O_LARGEFILE missing on some platforms

[brian-pane]

O_LARGEFILE isn't defined in the libc crate on some platforms. For example, this code:

use libc::{O_CREAT, O_LARGEFILE, O_EXCL};

fn main() {
    let _ = O_CREAT | O_LARGEFILE | O_EXCL;
}

yields a compiler error on aarch64-apple-darwin, where O_LARGEFILE doesn't exist.

I ran into this while porting a C library to Rust. Since the C libc doesn't have O_LARGEFILE on all platforms, the C idiom is:

#ifdef O_LARGEFILE
   ...
#endif

On targets where the C libc doesn't have a O_LARGEFILE, would it make sense for Rust libc to provide

const O_LARGEFILE: c_int = 0;

to support apps that need to compile for many platforms? If so, I'm willing to submit a PR to cover the macOS case.

[tgross35]

Are there platforms that define O_LARGEFILE but our libc doesn't have it? If so then we should add them, but we generally shouldn't be polyfilling anything that isn't also provided by the system libc. The closest idiom to the C preprocessor version would probably be to use something like https://crates.io/crates/autocfg to check if it is defined.

[brian-pane]

Thanks, I'll check out autocfg.