address review: move clamping logic

tokio/src/fs/write.rs

@@ -57,20 +57,18 @@ async fn write_uring(path: &Path, mut buf: OwnedBuf) -> io::Result<()> {
         .into();
 
     let total: usize = buf.as_ref().len();
-    let mut offset: usize = 0;
-    while offset < total {
-        // There is a cap on how many bytes we can write in a single uring write operation.
-        // ref: https://github.com/axboe/liburing/discussions/497
-        let len = std::cmp::min(total - offset, u32::MAX as usize) as u32;
-
-        let (n, _buf, _fd) = Op::write_at(fd, buf, offset, len, offset as u64)?.await?;
+    let mut buf_offset: usize = 0;
+    let mut file_offset: u64 = 0;
+    while buf_offset < total {
+        let (n, _buf, _fd) = Op::write_at(fd, buf, buf_offset, file_offset)?.await?;
         if n == 0 {
             return Err(io::ErrorKind::WriteZero.into());
         }
 
         buf = _buf;
         fd = _fd;
-        offset += n as usize;
+        buf_offset += n as usize;
+        file_offset += n as u64;
     }
 
     Ok(())

tokio/src/io/uring/write.rs

@@ -28,15 +28,16 @@ impl Cancellable for Write {
 }
 
 impl Op<Write> {
-    /// Issue a write that starts at `buf_offset` within `buf` and writes `len` bytes
+    /// Issue a write that starts at `buf_offset` within `buf` and writes some bytes
     /// into `file` at `file_offset`.
     pub(crate) fn write_at(
         fd: OwnedFd,
         buf: OwnedBuf,
         buf_offset: usize,
-        len: u32,
         file_offset: u64,
     ) -> io::Result<Self> {
+        let len = u32::try_from(buf.as_ref().len() - buf_offset).unwrap_or(u32::MAX);
+
         let ptr = buf.as_ref()[buf_offset..buf_offset + len as usize].as_ptr();
 
         let sqe = opcode::Write::new(types::Fd(fd.as_raw_fd()), ptr, len)