dirfd: initial quick and dirty implementation for unix

Author: Qelxiros

library/std/src/fs.rs

@@ -153,6 +153,13 @@ pub enum TryLockError {
     WouldBlock,
 }
 
+#[unstable(feature = "dirfd", issue = "120426")]
+#[cfg(target_family = "unix")]
+/// An object providing access to a directory on the filesystem.
+pub struct Dir {
+    inner: fs_imp::Dir,
+}
+
 /// Metadata information about a file.
 ///
 /// This structure is returned from the [`metadata`] or
@@ -1474,6 +1481,25 @@ impl Seek for Arc<File> {
     }
 }
 
+#[unstable(feature = "dirfd", issue = "120426")]
+impl Dir {
+    /// Opens a file relative to this directory.
+    pub fn open<P: AsRef<Path>>(&self, path: P) -> io::Result<File> {
+        self.inner.open(path).map(|f| File { inner: f })
+    }
+    /// Opens a file relative to this directory with the specified options.
+    pub fn open_with<P: AsRef<Path>>(&self, path: P, opts: &OpenOptions) -> io::Result<File> {
+        self.inner.open_with(path, &opts.0).map(|f| File { inner: f })
+    }
+}
+
+#[unstable(feature = "dirfd", issue = "120426")]
+impl fmt::Debug for Dir {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
 impl OpenOptions {
     /// Creates a blank new set of options ready for configuration.
     ///

library/std/src/sys/fs/mod.rs

@@ -52,6 +52,8 @@ pub fn with_native_path<T>(path: &Path, f: &dyn Fn(&Path) -> io::Result<T>) -> i
     f(path)
 }
 
+#[cfg(target_family = "unix")]
+pub use imp::Dir;
 pub use imp::{
     DirBuilder, DirEntry, File, FileAttr, FilePermissions, FileTimes, FileType, OpenOptions,
     ReadDir,

library/std/src/sys/fs/unix.rs

@@ -54,7 +54,7 @@ use libc::{c_int, mode_t};
 #[cfg(target_os = "android")]
 use libc::{
     dirent as dirent64, fstat as fstat64, fstatat as fstatat64, ftruncate64, lseek64,
-    lstat as lstat64, off64_t, open as open64, stat as stat64,
+    lstat as lstat64, off64_t, open as open64, openat as openat64, stat as stat64,
 };
 #[cfg(not(any(
     all(target_os = "linux", not(target_env = "musl")),
@@ -64,14 +64,14 @@ use libc::{
 )))]
 use libc::{
     dirent as dirent64, fstat as fstat64, ftruncate as ftruncate64, lseek as lseek64,
-    lstat as lstat64, off_t as off64_t, open as open64, stat as stat64,
+    lstat as lstat64, off_t as off64_t, open as open64, openat as openat64, stat as stat64,
 };
 #[cfg(any(
     all(target_os = "linux", not(target_env = "musl")),
     target_os = "l4re",
     target_os = "hurd"
 ))]
-use libc::{dirent64, fstat64, ftruncate64, lseek64, lstat64, off64_t, open64, stat64};
+use libc::{dirent64, fstat64, ftruncate64, lseek64, lstat64, off64_t, open64, openat64, stat64};
 
 use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt::{self, Write as _};
@@ -265,7 +265,154 @@ impl ReadDir {
     }
 }
 
-struct Dir(*mut libc::DIR);
+pub struct Dir(*mut libc::DIR);
+
+// dirfd isn't supported everywhere
+#[cfg(not(any(
+    miri,
+    target_os = "redox",
+    target_os = "nto",
+    target_os = "vita",
+    target_os = "hurd",
+    target_os = "espidf",
+    target_os = "horizon",
+    target_os = "vxworks",
+    target_os = "rtems",
+    target_os = "nuttx",
+)))]
+impl Dir {
+    pub fn open<P: AsRef<Path>>(&self, path: P) -> io::Result<File> {
+        let mut opts = OpenOptions::new();
+        opts.read(true);
+        run_path_with_cstr(path.as_ref(), &|path| self.open_c(path, &opts))
+    }
+
+    pub fn open_with<P: AsRef<Path>>(&self, path: P, opts: &OpenOptions) -> io::Result<File> {
+        run_path_with_cstr(path.as_ref(), &|path| self.open_c(path, opts))
+    }
+
+    pub fn open_c(&self, path: &CStr, opts: &OpenOptions) -> io::Result<File> {
+        let flags = libc::O_CLOEXEC
+            | opts.get_access_mode()?
+            | opts.get_creation_mode()?
+            | (opts.custom_flags as c_int & !libc::O_ACCMODE);
+        let fd = cvt_r(|| unsafe {
+            openat64(libc::dirfd(self.0), path.as_ptr(), flags, opts.mode as c_int)
+        })?;
+        Ok(File(unsafe { FileDesc::from_raw_fd(fd) }))
+    }
+
+    // pub fn create_dir<P: AsRef<Path>>(&self, path: P) -> Result<()>
+    // pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(&self, from: P, to_dir: &Self, to: Q) -> Result<()>
+    // pub fn remove_file<P: AsRef<Path>>(&self, path: P) -> Result<()>
+    // pub fn remove_dir<P: AsRef<Path>>(&self, path: P) -> Result<()>
+    // pub fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(&self, original: P, link: Q)
+}
+
+fn get_path_from_fd(fd: c_int) -> Option<PathBuf> {
+    #[cfg(any(target_os = "linux", target_os = "illumos", target_os = "solaris"))]
+    fn get_path(fd: c_int) -> Option<PathBuf> {
+        let mut p = PathBuf::from("/proc/self/fd");
+        p.push(&fd.to_string());
+        run_path_with_cstr(&p, &readlink).ok()
+    }
+
+    #[cfg(any(target_vendor = "apple", target_os = "netbsd"))]
+    fn get_path(fd: c_int) -> Option<PathBuf> {
+        // FIXME: The use of PATH_MAX is generally not encouraged, but it
+        // is inevitable in this case because Apple targets and NetBSD define `fcntl`
+        // with `F_GETPATH` in terms of `MAXPATHLEN`, and there are no
+        // alternatives. If a better method is invented, it should be used
+        // instead.
+        let mut buf = vec![0; libc::PATH_MAX as usize];
+        let n = unsafe { libc::fcntl(fd, libc::F_GETPATH, buf.as_ptr()) };
+        if n == -1 {
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "netbsd")] {
+                    // fallback to procfs as last resort
+                    let mut p = PathBuf::from("/proc/self/fd");
+                    p.push(&fd.to_string());
+                    return run_path_with_cstr(&p, &readlink).ok()
+                } else {
+                    return None;
+                }
+            }
+        }
+        let l = buf.iter().position(|&c| c == 0).unwrap();
+        buf.truncate(l as usize);
+        buf.shrink_to_fit();
+        Some(PathBuf::from(OsString::from_vec(buf)))
+    }
+
+    #[cfg(target_os = "freebsd")]
+    fn get_path(fd: c_int) -> Option<PathBuf> {
+        let info = Box::<libc::kinfo_file>::new_zeroed();
+        let mut info = unsafe { info.assume_init() };
+        info.kf_structsize = size_of::<libc::kinfo_file>() as libc::c_int;
+        let n = unsafe { libc::fcntl(fd, libc::F_KINFO, &mut *info) };
+        if n == -1 {
+            return None;
+        }
+        let buf = unsafe { CStr::from_ptr(info.kf_path.as_mut_ptr()).to_bytes().to_vec() };
+        Some(PathBuf::from(OsString::from_vec(buf)))
+    }
+
+    #[cfg(target_os = "vxworks")]
+    fn get_path(fd: c_int) -> Option<PathBuf> {
+        let mut buf = vec![0; libc::PATH_MAX as usize];
+        let n = unsafe { libc::ioctl(fd, libc::FIOGETNAME, buf.as_ptr()) };
+        if n == -1 {
+            return None;
+        }
+        let l = buf.iter().position(|&c| c == 0).unwrap();
+        buf.truncate(l as usize);
+        Some(PathBuf::from(OsString::from_vec(buf)))
+    }
+
+    #[cfg(not(any(
+        target_os = "linux",
+        target_os = "vxworks",
+        target_os = "freebsd",
+        target_os = "netbsd",
+        target_os = "illumos",
+        target_os = "solaris",
+        target_vendor = "apple",
+    )))]
+    fn get_path(_fd: c_int) -> Option<PathBuf> {
+        // FIXME(#24570): implement this for other Unix platforms
+        None
+    }
+
+    get_path(fd)
+}
+
+impl fmt::Debug for Dir {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fn get_mode(fd: c_int) -> Option<(bool, bool)> {
+            let mode = unsafe { libc::fcntl(fd, libc::F_GETFL) };
+            if mode == -1 {
+                return None;
+            }
+            match mode & libc::O_ACCMODE {
+                libc::O_RDONLY => Some((true, false)),
+                libc::O_RDWR => Some((true, true)),
+                libc::O_WRONLY => Some((false, true)),
+                _ => None,
+            }
+        }
+
+        let fd = unsafe { dirfd(self.0) };
+        let mut b = f.debug_struct("Dir");
+        b.field("fd", &fd);
+        if let Some(path) = get_path_from_fd(fd) {
+            b.field("path", &path);
+        }
+        if let Some((read, write)) = get_mode(fd) {
+            b.field("read", &read).field("write", &write);
+        }
+        b.finish()
+    }
+}
 
 unsafe impl Send for Dir {}
 unsafe impl Sync for Dir {}
@@ -1764,7 +1911,7 @@ impl fmt::Debug for File {
         let fd = self.as_raw_fd();
         let mut b = f.debug_struct("File");
         b.field("fd", &fd);
-        if let Some(path) = get_path(fd) {
+        if let Some(path) = get_path_from_fd(fd) {
             b.field("path", &path);
         }
         if let Some((read, write)) = get_mode(fd) {