block: introduce trait BlockBackend for block types

This commit introduces the trait `BlockBackend` with generic ops
including read, write and seek, which can be used for common I/O
interfaces for the block types without using `DiskFile` and `AsyncIo`.

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>

block/src/fixed_vhd.rs

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use crate::vhd::VhdFooter;
+use crate::BlockBackend;
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::os::unix::io::{AsRawFd, RawFd};
@@ -24,10 +25,6 @@ impl FixedVhd {
             position: 0,
         })
     }
-
-    pub fn size(&self) -> u64 {
-        self.size
-    }
 }
 
 impl AsRawFd for FixedVhd {
@@ -76,6 +73,12 @@ impl Seek for FixedVhd {
     }
 }
 
+impl BlockBackend for FixedVhd {
+    fn size(&self) -> std::result::Result<u64, crate::Error> {
+        Ok(self.size)
+    }
+}
+
 impl Clone for FixedVhd {
     fn clone(&self) -> Self {
         Self {

block/src/fixed_vhd_async.rs

@@ -7,6 +7,7 @@ use crate::async_io::{
 };
 use crate::fixed_vhd::FixedVhd;
 use crate::raw_async::RawFileAsync;
+use crate::BlockBackend;
 use std::fs::File;
 use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
@@ -21,12 +22,12 @@ impl FixedVhdDiskAsync {
 
 impl DiskFile for FixedVhdDiskAsync {
     fn size(&mut self) -> DiskFileResult<u64> {
-        Ok(self.0.size())
+        Ok(self.0.size().unwrap())
     }
 
     fn new_async_io(&self, ring_depth: u32) -> DiskFileResult<Box<dyn AsyncIo>> {
         Ok(Box::new(
-            FixedVhdAsync::new(self.0.as_raw_fd(), ring_depth, self.0.size())
+            FixedVhdAsync::new(self.0.as_raw_fd(), ring_depth, self.0.size().unwrap())
                 .map_err(DiskFileError::NewAsyncIo)?,
         ) as Box<dyn AsyncIo>)
     }

block/src/fixed_vhd_sync.rs

@@ -7,6 +7,7 @@ use crate::async_io::{
 };
 use crate::fixed_vhd::FixedVhd;
 use crate::raw_sync::RawFileSync;
+use crate::BlockBackend;
 use std::fs::File;
 use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
@@ -21,12 +22,12 @@ impl FixedVhdDiskSync {
 
 impl DiskFile for FixedVhdDiskSync {
     fn size(&mut self) -> DiskFileResult<u64> {
-        Ok(self.0.size())
+        Ok(self.0.size().unwrap())
     }
 
     fn new_async_io(&self, _ring_depth: u32) -> DiskFileResult<Box<dyn AsyncIo>> {
         Ok(Box::new(
-            FixedVhdSync::new(self.0.as_raw_fd(), self.0.size())
+            FixedVhdSync::new(self.0.as_raw_fd(), self.0.size().unwrap())
                 .map_err(DiskFileError::NewAsyncIo)?,
         ) as Box<dyn AsyncIo>)
     }

block/src/lib.rs

@@ -30,6 +30,9 @@ pub mod vhdx;
 pub mod vhdx_sync;
 
 use crate::async_io::{AsyncIo, AsyncIoError, AsyncIoResult};
+use crate::fixed_vhd::FixedVhd;
+use crate::qcow::{QcowFile, RawFile};
+use crate::vhdx::{Vhdx, VhdxError};
 #[cfg(feature = "io_uring")]
 use io_uring::{opcode, IoUring, Probe};
 use smallvec::SmallVec;
@@ -37,6 +40,7 @@ use std::alloc::{alloc_zeroed, dealloc, Layout};
 use std::cmp;
 use std::collections::VecDeque;
 use std::convert::TryInto;
+use std::fmt::Debug;
 use std::fs::File;
 use std::io::{self, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
 use std::os::linux::fs::MetadataExt;
@@ -76,12 +80,22 @@ pub enum Error {
     DescriptorChainTooShort,
     #[error("Guest gave us a descriptor that was too short to use")]
     DescriptorLengthTooSmall,
+    #[error("Failed to detect image type: {0}")]
+    DetectImageType(std::io::Error),
+    #[error("Failure in fixed vhd: {0}")]
+    FixedVhdError(std::io::Error),
     #[error("Getting a block's metadata fails for any reason")]
     GetFileMetadata,
     #[error("The requested operation would cause a seek beyond disk end")]
     InvalidOffset,
+    #[error("Failure in qcow: {0}")]
+    QcowError(qcow::Error),
+    #[error("Failure in raw file: {0}")]
+    RawFileError(std::io::Error),
     #[error("The requested operation does not support multiple descriptors")]
     TooManyDescriptors,
+    #[error("Failure in vhdx: {0}")]
+    VhdxError(VhdxError),
 }
 
 fn build_device_id(disk_path: &Path) -> result::Result<String, Error> {
@@ -739,3 +753,26 @@ pub fn detect_image_type(f: &mut File) -> std::io::Result<ImageType> {
 
     Ok(image_type)
 }
+
+pub trait BlockBackend: Read + Write + Seek + Send + Debug {
+    fn size(&self) -> Result<u64, Error>;
+}
+
+/// Inspect the image file type and create an appropriate disk file to match it.
+pub fn create_disk_file(mut file: File, direct_io: bool) -> Result<Box<dyn BlockBackend>, Error> {
+    let image_type = detect_image_type(&mut file).map_err(Error::DetectImageType)?;
+
+    Ok(match image_type {
+        ImageType::Qcow2 => {
+            Box::new(QcowFile::from(RawFile::new(file, direct_io)).map_err(Error::QcowError)?)
+                as Box<dyn BlockBackend>
+        }
+        ImageType::FixedVhd => {
+            Box::new(FixedVhd::new(file).map_err(Error::FixedVhdError)?) as Box<dyn BlockBackend>
+        }
+        ImageType::Vhdx => {
+            Box::new(Vhdx::new(file).map_err(Error::VhdxError)?) as Box<dyn BlockBackend>
+        }
+        ImageType::Raw => Box::new(RawFile::new(file, direct_io)) as Box<dyn BlockBackend>,
+    })
+}

block/src/qcow/mod.rs

@@ -12,6 +12,7 @@ use crate::qcow::{
     refcount::RefCount,
     vec_cache::{CacheMap, Cacheable, VecCache},
 };
+use crate::BlockBackend;
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
 use libc::{EINVAL, ENOSPC, ENOTSUP};
 use remain::sorted;
@@ -1555,6 +1556,12 @@ impl SeekHole for QcowFile {
     }
 }
 
+impl BlockBackend for QcowFile {
+    fn size(&self) -> std::result::Result<u64, crate::Error> {
+        Ok(self.virtual_size())
+    }
+}
+
 // Returns an Error if the given offset doesn't align to a cluster boundary.
 fn offset_is_cluster_boundary(offset: u64, cluster_bits: u32) -> Result<()> {
     if offset & ((0x01 << cluster_bits) - 1) != 0 {

block/src/qcow/raw_file.rs

@@ -8,6 +8,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
+use crate::BlockBackend;
 use libc::c_void;
 use std::alloc::{alloc_zeroed, dealloc, Layout};
 use std::convert::TryInto;
@@ -343,6 +344,12 @@ impl SeekHole for RawFile {
     }
 }
 
+impl BlockBackend for RawFile {
+    fn size(&self) -> std::result::Result<u64, crate::Error> {
+        Ok(self.metadata().map_err(crate::Error::RawFileError)?.len())
+    }
+}
+
 impl Clone for RawFile {
     fn clone(&self) -> Self {
         RawFile {

block/src/vhdx/mod.rs

@@ -8,6 +8,7 @@ use crate::vhdx::{
     vhdx_io::VhdxIoError,
     vhdx_metadata::{DiskSpec, VhdxMetadataError},
 };
+use crate::BlockBackend;
 use byteorder::{BigEndian, ByteOrder};
 use remain::sorted;
 use std::collections::btree_map::BTreeMap;
@@ -208,6 +209,12 @@ impl Seek for Vhdx {
     }
 }
 
+impl BlockBackend for Vhdx {
+    fn size(&self) -> std::result::Result<u64, crate::Error> {
+        Ok(self.virtual_disk_size())
+    }
+}
+
 impl Clone for Vhdx {
     fn clone(&self) -> Self {
         Vhdx {