block_util: provide and use AsyncAdaptor trait

The observation is that the code in question was used to bridge
synchronized and asynchronized code.

We can group the functions for that purpose under an adaptor trait. To
limit the scope of locking, the users of the trait are required to
implement a method to return a MutexGuard for the underlying file.

This then allows us to use concrete types (QcowFile and Vhdx) in code,
which is easier to read than a bunch of traits.

No functional change intended.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

block_util/src/lib.rs

@@ -23,7 +23,6 @@ pub mod vhdx_sync;
 use crate::async_io::{AsyncIo, AsyncIoError, AsyncIoResult};
 #[cfg(feature = "io_uring")]
 use io_uring::{opcode, IoUring, Probe};
-use std::any::Any;
 use std::cmp;
 use std::convert::TryInto;
 use std::fs::File;
@@ -31,7 +30,7 @@ use std::io::{self, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
 use std::os::linux::fs::MetadataExt;
 use std::path::Path;
 use std::result;
-use std::sync::{Arc, Mutex};
+use std::sync::MutexGuard;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use virtio_bindings::bindings::virtio_blk::*;
@@ -477,103 +476,98 @@ pub fn block_io_uring_is_supported() -> bool {
     false
 }
 
-pub trait ReadWriteSeekFile: Read + Write + Seek {
-    // Provides a mutable reference to the Any trait. This is useful to let
-    // the caller have access to the underlying type behind the trait.
-    fn as_any(&mut self) -> &mut dyn Any;
-}
+pub trait AsyncAdaptor<F>
+where
+    F: Read + Write + Seek,
+{
+    fn read_vectored_sync(
+        &mut self,
+        offset: libc::off_t,
+        iovecs: Vec<libc::iovec>,
+        user_data: u64,
+        eventfd: &EventFd,
+        completion_list: &mut Vec<(u64, i32)>,
+    ) -> AsyncIoResult<()> {
+        // Convert libc::iovec into IoSliceMut
+        let mut slices = Vec::new();
+        for iovec in iovecs.iter() {
+            slices.push(IoSliceMut::new(unsafe { std::mem::transmute(*iovec) }));
+        }
 
-impl<F: Read + Write + Seek + 'static> ReadWriteSeekFile for F {
-    fn as_any(&mut self) -> &mut dyn Any {
-        self
-    }
-}
+        let result = {
+            let mut file = self.file();
 
-pub fn read_vectored_sync(
-    offset: libc::off_t,
-    iovecs: Vec<libc::iovec>,
-    user_data: u64,
-    file: &mut Arc<Mutex<dyn ReadWriteSeekFile + Send + Sync>>,
-    eventfd: &EventFd,
-    completion_list: &mut Vec<(u64, i32)>,
-) -> AsyncIoResult<()> {
-    // Convert libc::iovec into IoSliceMut
-    let mut slices = Vec::new();
-    for iovec in iovecs.iter() {
-        slices.push(IoSliceMut::new(unsafe { std::mem::transmute(*iovec) }));
-    }
+            // Move the cursor to the right offset
+            file.seek(SeekFrom::Start(offset as u64))
+                .map_err(AsyncIoError::ReadVectored)?;
 
-    let result = {
-        let mut file = file.lock().unwrap();
+            // Read vectored
+            file.read_vectored(slices.as_mut_slice())
+                .map_err(AsyncIoError::ReadVectored)?
+        };
 
-        // Move the cursor to the right offset
-        file.seek(SeekFrom::Start(offset as u64))
-            .map_err(AsyncIoError::ReadVectored)?;
-
-        // Read vectored
-        file.read_vectored(slices.as_mut_slice())
-            .map_err(AsyncIoError::ReadVectored)?
-    };
-
-    completion_list.push((user_data, result as i32));
-    eventfd.write(1).unwrap();
-
-    Ok(())
-}
-
-pub fn write_vectored_sync(
-    offset: libc::off_t,
-    iovecs: Vec<libc::iovec>,
-    user_data: u64,
-    file: &mut Arc<Mutex<dyn ReadWriteSeekFile + Sync + Send>>,
-    eventfd: &EventFd,
-    completion_list: &mut Vec<(u64, i32)>,
-) -> AsyncIoResult<()> {
-    // Convert libc::iovec into IoSlice
-    let mut slices = Vec::new();
-    for iovec in iovecs.iter() {
-        slices.push(IoSlice::new(unsafe { std::mem::transmute(*iovec) }));
-    }
-
-    let result = {
-        let mut file = file.lock().unwrap();
-
-        // Move the cursor to the right offset
-        file.seek(SeekFrom::Start(offset as u64))
-            .map_err(AsyncIoError::WriteVectored)?;
-
-        // Write vectored
-        file.write_vectored(slices.as_slice())
-            .map_err(AsyncIoError::WriteVectored)?
-    };
-
-    completion_list.push((user_data, result as i32));
-    eventfd.write(1).unwrap();
-
-    Ok(())
-}
-
-pub fn fsync_sync(
-    user_data: Option<u64>,
-    file: &mut Arc<Mutex<dyn ReadWriteSeekFile + Sync + Send>>,
-    eventfd: &EventFd,
-    completion_list: &mut Vec<(u64, i32)>,
-) -> AsyncIoResult<()> {
-    let result: i32 = {
-        let mut file = file.lock().unwrap();
-
-        // Flush
-        file.flush().map_err(AsyncIoError::Fsync)?;
-
-        0
-    };
-
-    if let Some(user_data) = user_data {
-        completion_list.push((user_data, result));
+        completion_list.push((user_data, result as i32));
         eventfd.write(1).unwrap();
+
+        Ok(())
     }
 
-    Ok(())
+    fn write_vectored_sync(
+        &mut self,
+        offset: libc::off_t,
+        iovecs: Vec<libc::iovec>,
+        user_data: u64,
+        eventfd: &EventFd,
+        completion_list: &mut Vec<(u64, i32)>,
+    ) -> AsyncIoResult<()> {
+        // Convert libc::iovec into IoSlice
+        let mut slices = Vec::new();
+        for iovec in iovecs.iter() {
+            slices.push(IoSlice::new(unsafe { std::mem::transmute(*iovec) }));
+        }
+
+        let result = {
+            let mut file = self.file();
+
+            // Move the cursor to the right offset
+            file.seek(SeekFrom::Start(offset as u64))
+                .map_err(AsyncIoError::WriteVectored)?;
+
+            // Write vectored
+            file.write_vectored(slices.as_slice())
+                .map_err(AsyncIoError::WriteVectored)?
+        };
+
+        completion_list.push((user_data, result as i32));
+        eventfd.write(1).unwrap();
+
+        Ok(())
+    }
+
+    fn fsync_sync(
+        &mut self,
+        user_data: Option<u64>,
+        eventfd: &EventFd,
+        completion_list: &mut Vec<(u64, i32)>,
+    ) -> AsyncIoResult<()> {
+        let result: i32 = {
+            let mut file = self.file();
+
+            // Flush
+            file.flush().map_err(AsyncIoError::Fsync)?;
+
+            0
+        };
+
+        if let Some(user_data) = user_data {
+            completion_list.push((user_data, result));
+            eventfd.write(1).unwrap();
+        }
+
+        Ok(())
+    }
+
+    fn file(&mut self) -> MutexGuard<F>;
 }
 
 pub enum ImageType {

block_util/src/qcow_sync.rs

@@ -3,15 +3,15 @@
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
 use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
-use crate::{fsync_sync, read_vectored_sync, write_vectored_sync, ReadWriteSeekFile};
+use crate::AsyncAdaptor;
 use qcow::{QcowFile, RawFile, Result as QcowResult};
 use std::fs::File;
-use std::io::SeekFrom;
-use std::sync::{Arc, Mutex};
+use std::io::{Seek, SeekFrom};
+use std::sync::{Arc, Mutex, MutexGuard};
 use vmm_sys_util::eventfd::EventFd;
 
 pub struct QcowDiskSync {
-    qcow_file: Arc<Mutex<dyn ReadWriteSeekFile + Send + Sync>>,
+    qcow_file: Arc<Mutex<QcowFile>>,
 }
 
 impl QcowDiskSync {
@@ -35,13 +35,13 @@ impl DiskFile for QcowDiskSync {
 }
 
 pub struct QcowSync {
-    qcow_file: Arc<Mutex<dyn ReadWriteSeekFile + Send + Sync>>,
+    qcow_file: Arc<Mutex<QcowFile>>,
     eventfd: EventFd,
     completion_list: Vec<(u64, i32)>,
 }
 
 impl QcowSync {
-    pub fn new(qcow_file: Arc<Mutex<dyn ReadWriteSeekFile + Send + Sync>>) -> Self {
+    pub fn new(qcow_file: Arc<Mutex<QcowFile>>) -> Self {
         QcowSync {
             qcow_file,
             eventfd: EventFd::new(libc::EFD_NONBLOCK)
@@ -51,6 +51,12 @@ impl QcowSync {
     }
 }
 
+impl AsyncAdaptor<QcowFile> for Arc<Mutex<QcowFile>> {
+    fn file(&mut self) -> MutexGuard<QcowFile> {
+        self.lock().unwrap()
+    }
+}
+
 impl AsyncIo for QcowSync {
     fn notifier(&self) -> &EventFd {
         &self.eventfd
@@ -62,11 +68,10 @@ impl AsyncIo for QcowSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
-        read_vectored_sync(
+        self.qcow_file.read_vectored_sync(
             offset,
             iovecs,
             user_data,
-            &mut self.qcow_file,
             &self.eventfd,
             &mut self.completion_list,
         )
@@ -78,23 +83,18 @@ impl AsyncIo for QcowSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
-        write_vectored_sync(
+        self.qcow_file.write_vectored_sync(
             offset,
             iovecs,
             user_data,
-            &mut self.qcow_file,
             &self.eventfd,
             &mut self.completion_list,
         )
     }
 
     fn fsync(&mut self, user_data: Option<u64>) -> AsyncIoResult<()> {
-        fsync_sync(
-            user_data,
-            &mut self.qcow_file,
-            &self.eventfd,
-            &mut self.completion_list,
-        )
+        self.qcow_file
+            .fsync_sync(user_data, &self.eventfd, &mut self.completion_list)
     }
 
     fn complete(&mut self) -> Vec<(u64, i32)> {

block_util/src/vhdx_sync.rs

@@ -3,14 +3,14 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
-use crate::{fsync_sync, read_vectored_sync, write_vectored_sync, ReadWriteSeekFile};
+use crate::AsyncAdaptor;
 use std::fs::File;
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, MutexGuard};
 use vhdx::vhdx::{Result as VhdxResult, Vhdx};
 use vmm_sys_util::eventfd::EventFd;
 
 pub struct VhdxDiskSync {
-    vhdx_file: Arc<Mutex<dyn ReadWriteSeekFile + Sync + Send>>,
+    vhdx_file: Arc<Mutex<Vhdx>>,
 }
 
 impl VhdxDiskSync {
@@ -23,14 +23,7 @@ impl VhdxDiskSync {
 
 impl DiskFile for VhdxDiskSync {
     fn size(&mut self) -> DiskFileResult<u64> {
-        Ok(self
-            .vhdx_file
-            .lock()
-            .unwrap()
-            .as_any()
-            .downcast_ref::<Vhdx>()
-            .unwrap()
-            .virtual_disk_size())
+        Ok(self.vhdx_file.lock().unwrap().virtual_disk_size())
     }
 
     fn new_async_io(&self, _ring_depth: u32) -> DiskFileResult<Box<dyn AsyncIo>> {
@@ -42,15 +35,13 @@ impl DiskFile for VhdxDiskSync {
 }
 
 pub struct VhdxSync {
-    vhdx_file: Arc<Mutex<dyn ReadWriteSeekFile + Sync + Send>>,
+    vhdx_file: Arc<Mutex<Vhdx>>,
     eventfd: EventFd,
     completion_list: Vec<(u64, i32)>,
 }
 
 impl VhdxSync {
-    pub fn new(
-        vhdx_file: Arc<Mutex<dyn ReadWriteSeekFile + Sync + Send>>,
-    ) -> std::io::Result<Self> {
+    pub fn new(vhdx_file: Arc<Mutex<Vhdx>>) -> std::io::Result<Self> {
         Ok(VhdxSync {
             vhdx_file,
             eventfd: EventFd::new(libc::EFD_NONBLOCK)?,
@@ -59,6 +50,12 @@ impl VhdxSync {
     }
 }
 
+impl AsyncAdaptor<Vhdx> for Arc<Mutex<Vhdx>> {
+    fn file(&mut self) -> MutexGuard<Vhdx> {
+        self.lock().unwrap()
+    }
+}
+
 impl AsyncIo for VhdxSync {
     fn notifier(&self) -> &EventFd {
         &self.eventfd
@@ -70,11 +67,10 @@ impl AsyncIo for VhdxSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
-        read_vectored_sync(
+        self.vhdx_file.read_vectored_sync(
             offset,
             iovecs,
             user_data,
-            &mut self.vhdx_file,
             &self.eventfd,
             &mut self.completion_list,
         )
@@ -86,23 +82,18 @@ impl AsyncIo for VhdxSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
-        write_vectored_sync(
+        self.vhdx_file.write_vectored_sync(
             offset,
             iovecs,
             user_data,
-            &mut self.vhdx_file,
             &self.eventfd,
             &mut self.completion_list,
         )
     }
 
     fn fsync(&mut self, user_data: Option<u64>) -> AsyncIoResult<()> {
-        fsync_sync(
-            user_data,
-            &mut self.vhdx_file,
-            &self.eventfd,
-            &mut self.completion_list,
-        )
+        self.vhdx_file
+            .fsync_sync(user_data, &self.eventfd, &mut self.completion_list)
     }
 
     fn complete(&mut self) -> Vec<(u64, i32)> {