert_eq!(q.virtual_size(), 0x20_0000_0000);
});
@ -1789,7 +1858,7 @@ mod tests {
#[test]
fn read_small_buffer() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
let mut b = [5u8; 16];
q.seek(SeekFrom::Start(1000)).expect("Failed to seek.");
@ -1801,7 +1870,7 @@ mod tests {
#[test]
fn replay_ext4() {
with_basic_file(&valid_header(), |disk_file: File| {
with_basic_file(&valid_header_v3(), |disk_file: File| {
let mut q = QcowFile::from(disk_file).unwrap();
const BUF_SIZE: usize = 0x1000;
let mut b = [0u8; BUF_SIZE];
@ -2337,7 +2406,7 @@ mod tests {
#[test]
fn rebuild_refcounts() {
with_basic_file(&valid_header(), |mut disk_file: File| {
with_basic_file(&valid_header_v3(), |mut disk_file: File| {
let header = QcowHeader::new(&mut disk_file).expect("Failed to create Header.");
let cluster_size = 65536;
let mut raw_file =