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

use crate::ffi::{CStr, CString, OsStr, OsString};
use crate::fmt;
use crate::io::{self, Error, IoSlice, IoSliceMut, ReadBuf, SeekFrom};
use crate::mem;
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::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",
))]
use crate::sys::weak::syscall;
#[cfg(target_os = "macos")]
use crate::sys::weak::weak;

use libc::{c_int, mode_t};

#[cfg(any(
    target_os = "macos",
    target_os = "ios",
    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(not(any(
    target_os = "linux",
    target_os = "emscripten",
    target_os = "solaris",
    target_os = "illumos",
    target_os = "l4re",
    target_os = "fuchsia",
    target_os = "redox"
)))]
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, readdir64_r, stat64,
};

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

pub struct File(FileDesc);

// FIXME: Linux 和所有 `target_env` 上都应该可用。
// 但是目前只有 glibc 公开 `statx` fn 和结构体。
// 我们不想在这里直接导入未经验证的原始 C 结构体。
// 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 {
        // 这是检查文件系统是否支持 btime 所必需的。
        stx_mask: u32,
        stx_btime: libc::statx_timestamp,
    }

    // 如果可用，我们更喜欢 Linux 上的 `statx`，它包含文件创建时间。
    // 默认 `stat64` 不包含创建时间。
    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};

        // 4.11 之前的 Linux 内核或 glibc 之前的 glibc 2.28 不支持 `statx`，我们将可用性存储在全局中，以避免不必要的系统调用。
        //
        // 0: Unknown
        // 1: 无法使用
        // 2: Available
        static STATX_STATE: AtomicU8 = AtomicU8::new(0);
        syscall! {
            fn statx(
                fd: c_int,
                pathname: *const c_char,
                flags: c_int,
                mask: libc::c_uint,
                statxbuf: *mut libc::statx
            ) -> c_int
        }

        match STATX_STATE.load(Ordering::Relaxed) {
            0 => {
                // 这是一个用空指针调用 `statx` 来检查系统调用是否可用的技巧。
                // 根据手册，预期会因 EFAULT 而失败。
                // 我们这样做主要是为了提高性能，因为它比正常的成功调用快近数百倍。
                //
                let err = cvt(statx(0, ptr::null(), 0, libc::STATX_ALL, ptr::null_mut()))
                    .err()
                    .and_then(|e| e.raw_os_error());
                // 我们不检查 `err == Some(libc::ENOSYS)`，因为系统调用可能受到限制并返回 `EPERM`。
                // 列出所有可能的错误似乎不是一个好主意。
                // 请参见：https://github.com/rust-lang/rust/issues/65662
                if err != Some(libc::EFAULT) {
                    STATX_STATE.store(1, Ordering::Relaxed);
                    return None;
                }
                STATX_STATE.store(2, Ordering::Relaxed);
            }
            1 => return None,
            _ => {}
        }

        let mut buf: libc::statx = mem::zeroed();
        if let Err(err) = cvt(statx(fd, path, flags, mask, &mut buf)) {
            return Some(Err(err));
        }

        // 由于专用的填充字段，我们无法详尽地填充 `stat64`。
        let mut stat: stat64 = mem::zeroed();
        // 在 gnu-mips 上使用 `c_ulong`，否则使用 `dev_t`
        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;
        // 在 `i64` 上使用 gnu-x86_64-x32 上，否则使用 `c_ulong`。
        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,
        };

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

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

// 所有 DirEntry 都会对此结构体进行引用
struct InnerReadDir {
    dirp: Dir,
    root: PathBuf,
}

pub struct ReadDir {
    inner: Arc<InnerReadDir>,
    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox",
    )))]
    end_of_stream: bool,
}

struct Dir(*mut libc::DIR);

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

pub struct DirEntry {
    entry: dirent64,
    dir: Arc<InnerReadDir>,
    // 我们需要在 Solaris 和 Fuchsia 上存储条目名称的拥有副本，因为 a) 它使用零长度数组存储名称，b) 不能保证 readdir 调用之间的生命周期。
    //
    //
    //
    #[cfg(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox"
    ))]
    name: CString,
}

#[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, PartialEq, Eq, Hash, Debug)]
pub struct FileType {
    mode: mode_t,
}

#[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 }
        }
    }
} 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::from(libc::timespec {
            tv_sec: self.stat.st_mtime as libc::time_t,
            tv_nsec: self.stat.st_mtimensec as libc::c_long,
        }))
    }

    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_atime as libc::time_t,
            tv_nsec: self.stat.st_atimensec as libc::c_long,
        }))
    }

    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_birthtime as libc::time_t,
            tv_nsec: self.stat.st_birthtimensec as libc::c_long,
        }))
    }
}

#[cfg(not(target_os = "netbsd"))]
impl FileAttr {
    #[cfg(all(not(target_os = "vxworks"), not(target_os = "espidf")))]
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_mtime as libc::time_t,
            tv_nsec: self.stat.st_mtime_nsec as _,
        }))
    }

    #[cfg(any(target_os = "vxworks", target_os = "espidf"))]
    pub fn modified(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_mtime as libc::time_t,
            tv_nsec: 0,
        }))
    }

    #[cfg(all(not(target_os = "vxworks"), not(target_os = "espidf")))]
    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_atime as libc::time_t,
            tv_nsec: self.stat.st_atime_nsec as _,
        }))
    }

    #[cfg(any(target_os = "vxworks", target_os = "espidf"))]
    pub fn accessed(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_atime as libc::time_t,
            tv_nsec: 0,
        }))
    }

    #[cfg(any(
        target_os = "freebsd",
        target_os = "openbsd",
        target_os = "macos",
        target_os = "ios"
    ))]
    pub fn created(&self) -> io::Result<SystemTime> {
        Ok(SystemTime::from(libc::timespec {
            tv_sec: self.stat.st_birthtime as libc::time_t,
            tv_nsec: self.stat.st_birthtime_nsec as libc::c_long,
        }))
    }

    #[cfg(not(any(
        target_os = "freebsd",
        target_os = "openbsd",
        target_os = "macos",
        target_os = "ios"
    )))]
    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::from(libc::timespec {
                        tv_sec: ext.stx_btime.tv_sec as libc::time_t,
                        tv_nsec: ext.stx_btime.tv_nsec as _,
                    }))
                } else {
                    Err(io::Error::new_const(
                        io::ErrorKind::Uncategorized,
                        &"creation time is not available for the filesystem",
                    ))
                };
            }
        }

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

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

impl FilePermissions {
    pub fn readonly(&self) -> bool {
        // 检查是否有任何类 (所有者，组，其他) 具有写权限
        self.mode & 0o222 == 0
    }

    pub fn set_readonly(&mut self, readonly: bool) {
        if readonly {
            // 删除所有类的写权限； 相当于 `chmod a-w <file>`
            self.mode &= !0o222;
        } else {
            // 为所有类添加写权限； 相当于 `chmod a+w <file>`
            self.mode |= 0o222;
        }
    }
    pub fn mode(&self) -> u32 {
        self.mode as u32
    }
}

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.mode & libc::S_IFMT == mode
    }
}

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 {
        // 这只能从 std::fs::ReadDir 调用，std::fs::ReadDir 将添加 "ReadDir()" 框架。
        // 因此结果将是例如 'ReadDir("/home")'
        fmt::Debug::fmt(&*self.inner.root, f)
    }
}

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

    #[cfg(any(
        target_os = "solaris",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "illumos"
    ))]
    fn next(&mut self) -> Option<io::Result<DirEntry>> {
        unsafe {
            loop {
                // 尽管 readdir_r(3) 由于线程安全而在此处使用是正确的函数，但在 Illumos 和 Fuchsia 上，readdir(3C) 函数在线程应用程序中可以安全使用，并且通常比 readdir_r(3C) 函数更可取。
                //
                //
                //
                super::os::set_errno(0);
                let entry_ptr = libc::readdir(self.inner.dirp.0);
                if entry_ptr.is_null() {
                    // null 可能意味着到达终点或发生错误。
                    // 因此，我们必须事先清除 errno 才能检查错误。
                    return match super::os::errno() {
                        0 => None,
                        e => Some(Err(Error::from_raw_os_error(e))),
                    };
                }

                let ret = DirEntry {
                    entry: *entry_ptr,
                    // d_name 保证以 null 值结尾。
                    name: CStr::from_ptr((*entry_ptr).d_name.as_ptr()).to_owned(),
                    dir: Arc::clone(&self.inner),
                };
                if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                    return Some(Ok(ret));
                }
            }
        }
    }

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "fuchsia",
        target_os = "redox",
        target_os = "illumos"
    )))]
    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() {
                        // 我们遇到了一个错误 (将在此迭代中返回)，但我们也到达了目录流的末尾。
                        // `end_of_stream` 标志已启用，以确保我们在下一次迭代中返回 `None` (而不是永远循环)
                        //
                        //
                        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) };
        debug_assert_eq!(r, 0);
    }
}

impl DirEntry {
    pub fn path(&self) -> PathBuf {
        self.dir.root.join(OsStr::from_bytes(self.name_bytes()))
    }

    pub fn file_name(&self) -> OsString {
        OsStr::from_bytes(self.name_bytes()).to_os_string()
    }

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

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

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks"
    )))]
    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 }),
            _ => lstat(&self.path()).map(|m| m.file_type()),
        }
    }

    #[cfg(any(
        target_os = "macos",
        target_os = "ios",
        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"
    ))]
    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 = "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(any(
        target_os = "android",
        target_os = "linux",
        target_os = "emscripten",
        target_os = "l4re",
        target_os = "haiku",
        target_os = "vxworks",
        target_os = "espidf"
    ))]
    fn name_bytes(&self) -> &[u8] {
        unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()).to_bytes() }
    }
    #[cfg(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox"
    ))]
    fn name_bytes(&self) -> &[u8] {
        self.name.as_bytes()
    }

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "fuchsia",
        target_os = "redox"
    )))]
    fn name_cstr(&self) -> &CStr {
        unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()) }
    }
    #[cfg(any(target_os = "solaris", target_os = "illumos", target_os = "fuchsia"))]
    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> {
        let path = cstr(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);
        // `open64` 的第三个参数记录为具有 `mode_t` 类型。在某些平台上 (例如 macOS，其中 `open64` 实际上是 `open`)，`mode_t` 是 `u16`。
        // 但是，由于这是一个可变参数，C 整数提升规则意味着在 ABI 级别上，它仍会作为 `c_int` (在 Unix 平台上称为 `u32`) 传递。
        //
        //
        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"))]
        unsafe fn os_fsync(fd: c_int) -> c_int {
            libc::fcntl(fd, libc::F_FULLFSYNC)
        }
        #[cfg(not(any(target_os = "macos", target_os = "ios")))]
        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"))]
        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"
        ))]
        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 = "linux",
            target_os = "macos",
            target_os = "netbsd",
            target_os = "openbsd"
        )))]
        unsafe fn os_datasync(fd: c_int) -> c_int {
            libc::fsync(fd)
        }
    }

    pub fn truncate(&self, size: u64) -> io::Result<()> {
        use crate::convert::TryInto;
        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, buf: &mut ReadBuf<'_>) -> io::Result<()> {
        self.0.read_buf(buf)
    }

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

    pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
        let (whence, pos) = match pos {
            // 强制转换为 `i64`，太大的值最终将变为负数，这将导致 `lseek64` 中的错误。
            //
            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, 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(())
    }
}

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

    pub fn mkdir(&self, p: &Path) -> io::Result<()> {
        let p = cstr(p)?;
        cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) })?;
        Ok(())
    }

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

fn cstr(path: &Path) -> io::Result<CString> {
    Ok(CString::new(path.as_os_str().as_bytes())?)
}

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

impl AsInnerMut<FileDesc> for File {
    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 {
    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"))]
        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: 通常不鼓励使用 PATH_MAX，但是在这种情况下，这是不可避免的，因为 macOS 根据 `MAXPATHLEN` 定义了 `fcntl` 和 `F_GETPATH`，并且没有其他选择。
            // 如果发明了更好的方法，则应改用它。
            //
            //
            //
            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(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",
            target_os = "netbsd"
        )))]
        fn get_path(_fd: c_int) -> Option<PathBuf> {
            // FIXME(#24570): 在其他 Unix 平台上实现此功能
            None
        }

        #[cfg(any(target_os = "linux", target_os = "macos", 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 = "vxworks")))]
        fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
            // FIXME(#24570): 在其他 Unix 平台上实现此功能
            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(p: &Path) -> io::Result<ReadDir> {
    let root = p.to_path_buf();
    let p = cstr(p)?;
    unsafe {
        let ptr = libc::opendir(p.as_ptr());
        if ptr.is_null() {
            Err(Error::last_os_error())
        } else {
            let inner = InnerReadDir { dirp: Dir(ptr), root };
            Ok(ReadDir {
                inner: Arc::new(inner),
                #[cfg(not(any(
                    target_os = "solaris",
                    target_os = "illumos",
                    target_os = "fuchsia",
                    target_os = "redox",
                )))]
                end_of_stream: false,
            })
        }
    }
}

pub fn unlink(p: &Path) -> io::Result<()> {
    let p = cstr(p)?;
    cvt(unsafe { libc::unlink(p.as_ptr()) })?;
    Ok(())
}

pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
    let old = cstr(old)?;
    let new = cstr(new)?;
    cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) })?;
    Ok(())
}

pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
    let p = cstr(p)?;
    cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) })?;
    Ok(())
}

pub fn rmdir(p: &Path) -> io::Result<()> {
    let p = cstr(p)?;
    cvt(unsafe { libc::rmdir(p.as_ptr()) })?;
    Ok(())
}

pub fn readlink(p: &Path) -> io::Result<PathBuf> {
    let c_path = cstr(p)?;
    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)));
        }

        // 通过需要比当前容量更多的空间来触发 `Vec` 的内部缓冲区大小调整逻辑。
        // 由于上面的 if 语句，长度保证与容量相同。
        //
        buf.reserve(1);
    }
}

pub fn symlink(original: &Path, link: &Path) -> io::Result<()> {
    let original = cstr(original)?;
    let link = cstr(link)?;
    cvt(unsafe { libc::symlink(original.as_ptr(), link.as_ptr()) })?;
    Ok(())
}

pub fn link(original: &Path, link: &Path) -> io::Result<()> {
    let original = cstr(original)?;
    let link = cstr(link)?;
    cfg_if::cfg_if! {
        if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf"))] {
            // VxWorks、Redox 和 ESP-IDF 缺少 `linkat`，因此请使用 `link`。
            // POSIX 保留 `link` 是否遵循符号链接的实现定义，因此依靠 library/std/src/fs/tests.rs 中的 `symlink_hard_link` 测试来检查行为。
            //
            // Android 在较新版本上有 `linkat`，但我们碰巧知道 `link` 总是具有正确的行为，所以它也在这里。
            //
            cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
        } else if #[cfg(target_os = "macos")] {
            // 在 MacOS 上，旧版本的 (<=10.9) 缺乏对 linkat 的支持，而较新的版本有它。
            // 我们想使用 linkat，如果它可用，所以我们使用 weak!
            // 去检查。`linkat` 比 `link` 更可取，因为它给了我们一个标志来指定应该如何处理符号链接。
            //
            // 我们将 0 作为标志 Parameter 传递，这意味着它不应该遵循符号链接。
            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 {
            // 在我们可以的情况下，使用 `linkat` 代替 `link`； 有关原因的详细信息，请参见此评论上方的评论。
            //
            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> {
    let p = cstr(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> {
    let p = cstr(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 path = CString::new(p.as_os_str().as_bytes())?;
    let buf;
    unsafe {
        let r = libc::realpath(path.as_ptr(), ptr::null_mut());
        if r.is_null() {
            return Err(io::Error::last_os_error());
        }
        buf = CStr::from_ptr(r).to_bytes().to_vec();
        libc::free(r as *mut _);
    }
    Ok(PathBuf::from(OsString::from_vec(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()
        // 立即以正确的模式创建文件
        .mode(perm.mode())
        .write(true)
        .create(true)
        .truncate(true)
        .open(to)?;
    let writer_metadata = writer.metadata()?;
    if writer_metadata.is_file() {
        // 如果文件已经存在，请设置正确的文件许可权。
        // 不要在已经存在的非文件 (例如 pipes/FIFOs 或设备节点) 上设置权限。
        //
        writer.set_permissions(perm)?;
    }
    Ok((writer, writer_metadata))
}

#[cfg(not(any(
    target_os = "linux",
    target_os = "android",
    target_os = "macos",
    target_os = "ios"
)))]
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"))]
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) {
            // 下面的代码确保 `FreeOnDrop` 永远不会为空指针
            unsafe {
                // 如果 `to` 或 `from` 文件无法关闭，`copyfile_state_free` 将返回 -1。
                // 但是，这不被视为错误。
                //
                copyfile_state_free(self.0);
            }
        }
    }

    // 10.12 之前的 MacOS 不支持 `fclonefileat` 我们将可用性存储在一个全局中，以避免不必要的系统调用
    //
    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)?;

    // 机会性地尝试使用 `fclonefileat` 创建 `from` 的写时复制副本。
    //
    if HAS_FCLONEFILEAT.load(Ordering::Relaxed) {
        let to = cstr(to)?;
        let clonefile_result =
            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() {
                // 如果目标已经存在，或者如果源和目标位于不同的设备上，则 `fclonefileat` 将在非 APFS 卷上失败。
                // 在所有这些情况下，`fcopyfile` 应该会成功。
                //
                //
                Some(libc::ENOTSUP) | Some(libc::EEXIST) | Some(libc::EXDEV) => (),
                Some(libc::ENOSYS) => HAS_FCLONEFILEAT.store(false, Ordering::Relaxed),
                _ => return Err(err),
            },
        }
    }

    // 如果 `fclonefileat` 不成功，则回退到使用 `fcopyfile`。
    let (writer, writer_metadata) = open_to_and_set_permissions(to, reader_metadata)?;

    // 我们确保 `FreeOnDrop` 绝不包含空指针，因此调用 `copyfile_state_free` 始终是安全的
    //
    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<()> {
    let path = cstr(path)?;
    cvt(unsafe { libc::chown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })?;
    Ok(())
}

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<()> {
    let path = cstr(path)?;
    cvt(unsafe { libc::lchown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })?;
    Ok(())
}

#[cfg(not(any(target_os = "fuchsia", target_os = "vxworks")))]
pub fn chroot(dir: &Path) -> io::Result<()> {
    let dir = cstr(dir)?;
    cvt(unsafe { libc::chroot(dir.as_ptr()) })?;
    Ok(())
}

pub use remove_dir_impl::remove_dir_all;

// REDOX 的后备方案
#[cfg(target_os = "redox")]
mod remove_dir_impl {
    pub use crate::sys_common::fs::remove_dir_all;
}

// 动态选择实现 Macos x86-64: 现代的用于 10.10+，回退的用于旧版本
#[cfg(all(target_os = "macos", target_arch = "x86_64"))]
mod remove_dir_impl {
    use super::{cstr, lstat, Dir, 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::sync::Arc;
    use crate::sys::weak::weak;
    use crate::sys::{cvt, cvt_r};
    use libc::{c_char, c_int, DIR};

    pub fn openat_nofollow_dironly(parent_fd: Option<RawFd>, p: &CStr) -> io::Result<OwnedFd> {
        weak!(fn openat(c_int, *const c_char, c_int) -> c_int);
        let fd = cvt_r(|| unsafe {
            openat.get().unwrap()(
                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)> {
        weak!(fn fdopendir(c_int) -> *mut DIR, "fdopendir$INODE64");
        let ptr = unsafe { fdopendir.get().unwrap()(dir_fd.as_raw_fd()) };
        if ptr.is_null() {
            return Err(io::Error::last_os_error());
        }
        let dirp = Dir(ptr);
        // 文件描述符现在被 libc::closedir() 自动关闭，所以放弃所有权
        let new_parent_fd = dir_fd.into_raw_fd();
        // 不需要有效的根，因为我们不调用任何涉及 DirEntrys 完整路径的函数。
        //
        let dummy_root = PathBuf::new();
        Ok((
            ReadDir {
                inner: Arc::new(InnerReadDir { dirp, root: dummy_root }),
                end_of_stream: false,
            },
            new_parent_fd,
        ))
    }

    fn remove_dir_all_recursive(parent_fd: Option<RawFd>, p: &Path) -> io::Result<()> {
        weak!(fn unlinkat(c_int, *const c_char, c_int) -> c_int);

        let pcstr = cstr(p)?;

        // entry 应该是一个目录，这样打开
        let fd = openat_nofollow_dironly(parent_fd, &pcstr)?;

        // 打开传递 fd 所有权的目录
        let (dir, fd) = fdreaddir(fd)?;
        for child in dir {
            let child = child?;
            match child.entry.d_type {
                libc::DT_DIR => {
                    remove_dir_all_recursive(Some(fd), Path::new(&child.file_name()))?;
                }
                libc::DT_UNKNOWN => {
                    match cvt(unsafe { unlinkat.get().unwrap()(fd, child.name_cstr().as_ptr(), 0) })
                    {
                        // 类型未知 - 尝试取消链接
                        Err(err) if err.raw_os_error() == Some(libc::EPERM) => {
                            // 如果文件是目录，则取消链接失败并显示 EPERM
                            remove_dir_all_recursive(Some(fd), Path::new(&child.file_name()))?;
                        }
                        result => {
                            result?;
                        }
                    }
                }
                _ => {
                    // 不是目录 -> 取消链接
                    cvt(unsafe { unlinkat.get().unwrap()(fd, child.name_cstr().as_ptr(), 0) })?;
                }
            }
        }

        // 删除目录后，取消对目录的链接
        cvt(unsafe {
            unlinkat.get().unwrap()(
                parent_fd.unwrap_or(libc::AT_FDCWD),
                pcstr.as_ptr(),
                libc::AT_REMOVEDIR,
            )
        })?;
        Ok(())
    }

    fn remove_dir_all_modern(p: &Path) -> io::Result<()> {
        // 我们不能在这里只调用 remove_dir_all_recursive()，因为这不会删除传递的符号链接。
        // 无需担心比赛，因为 remove_dir_all_recursive() 不会递归到符号链接中。
        //
        let attr = lstat(p)?;
        if attr.file_type().is_symlink() {
            crate::fs::remove_file(p)
        } else {
            remove_dir_all_recursive(None, p)
        }
    }

    pub fn remove_dir_all(p: &Path) -> io::Result<()> {
        weak!(fn openat(c_int, *const c_char, c_int) -> c_int);
        if openat.get().is_some() {
            // openat() 适用于 macOS 10.10+，就像 unlinkat() 和 fdopendir()
            remove_dir_all_modern(p)
        } else {
            // 回退到经典实现
            crate::sys_common::fs::remove_dir_all(p)
        }
    }
}

// 使用 openat()、unlinkat() 和 fdopendir() 的现代实现
#[cfg(not(any(all(target_os = "macos", target_arch = "x86_64"), target_os = "redox")))]
mod remove_dir_impl {
    use super::{cstr, 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::sync::Arc;
    use crate::sys::{cvt, cvt_r};
    use libc::{fdopendir, openat, unlinkat};

    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);
        // 文件描述符现在被 libc::closedir() 自动关闭，所以放弃所有权
        let new_parent_fd = dir_fd.into_raw_fd();
        // 不需要有效的根，因为我们不调用任何涉及 DirEntrys 完整路径的函数。
        //
        let dummy_root = PathBuf::new();
        Ok((
            ReadDir {
                inner: Arc::new(InnerReadDir { dirp, root: dummy_root }),
                #[cfg(not(any(
                    target_os = "solaris",
                    target_os = "illumos",
                    target_os = "fuchsia",
                    target_os = "redox",
                )))]
                end_of_stream: false,
            },
            new_parent_fd,
        ))
    }

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

    #[cfg(not(any(
        target_os = "solaris",
        target_os = "illumos",
        target_os = "haiku",
        target_os = "vxworks",
        target_os = "fuchsia"
    )))]
    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>, p: &Path) -> io::Result<()> {
        let pcstr = cstr(p)?;

        // entry 应该是一个目录，这样打开
        let fd = openat_nofollow_dironly(parent_fd, &pcstr)?;

        // 打开传递 fd 所有权的目录
        let (dir, fd) = fdreaddir(fd)?;
        for child in dir {
            let child = child?;
            match is_dir(&child) {
                Some(true) => {
                    remove_dir_all_recursive(Some(fd), Path::new(&child.file_name()))?;
                }
                Some(false) => {
                    cvt(unsafe { unlinkat(fd, child.name_cstr().as_ptr(), 0) })?;
                }
                None => match cvt(unsafe { unlinkat(fd, child.name_cstr().as_ptr(), 0) }) {
                    // 类型未知 - 尝试取消链接
                    Err(err)
                        if err.raw_os_error() == Some(libc::EISDIR)
                            || err.raw_os_error() == Some(libc::EPERM) =>
                    {
                        // 如果文件是一个目录，Linux 和 EPERM 上的 EISDIR 在其他任何地方都无法取消链接
                        remove_dir_all_recursive(Some(fd), Path::new(&child.file_name()))?;
                    }
                    result => {
                        result?;
                    }
                },
            }
        }

        // 删除目录后，取消对目录的链接
        cvt(unsafe {
            unlinkat(parent_fd.unwrap_or(libc::AT_FDCWD), pcstr.as_ptr(), libc::AT_REMOVEDIR)
        })?;
        Ok(())
    }

    pub fn remove_dir_all(p: &Path) -> io::Result<()> {
        // 我们不能在这里只调用 remove_dir_all_recursive()，因为这不会删除传递的符号链接。
        // 无需担心比赛，因为 remove_dir_all_recursive() 不会递归到符号链接中。
        //
        let attr = lstat(p)?;
        if attr.file_type().is_symlink() {
            crate::fs::remove_file(p)
        } else {
            remove_dir_all_recursive(None, p)
        }
    }
}