feat(fs): add splice

[tontinton]

built on #609

Usage (file -> socket example)

use compio_fs::pipe::{anonymous, splice};
use compio_fs::File;

let file = File::open("data.bin").await?;
let (rx, tx) = anonymous()?;

// Splice file -> pipe (zero-copy)
let n = splice(&file, &tx, 4096).offset_in(0).await?;

// Then splice pipe -> socket (zero-copy)
let n = splice(&rx, &socket, 4096).await?;

[Berrysoft]

Please don't use Box. It's OK to add a new async fn to do so. Actually I guess a simple splice method is OK instead of a builder...

[Berrysoft]

It's OK to keep the builder. Just don't Box please.

[tontinton]

Oh so I need to add a build() method to create the Splice, do we want to keep that API? or should I make a simple splice method that receives all arguments instead?

[George-Miao]

Hi! I have exposed the future type for submit in #614. You can rebase and use that directly so no need for the Box.

[Berrysoft]

Another problem is that, it's OK to assume nonblocking everywhere on polling driver. Therefore, we should wait for the readiness of the fds, either in the driver, or here with PollFd.

[tontinton]

This is the same comment as #609 (comment), right?

[Berrysoft]

Yes. I made it to check the in fd in the driver, but the out fd has to be polled manually. The flags should also be modified to use the nonblocking IO. Please check the driver type at runtime.

[Berrysoft]

Could you rebase this PR?

[tontinton]

rebased

[Berrysoft]

Thanks for the rebase. I think there are some existing issues to be solved.

[tontinton]

yeah I only rebased :)
now I think I resolved all comments

[tontinton]

I modified the driver to include op_type() like other opcodes in file, otherwise the test (nightly, ubuntu-22.04, polling,ring, true) and test (nightly, ubuntu-22.04, polling,native-tls,ring, true) tests failed for me

[Berrysoft]

Thanks! Your changes for op_type is correct.

However, I still think that it's not easy to implement IntoFuture or Future directly. Splice on polling driver only polls one fd, but the other one should also be polled. The method should be like

if driver_type == DriverType::Poll {
    loop {
        let poll_in = PollFd::new(in_fd, Read);
        let poll_out = PollFd::new(out_fd, Write);
        try_join!(submit(poll_in), submit(poll_out))?;
        match syscall!(libc::splice(...)) {
            Ok(n) => break Ok(n),
            Err(e) if e.kind() == ErrorKind::WouldBlock => continue,
            Err(e) => break Err(e),
        }
    }
} else {
    let op = Splice::new(...);
    submit(op).await
}

[George-Miao]

Can you move the safe compuation of arguments out of the unsafe block so that we don't accidently missing any unwanted unsafe calls?

[George-Miao]

Okay I'm thinking maybe we want to have a dedicated linux_all mod for these operations. Slapping cfg(linux_all) everywhere seems too tedious.

[tontinton]

ok I've sat on it some time now, I got to something working, but I think we should wait for #617, it will improve the solution

[George-Miao]

@tontinton Yeah.. we are having some trouble actually implement #617 (for now it still wakes whenever fd has an event). It's kind of hard.

[tontinton]

@tontinton Yeah.. we are having some trouble actually implement #617 (for now it still wakes whenever fd has an event). It's kind of hard.

Maybe we can merge this anyway then?