block: bind FD lifetime of DiskFile

As we can't use BorrowedFd, we should at least create a similar
safe alternative.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

block/src/async_io.rs

@@ -2,7 +2,8 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use std::os::fd::RawFd;
+use std::marker::PhantomData;
+use std::os::fd::{AsRawFd, OwnedFd, RawFd};
 
 use thiserror::Error;
 use vmm_sys_util::eventfd::EventFd;
@@ -21,6 +22,39 @@ pub enum DiskFileError {
 
 pub type DiskFileResult<T> = std::result::Result<T, DiskFileError>;
 
+/// A wrapper for [`RawFd`] capturing the lifetime of a corresponding [`DiskFile`].
+///
+/// This fulfills the same role as [`BorrowedFd`] but is tailored to the limitations
+/// by some implementations of [`DiskFile`], which wrap the effective [`File`]
+/// in an `Arc<Mutex<T>>`, making the use of [`BorrowedFd`] impossible.
+///
+/// [`BorrowedFd`]: std::os::fd::BorrowedFd
+#[derive(Copy, Clone, Debug)]
+pub struct BorrowedDiskFd<'fd> {
+    raw_fd: RawFd,
+    _lifetime: PhantomData<&'fd OwnedFd>,
+}
+
+impl BorrowedDiskFd<'_> {
+    pub(super) fn new(raw_fd: RawFd) -> Self {
+        Self {
+            raw_fd,
+            _lifetime: PhantomData,
+        }
+    }
+}
+
+impl AsRawFd for BorrowedDiskFd<'_> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.raw_fd
+    }
+}
+
+/// Abstraction over the effective [`File`] backing up a block device,
+/// with support for synchronous and asynchronous I/O.
+///
+/// This allows abstracting over raw image formats as well as structured
+/// image formats.
 pub trait DiskFile: Send {
     fn size(&mut self) -> DiskFileResult<u64>;
     fn new_async_io(&self, ring_depth: u32) -> DiskFileResult<Box<dyn AsyncIo>>;
@@ -28,11 +62,10 @@ pub trait DiskFile: Send {
         DiskTopology::default()
     }
     /// Returns the file descriptor of the underlying disk image file.
-    // Impl Note:
-    // This must be `RawFd` instead of `BorrowedFd` or `&File`, as some
-    // implementations wrap the file in an `Arc<Mutex<T>>`, which makes it
-    // impossible to return a reference.
-    fn fd(&mut self) -> RawFd;
+    ///
+    /// The file descriptor is supposed to be used for `fcntl()` calls but no
+    /// other operation.
+    fn fd(&mut self) -> BorrowedDiskFd;
 }
 
 #[derive(Error, Debug)]

block/src/fixed_vhd_async.rs

@@ -8,7 +8,7 @@ use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::fixed_vhd::FixedVhd;
 use crate::raw_async::RawFileAsync;
@@ -34,8 +34,8 @@ impl DiskFile for FixedVhdDiskAsync {
         ) as Box<dyn AsyncIo>)
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.0.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.0.as_raw_fd())
     }
 }
 

block/src/fixed_vhd_sync.rs

@@ -8,7 +8,7 @@ use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::fixed_vhd::FixedVhd;
 use crate::raw_sync::RawFileSync;
@@ -34,8 +34,8 @@ impl DiskFile for FixedVhdDiskSync {
         ) as Box<dyn AsyncIo>)
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.0.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.0.as_raw_fd())
     }
 }
 

block/src/qcow_sync.rs

@@ -5,12 +5,14 @@
 use std::collections::VecDeque;
 use std::fs::File;
 use std::io::{Seek, SeekFrom};
-use std::os::fd::{AsRawFd, RawFd};
+use std::os::fd::AsRawFd;
 use std::sync::{Arc, Mutex, MutexGuard};
 
 use vmm_sys_util::eventfd::EventFd;
 
-use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
+use crate::async_io::{
+    AsyncIo, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
+};
 use crate::qcow::{QcowFile, RawFile, Result as QcowResult};
 use crate::AsyncAdaptor;
 
@@ -37,9 +39,9 @@ impl DiskFile for QcowDiskSync {
         Ok(Box::new(QcowSync::new(self.qcow_file.clone())) as Box<dyn AsyncIo>)
     }
 
-    fn fd(&mut self) -> RawFd {
+    fn fd(&mut self) -> BorrowedDiskFd {
         let lock = self.qcow_file.lock().unwrap();
-        lock.as_raw_fd()
+        BorrowedDiskFd::new(lock.as_raw_fd())
     }
 }
 

block/src/raw_async.rs

@@ -10,7 +10,7 @@ use io_uring::{opcode, types, IoUring};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::DiskTopology;
 
@@ -47,8 +47,8 @@ impl DiskFile for RawFileDisk {
         }
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.file.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.file.as_raw_fd())
     }
 }
 

block/src/raw_async_aio.rs

@@ -13,7 +13,7 @@ use vmm_sys_util::aio;
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::DiskTopology;
 
@@ -50,8 +50,8 @@ impl DiskFile for RawFileDiskAio {
         }
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.file.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.file.as_raw_fd())
     }
 }
 

block/src/raw_sync.rs

@@ -10,7 +10,7 @@ use std::os::unix::io::{AsRawFd, RawFd};
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::async_io::{
-    AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult,
+    AsyncIo, AsyncIoError, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
 };
 use crate::DiskTopology;
 
@@ -44,8 +44,8 @@ impl DiskFile for RawFileDiskSync {
         }
     }
 
-    fn fd(&mut self) -> RawFd {
-        self.file.as_raw_fd()
+    fn fd(&mut self) -> BorrowedDiskFd {
+        BorrowedDiskFd::new(self.file.as_raw_fd())
     }
 }
 

block/src/vhdx_sync.rs

@@ -4,12 +4,14 @@
 
 use std::collections::VecDeque;
 use std::fs::File;
-use std::os::fd::{AsRawFd, RawFd};
+use std::os::fd::AsRawFd;
 use std::sync::{Arc, Mutex, MutexGuard};
 
 use vmm_sys_util::eventfd::EventFd;
 
-use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
+use crate::async_io::{
+    AsyncIo, AsyncIoResult, BorrowedDiskFd, DiskFile, DiskFileError, DiskFileResult,
+};
 use crate::vhdx::{Result as VhdxResult, Vhdx};
 use crate::AsyncAdaptor;
 
@@ -37,9 +39,9 @@ impl DiskFile for VhdxDiskSync {
         )
     }
 
-    fn fd(&mut self) -> RawFd {
+    fn fd(&mut self) -> BorrowedDiskFd {
         let lock = self.vhdx_file.lock().unwrap();
-        lock.as_raw_fd()
+        BorrowedDiskFd::new(lock.as_raw_fd())
     }
 }