rustix/fs/
statx.rs

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1//! Linux `statx`.
2
3use crate::fd::AsFd;
4use crate::fs::AtFlags;
5use crate::{backend, io, path};
6use backend::fs::types::{Statx, StatxFlags};
7
8#[cfg(feature = "linux_4_11")]
9use backend::fs::syscalls::statx as _statx;
10#[cfg(not(feature = "linux_4_11"))]
11use compat::statx as _statx;
12
13/// `statx(dirfd, path, flags, mask, statxbuf)`
14///
15/// This function returns [`io::Errno::NOSYS`] if `statx` is not available on
16/// the platform, such as Linux before 4.11. This also includes older Docker
17/// versions where the actual syscall fails with different error codes; rustix
18/// handles this and translates them into `NOSYS`.
19///
20/// # References
21///  - [Linux]
22///
23/// # Examples
24///
25/// ```
26/// # use std::path::Path;
27/// # use std::io;
28/// # use rustix::fs::{AtFlags, StatxFlags};
29/// # use rustix::fd::BorrowedFd;
30/// /// Try to determine if the provided path is a mount root. Will return
31/// /// `Ok(None)` if the kernel is not new enough to support `statx` or
32/// /// [`libc::STATX_ATTR_MOUNT_ROOT`].
33/// fn is_mountpoint(root: BorrowedFd<'_>, path: &Path) -> io::Result<Option<bool>> {
34///     use rustix::fs::{AtFlags, StatxFlags};
35///
36///     let mountroot_flag = libc::STATX_ATTR_MOUNT_ROOT as u64;
37///     match rustix::fs::statx(
38///         root,
39///         path,
40///         AtFlags::NO_AUTOMOUNT | AtFlags::SYMLINK_NOFOLLOW,
41///         StatxFlags::empty(),
42///     ) {
43///         Ok(r) => {
44///             let present = (r.stx_attributes_mask & mountroot_flag) > 0;
45///             Ok(present.then(|| r.stx_attributes & mountroot_flag > 0))
46///         }
47///         Err(e) if e == rustix::io::Errno::NOSYS => Ok(None),
48///         Err(e) => Err(e.into()),
49///     }
50/// }
51/// ```
52///
53/// [Linux]: https://man7.org/linux/man-pages/man2/statx.2.html
54#[inline]
55pub fn statx<P: path::Arg, Fd: AsFd>(
56    dirfd: Fd,
57    path: P,
58    flags: AtFlags,
59    mask: StatxFlags,
60) -> io::Result<Statx> {
61    path.into_with_c_str(|path| _statx(dirfd.as_fd(), path, flags, mask))
62}
63
64#[cfg(not(feature = "linux_4_11"))]
65mod compat {
66    use crate::fd::BorrowedFd;
67    use crate::ffi::CStr;
68    use crate::fs::AtFlags;
69    use crate::{backend, io};
70    use core::sync::atomic::{AtomicU8, Ordering};
71
72    use backend::fs::types::{Statx, StatxFlags};
73
74    // Linux kernel prior to 4.11 and old versions of Docker don't support
75    // `statx`. We store the availability in a global to avoid unnecessary
76    // syscalls.
77    //
78    // 0: Unknown
79    // 1: Not available
80    // 2: Available
81    static STATX_STATE: AtomicU8 = AtomicU8::new(0);
82
83    #[inline]
84    pub fn statx(
85        dirfd: BorrowedFd<'_>,
86        path: &CStr,
87        flags: AtFlags,
88        mask: StatxFlags,
89    ) -> io::Result<Statx> {
90        match STATX_STATE.load(Ordering::Relaxed) {
91            0 => statx_init(dirfd, path, flags, mask),
92            1 => Err(io::Errno::NOSYS),
93            _ => backend::fs::syscalls::statx(dirfd, path, flags, mask),
94        }
95    }
96
97    /// The first `statx` call. We don't know if `statx` is available yet.
98    fn statx_init(
99        dirfd: BorrowedFd<'_>,
100        path: &CStr,
101        flags: AtFlags,
102        mask: StatxFlags,
103    ) -> io::Result<Statx> {
104        match backend::fs::syscalls::statx(dirfd, path, flags, mask) {
105            Err(io::Errno::NOSYS) => statx_error_nosys(),
106            Err(io::Errno::PERM) => statx_error_perm(),
107            result => {
108                STATX_STATE.store(2, Ordering::Relaxed);
109                result
110            }
111        }
112    }
113
114    /// The first `statx` call failed with `NOSYS` (or something we're treating
115    /// like `NOSYS`).
116    #[cold]
117    fn statx_error_nosys() -> io::Result<Statx> {
118        STATX_STATE.store(1, Ordering::Relaxed);
119        Err(io::Errno::NOSYS)
120    }
121
122    /// The first `statx` call failed with `PERM`.
123    #[cold]
124    fn statx_error_perm() -> io::Result<Statx> {
125        // Some old versions of Docker have `statx` fail with `PERM` when it
126        // isn't recognized. Check whether `statx` really is available, and if
127        // so, fail with `PERM`, and if not, treat it like `NOSYS`.
128        if backend::fs::syscalls::is_statx_available() {
129            STATX_STATE.store(2, Ordering::Relaxed);
130            Err(io::Errno::PERM)
131        } else {
132            statx_error_nosys()
133        }
134    }
135}
rustix/fs/statx.rs

rustix/fs/
statx.rs
