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Add a
rustix::fs::ABS
constant. (#1189)
Add a `rustix::fs::ABS` constant, which corresponds to the undocumented but commonly used convention of using `-EBADF` as the file descriptor in `openat` and similar calls. This makes them fail if the path is not absolute. Fixes #1187.
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,73 @@ | ||
//! The `CWD` and `ABS` constants, representing the current working directory | ||
//! and absolute-only paths, respectively. | ||
//! | ||
//! # Safety | ||
//! | ||
//! This file uses `AT_FDCWD`, which is a raw file descriptor, but which is | ||
//! always valid, and `-EBADF`, which is an undocumented by commonly used | ||
//! convention of passing a value which will always fail if the accompanying | ||
//! path isn't absolute. | ||
#![allow(unsafe_code)] | ||
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use crate::backend; | ||
use backend::c; | ||
use backend::fd::{BorrowedFd, RawFd}; | ||
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/// `AT_FDCWD`—A handle representing the current working directory. | ||
/// | ||
/// This is a file descriptor which refers to the process current directory | ||
/// which can be used as the directory argument in `*at` functions such as | ||
/// [`openat`]. | ||
/// | ||
/// # References | ||
/// - [POSIX] | ||
/// | ||
/// [`openat`]: crate::fs::openat | ||
/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/fcntl.h.html | ||
// SAFETY: `AT_FDCWD` is a reserved value that is never dynamically | ||
// allocated, so it'll remain valid for the duration of `'static`. | ||
#[doc(alias = "AT_FDCWD")] | ||
pub const CWD: BorrowedFd<'static> = | ||
unsafe { BorrowedFd::<'static>::borrow_raw(c::AT_FDCWD as RawFd) }; | ||
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/// `-EBADF`—A handle that requires paths to be absolute. | ||
/// | ||
/// This is a file descriptor which refers to no directory, which can be used | ||
/// as the directory argument in `*at` functions such as [`openat`], which | ||
/// causes them to fail with [`BADF`] if the accompanying path is not absolute. | ||
/// | ||
/// This corresponds to the undocumented by commonly used convention of | ||
/// passing `-EBADF` as the `dirfd` argument, which is ignored if the path | ||
/// is absolute, and evokes an `EBADF` error otherwise. | ||
/// | ||
/// [`openat`]: crate::fs::openat | ||
/// [`BADF`]: crate::io::Errno::BADF | ||
// SAFETY: This `-EBADF` convention is commonly used, such as in lxc, so OS's | ||
// aren't going to break it. | ||
pub const ABS: BorrowedFd<'static> = | ||
unsafe { BorrowedFd::<'static>::borrow_raw(c::EBADF.wrapping_neg() as RawFd) }; | ||
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
use crate::fd::AsRawFd; | ||
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#[test] | ||
fn test_cwd() { | ||
assert!(CWD.as_raw_fd() != -1); | ||
#[cfg(linux_kernel)] | ||
#[cfg(feature = "io_uring")] | ||
assert!(CWD.as_raw_fd() != linux_raw_sys::io_uring::IORING_REGISTER_FILES_SKIP); | ||
} | ||
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#[test] | ||
fn test_abs() { | ||
assert!(ABS.as_raw_fd() < 0); | ||
assert!(ABS.as_raw_fd() != -1); | ||
assert!(ABS.as_raw_fd() != c::AT_FDCWD); | ||
#[cfg(linux_kernel)] | ||
#[cfg(feature = "io_uring")] | ||
assert!(ABS.as_raw_fd() != linux_raw_sys::io_uring::IORING_REGISTER_FILES_SKIP); | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,57 @@ | ||
#[cfg(not(target_os = "wasi"))] | ||
#[test] | ||
fn test_special_fds() { | ||
use rustix::fs::{fstat, open, openat, Mode, OFlags, Stat, ABS, CWD}; | ||
use rustix::process::getcwd; | ||
use std::ffi::OsStr; | ||
use std::os::unix::ffi::OsStrExt; | ||
use std::path::PathBuf; | ||
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let cwd_path = getcwd(Vec::new()).unwrap().into_bytes(); | ||
let cwd_path = OsStr::from_bytes(&cwd_path).to_owned(); | ||
let cwd_path = PathBuf::from(cwd_path); | ||
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// Open the same file several ways using special constants and make sure | ||
// we get the same file. | ||
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// Use plain `open`. | ||
let a = open("Cargo.toml", OFlags::RDONLY, Mode::empty()).unwrap(); | ||
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// Use `CWD` with a relative path. | ||
let b = openat(CWD, "Cargo.toml", OFlags::RDONLY, Mode::empty()).unwrap(); | ||
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// Use `CWD` with an absolute path. | ||
let c = openat( | ||
CWD, | ||
cwd_path.join("Cargo.toml"), | ||
OFlags::RDONLY, | ||
Mode::empty(), | ||
) | ||
.unwrap(); | ||
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// Use `ABS` with an absolute path. | ||
let d = openat( | ||
ABS, | ||
cwd_path.join("Cargo.toml"), | ||
OFlags::RDONLY, | ||
Mode::empty(), | ||
) | ||
.unwrap(); | ||
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// Test that opening a relative path with `ABS` fails. | ||
let err = openat(ABS, "Cargo.toml", OFlags::RDONLY, Mode::empty()).unwrap_err(); | ||
assert_eq!(err, rustix::io::Errno::BADF); | ||
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let a_stat = fstat(a).unwrap(); | ||
let b_stat = fstat(b).unwrap(); | ||
let c_stat = fstat(c).unwrap(); | ||
let d_stat = fstat(d).unwrap(); | ||
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assert!(same(&a_stat, &b_stat)); | ||
assert!(same(&b_stat, &c_stat)); | ||
assert!(same(&c_stat, &d_stat)); | ||
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fn same(a: &Stat, b: &Stat) -> bool { | ||
a.st_ino == b.st_ino && a.st_dev == b.st_dev | ||
} | ||
} |