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block: qcow: support opening backing files

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This commit allows opening qcow with a backing file, which supports any
type implementing `BlockBackend`.

This commit is based on crosvm implementation:
9ca6039b03

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>
This commit is contained in:
Yu Li 2023-07-05 14:17:50 +08:00 committed by Rob Bradford
parent ffe78c98fd
commit 081a6ebb51
2 changed files with 167 additions and 31 deletions
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190
block/src/qcow/mod.rs
View File

@ -18,8 +18,10 @@ use libc::{EINVAL, ENOSPC, ENOTSUP};
use remain::sorted;
use std::cmp::{max, min};
use std::fmt::{self, Display};
use std::fs::OpenOptions;
use std::io::{self, Read, Seek, SeekFrom, Write};
use std::mem::size_of;
use std::str;
use vmm_sys_util::{
file_traits::FileSetLen, file_traits::FileSync, seek_hole::SeekHole, write_zeroes::PunchHole,
write_zeroes::WriteZeroesAt,
@ -30,12 +32,15 @@ pub use crate::qcow::raw_file::RawFile;
#[sorted]
#[derive(Debug)]
pub enum Error {
BackingFilesNotSupported,
BackingFileIo(io::Error),
BackingFileOpen(Box<crate::Error>),
BackingFileTooLong(usize),
CompressedBlocksNotSupported,
EvictingCache(io::Error),
FileTooBig(u64),
GettingFileSize(io::Error),
GettingRefcount(refcount::Error),
InvalidBackingFileName(str::Utf8Error),
InvalidClusterIndex,
InvalidClusterSize,
InvalidIndex,
@ -78,12 +83,17 @@ impl Display for Error {
#[sorted]
match self {
BackingFilesNotSupported => write!(f, "backing files not supported"),
BackingFileIo(e) => write!(f, "backing file io error: {}", e),
BackingFileOpen(e) => write!(f, "backing file open error: {}", *e),
BackingFileTooLong(len) => {
write!(f, "backing file name is too long: {} bytes over", len)
}
CompressedBlocksNotSupported => write!(f, "compressed blocks not supported"),
EvictingCache(e) => write!(f, "failed to evict cache: {e}"),
FileTooBig(size) => write!(f, "file larger than max of {MAX_QCOW_FILE_SIZE}: {size}"),
GettingFileSize(e) => write!(f, "failed to get file size: {e}"),
GettingRefcount(e) => write!(f, "failed to get refcount: {e}"),
InvalidBackingFileName(e) => write!(f, "failed to parse filename: {}", e),
InvalidClusterIndex => write!(f, "invalid cluster index"),
InvalidClusterSize => write!(f, "invalid cluster size"),
InvalidIndex => write!(f, "invalid index"),
@ -153,8 +163,14 @@ const COMPRESSED_FLAG: u64 = 1 << 62;
const CLUSTER_USED_FLAG: u64 = 1 << 63;
const COMPATIBLE_FEATURES_LAZY_REFCOUNTS: u64 = 1;
// The format supports a "header extension area", that crosvm does not use.
const QCOW_EMPTY_HEADER_EXTENSION_SIZE: u32 = 8;
// Defined by the specification
const MAX_BACKING_FILE_SIZE: u32 = 1023;
/// Contains the information from the header of a qcow file.
#[derive(Copy, Clone, Debug)]
#[derive(Clone, Debug)]
pub struct QcowHeader {
pub magic: u32,
pub version: u32,
@ -181,6 +197,9 @@ pub struct QcowHeader {
pub autoclear_features: u64,
pub refcount_order: u32,
pub header_size: u32,
// Post-header entries
pub backing_file_path: Option<String>,
}
impl QcowHeader {
@ -204,7 +223,7 @@ impl QcowHeader {
let version = read_u32_from_file(f)?;
Ok(QcowHeader {
let mut header = QcowHeader {
magic,
version,
backing_file_offset: read_u64_from_file(f)?,
@ -243,24 +262,58 @@ impl QcowHeader {
} else {
read_u32_from_file(f)?
},
})
backing_file_path: None,
};
if header.backing_file_size > MAX_BACKING_FILE_SIZE {
return Err(Error::BackingFileTooLong(header.backing_file_size as usize));
}
if header.backing_file_offset != 0 {
f.seek(SeekFrom::Start(header.backing_file_offset))
.map_err(Error::ReadingHeader)?;
let mut backing_file_name_bytes = vec![0u8; header.backing_file_size as usize];
f.read_exact(&mut backing_file_name_bytes)
.map_err(Error::ReadingHeader)?;
header.backing_file_path = Some(
String::from_utf8(backing_file_name_bytes)
.map_err(|err| Error::InvalidBackingFileName(err.utf8_error()))?,
);
}
Ok(header)
}
/// Create a header for the given `size`.
pub fn create_for_size(version: u32, size: u64) -> QcowHeader {
pub fn create_for_size_and_path(
version: u32,
size: u64,
backing_file: Option<&str>,
) -> Result<QcowHeader> {
let header_size = if version == 2 {
V2_BARE_HEADER_SIZE
} else {
V3_BARE_HEADER_SIZE + QCOW_EMPTY_HEADER_EXTENSION_SIZE
};
let cluster_bits: u32 = DEFAULT_CLUSTER_BITS;
let cluster_size: u32 = 0x01 << cluster_bits;
let max_length: usize = (cluster_size - header_size) as usize;
if let Some(path) = backing_file {
if path.len() > max_length {
return Err(Error::BackingFileTooLong(path.len() - max_length));
}
}
// L2 blocks are always one cluster long. They contain cluster_size/sizeof(u64) addresses.
let entries_per_cluster: u32 = cluster_size / size_of::<u64>() as u32;
let num_clusters: u32 = div_round_up_u64(size, u64::from(cluster_size)) as u32;
let num_l2_clusters: u32 = div_round_up_u32(num_clusters, entries_per_cluster);
let l1_clusters: u32 = div_round_up_u32(num_l2_clusters, entries_per_cluster);
let header_clusters = div_round_up_u32(size_of::<QcowHeader>() as u32, cluster_size);
QcowHeader {
Ok(QcowHeader {
magic: QCOW_MAGIC,
version,
backing_file_offset: 0,
backing_file_size: 0,
backing_file_offset: (if backing_file.is_none() {
0
} else {
header_size
}) as u64,
backing_file_size: backing_file.map_or(0, |x| x.len()) as u32,
cluster_bits: DEFAULT_CLUSTER_BITS,
size,
crypt_method: 0,
@ -289,12 +342,9 @@ impl QcowHeader {
compatible_features: 0,
autoclear_features: 0,
refcount_order: DEFAULT_REFCOUNT_ORDER,
header_size: if version == 2 {
V2_BARE_HEADER_SIZE
} else {
V3_BARE_HEADER_SIZE
},
}
header_size,
backing_file_path: backing_file.map(String::from),
})
}
/// Write the header to `file`.
@ -331,6 +381,12 @@ impl QcowHeader {
write_u64_to_file(file, self.autoclear_features)?;
write_u32_to_file(file, self.refcount_order)?;
write_u32_to_file(file, self.header_size)?;
write_u32_to_file(file, 0)?; // header extension type: end of header extension area
write_u32_to_file(file, 0)?; // length of header extension data: 0
}
if let Some(backing_file_path) = self.backing_file_path.as_ref() {
write!(file, "{}", backing_file_path).map_err(Error::WritingHeader)?;
}
// Set the file length by seeking and writing a zero to the last byte. This avoids needing
@ -376,7 +432,7 @@ fn max_refcount_clusters(refcount_order: u32, cluster_size: u32, num_clusters: u
/// # Ok(())
/// # }
/// ```
#[derive(Clone, Debug)]
#[derive(Debug)]
pub struct QcowFile {
raw_file: QcowRawFile,
header: QcowHeader,
@ -389,7 +445,7 @@ pub struct QcowFile {
// List of unreferenced clusters available to be used. unref clusters become available once the
// removal of references to them have been synced to disk.
avail_clusters: Vec<u64>,
//TODO(dgreid) Add support for backing files. - backing_file: Option<Box<QcowFile<T>>>,
backing_file: Option<Box<dyn BlockBackend>>,
}
impl QcowFile {
@ -418,10 +474,20 @@ impl QcowFile {
return Err(Error::FileTooBig(header.size));
}
// No current support for backing files.
if header.backing_file_offset != 0 {
return Err(Error::BackingFilesNotSupported);
}
let direct_io = file.is_direct();
let backing_file = if let Some(backing_file_path) = header.backing_file_path.as_ref() {
let path = backing_file_path.clone();
let backing_raw_file = OpenOptions::new()
.read(true)
.open(path)
.map_err(Error::BackingFileIo)?;
let backing_file = crate::create_disk_file(backing_raw_file, direct_io)
.map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
Some(backing_file)
} else {
None
};
// Only support two byte refcounts.
let refcount_bits: u64 = 0x01u64
@ -436,7 +502,6 @@ impl QcowFile {
if header.refcount_table_clusters == 0 {
return Err(Error::NoRefcountClusters);
}
offset_is_cluster_boundary(header.backing_file_offset, header.cluster_bits)?;
offset_is_cluster_boundary(header.l1_table_offset, header.cluster_bits)?;
offset_is_cluster_boundary(header.snapshots_offset, header.cluster_bits)?;
// refcount table must be a cluster boundary, and within the file's virtual or actual size.
@ -469,7 +534,7 @@ impl QcowFile {
let mut raw_file =
QcowRawFile::from(file, cluster_size).ok_or(Error::InvalidClusterSize)?;
if refcount_rebuild_required {
QcowFile::rebuild_refcounts(&mut raw_file, header)?;
QcowFile::rebuild_refcounts(&mut raw_file, header.clone())?;
}
let entries_per_cluster = cluster_size / size_of::<u64>() as u64;
@ -538,6 +603,7 @@ impl QcowFile {
current_offset: 0,
unref_clusters: Vec::new(),
avail_clusters: Vec::new(),
backing_file,
};
// Check that the L1 and refcount tables fit in a 64bit address space.
@ -556,8 +622,34 @@ impl QcowFile {
}
/// Creates a new QcowFile at the given path.
pub fn new(mut file: RawFile, version: u32, virtual_size: u64) -> Result<QcowFile> {
let header = QcowHeader::create_for_size(version, virtual_size);
pub fn new(file: RawFile, version: u32, virtual_size: u64) -> Result<QcowFile> {
let header = QcowHeader::create_for_size_and_path(version, virtual_size, None)?;
QcowFile::new_from_header(file, header)
}
/// Creates a new QcowFile at the given path.
pub fn new_from_backing(
file: RawFile,
version: u32,
backing_file_name: &str,
) -> Result<QcowFile> {
let direct_io = file.is_direct();
let backing_raw_file = OpenOptions::new()
.read(true)
.open(backing_file_name)
.map_err(Error::BackingFileIo)?;
let backing_file = crate::create_disk_file(backing_raw_file, direct_io)
.map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
let size = backing_file
.size()
.map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
let header = QcowHeader::create_for_size_and_path(version, size, Some(backing_file_name))?;
let mut result = QcowFile::new_from_header(file, header)?;
result.backing_file = Some(backing_file);
Ok(result)
}
fn new_from_header(mut file: RawFile, header: QcowHeader) -> Result<QcowFile> {
file.rewind().map_err(Error::SeekingFile)?;
header.write_to(&mut file)?;
@ -893,9 +985,9 @@ impl QcowFile {
// Find all references clusters and rebuild refcounts.
set_header_refcount(&mut refcounts, cluster_size)?;
set_l1_refcounts(&mut refcounts, header, cluster_size)?;
set_data_refcounts(&mut refcounts, header, cluster_size, raw_file)?;
set_refcount_table_refcounts(&mut refcounts, header, cluster_size)?;
set_l1_refcounts(&mut refcounts, header.clone(), cluster_size)?;
set_data_refcounts(&mut refcounts, header.clone(), cluster_size, raw_file)?;
set_refcount_table_refcounts(&mut refcounts, header.clone(), cluster_size)?;
// Allocate clusters to store the new reference count blocks.
let ref_table = alloc_refblocks(&mut refcounts, cluster_size, refblock_clusters)?;
@ -1799,9 +1891,10 @@ mod tests {
#[test]
fn default_header_v2() {
let header = QcowHeader::create_for_size(2, 0x10_0000);
let header = QcowHeader::create_for_size_and_path(2, 0x10_0000, None);
let mut disk_file: RawFile = RawFile::new(TempFile::new().unwrap().into_file(), false);
header
.expect("Failed to create header.")
.write_to(&mut disk_file)
.expect("Failed to write header to temporary file.");
disk_file.rewind().unwrap();
@ -1810,9 +1903,10 @@ mod tests {
#[test]
fn default_header_v3() {
let header = QcowHeader::create_for_size(3, 0x10_0000);
let header = QcowHeader::create_for_size_and_path(3, 0x10_0000, None);
let mut disk_file: RawFile = RawFile::new(TempFile::new().unwrap().into_file(), false);
header
.expect("Failed to create header.")
.write_to(&mut disk_file)
.expect("Failed to write header to temporary file.");
disk_file.rewind().unwrap();
@ -1835,6 +1929,40 @@ mod tests {
});
}
#[test]
fn header_v2_with_backing() {
let header = QcowHeader::create_for_size_and_path(2, 0x10_0000, Some("/my/path/to/a/file"))
.expect("Failed to create header.");
let mut disk_file: RawFile = RawFile::new(TempFile::new().unwrap().into_file(), false);
header
.write_to(&mut disk_file)
.expect("Failed to write header to shm.");
disk_file.rewind().unwrap();
let read_header = QcowHeader::new(&mut disk_file).expect("Failed to create header.");
assert_eq!(
header.backing_file_path,
Some(String::from("/my/path/to/a/file"))
);
assert_eq!(read_header.backing_file_path, header.backing_file_path);
}
#[test]
fn header_v3_with_backing() {
let header = QcowHeader::create_for_size_and_path(3, 0x10_0000, Some("/my/path/to/a/file"))
.expect("Failed to create header.");
let mut disk_file: RawFile = RawFile::new(TempFile::new().unwrap().into_file(), false);
header
.write_to(&mut disk_file)
.expect("Failed to write header to shm.");
disk_file.rewind().unwrap();
let read_header = QcowHeader::new(&mut disk_file).expect("Failed to create header.");
assert_eq!(
header.backing_file_path,
Some(String::from("/my/path/to/a/file"))
);
assert_eq!(read_header.backing_file_path, header.backing_file_path);
}
#[test]
fn invalid_magic() {
let invalid_header = vec![0x51u8, 0x46, 0x4a, 0xfb];

8
block/src/qcow/raw_file.rs
View File

@ -23,6 +23,7 @@ pub struct RawFile {
file: File,
alignment: usize,
position: u64,
direct_io: bool,
}
const BLK_ALIGNMENTS: [usize; 2] = [512, 4096];
@ -65,6 +66,7 @@ impl RawFile {
file,
alignment,
position: 0,
direct_io,
}
}
@ -103,6 +105,7 @@ impl RawFile {
file: self.file.try_clone().expect("RawFile cloning failed"),
alignment: self.alignment,
position: self.position,
direct_io: self.direct_io,
})
}
@ -113,6 +116,10 @@ impl RawFile {
pub fn sync_data(&self) -> std::io::Result<()> {
self.file.sync_data()
}
pub fn is_direct(&self) -> bool {
self.direct_io
}
}
impl Read for RawFile {
@ -356,6 +363,7 @@ impl Clone for RawFile {
file: self.file.try_clone().expect("RawFile cloning failed"),
alignment: self.alignment,
position: self.position,
direct_io: self.direct_io,
}
}
}