// miri has some special hacks here that make things unused.
#![cfg_attr(miri, allow(unused))]

use crate::os::unix::prelude::*;

use crate::ffi::{CStr, OsStr, OsString};
use crate::fmt;
use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
use crate::mem;
#[cfg(any(
    target_os = "android",
    target_os = "linux",
    target_os = "solaris",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "illumos",
    target_os = "nto",
    target_os = "vita",
))]
use crate::mem::MaybeUninit;
use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd};
use crate::path::{Path, PathBuf};
use crate::ptr;
use crate::sync::Arc;
use crate::sys::common::small_c_string::run_path_with_cstr;
use crate::sys::fd::FileDesc;
use crate::sys::time::SystemTime;
use crate::sys::{cvt, cvt_r};
use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};

#[cfg(any(
    all(target_os = "linux", target_env = "gnu"),
    target_os = "macos",
    target_os = "ios",
    target_os = "tvos",
    target_os = "watchos",
))]
use crate::sys::weak::syscall;
#[cfg(any(target_os = "android", target_os = "macos", target_os = "solaris"))]
use crate::sys::weak::weak;

use libc::{c_int, mode_t};

#[cfg(any(
    target_os = "macos",
    target_os = "ios",
    target_os = "tvos",
    target_os = "watchos",
    target_os = "solaris",
    all(target_os = "linux", target_env = "gnu")
))]
use libc::c_char;
#[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
use libc::dirfd;
#[cfg(any(target_os = "linux", target_os = "emscripten"))]
use libc::fstatat64;
#[cfg(any(
    target_os = "android",
    target_os = "solaris",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "illumos",
    target_os = "nto",
    target_os = "vita",
))]
use libc::readdir as readdir64;
#[cfg(target_os = "linux")]
use libc::readdir64;
#[cfg(any(target_os = "emscripten", target_os = "l4re"))]
use libc::readdir64_r;
#[cfg(not(any(
    target_os = "android",
    target_os = "linux",
    target_os = "emscripten",
    target_os = "solaris",
    target_os = "illumos",
    target_os = "l4re",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "nto",
    target_os = "vita",
)))]
use libc::readdir_r as readdir64_r;
#[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,
};
#[cfg(not(any(
    target_os = "linux",
    target_os = "emscripten",
    target_os = "l4re",
    target_os = "android"
)))]
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,
};
#[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))]
use libc::{dirent64, fstat64, ftruncate64, lseek64, lstat64, off64_t, open64, stat64};

pub use crate::sys_common::fs::try_exists;

pub struct File(FileDesc);

// FIXME: This should be available on Linux with all `target_env`.
// But currently only glibc exposes `statx` fn and structs.
// We don't want to import unverified raw C structs here directly.
// https://github.com/rust-lang/rust/pull/67774
macro_rules! cfg_has_statx {
    ({ $($then_tt:tt)* } else { $($else_tt:tt)* }) => {
        cfg_if::cfg_if! {
            if #[cfg(all(target_os = "linux", target_env = "gnu"))] {
                $($then_tt)*
            } else {
                $($else_tt)*
            }
        }
    };
    ($($block_inner:tt)*) => {
        #[cfg(all(target_os = "linux", target_env = "gnu"))]
        {
            $($block_inner)*
        }
    };
}

cfg_has_statx! {{
    #[derive(Clone)]
    pub struct FileAttr {
        stat: stat64,
        statx_extra_fields: Option<StatxExtraFields>,
    }

    #[derive(Clone)]
    struct StatxExtraFields {
        // This is needed to check if btime is supported by the filesystem.
        stx_mask: u32,
        stx_btime: libc::statx_timestamp,
        // With statx, we can overcome 32-bit `time_t` too.
        #[cfg(target_pointer_width = "32")]
        stx_atime: libc::statx_timestamp,
        #[cfg(target_pointer_width = "32")]
        stx_ctime: libc::statx_timestamp,
        #[cfg(target_pointer_width = "32")]
        stx_mtime: libc::statx_timestamp,

    }

    // We prefer `statx` on Linux if available, which contains file creation time,
    // as well as 64-bit timestamps of all kinds.
    // Default `stat64` contains no creation time and may have 32-bit `time_t`.
    unsafe fn try_statx(
        fd: c_int,
        path: *const c_char,
        flags: i32,
        mask: u32,
    ) -> Option<io::Result<FileAttr>> {
        use crate::sync::atomic::{AtomicU8, Ordering};

        // Linux kernel prior to 4.11 or glibc prior to glibc 2.28 don't support `statx`.
        // We check for it on first failure and remember availability to avoid having to
        // do it again.
        #[repr(u8)]
        enum STATX_STATE{ Unknown = 0, Present, Unavailable }
        static STATX_SAVED_STATE: AtomicU8 = AtomicU8::new(STATX_STATE::Unknown as u8);

        syscall! {
            fn statx(
                fd: c_int,
                pathname: *const c_char,
                flags: c_int,
                mask: libc::c_uint,
                statxbuf: *mut libc::statx
            ) -> c_int
        }

        if STATX_SAVED_STATE.load(Ordering::Relaxed) == STATX_STATE::Unavailable as u8 {
            return None;
        }

        let mut buf: libc::statx = mem::zeroed();
        if let Err(err) = cvt(statx(fd, path, flags, mask, &mut buf)) {
            if STATX_SAVED_STATE.load(Ordering::Relaxed) == STATX_STATE::Present as u8 {
                return Some(Err(err));
            }

            // Availability not checked yet.
            //
            // First try the cheap way.
            if err.raw_os_error() == Some(libc::ENOSYS) {
                STATX_SAVED_STATE.store(STATX_STATE::Unavailable as u8, Ordering::Relaxed);
                return None;
            }

            // Error other than `ENOSYS` is not a good enough indicator -- it is
            // known that `EPERM` can be returned as a result of using seccomp to
            // block the syscall.
            // Availability is checked by performing a call which expects `EFAULT`
            // if the syscall is usable.
            // See: https://github.com/rust-lang/rust/issues/65662
            // FIXME this can probably just do the call if `EPERM` was received, but
            // previous iteration of the code checked it for all errors and for now
            // this is retained.
            // FIXME what about transient conditions like `ENOMEM`?
            let err2 = cvt(statx(0, ptr::null(), 0, libc::STATX_ALL, ptr::null_mut()))
                .err()
                .and_then(|e| e.raw_os_error());
            if err2 == Some(libc::EFAULT) {
                STATX_SAVED_STATE.store(STATX_STATE::Present as u8, Ordering::Relaxed);
                return Some(Err(err));
            } else {
                STATX_SAVED_STATE.store(STATX_STATE::Unavailable as u8, Ordering::Relaxed);
                return None;
            }
        }

        // We cannot fill `stat64` exhaustively because of private padding fields.
        let mut stat: stat64 = mem::zeroed();
        // `c_ulong` on gnu-mips, `dev_t` otherwise
        stat.st_dev = libc::makedev(buf.stx_dev_major, buf.stx_dev_minor) as _;
        stat.st_ino = buf.stx_ino as libc::ino64_t;
        stat.st_nlink = buf.stx_nlink as libc::nlink_t;
        stat.st_mode = buf.stx_mode as libc::mode_t;
        stat.st_uid = buf.stx_uid as libc::uid_t;
        stat.st_gid = buf.stx_gid as libc::gid_t;
        stat.st_rdev = libc::makedev(buf.stx_rdev_major, buf.stx_rdev_minor) as _;
        stat.st_size = buf.stx_size as off64_t;
        stat.st_blksize = buf.stx_blksize as libc::blksize_t;
        stat.st_blocks = buf.stx_blocks as libc::blkcnt64_t;
        stat.st_atime = buf.stx_atime.tv_sec as libc::time_t;
        // `i64` on gnu-x86_64-x32, `c_ulong` otherwise.
        stat.st_atime_nsec = buf.stx_atime.tv_nsec as _;
        stat.st_mtime = buf.stx_mtime.tv_sec as libc::time_t;
        stat.st_mtime_nsec = buf.stx_mtime.tv_nsec as _;
        stat.st_ctime = buf.stx_ctime.tv_sec as libc::time_t;
        stat.st_ctime_nsec = buf.stx_ctime.tv_nsec as _;

        let extra = StatxExtraFields {
            stx_mask: buf.stx_mask,
            stx_btime: buf.stx_btime,
            // Store full times to avoid 32-bit `time_t` truncation.
            #[cfg(target_pointer_width = "32")]
            stx_atime: buf.stx_atime,
            #[cfg(target_pointer_width = "32")]
            stx_ctime: buf.stx_ctime,
            #[cfg(target_pointer_width = "32")]
            stx_mtime: buf.stx_mtime,
        };

        Some(Ok(FileAttr { stat, statx_extra_fields: Some(extra) }))
    }

} else {
    #[derive(Clone)]
    pub struct FileAttr {
        stat: stat64,
    }
}}

// all DirEntry's will have a reference to this struct
struct InnerReadDir {
    dirp: Dir,
    root: PathBuf,
}

pub struct ReadDir {
    inner: Arc<InnerReadDir>,
    end_of_stream: bool,
}

impl ReadDir {
    fn new(inner: InnerReadDir) -> Self {
        Self { inner: Arc::new(inner), end_of_stream: false }
    }
}

struct Dir(*mut libc::DIR);

unsafe impl Send for Dir {}
unsafe impl Sync for Dir {}

#[cfg(any(
    target_os = "android",
    target_os = "linux",
    target_os = "solaris",
    target_os = "illumos",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "nto",
    target_os = "vita"
))]
pub struct DirEntry {
    dir: Arc<InnerReadDir>,
    entry: dirent64_min,
    // We need to store an owned copy of the entry name on platforms that use
    // readdir() (not readdir_r()), because a) struct dirent may use a flexible
    // array to store the name, b) it lives only until the next readdir() call.
    name: crate::ffi::CString,
}

// Define a minimal subset of fields we need from `dirent64`, especially since
// we're not using the immediate `d_name` on these targets. Keeping this as an
// `entry` field in `DirEntry` helps reduce the `cfg` boilerplate elsewhere.
#[cfg(any(
    target_os = "android",
    target_os = "linux",
    target_os = "solaris",
    target_os = "illumos",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "nto",
    target_os = "vita",
))]
struct dirent64_min {
    d_ino: u64,
    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "nto",
        target_os = "vita"
    )))]
    d_type: u8,
}

#[cfg(not(any(
    target_os = "android",
    target_os = "linux",
    target_os = "solaris",
    target_os = "illumos",
    target_os = "fuchsia",
    target_os = "redox",
    target_os = "nto",
    target_os = "vita",
)))]
pub struct DirEntry {
    dir: Arc<InnerReadDir>,
    // The full entry includes a fixed-length `d_name`.
    entry: dirent64,
}

#[derive(Clone, Debug)]
pub struct OpenOptions {
    // generic
    read: bool,
    write: bool,
    append: bool,
    truncate: bool,
    create: bool,
    create_new: bool,
    // system-specific
    custom_flags: i32,
    mode: mode_t,
}

#[derive(Clone, PartialEq, Eq, Debug)]
pub struct FilePermissions {
    mode: mode_t,
}

#[derive(Copy, Clone, Debug, Default)]
pub struct FileTimes {
    accessed: Option<SystemTime>,
    modified: Option<SystemTime>,
    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos", target_os = "tvos"))]
    created: Option<SystemTime>,
}

#[derive(Copy, Clone, Eq, Debug)]
pub struct FileType {
    mode: mode_t,
}

impl PartialEq for FileType {
    fn eq(&self, other: &Self) -> bool {
        self.masked() == other.masked()
    }
}

impl core::hash::Hash for FileType {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.masked().hash(state);
    }
}

#[derive(Debug)]
pub struct DirBuilder {
    mode: mode_t,
}

cfg_has_statx! {{
    impl FileAttr {
        fn from_stat64(stat: stat64) -> Self {
            Self { stat, statx_extra_fields: None }
        }

        #[cfg(target_pointer_width = "32")]
        pub fn stx_mtime(&self) -> Option<&libc::statx_timestamp> {
            if let Some(ext) = &self.statx_extra_fields {
                if (ext.stx_mask & libc::STATX_MTIME) != 0 {
                    return Some(&ext.stx_mtime);
                }
            }
            None
        }

        #[cfg(target_pointer_width = "32")]
        pub fn stx_atime(&self) -> Option<&libc::statx_timestamp> {
            if let Some(ext) = &self.statx_extra_fields {
                if (ext.stx_mask & libc::STATX_ATIME) != 0 {
                    return Some(&ext.stx_atime);
                }
            }
            None
        }

        #[cfg(target_pointer_width = "32")]
        pub fn stx_ctime(&self) -> Option<&libc::statx_timestamp> {
            if let Some(ext) = &self.statx_extra_fields {
                if (ext.stx_mask & libc::STATX_CTIME) != 0 {
                    return Some(&ext.stx_ctime);
                }
            }
            None
        }
    }
} else {
    impl FileAttr {
        fn from_stat64(stat: stat64) -> Self {
            Self { stat }
        }
    }
}}

impl FileAttr {
    pub fn size(&self) -> u64 {
        self.stat.st_size as u64
    }
    pub fn perm(&self) -> FilePermissions {
        FilePermissions { mode: (self.stat.st_mode as mode_t) }
    }

    pub fn file_type(&self) -> FileType {
        FileType { mode: self.stat.st_mode as mode_t }
    }
}

#[cfg(target_os = "netbsd")]
impl FileAttr {
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_mtime as i64, self.stat.st_mtimensec as i64))
    }

    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_atime as i64, self.stat.st_atimensec as i64))
    }

    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_birthtime as i64, self.stat.st_birthtimensec as i64))
    }
}

#[cfg(not(any(target_os = "netbsd", target_os = "nto")))]
impl FileAttr {
    #[cfg(not(any(
        target_os = "vxworks",
        target_os = "espidf",
        target_os = "horizon",
        target_os = "vita"
    )))]
    pub fn modified(&self) -> io::Result<SystemTime> {
        #[cfg(target_pointer_width = "32")]
        cfg_has_statx! {
            if let Some(mtime) = self.stx_mtime() {
                return Ok(SystemTime::new(mtime.tv_sec, mtime.tv_nsec as i64));
            }
        }

        Ok(SystemTime::new(self.stat.st_mtime as i64, self.stat.st_mtime_nsec as i64))
    }

    #[cfg(any(target_os = "vxworks", target_os = "espidf", target_os = "vita"))]
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_mtime as i64, 0))
    }

    #[cfg(target_os = "horizon")]
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(self.stat.st_mtim))
    }

    #[cfg(not(any(
        target_os = "vxworks",
        target_os = "espidf",
        target_os = "horizon",
        target_os = "vita"
    )))]
    pub fn accessed(&self) -> io::Result<SystemTime> {
        #[cfg(target_pointer_width = "32")]
        cfg_has_statx! {
            if let Some(atime) = self.stx_atime() {
                return Ok(SystemTime::new(atime.tv_sec, atime.tv_nsec as i64));
            }
        }

        Ok(SystemTime::new(self.stat.st_atime as i64, self.stat.st_atime_nsec as i64))
    }

    #[cfg(any(target_os = "vxworks", target_os = "espidf", target_os = "vita"))]
    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_atime as i64, 0))
    }

    #[cfg(target_os = "horizon")]
    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(self.stat.st_atim))
    }

    #[cfg(any(
        target_os = "freebsd",
        target_os = "openbsd",
        target_os = "macos",
        target_os = "ios",
        target_os = "tvos",
        target_os = "watchos",
    ))]
    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_birthtime as i64, self.stat.st_birthtime_nsec as i64))
    }

    #[cfg(not(any(
        target_os = "freebsd",
        target_os = "openbsd",
        target_os = "macos",
        target_os = "ios",
        target_os = "tvos",
        target_os = "watchos",
        target_os = "vita",
    )))]
    pub fn created(&self) -> io::Result<SystemTime> {
        cfg_has_statx! {
            if let Some(ext) = &self.statx_extra_fields {
                return if (ext.stx_mask & libc::STATX_BTIME) != 0 {
                    Ok(SystemTime::new(ext.stx_btime.tv_sec, ext.stx_btime.tv_nsec as i64))
                } else {
                    Err(io::const_io_error!(
                        io::ErrorKind::Uncategorized,
                        "creation time is not available for the filesystem",
                    ))
                };
            }
        }

        Err(io::const_io_error!(
            io::ErrorKind::Unsupported,
            "creation time is not available on this platform \
                            currently",
        ))
    }

    #[cfg(target_os = "vita")]
    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_ctime as i64, 0))
    }
}

#[cfg(target_os = "nto")]
impl FileAttr {
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_mtim.tv_sec, self.stat.st_mtim.tv_nsec))
    }

    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_atim.tv_sec, self.stat.st_atim.tv_nsec))
    }

    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::new(self.stat.st_ctim.tv_sec, self.stat.st_ctim.tv_nsec))
    }
}

impl AsInner<stat64> for FileAttr {
    #[inline]
    fn as_inner(&self) -> &stat64 {
        &self.stat
    }
}

impl FilePermissions {
    pub fn readonly(&self) -> bool {
        // check if any class (owner, group, others) has write permission
        self.mode & 0o222 == 0
    }

    pub fn set_readonly(&mut self, readonly: bool) {
        if readonly {
            // remove write permission for all classes; equivalent to `chmod a-w <file>`
            self.mode &= !0o222;
        } else {
            // add write permission for all classes; equivalent to `chmod a+w <file>`
            self.mode |= 0o222;
        }
    }
    pub fn mode(&self) -> u32 {
        self.mode as u32
    }
}

impl FileTimes {
    pub fn set_accessed(&mut self, t: SystemTime) {
        self.accessed = Some(t);
    }

    pub fn set_modified(&mut self, t: SystemTime) {
        self.modified = Some(t);
    }

    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos", target_os = "tvos"))]
    pub fn set_created(&mut self, t: SystemTime) {
        self.created = Some(t);
    }
}

impl FileType {
    pub fn is_dir(&self) -> bool {
        self.is(libc::S_IFDIR)
    }
    pub fn is_file(&self) -> bool {
        self.is(libc::S_IFREG)
    }
    pub fn is_symlink(&self) -> bool {
        self.is(libc::S_IFLNK)
    }

    pub fn is(&self, mode: mode_t) -> bool {
        self.masked() == mode
    }

    fn masked(&self) -> mode_t {
        self.mode & libc::S_IFMT
    }
}

impl FromInner<u32> for FilePermissions {
    fn from_inner(mode: u32) -> FilePermissions {
        FilePermissions { mode: mode as mode_t }
    }
}

impl fmt::Debug for ReadDir {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
        // Thus the result will be e g 'ReadDir("/home")'
        fmt::Debug::fmt(&*self.inner.root, f)
    }
}

impl Iterator for ReadDir {
    type Item = io::Result<DirEntry>;

    #[cfg(any(
        target_os = "android",
        target_os = "linux",
        target_os = "solaris",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "illumos",
        target_os = "nto",
        target_os = "vita",
    ))]
    fn next(&mut self) -> Option<io::Result<DirEntry>> {
        if self.end_of_stream {
            return None;
        }

        unsafe {
            loop {
                // As of POSIX.1-2017, readdir() is not required to be thread safe; only
                // readdir_r() is. However, readdir_r() cannot correctly handle platforms
                // with unlimited or variable NAME_MAX. Many modern platforms guarantee
                // thread safety for readdir() as long an individual DIR* is not accessed
                // concurrently, which is sufficient for Rust.
                super::os::set_errno(0);
                let entry_ptr = readdir64(self.inner.dirp.0);
                if entry_ptr.is_null() {
                    // We either encountered an error, or reached the end. Either way,
                    // the next call to next() should return None.
                    self.end_of_stream = true;

                    // To distinguish between errors and end-of-directory, we had to clear
                    // errno beforehand to check for an error now.
                    return match super::os::errno() {
                        0 => None,
                        e => Some(Err(Error::from_raw_os_error(e))),
                    };
                }

                // The dirent64 struct is a weird imaginary thing that isn't ever supposed
                // to be worked with by value. Its trailing d_name field is declared
                // variously as [c_char; 256] or [c_char; 1] on different systems but
                // either way that size is meaningless; only the offset of d_name is
                // meaningful. The dirent64 pointers that libc returns from readdir64 are
                // allowed to point to allocations smaller _or_ LARGER than implied by the
                // definition of the struct.
                //
                // As such, we need to be even more careful with dirent64 than if its
                // contents were "simply" partially initialized data.
                //
                // Like for uninitialized contents, converting entry_ptr to `&dirent64`
                // would not be legal. However, unique to dirent64 is that we don't even
                // get to use `addr_of!((*entry_ptr).d_name)` because that operation
                // requires the full extent of *entry_ptr to be in bounds of the same
                // allocation, which is not necessarily the case here.
                //
                // Absent any other way to obtain a pointer to `(*entry_ptr).d_name`
                // legally in Rust analogously to how it would be done in C, we instead
                // need to make our own non-libc allocation that conforms to the weird
                // imaginary definition of dirent64, and use that for a field offset
                // computation.
                macro_rules! offset_ptr {
                    ($entry_ptr:expr, $field:ident) => {{
                        const OFFSET: isize = {
                            let delusion = MaybeUninit::<dirent64>::uninit();
                            let entry_ptr = delusion.as_ptr();
                            unsafe {
                                ptr::addr_of!((*entry_ptr).$field)
                                    .cast::<u8>()
                                    .offset_from(entry_ptr.cast::<u8>())
                            }
                        };
                        if true {
                            // Cast to the same type determined by the else branch.
                            $entry_ptr.byte_offset(OFFSET).cast::<_>()
                        } else {
                            #[allow(deref_nullptr)]
                            {
                                ptr::addr_of!((*ptr::null::<dirent64>()).$field)
                            }
                        }
                    }};
                }

                // d_name is guaranteed to be null-terminated.
                let name = CStr::from_ptr(offset_ptr!(entry_ptr, d_name).cast());
                let name_bytes = name.to_bytes();
                if name_bytes == b"." || name_bytes == b".." {
                    continue;
                }

                #[cfg(not(target_os = "vita"))]
                let entry = dirent64_min {
                    d_ino: *offset_ptr!(entry_ptr, d_ino) as u64,
                    #[cfg(not(any(
                        target_os = "solaris",
                        target_os = "illumos",
                        target_os = "nto",
                    )))]
                    d_type: *offset_ptr!(entry_ptr, d_type) as u8,
                };

                #[cfg(target_os = "vita")]
                let entry = dirent64_min { d_ino: 0u64 };

                return Some(Ok(DirEntry {
                    entry,
                    name: name.to_owned(),
                    dir: Arc::clone(&self.inner),
                }));
            }
        }
    }

    #[cfg(not(any(
        target_os = "android",
        target_os = "linux",
        target_os = "solaris",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "illumos",
        target_os = "nto",
        target_os = "vita",
    )))]
    fn next(&mut self) -> Option<io::Result<DirEntry>> {
        if self.end_of_stream {
            return None;
        }

        unsafe {
            let mut ret = DirEntry { entry: mem::zeroed(), dir: Arc::clone(&self.inner) };
            let mut entry_ptr = ptr::null_mut();
            loop {
                let err = readdir64_r(self.inner.dirp.0, &mut ret.entry, &mut entry_ptr);
                if err != 0 {
                    if entry_ptr.is_null() {
                        // We encountered an error (which will be returned in this iteration), but
                        // we also reached the end of the directory stream. The `end_of_stream`
                        // flag is enabled to make sure that we return `None` in the next iteration
                        // (instead of looping forever)
                        self.end_of_stream = true;
                    }
                    return Some(Err(Error::from_raw_os_error(err)));
                }
                if entry_ptr.is_null() {
                    return None;
                }
                if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                    return Some(Ok(ret));
                }
            }
        }
    }
}

impl Drop for Dir {
    fn drop(&mut self) {
        let r = unsafe { libc::closedir(self.0) };
        assert!(
            r == 0 || crate::io::Error::last_os_error().kind() == crate::io::ErrorKind::Interrupted,
            "unexpected error during closedir: {:?}",
            crate::io::Error::last_os_error()
        );
    }
}

impl DirEntry {
    pub fn path(&self) -> PathBuf {
        self.dir.root.join(self.file_name_os_str())
    }

    pub fn file_name(&self) -> OsString {
        self.file_name_os_str().to_os_string()
    }

    #[cfg(all(
        any(target_os = "linux", target_os = "emscripten", target_os = "android"),
        not(miri)
    ))]
    pub fn metadata(&self) -> io::Result<FileAttr> {
        let fd = cvt(unsafe { dirfd(self.dir.dirp.0) })?;
        let name = self.name_cstr().as_ptr();

        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                fd,
                name,
                libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { fstatat64(fd, name, &mut stat, libc::AT_SYMLINK_NOFOLLOW) })?;
        Ok(FileAttr::from_stat64(stat))
    }

    #[cfg(any(
        not(any(target_os = "linux", target_os = "emscripten", target_os = "android")),
        miri
    ))]
    pub fn metadata(&self) -> io::Result<FileAttr> {
        lstat(&self.path())
    }

    #[cfg(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks",
        target_os = "nto",
        target_os = "vita",
    ))]
    pub fn file_type(&self) -> io::Result<FileType> {
        self.metadata().map(|m| m.file_type())
    }

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks",
        target_os = "nto",
        target_os = "vita",
    )))]
    pub fn file_type(&self) -> io::Result<FileType> {
        match self.entry.d_type {
            libc::DT_CHR => Ok(FileType { mode: libc::S_IFCHR }),
            libc::DT_FIFO => Ok(FileType { mode: libc::S_IFIFO }),
            libc::DT_LNK => Ok(FileType { mode: libc::S_IFLNK }),
            libc::DT_REG => Ok(FileType { mode: libc::S_IFREG }),
            libc::DT_SOCK => Ok(FileType { mode: libc::S_IFSOCK }),
            libc::DT_DIR => Ok(FileType { mode: libc::S_IFDIR }),
            libc::DT_BLK => Ok(FileType { mode: libc::S_IFBLK }),
            _ => self.metadata().map(|m| m.file_type()),
        }
    }

    #[cfg(any(
        target_os = "macos",
        target_os = "ios",
        target_os = "tvos",
        target_os = "watchos",
        target_os = "linux",
        target_os = "emscripten",
        target_os = "android",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "l4re",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "vxworks",
        target_os = "espidf",
        target_os = "horizon",
        target_os = "vita",
        target_os = "nto",
    ))]
    pub fn ino(&self) -> u64 {
        self.entry.d_ino as u64
    }

    #[cfg(any(
        target_os = "freebsd",
        target_os = "openbsd",
        target_os = "netbsd",
        target_os = "dragonfly"
    ))]
    pub fn ino(&self) -> u64 {
        self.entry.d_fileno as u64
    }

    #[cfg(any(
        target_os = "macos",
        target_os = "ios",
        target_os = "tvos",
        target_os = "watchos",
        target_os = "netbsd",
        target_os = "openbsd",
        target_os = "freebsd",
        target_os = "dragonfly"
    ))]
    fn name_bytes(&self) -> &[u8] {
        use crate::slice;
        unsafe {
            slice::from_raw_parts(
                self.entry.d_name.as_ptr() as *const u8,
                self.entry.d_namlen as usize,
            )
        }
    }
    #[cfg(not(any(
        target_os = "macos",
        target_os = "ios",
        target_os = "tvos",
        target_os = "watchos",
        target_os = "netbsd",
        target_os = "openbsd",
        target_os = "freebsd",
        target_os = "dragonfly"
    )))]
    fn name_bytes(&self) -> &[u8] {
        self.name_cstr().to_bytes()
    }

    #[cfg(not(any(
        target_os = "android",
        target_os = "linux",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "nto",
        target_os = "vita",
    )))]
    fn name_cstr(&self) -> &CStr {
        unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()) }
    }
    #[cfg(any(
        target_os = "android",
        target_os = "linux",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "nto",
        target_os = "vita",
    ))]
    fn name_cstr(&self) -> &CStr {
        &self.name
    }

    pub fn file_name_os_str(&self) -> &OsStr {
        OsStr::from_bytes(self.name_bytes())
    }
}

impl OpenOptions {
    pub fn new() -> OpenOptions {
        OpenOptions {
            // generic
            read: false,
            write: false,
            append: false,
            truncate: false,
            create: false,
            create_new: false,
            // system-specific
            custom_flags: 0,
            mode: 0o666,
        }
    }

    pub fn read(&mut self, read: bool) {
        self.read = read;
    }
    pub fn write(&mut self, write: bool) {
        self.write = write;
    }
    pub fn append(&mut self, append: bool) {
        self.append = append;
    }
    pub fn truncate(&mut self, truncate: bool) {
        self.truncate = truncate;
    }
    pub fn create(&mut self, create: bool) {
        self.create = create;
    }
    pub fn create_new(&mut self, create_new: bool) {
        self.create_new = create_new;
    }

    pub fn custom_flags(&mut self, flags: i32) {
        self.custom_flags = flags;
    }
    pub fn mode(&mut self, mode: u32) {
        self.mode = mode as mode_t;
    }

    fn get_access_mode(&self) -> io::Result<c_int> {
        match (self.read, self.write, self.append) {
            (true, false, false) => Ok(libc::O_RDONLY),
            (false, true, false) => Ok(libc::O_WRONLY),
            (true, true, false) => Ok(libc::O_RDWR),
            (false, _, true) => Ok(libc::O_WRONLY | libc::O_APPEND),
            (true, _, true) => Ok(libc::O_RDWR | libc::O_APPEND),
            (false, false, false) => Err(Error::from_raw_os_error(libc::EINVAL)),
        }
    }

    fn get_creation_mode(&self) -> io::Result<c_int> {
        match (self.write, self.append) {
            (true, false) => {}
            (false, false) => {
                if self.truncate || self.create || self.create_new {
                    return Err(Error::from_raw_os_error(libc::EINVAL));
                }
            }
            (_, true) => {
                if self.truncate && !self.create_new {
                    return Err(Error::from_raw_os_error(libc::EINVAL));
                }
            }
        }

        Ok(match (self.create, self.truncate, self.create_new) {
            (false, false, false) => 0,
            (true, false, false) => libc::O_CREAT,
            (false, true, false) => libc::O_TRUNC,
            (true, true, false) => libc::O_CREAT | libc::O_TRUNC,
            (_, _, true) => libc::O_CREAT | libc::O_EXCL,
        })
    }
}

impl File {
    pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
        run_path_with_cstr(path, |path| File::open_c(path, opts))
    }

    pub fn open_c(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);
        // The third argument of `open64` is documented to have type `mode_t`. On
        // some platforms (like macOS, where `open64` is actually `open`), `mode_t` is `u16`.
        // However, since this is a variadic function, C integer promotion rules mean that on
        // the ABI level, this still gets passed as `c_int` (aka `u32` on Unix platforms).
        let fd = cvt_r(|| unsafe { open64(path.as_ptr(), flags, opts.mode as c_int) })?;
        Ok(File(unsafe { FileDesc::from_raw_fd(fd) }))
    }

    pub fn file_attr(&self) -> io::Result<FileAttr> {
        let fd = self.as_raw_fd();

        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                fd,
                b"\0" as *const _ as *const c_char,
                libc::AT_EMPTY_PATH | libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { fstat64(fd, &mut stat) })?;
        Ok(FileAttr::from_stat64(stat))
    }

    pub fn fsync(&self) -> io::Result<()> {
        cvt_r(|| unsafe { os_fsync(self.as_raw_fd()) })?;
        return Ok(());

        #[cfg(any(
            target_os = "macos",
            target_os = "ios",
            target_os = "tvos",
            target_os = "watchos",
        ))]
        unsafe fn os_fsync(fd: c_int) -> c_int {
            libc::fcntl(fd, libc::F_FULLFSYNC)
        }
        #[cfg(not(any(
            target_os = "macos",
            target_os = "ios",
            target_os = "tvos",
            target_os = "watchos",
        )))]
        unsafe fn os_fsync(fd: c_int) -> c_int {
            libc::fsync(fd)
        }
    }

    pub fn datasync(&self) -> io::Result<()> {
        cvt_r(|| unsafe { os_datasync(self.as_raw_fd()) })?;
        return Ok(());

        #[cfg(any(
            target_os = "macos",
            target_os = "ios",
            target_os = "tvos",
            target_os = "watchos",
        ))]
        unsafe fn os_datasync(fd: c_int) -> c_int {
            libc::fcntl(fd, libc::F_FULLFSYNC)
        }
        #[cfg(any(
            target_os = "freebsd",
            target_os = "linux",
            target_os = "android",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "nto",
        ))]
        unsafe fn os_datasync(fd: c_int) -> c_int {
            libc::fdatasync(fd)
        }
        #[cfg(not(any(
            target_os = "android",
            target_os = "freebsd",
            target_os = "ios",
            target_os = "tvos",
            target_os = "linux",
            target_os = "macos",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "watchos",
            target_os = "nto",
        )))]
        unsafe fn os_datasync(fd: c_int) -> c_int {
            libc::fsync(fd)
        }
    }

    pub fn truncate(&self, size: u64) -> io::Result<()> {
        let size: off64_t =
            size.try_into().map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
        cvt_r(|| unsafe { ftruncate64(self.as_raw_fd(), size) }).map(drop)
    }

    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.0.read(buf)
    }

    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        self.0.read_vectored(bufs)
    }

    #[inline]
    pub fn is_read_vectored(&self) -> bool {
        self.0.is_read_vectored()
    }

    pub fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        self.0.read_at(buf, offset)
    }

    pub fn read_buf(&self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
        self.0.read_buf(cursor)
    }

    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        self.0.read_vectored_at(bufs, offset)
    }

    pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
        self.0.write(buf)
    }

    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        self.0.write_vectored(bufs)
    }

    #[inline]
    pub fn is_write_vectored(&self) -> bool {
        self.0.is_write_vectored()
    }

    pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
        self.0.write_at(buf, offset)
    }

    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        self.0.write_vectored_at(bufs, offset)
    }

    pub fn flush(&self) -> io::Result<()> {
        Ok(())
    }

    pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
        let (whence, pos) = match pos {
            // Casting to `i64` is fine, too large values will end up as
            // negative which will cause an error in `lseek64`.
            SeekFrom::Start(off) => (libc::SEEK_SET, off as i64),
            SeekFrom::End(off) => (libc::SEEK_END, off),
            SeekFrom::Current(off) => (libc::SEEK_CUR, off),
        };
        let n = cvt(unsafe { lseek64(self.as_raw_fd(), pos as off64_t, whence) })?;
        Ok(n as u64)
    }

    pub fn duplicate(&self) -> io::Result<File> {
        self.0.duplicate().map(File)
    }

    pub fn set_permissions(&self, perm: FilePermissions) -> io::Result<()> {
        cvt_r(|| unsafe { libc::fchmod(self.as_raw_fd(), perm.mode) })?;
        Ok(())
    }

    pub fn set_times(&self, times: FileTimes) -> io::Result<()> {
        #[cfg(not(any(target_os = "redox", target_os = "espidf", target_os = "horizon")))]
        let to_timespec = |time: Option<SystemTime>| {
            match time {
                Some(time) if let Some(ts) = time.t.to_timespec() => Ok(ts),
                Some(time) if time > crate::sys::time::UNIX_EPOCH => Err(io::const_io_error!(io::ErrorKind::InvalidInput, "timestamp is too large to set as a file time")),
                Some(_) => Err(io::const_io_error!(io::ErrorKind::InvalidInput, "timestamp is too small to set as a file time")),
                None => Ok(libc::timespec { tv_sec: 0, tv_nsec: libc::UTIME_OMIT as _ }),
            }
        };
        cfg_if::cfg_if! {
            if #[cfg(any(target_os = "redox", target_os = "espidf", target_os = "horizon"))] {
                // Redox doesn't appear to support `UTIME_OMIT`.
                // ESP-IDF and HorizonOS do not support `futimens` at all and the behavior for those OS is therefore
                // the same as for Redox.
                let _ = times;
                Err(io::const_io_error!(
                    io::ErrorKind::Unsupported,
                    "setting file times not supported",
                ))
            } else if #[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))] {
                let mut buf = [mem::MaybeUninit::<libc::timespec>::uninit(); 3];
                let mut num_times = 0;
                let mut attrlist: libc::attrlist = unsafe { mem::zeroed() };
                attrlist.bitmapcount = libc::ATTR_BIT_MAP_COUNT;
                if times.created.is_some() {
                    buf[num_times].write(to_timespec(times.created)?);
                    num_times += 1;
                    attrlist.commonattr |= libc::ATTR_CMN_CRTIME;
                }
                if times.modified.is_some() {
                    buf[num_times].write(to_timespec(times.modified)?);
                    num_times += 1;
                    attrlist.commonattr |= libc::ATTR_CMN_MODTIME;
                }
                if times.accessed.is_some() {
                    buf[num_times].write(to_timespec(times.accessed)?);
                    num_times += 1;
                    attrlist.commonattr |= libc::ATTR_CMN_ACCTIME;
                }
                cvt(unsafe { libc::fsetattrlist(
                    self.as_raw_fd(),
                    (&attrlist as *const libc::attrlist).cast::<libc::c_void>().cast_mut(),
                    buf.as_ptr().cast::<libc::c_void>().cast_mut(),
                    num_times * mem::size_of::<libc::timespec>(),
                    0
                ) })?;
                Ok(())
            } else if #[cfg(target_os = "android")] {
                let times = [to_timespec(times.accessed)?, to_timespec(times.modified)?];
                // futimens requires Android API level 19
                cvt(unsafe {
                    weak!(fn futimens(c_int, *const libc::timespec) -> c_int);
                    match futimens.get() {
                        Some(futimens) => futimens(self.as_raw_fd(), times.as_ptr()),
                        None => return Err(io::const_io_error!(
                            io::ErrorKind::Unsupported,
                            "setting file times requires Android API level >= 19",
                        )),
                    }
                })?;
                Ok(())
            } else {
                #[cfg(all(target_os = "linux", target_env = "gnu", target_pointer_width = "32", not(target_arch = "riscv32")))]
                {
                    use crate::sys::{time::__timespec64, weak::weak};

                    // Added in glibc 2.34
                    weak!(fn __futimens64(libc::c_int, *const __timespec64) -> libc::c_int);

                    if let Some(futimens64) = __futimens64.get() {
                        let to_timespec = |time: Option<SystemTime>| time.map(|time| time.t.to_timespec64())
                            .unwrap_or(__timespec64::new(0, libc::UTIME_OMIT as _));
                        let times = [to_timespec(times.accessed), to_timespec(times.modified)];
                        cvt(unsafe { futimens64(self.as_raw_fd(), times.as_ptr()) })?;
                        return Ok(());
                    }
                }
                let times = [to_timespec(times.accessed)?, to_timespec(times.modified)?];
                cvt(unsafe { libc::futimens(self.as_raw_fd(), times.as_ptr()) })?;
                Ok(())
            }
        }
    }
}

impl DirBuilder {
    pub fn new() -> DirBuilder {
        DirBuilder { mode: 0o777 }
    }

    pub fn mkdir(&self, p: &Path) -> io::Result<()> {
        run_path_with_cstr(p, |p| cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) }).map(|_| ()))
    }

    pub fn set_mode(&mut self, mode: u32) {
        self.mode = mode as mode_t;
    }
}

impl AsInner<FileDesc> for File {
    #[inline]
    fn as_inner(&self) -> &FileDesc {
        &self.0
    }
}

impl AsInnerMut<FileDesc> for File {
    #[inline]
    fn as_inner_mut(&mut self) -> &mut FileDesc {
        &mut self.0
    }
}

impl IntoInner<FileDesc> for File {
    fn into_inner(self) -> FileDesc {
        self.0
    }
}

impl FromInner<FileDesc> for File {
    fn from_inner(file_desc: FileDesc) -> Self {
        Self(file_desc)
    }
}

impl AsFd for File {
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.0.as_fd()
    }
}

impl AsRawFd for File {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.0.as_raw_fd()
    }
}

impl IntoRawFd for File {
    fn into_raw_fd(self) -> RawFd {
        self.0.into_raw_fd()
    }
}

impl FromRawFd for File {
    unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
        Self(FromRawFd::from_raw_fd(raw_fd))
    }
}

impl fmt::Debug for File {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        #[cfg(any(
            target_os = "linux",
            target_os = "netbsd",
            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());
            readlink(&p).ok()
        }

        #[cfg(target_os = "macos")]
        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 macOS defines `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 {
                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(all(target_os = "freebsd", target_arch = "x86_64"))]
        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 = mem::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 = "macos",
            target_os = "vxworks",
            all(target_os = "freebsd", target_arch = "x86_64"),
            target_os = "netbsd",
            target_os = "illumos",
            target_os = "solaris"
        )))]
        fn get_path(_fd: c_int) -> Option<PathBuf> {
            // FIXME(#24570): implement this for other Unix platforms
            None
        }

        #[cfg(any(
            target_os = "linux",
            target_os = "macos",
            target_os = "freebsd",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "vxworks"
        ))]
        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,
            }
        }

        #[cfg(not(any(
            target_os = "linux",
            target_os = "macos",
            target_os = "freebsd",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "vxworks"
        )))]
        fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
            // FIXME(#24570): implement this for other Unix platforms
            None
        }

        let fd = self.as_raw_fd();
        let mut b = f.debug_struct("File");
        b.field("fd", &fd);
        if let Some(path) = get_path(fd) {
            b.field("path", &path);
        }
        if let Some((read, write)) = get_mode(fd) {
            b.field("read", &read).field("write", &write);
        }
        b.finish()
    }
}

pub fn readdir(path: &Path) -> io::Result<ReadDir> {
    let ptr = run_path_with_cstr(path, |p| unsafe { Ok(libc::opendir(p.as_ptr())) })?;
    if ptr.is_null() {
        Err(Error::last_os_error())
    } else {
        let root = path.to_path_buf();
        let inner = InnerReadDir { dirp: Dir(ptr), root };
        Ok(ReadDir::new(inner))
    }
}

pub fn unlink(p: &Path) -> io::Result<()> {
    run_path_with_cstr(p, |p| cvt(unsafe { libc::unlink(p.as_ptr()) }).map(|_| ()))
}

pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
    run_path_with_cstr(old, |old| {
        run_path_with_cstr(new, |new| {
            cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) }).map(|_| ())
        })
    })
}

pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
    run_path_with_cstr(p, |p| cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) }).map(|_| ()))
}

pub fn rmdir(p: &Path) -> io::Result<()> {
    run_path_with_cstr(p, |p| cvt(unsafe { libc::rmdir(p.as_ptr()) }).map(|_| ()))
}

pub fn readlink(p: &Path) -> io::Result<PathBuf> {
    run_path_with_cstr(p, |c_path| {
        let p = c_path.as_ptr();

        let mut buf = Vec::with_capacity(256);

        loop {
            let buf_read =
                cvt(unsafe { libc::readlink(p, buf.as_mut_ptr() as *mut _, buf.capacity()) })?
                    as usize;

            unsafe {
                buf.set_len(buf_read);
            }

            if buf_read != buf.capacity() {
                buf.shrink_to_fit();

                return Ok(PathBuf::from(OsString::from_vec(buf)));
            }

            // Trigger the internal buffer resizing logic of `Vec` by requiring
            // more space than the current capacity. The length is guaranteed to be
            // the same as the capacity due to the if statement above.
            buf.reserve(1);
        }
    })
}

pub fn symlink(original: &Path, link: &Path) -> io::Result<()> {
    run_path_with_cstr(original, |original| {
        run_path_with_cstr(link, |link| {
            cvt(unsafe { libc::symlink(original.as_ptr(), link.as_ptr()) }).map(|_| ())
        })
    })
}

pub fn link(original: &Path, link: &Path) -> io::Result<()> {
    run_path_with_cstr(original, |original| {
        run_path_with_cstr(link, |link| {
            cfg_if::cfg_if! {
                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon", target_os = "vita"))] {
                    // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
                    // it implementation-defined whether `link` follows symlinks, so rely on the
                    // `symlink_hard_link` test in library/std/src/fs/tests.rs to check the behavior.
                    // Android has `linkat` on newer versions, but we happen to know `link`
                    // always has the correct behavior, so it's here as well.
                    cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
                } else if #[cfg(any(target_os = "macos", target_os = "solaris"))] {
                    // MacOS (<=10.9) and Solaris 10 lack support for linkat while newer
                    // versions have it. We want to use linkat if it is available, so we use weak!
                    // to check. `linkat` is preferable to `link` because it gives us a flag to
                    // specify how symlinks should be handled. We pass 0 as the flags argument,
                    // meaning it shouldn't follow symlinks.
                    weak!(fn linkat(c_int, *const c_char, c_int, *const c_char, c_int) -> c_int);

                    if let Some(f) = linkat.get() {
                        cvt(unsafe { f(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
                    } else {
                        cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
                    };
                } else {
                    // Where we can, use `linkat` instead of `link`; see the comment above
                    // this one for details on why.
                    cvt(unsafe { libc::linkat(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
                }
            }
            Ok(())
        })
    })
}

pub fn stat(p: &Path) -> io::Result<FileAttr> {
    run_path_with_cstr(p, |p| {
        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                libc::AT_FDCWD,
                p.as_ptr(),
                libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { stat64(p.as_ptr(), &mut stat) })?;
        Ok(FileAttr::from_stat64(stat))
    })
}

pub fn lstat(p: &Path) -> io::Result<FileAttr> {
    run_path_with_cstr(p, |p| {
        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                libc::AT_FDCWD,
                p.as_ptr(),
                libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { lstat64(p.as_ptr(), &mut stat) })?;
        Ok(FileAttr::from_stat64(stat))
    })
}

pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
    let r = run_path_with_cstr(p, |path| unsafe {
        Ok(libc::realpath(path.as_ptr(), ptr::null_mut()))
    })?;
    if r.is_null() {
        return Err(io::Error::last_os_error());
    }
    Ok(PathBuf::from(OsString::from_vec(unsafe {
        let buf = CStr::from_ptr(r).to_bytes().to_vec();
        libc::free(r as *mut _);
        buf
    })))
}

fn open_from(from: &Path) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
    use crate::fs::File;
    use crate::sys_common::fs::NOT_FILE_ERROR;

    let reader = File::open(from)?;
    let metadata = reader.metadata()?;
    if !metadata.is_file() {
        return Err(NOT_FILE_ERROR);
    }
    Ok((reader, metadata))
}

#[cfg(target_os = "espidf")]
fn open_to_and_set_permissions(
    to: &Path,
    reader_metadata: crate::fs::Metadata,
) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
    use crate::fs::OpenOptions;
    let writer = OpenOptions::new().open(to)?;
    let writer_metadata = writer.metadata()?;
    Ok((writer, writer_metadata))
}

#[cfg(not(target_os = "espidf"))]
fn open_to_and_set_permissions(
    to: &Path,
    reader_metadata: crate::fs::Metadata,
) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
    use crate::fs::OpenOptions;
    use crate::os::unix::fs::{OpenOptionsExt, PermissionsExt};

    let perm = reader_metadata.permissions();
    let writer = OpenOptions::new()
        // create the file with the correct mode right away
        .mode(perm.mode())
        .write(true)
        .create(true)
        .truncate(true)
        .open(to)?;
    let writer_metadata = writer.metadata()?;
    // fchmod is broken on vita
    #[cfg(not(target_os = "vita"))]
    if writer_metadata.is_file() {
        // Set the correct file permissions, in case the file already existed.
        // Don't set the permissions on already existing non-files like
        // pipes/FIFOs or device nodes.
        writer.set_permissions(perm)?;
    }
    Ok((writer, writer_metadata))
}

#[cfg(not(any(
    target_os = "linux",
    target_os = "android",
    target_os = "macos",
    target_os = "ios",
    target_os = "tvos",
    target_os = "watchos",
)))]
pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
    let (mut reader, reader_metadata) = open_from(from)?;
    let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;

    io::copy(&mut reader, &mut writer)
}

#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
    let (mut reader, reader_metadata) = open_from(from)?;
    let max_len = u64::MAX;
    let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;

    use super::kernel_copy::{copy_regular_files, CopyResult};

    match copy_regular_files(reader.as_raw_fd(), writer.as_raw_fd(), max_len) {
        CopyResult::Ended(bytes) => Ok(bytes),
        CopyResult::Error(e, _) => Err(e),
        CopyResult::Fallback(written) => match io::copy::generic_copy(&mut reader, &mut writer) {
            Ok(bytes) => Ok(bytes + written),
            Err(e) => Err(e),
        },
    }
}

#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos"))]
pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
    use crate::sync::atomic::{AtomicBool, Ordering};

    const COPYFILE_ACL: u32 = 1 << 0;
    const COPYFILE_STAT: u32 = 1 << 1;
    const COPYFILE_XATTR: u32 = 1 << 2;
    const COPYFILE_DATA: u32 = 1 << 3;

    const COPYFILE_SECURITY: u32 = COPYFILE_STAT | COPYFILE_ACL;
    const COPYFILE_METADATA: u32 = COPYFILE_SECURITY | COPYFILE_XATTR;
    const COPYFILE_ALL: u32 = COPYFILE_METADATA | COPYFILE_DATA;

    const COPYFILE_STATE_COPIED: u32 = 8;

    #[allow(non_camel_case_types)]
    type copyfile_state_t = *mut libc::c_void;
    #[allow(non_camel_case_types)]
    type copyfile_flags_t = u32;

    extern "C" {
        fn fcopyfile(
            from: libc::c_int,
            to: libc::c_int,
            state: copyfile_state_t,
            flags: copyfile_flags_t,
        ) -> libc::c_int;
        fn copyfile_state_alloc() -> copyfile_state_t;
        fn copyfile_state_free(state: copyfile_state_t) -> libc::c_int;
        fn copyfile_state_get(
            state: copyfile_state_t,
            flag: u32,
            dst: *mut libc::c_void,
        ) -> libc::c_int;
    }

    struct FreeOnDrop(copyfile_state_t);
    impl Drop for FreeOnDrop {
        fn drop(&mut self) {
            // The code below ensures that `FreeOnDrop` is never a null pointer
            unsafe {
                // `copyfile_state_free` returns -1 if the `to` or `from` files
                // cannot be closed. However, this is not considered this an
                // error.
                copyfile_state_free(self.0);
            }
        }
    }

    // MacOS prior to 10.12 don't support `fclonefileat`
    // We store the availability in a global to avoid unnecessary syscalls
    static HAS_FCLONEFILEAT: AtomicBool = AtomicBool::new(true);
    syscall! {
        fn fclonefileat(
            srcfd: libc::c_int,
            dst_dirfd: libc::c_int,
            dst: *const c_char,
            flags: libc::c_int
        ) -> libc::c_int
    }

    let (reader, reader_metadata) = open_from(from)?;

    // Opportunistically attempt to create a copy-on-write clone of `from`
    // using `fclonefileat`.
    if HAS_FCLONEFILEAT.load(Ordering::Relaxed) {
        let clonefile_result = run_path_with_cstr(to, |to| {
            cvt(unsafe { fclonefileat(reader.as_raw_fd(), libc::AT_FDCWD, to.as_ptr(), 0) })
        });
        match clonefile_result {
            Ok(_) => return Ok(reader_metadata.len()),
            Err(err) => match err.raw_os_error() {
                // `fclonefileat` will fail on non-APFS volumes, if the
                // destination already exists, or if the source and destination
                // are on different devices. In all these cases `fcopyfile`
                // should succeed.
                Some(libc::ENOTSUP) | Some(libc::EEXIST) | Some(libc::EXDEV) => (),
                Some(libc::ENOSYS) => HAS_FCLONEFILEAT.store(false, Ordering::Relaxed),
                _ => return Err(err),
            },
        }
    }

    // Fall back to using `fcopyfile` if `fclonefileat` does not succeed.
    let (writer, writer_metadata) = open_to_and_set_permissions(to, reader_metadata)?;

    // We ensure that `FreeOnDrop` never contains a null pointer so it is
    // always safe to call `copyfile_state_free`
    let state = unsafe {
        let state = copyfile_state_alloc();
        if state.is_null() {
            return Err(crate::io::Error::last_os_error());
        }
        FreeOnDrop(state)
    };

    let flags = if writer_metadata.is_file() { COPYFILE_ALL } else { COPYFILE_DATA };

    cvt(unsafe { fcopyfile(reader.as_raw_fd(), writer.as_raw_fd(), state.0, flags) })?;

    let mut bytes_copied: libc::off_t = 0;
    cvt(unsafe {
        copyfile_state_get(
            state.0,
            COPYFILE_STATE_COPIED,
            &mut bytes_copied as *mut libc::off_t as *mut libc::c_void,
        )
    })?;
    Ok(bytes_copied as u64)
}

pub fn chown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
    run_path_with_cstr(path, |path| {
        cvt(unsafe { libc::chown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
            .map(|_| ())
    })
}

pub fn fchown(fd: c_int, uid: u32, gid: u32) -> io::Result<()> {
    cvt(unsafe { libc::fchown(fd, uid as libc::uid_t, gid as libc::gid_t) })?;
    Ok(())
}

pub fn lchown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
    run_path_with_cstr(path, |path| {
        cvt(unsafe { libc::lchown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
            .map(|_| ())
    })
}

#[cfg(not(any(target_os = "fuchsia", target_os = "vxworks")))]
pub fn chroot(dir: &Path) -> io::Result<()> {
    run_path_with_cstr(dir, |dir| cvt(unsafe { libc::chroot(dir.as_ptr()) }).map(|_| ()))
}

pub use remove_dir_impl::remove_dir_all;

// Fallback for REDOX, ESP-ID, Horizon, Vita and Miri
#[cfg(any(
    target_os = "redox",
    target_os = "espidf",
    target_os = "horizon",
    target_os = "vita",
    target_os = "nto",
    miri
))]
mod remove_dir_impl {
    pub use crate::sys_common::fs::remove_dir_all;
}

// Modern implementation using openat(), unlinkat() and fdopendir()
#[cfg(not(any(
    target_os = "redox",
    target_os = "espidf",
    target_os = "horizon",
    target_os = "vita",
    target_os = "nto",
    miri
)))]
mod remove_dir_impl {
    use super::{lstat, Dir, DirEntry, InnerReadDir, ReadDir};
    use crate::ffi::CStr;
    use crate::io;
    use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
    use crate::os::unix::prelude::{OwnedFd, RawFd};
    use crate::path::{Path, PathBuf};
    use crate::sys::common::small_c_string::run_path_with_cstr;
    use crate::sys::{cvt, cvt_r};

    #[cfg(not(any(
        all(target_os = "linux", target_env = "gnu"),
        all(target_os = "macos", not(target_arch = "aarch64"))
    )))]
    use libc::{fdopendir, openat, unlinkat};
    #[cfg(all(target_os = "linux", target_env = "gnu"))]
    use libc::{fdopendir, openat64 as openat, unlinkat};
    #[cfg(all(target_os = "macos", not(target_arch = "aarch64")))]
    use macos_weak::{fdopendir, openat, unlinkat};

    #[cfg(all(target_os = "macos", not(target_arch = "aarch64")))]
    mod macos_weak {
        use crate::sys::weak::weak;
        use libc::{c_char, c_int, DIR};

        fn get_openat_fn() -> Option<unsafe extern "C" fn(c_int, *const c_char, c_int) -> c_int> {
            weak!(fn openat(c_int, *const c_char, c_int) -> c_int);
            openat.get()
        }

        pub fn has_openat() -> bool {
            get_openat_fn().is_some()
        }

        pub unsafe fn openat(dirfd: c_int, pathname: *const c_char, flags: c_int) -> c_int {
            get_openat_fn().map(|openat| openat(dirfd, pathname, flags)).unwrap_or_else(|| {
                crate::sys::unix::os::set_errno(libc::ENOSYS);
                -1
            })
        }

        pub unsafe fn fdopendir(fd: c_int) -> *mut DIR {
            #[cfg(all(target_os = "macos", target_arch = "x86"))]
            weak!(fn fdopendir(c_int) -> *mut DIR, "fdopendir$INODE64$UNIX2003");
            #[cfg(all(target_os = "macos", target_arch = "x86_64"))]
            weak!(fn fdopendir(c_int) -> *mut DIR, "fdopendir$INODE64");
            fdopendir.get().map(|fdopendir| fdopendir(fd)).unwrap_or_else(|| {
                crate::sys::unix::os::set_errno(libc::ENOSYS);
                crate::ptr::null_mut()
            })
        }

        pub unsafe fn unlinkat(dirfd: c_int, pathname: *const c_char, flags: c_int) -> c_int {
            weak!(fn unlinkat(c_int, *const c_char, c_int) -> c_int);
            unlinkat.get().map(|unlinkat| unlinkat(dirfd, pathname, flags)).unwrap_or_else(|| {
                crate::sys::unix::os::set_errno(libc::ENOSYS);
                -1
            })
        }
    }

    pub fn openat_nofollow_dironly(parent_fd: Option<RawFd>, p: &CStr) -> io::Result<OwnedFd> {
        let fd = cvt_r(|| unsafe {
            openat(
                parent_fd.unwrap_or(libc::AT_FDCWD),
                p.as_ptr(),
                libc::O_CLOEXEC | libc::O_RDONLY | libc::O_NOFOLLOW | libc::O_DIRECTORY,
            )
        })?;
        Ok(unsafe { OwnedFd::from_raw_fd(fd) })
    }

    fn fdreaddir(dir_fd: OwnedFd) -> io::Result<(ReadDir, RawFd)> {
        let ptr = unsafe { fdopendir(dir_fd.as_raw_fd()) };
        if ptr.is_null() {
            return Err(io::Error::last_os_error());
        }
        let dirp = Dir(ptr);
        // file descriptor is automatically closed by libc::closedir() now, so give up ownership
        let new_parent_fd = dir_fd.into_raw_fd();
        // a valid root is not needed because we do not call any functions involving the full path
        // of the `DirEntry`s.
        let dummy_root = PathBuf::new();
        let inner = InnerReadDir { dirp, root: dummy_root };
        Ok((ReadDir::new(inner), new_parent_fd))
    }

    #[cfg(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks",
    ))]
    fn is_dir(_ent: &DirEntry) -> Option<bool> {
        None
    }

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks",
    )))]
    fn is_dir(ent: &DirEntry) -> Option<bool> {
        match ent.entry.d_type {
            libc::DT_UNKNOWN => None,
            libc::DT_DIR => Some(true),
            _ => Some(false),
        }
    }

    fn remove_dir_all_recursive(parent_fd: Option<RawFd>, path: &CStr) -> io::Result<()> {
        // try opening as directory
        let fd = match openat_nofollow_dironly(parent_fd, &path) {
            Err(err) if matches!(err.raw_os_error(), Some(libc::ENOTDIR | libc::ELOOP)) => {
                // not a directory - don't traverse further
                // (for symlinks, older Linux kernels may return ELOOP instead of ENOTDIR)
                return match parent_fd {
                    // unlink...
                    Some(parent_fd) => {
                        cvt(unsafe { unlinkat(parent_fd, path.as_ptr(), 0) }).map(drop)
                    }
                    // ...unless this was supposed to be the deletion root directory
                    None => Err(err),
                };
            }
            result => result?,
        };

        // open the directory passing ownership of the fd
        let (dir, fd) = fdreaddir(fd)?;
        for child in dir {
            let child = child?;
            let child_name = child.name_cstr();
            match is_dir(&child) {
                Some(true) => {
                    remove_dir_all_recursive(Some(fd), child_name)?;
                }
                Some(false) => {
                    cvt(unsafe { unlinkat(fd, child_name.as_ptr(), 0) })?;
                }
                None => {
                    // POSIX specifies that calling unlink()/unlinkat(..., 0) on a directory can succeed
                    // if the process has the appropriate privileges. This however can causing orphaned
                    // directories requiring an fsck e.g. on Solaris and Illumos. So we try recursing
                    // into it first instead of trying to unlink() it.
                    remove_dir_all_recursive(Some(fd), child_name)?;
                }
            }
        }

        // unlink the directory after removing its contents
        cvt(unsafe {
            unlinkat(parent_fd.unwrap_or(libc::AT_FDCWD), path.as_ptr(), libc::AT_REMOVEDIR)
        })?;
        Ok(())
    }

    fn remove_dir_all_modern(p: &Path) -> io::Result<()> {
        // We cannot just call remove_dir_all_recursive() here because that would not delete a passed
        // symlink. No need to worry about races, because remove_dir_all_recursive() does not recurse
        // into symlinks.
        let attr = lstat(p)?;
        if attr.file_type().is_symlink() {
            crate::fs::remove_file(p)
        } else {
            run_path_with_cstr(p, |p| remove_dir_all_recursive(None, &p))
        }
    }

    #[cfg(not(all(target_os = "macos", not(target_arch = "aarch64"))))]
    pub fn remove_dir_all(p: &Path) -> io::Result<()> {
        remove_dir_all_modern(p)
    }

    #[cfg(all(target_os = "macos", not(target_arch = "aarch64")))]
    pub fn remove_dir_all(p: &Path) -> io::Result<()> {
        if macos_weak::has_openat() {
            // openat() is available with macOS 10.10+, just like unlinkat() and fdopendir()
            remove_dir_all_modern(p)
        } else {
            // fall back to classic implementation
            crate::sys_common::fs::remove_dir_all(p)
        }
    }
}