possible Op poll simplification

[FrankReh]

Look at this simplication I found possible in the src/driver/read.rs

    pub(crate) async fn read(self) -> BufResult<usize, T> {
        let complete = self.await;

        // Convert the operation result to `usize`
        let res = complete.result.map(|v| v as usize);
        // Recover the buffer
        let mut buf = complete.data.buf;

        // If the operation was successful, advance the initialized cursor.
        if let Ok(n) = res {
            // Safety: the kernel wrote `n` bytes to the buffer.
            unsafe {
                buf.set_init(n);
            }
        }

        (res, buf)
    }

    /* old
    pub(crate) async fn read(mut self) -> BufResult<usize, T> {
        crate::future::poll_fn(move |cx| self.poll_i(cx)).await
    }

    fn poll_i(&mut self, cx: &mut Context<'_>) -> Poll<BufResult<usize, T>> {
        use std::future::Future;
        use std::pin::Pin;

        let complete = ready!(Pin::new(self).poll(cx));

        // Convert the operation result to `usize`
        let res = complete.result.map(|v| v as usize);
        // Recover the buffer
        let mut buf = complete.data.buf;

        // If the operation was successful, advance the initialized cursor.
        if let Ok(n) = res {
            // Safety: the kernel wrote `n` bytes to the buffer.
            unsafe {
                buf.set_init(n);
            }
        }

        Poll::Ready((res, buf))
    }
    */

It compiles and runs. Is fewer lines of code, one function instead of three, probably less cpu and less stack. Maybe less heap.

Any other driver operations that followed the earlier model might be easily swapped for this too.

Is anything important being lost with this?

[FrankReh]

I think this is possible as a result of the introduction of the Completion trait.

[Noah-Kennedy]

Yeah the completion trait was meant to also allow this sort of work. I had actually meant to do this not long after I introduced that PR, but didn't get around to it.

[ollie-etl]

@FrankReh I think this is closed?