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//! Linux `statx`.

use crate::fd::{AsFd, BorrowedFd};
use crate::ffi::CStr;
use crate::fs::AtFlags;
use crate::{backend, io, path};
use core::sync::atomic::{AtomicU8, Ordering};

pub use backend::fs::types::{Statx, StatxFlags, StatxTimestamp};

/// `statx(dirfd, path, flags, mask, statxbuf)`
///
/// This function returns [`io::Errno::NOSYS`] if `statx` is not available on
/// the platform, such as Linux before 4.11. This also includes older Docker
/// versions where the actual syscall fails with different error codes; Rustix
/// handles this and translates them into `NOSYS`.
///
/// # References
///  - [Linux]
///
/// [Linux]: https://man7.org/linux/man-pages/man2/statx.2.html
#[inline]
pub fn statx<P: path::Arg, Fd: AsFd>(
    dirfd: Fd,
    path: P,
    flags: AtFlags,
    mask: StatxFlags,
) -> io::Result<Statx> {
    path.into_with_c_str(|path| _statx(dirfd.as_fd(), path, flags, mask))
}

// Linux kernel prior to 4.11 old versions of Docker don't support `statx`. We
// store the availability in a global to avoid unnecessary syscalls.
//
// 0: Unknown
// 1: Not available
// 2: Available
static STATX_STATE: AtomicU8 = AtomicU8::new(0);

#[inline]
fn _statx(
    dirfd: BorrowedFd<'_>,
    path: &CStr,
    flags: AtFlags,
    mask: StatxFlags,
) -> io::Result<Statx> {
    match STATX_STATE.load(Ordering::Relaxed) {
        0 => statx_init(dirfd, path, flags, mask),
        1 => Err(io::Errno::NOSYS),
        _ => backend::fs::syscalls::statx(dirfd, path, flags, mask),
    }
}

/// The first `statx` call. We don't know if `statx` is available yet.
fn statx_init(
    dirfd: BorrowedFd<'_>,
    path: &CStr,
    flags: AtFlags,
    mask: StatxFlags,
) -> io::Result<Statx> {
    match backend::fs::syscalls::statx(dirfd, path, flags, mask) {
        Err(io::Errno::NOSYS) => statx_error_nosys(),
        Err(io::Errno::PERM) => statx_error_perm(),
        result => {
            STATX_STATE.store(2, Ordering::Relaxed);
            result
        }
    }
}

/// The first `statx` call failed with `NOSYS` (or something we're treating
/// like `NOSYS`).
#[cold]
fn statx_error_nosys() -> io::Result<Statx> {
    STATX_STATE.store(1, Ordering::Relaxed);
    Err(io::Errno::NOSYS)
}

/// The first `statx` call failed with `PERM`.
#[cold]
fn statx_error_perm() -> io::Result<Statx> {
    // Some old versions of Docker have `statx` fail with `PERM` when it isn't
    // recognized. Check whether `statx` really is available, and if so, fail
    // with `PERM`, and if not, treat it like `NOSYS`.
    if backend::fs::syscalls::is_statx_available() {
        STATX_STATE.store(2, Ordering::Relaxed);
        Err(io::Errno::PERM)
    } else {
        statx_error_nosys()
    }
}