Add UnsubmittedRead to follow new API for read part.

Currently, there's no unsubmitted API change in read part yet. Add the
new API following write part.

Add simple link operation test cases to use read/write submittable
operations.

examples/cat.rs

@@ -29,7 +29,7 @@ fn main() {
 
         loop {
             // Read a chunk
-            let (res, b) = file.read_at(buf, pos).await;
+            let (res, b) = file.read_at(buf, pos).submit().await;
             let n = res.unwrap();
 
             if n == 0 {

examples/mix.rs

@@ -34,7 +34,7 @@ fn main() {
 
                 loop {
                     // Read a chunk
-                    let (res, b) = file.read_at(buf, pos).await;
+                    let (res, b) = file.read_at(buf, pos).submit().await;
                     let n = res.unwrap();
 
                     if n == 0 {

src/fs/file.rs

@@ -4,7 +4,7 @@ use crate::fs::OpenOptions;
 use crate::io::SharedFd;
 
 use crate::runtime::driver::op::Op;
-use crate::{UnsubmittedOneshot, UnsubmittedWrite};
+use crate::{UnsubmittedOneshot, UnsubmittedRead, UnsubmittedWrite};
 use std::fmt;
 use std::io;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
@@ -165,7 +165,7 @@ impl File {
     ///         let buffer = vec![0; 10];
     ///
     ///         // Read up to 10 bytes
-    ///         let (res, buffer) = f.read_at(buffer, 0).await;
+    ///         let (res, buffer) = f.read_at(buffer, 0).submit().await;
     ///         let n = res?;
     ///
     ///         println!("The bytes: {:?}", &buffer[..n]);
@@ -176,10 +176,8 @@ impl File {
     ///     })
     /// }
     /// ```
-    pub async fn read_at<T: BoundedBufMut>(&self, buf: T, pos: u64) -> crate::BufResult<usize, T> {
-        // Submit the read operation
-        let op = Op::read_at(&self.fd, buf, pos).unwrap();
-        op.await
+    pub fn read_at<T: BoundedBufMut>(&self, buf: T, pos: u64) -> UnsubmittedRead<T> {
+        UnsubmittedOneshot::read_at(&self.fd, buf, pos)
     }
 
     /// Read some bytes at the specified offset from the file into the specified
@@ -417,7 +415,7 @@ impl File {
         }
 
         while buf.bytes_total() != 0 {
-            let (res, slice) = self.read_at(buf, pos).await;
+            let (res, slice) = self.read_at(buf, pos).submit().await;
             match res {
                 Ok(0) => {
                     return (

src/io/mod.rs

@@ -15,7 +15,7 @@ pub(crate) use noop::NoOp;
 
 mod open;
 
-mod read;
+pub(crate) mod read;
 
 mod read_fixed;
 

src/io/read.rs

@@ -1,64 +1,69 @@
+use io_uring::cqueue::Entry;
+
 use crate::buf::BoundedBufMut;
 use crate::io::SharedFd;
-use crate::BufResult;
+use crate::{BufResult, OneshotOutputTransform, UnsubmittedOneshot};
 
-use crate::runtime::driver::op::{Completable, CqeResult, Op};
-use crate::runtime::CONTEXT;
 use std::io;
+use std::marker::PhantomData;
+
+/// An unsubmitted read operation.
+pub type UnsubmittedRead<T> = UnsubmittedOneshot<ReadData<T>, ReadTransform<T>>;
 
-pub(crate) struct Read<T> {
+#[allow(missing_docs)]
+pub struct ReadData<T> {
     /// Holds a strong ref to the FD, preventing the file from being closed
     /// while the operation is in-flight.
-    #[allow(dead_code)]
-    fd: SharedFd,
+    _fd: SharedFd,
 
-    /// Reference to the in-flight buffer.
-    pub(crate) buf: T,
+    buf: T,
 }
 
-impl<T: BoundedBufMut> Op<Read<T>> {
-    pub(crate) fn read_at(fd: &SharedFd, buf: T, offset: u64) -> io::Result<Op<Read<T>>> {
-        use io_uring::{opcode, types};
-
-        CONTEXT.with(|x| {
-            x.handle().expect("Not in a runtime context").submit_op(
-                Read {
-                    fd: fd.clone(),
-                    buf,
-                },
-                |read| {
-                    // Get raw buffer info
-                    let ptr = read.buf.stable_mut_ptr();
-                    let len = read.buf.bytes_total();
-                    opcode::Read::new(types::Fd(fd.raw_fd()), ptr, len as _)
-                        .offset(offset as _)
-                        .build()
-                },
-            )
-        })
-    }
+#[allow(missing_docs)]
+pub struct ReadTransform<T> {
+    _phantom: PhantomData<T>,
 }
 
-impl<T> Completable for Read<T>
+impl<T> OneshotOutputTransform for ReadTransform<T>
 where
     T: BoundedBufMut,
 {
     type Output = BufResult<usize, T>;
+    type StoredData = ReadData<T>;
 
-    fn complete(self, cqe: CqeResult) -> Self::Output {
-        // Convert the operation result to `usize`
-        let res = cqe.result.map(|v| v as usize);
-        // Recover the buffer
-        let mut buf = self.buf;
-
-        // If the operation was successful, advance the initialized cursor.
-        if let Ok(n) = res {
+    fn transform_oneshot_output(self, mut data: Self::StoredData, cqe: Entry) -> Self::Output {
+        let n = cqe.result();
+        let res = if n >= 0 {
             // Safety: the kernel wrote `n` bytes to the buffer.
-            unsafe {
-                buf.set_init(n);
-            }
-        }
+            unsafe { data.buf.set_init(n as usize) };
+            Ok(n as usize)
+        } else {
+            Err(io::Error::from_raw_os_error(-n))
+        };
+
+        (res, data.buf)
+    }
+}
+
+impl<T: BoundedBufMut> UnsubmittedRead<T> {
+    pub(crate) fn read_at(fd: &SharedFd, mut buf: T, offset: u64) -> Self {
+        use io_uring::{opcode, types};
+
+        // Get raw buffer info
+        let ptr = buf.stable_mut_ptr();
+        let len = buf.bytes_total();
 
-        (res, buf)
+        Self::new(
+            ReadData {
+                _fd: fd.clone(),
+                buf,
+            },
+            ReadTransform {
+                _phantom: PhantomData,
+            },
+            opcode::Read::new(types::Fd(fd.raw_fd()), ptr, len as _)
+                .offset(offset as _)
+                .build(),
+        )
     }
 }

src/io/socket.rs

@@ -169,8 +169,7 @@ impl Socket {
     }
 
     pub(crate) async fn read<T: BoundedBufMut>(&self, buf: T) -> crate::BufResult<usize, T> {
-        let op = Op::read_at(&self.fd, buf, 0).unwrap();
-        op.await
+        UnsubmittedOneshot::read_at(&self.fd, buf, 0).submit().await
     }
 
     pub(crate) async fn read_fixed<T>(&self, buf: T) -> crate::BufResult<usize, T>

src/lib.rs

@@ -20,7 +20,7 @@
 //!         // Read some data, the buffer is passed by ownership and
 //!         // submitted to the kernel. When the operation completes,
 //!         // we get the buffer back.
-//!         let (res, buf) = file.read_at(buf, 0).await;
+//!         let (res, buf) = file.read_at(buf, 0).submit().await;
 //!         let n = res?;
 //!
 //!         // Display the contents
@@ -78,6 +78,7 @@ pub mod buf;
 pub mod fs;
 pub mod net;
 
+pub use io::read::*;
 pub use io::write::*;
 pub use runtime::driver::op::{InFlightOneshot, OneshotOutputTransform, UnsubmittedOneshot};
 pub use runtime::spawn;
@@ -115,7 +116,7 @@ use std::future::Future;
 ///         // Read some data, the buffer is passed by ownership and
 ///         // submitted to the kernel. When the operation completes,
 ///         // we get the buffer back.
-///         let (res, buf) = file.read_at(buf, 0).await;
+///         let (res, buf) = file.read_at(buf, 0).submit().await;
 ///         let n = res?;
 ///
 ///         // Display the contents
@@ -254,7 +255,7 @@ impl Builder {
 ///         // Read some data, the buffer is passed by ownership and
 ///         // submitted to the kernel. When the operation completes,
 ///         // we get the buffer back.
-///         let (res, buf) = file.read_at(buf, 0).await;
+///         let (res, buf) = file.read_at(buf, 0).submit().await;
 ///         let n = res?;
 ///
 ///         // Display the contents

tests/driver.rs

@@ -58,6 +58,7 @@ fn complete_ops_on_drop() {
                 },
                 25 * 1024 * 1024,
             )
+            .submit()
             .await
             .0
             .unwrap();

tests/fs_file.rs

@@ -19,7 +19,7 @@ const HELLO: &[u8] = b"hello world...";
 
 async fn read_hello(file: &File) {
     let buf = Vec::with_capacity(1024);
-    let (res, buf) = file.read_at(buf, 0).await;
+    let (res, buf) = file.read_at(buf, 0).submit().await;
     let n = res.unwrap();
 
     assert_eq!(n, HELLO.len());
@@ -315,6 +315,55 @@ fn basic_fallocate() {
     });
 }
 
+#[test]
+fn write_linked() {
+    tokio_uring::start(async {
+        let tempfile = tempfile();
+        let file = File::create(tempfile.path()).await.unwrap();
+
+        let write1 = file
+            .write_at(HELLO, 0)
+            .set_flags(io_uring::squeue::Flags::IO_LINK)
+            .submit();
+        let write2 = file.write_at(HELLO, HELLO.len() as u64).submit();
+
+        let res1 = write1.await;
+        let res2 = write2.await;
+        res1.0.unwrap();
+        res2.0.unwrap();
+
+        let file = std::fs::read(tempfile.path()).unwrap();
+        assert_eq!(file, [HELLO, HELLO].concat());
+    });
+}
+
+#[test]
+fn read_linked() {
+    tokio_uring::start(async {
+        let mut tempfile = tempfile();
+        let file = File::open(tempfile.path()).await.unwrap();
+
+        tempfile.write_all(&[HELLO, HELLO].concat()).unwrap();
+
+        let buf1 = Vec::with_capacity(HELLO.len());
+        let buf2 = Vec::with_capacity(HELLO.len());
+
+        let read1 = file
+            .read_at(buf1, 0)
+            .set_flags(io_uring::squeue::Flags::IO_LINK)
+            .submit();
+        let read2 = file.read_at(buf2, HELLO.len() as u64).submit();
+
+        let res1 = read1.await;
+        let res2 = read2.await;
+
+        res1.0.unwrap();
+        res2.0.unwrap();
+
+        assert_eq!([HELLO, HELLO].concat(), [res1.1, res2.1].concat());
+    });
+}
+
 fn tempfile() -> NamedTempFile {
     NamedTempFile::new().unwrap()
 }