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//! Linux `statx`.
use crate::fd::AsFd;
use crate::fs::AtFlags;
use crate::{backend, io, path};
use backend::fs::types::{Statx, StatxFlags};
#[cfg(feature = "linux_4_11")]
use backend::fs::syscalls::statx as _statx;
#[cfg(not(feature = "linux_4_11"))]
use compat::statx as _statx;
/// `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]
///
/// # Examples
///
/// ```
/// # use std::path::Path;
/// # use std::io;
/// # use rustix::fs::{AtFlags, StatxFlags};
/// # use rustix::fd::BorrowedFd;
/// /// Try to determine if the provided path is a mount root. Will return
/// /// `Ok(None)` if the kernel is not new enough to support `statx` or
/// /// [`libc::STATX_ATTR_MOUNT_ROOT`].
/// fn is_mountpoint(root: BorrowedFd<'_>, path: &Path) -> io::Result<Option<bool>> {
/// use rustix::fs::{AtFlags, StatxFlags};
///
/// let mountroot_flag = libc::STATX_ATTR_MOUNT_ROOT as u64;
/// match rustix::fs::statx(
/// root,
/// path,
/// AtFlags::NO_AUTOMOUNT | AtFlags::SYMLINK_NOFOLLOW,
/// StatxFlags::empty(),
/// ) {
/// Ok(r) => {
/// let present = (r.stx_attributes_mask & mountroot_flag) > 0;
/// Ok(present.then(|| r.stx_attributes & mountroot_flag > 0))
/// }
/// Err(e) if e == rustix::io::Errno::NOSYS => Ok(None),
/// Err(e) => Err(e.into()),
/// }
/// }
/// ```
///
#[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))
}
#[cfg(not(feature = "linux_4_11"))]
mod compat {
use crate::fd::BorrowedFd;
use crate::ffi::CStr;
use crate::fs::AtFlags;
use crate::{backend, io};
use core::sync::atomic::{AtomicU8, Ordering};
use backend::fs::types::{Statx, StatxFlags};
// Linux kernel prior to 4.11 and 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]
pub 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(err) => statx_error(err),
result => {
STATX_STATE.store(2, Ordering::Relaxed);
result
}
}
}
/// The first `statx` call failed. We can get a variety of error codes
/// from seccomp configs or faulty FUSE drivers, so we don't trust
/// `ENOSYS` or `EPERM` to tell us whether statx is available.
#[cold]
fn statx_error(err: io::Errno) -> io::Result<Statx> {
if backend::fs::syscalls::is_statx_available() {
// Statx is available. Record this, and fail with the error
// code of the initial `statx` call.
STATX_STATE.store(2, Ordering::Relaxed);
Err(err)
} else {
// Statx is not available. Record this, and fail with `NOSYS`.
STATX_STATE.store(1, Ordering::Relaxed);
Err(io::Errno::NOSYS)
}
}
}