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feat: I/O safety for 'sys/wait' #1923

Merged
merged 1 commit into from
Dec 11, 2022
Merged

feat: I/O safety for 'sys/wait' #1923

merged 1 commit into from
Dec 11, 2022

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SteveLauC
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@SteveLauC SteveLauC commented Dec 7, 2022 •
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What this PR does:

  1. Adds I/O safety for sys/wait

Actually, I am not sure about which type to use here:

pub enum Id<'fd> {
    /// Wait for the child referred to by the given PID file descriptor
    #[cfg(any(target_os = "android", target_os = "linux"))]
    PIDFd(RawFd),
    PIDFd(BorrowedFd<'fd>),
}

If we use Fd: AsFd

pub enum Id<'fd, Fd: AsFd> {
    /// Wait for the child referred to by the given PID file descriptor
    #[cfg(any(target_os = "android", target_os = "linux"))]
    PIDFd(RawFd),
    PIDFd(&'fd Fd),
}

then the user has to specify that generic type when using this interface, which is kinda user-unfriendly...

The typical usage of this interface will be something like:

// Thought currently we don't have pidfd_open(2) in `Nix`
let fd_referring_to_a_process: OwnedFd  = pidfd_open().unwrap();
let status = waitid(Id::PIDFd(fd_referring_to_a_process), WaitPidFlag::XXXX).unwrap();

UPDATE: pidfd_open(2) will be added in #1859 or #1868 .

@SteveLauC SteveLauC mentioned this pull request Dec 7, 2022
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@SteveLauC
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The reason why CI failed is that enum Id<'fd> is available on:

  1. Linux (glibc/musl)
  2. Android
  3. FreeBSD
  4. Haiku

And that 'fd parameter is used only on Android and Linux(glibc/musl) as the cfg here:

    /// Wait for the child referred to by the given PID file descriptor
    #[cfg(any(target_os = "android", target_os = "linux"))]
    PIDFd(BorrowedFd<'fd>),

So 'fd becomes unused on FreeBSD and haiku, and Rust does not like this.

Honestly, I don't have a good solution to this problem, perhaps then BorrowedFd<'_> is not an appropriate option for this PR...

Similar Problem: Type parameter not used on enums

@asomers
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asomers commented Dec 9, 2022

I think the easiest way to fix the tests on non-Linux is to add a PhantomData<'fd> field. For non-Linux systems, the lifetime will always end up being 'static, so it shouldn't be much of an inconvenience to the users.

asomers
asomers approved these changes Dec 11, 2022
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bors r+

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bors bot commented Dec 11, 2022

Build succeeded:

@bors bors bot merged commit b7b0a65 into nix-rust:master Dec 11, 2022
@SteveLauC SteveLauC deleted the io-safety-sys/wait branch December 11, 2022 21:48
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