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    // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

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

    use ffi::{CString, CStr, OsString, OsStr};
    use fmt;
    use io::{self, Error, ErrorKind, SeekFrom};
    use libc::{self, c_int, mode_t};
    use mem;
    use path::{Path, PathBuf};
    use ptr;
    use sync::Arc;
    use sys::fd::FileDesc;
    use sys::time::SystemTime;
    use sys::{cvt, cvt_r};
    use sys_common::{AsInner, FromInner};

    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))]
    use libc::{stat64, fstat64, lstat64, off64_t, ftruncate64, lseek64, dirent64, readdir64_r, open64};
    #[cfg(any(target_os = "linux", target_os = "emscripten"))]
    use libc::fstatat64;
    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
    use libc::dirfd;
    #[cfg(target_os = "android")]
    use libc::{stat as stat64, fstat as fstat64, fstatat as fstatat64, lstat as lstat64, lseek64,
               dirent as dirent64, open as open64};
    #[cfg(not(any(target_os = "linux",
                  target_os = "emscripten",
                  target_os = "l4re",
                  target_os = "android")))]
    use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, off_t as off64_t,
               ftruncate as ftruncate64, lseek as lseek64, dirent as dirent64, open as open64};
    #[cfg(not(any(target_os = "linux",
                  target_os = "emscripten",
                  target_os = "solaris",
                  target_os = "l4re",
                  target_os = "fuchsia")))]
    use libc::{readdir_r as readdir64_r};

    pub struct File(FileDesc);

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

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

    #[derive(Clone)]
    pub struct ReadDir(Arc<InnerReadDir>);

    struct Dir(*mut libc::DIR);

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

    pub struct DirEntry {
        entry: dirent64,
        dir: ReadDir,
        // We need to store an owned copy of the entry name
        // on Solaris and Fuchsia because a) it uses a zero-length
        // array to store the name, b) its lifetime between readdir
        // calls is not guaranteed.
        #[cfg(any(target_os = "solaris", target_os = "fuchsia"))]
        name: Box<[u8]>
    }

    #[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 }

    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 {
        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 _,
            }))
        }

        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 = "bitrig",
                  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 = "bitrig",
                      target_os = "freebsd",
                      target_os = "openbsd",
                      target_os = "macos",
                      target_os = "ios")))]
        pub fn created(&self) -> io::Result<SystemTime> {
            Err(io::Error::new(io::ErrorKind::Other,
                               "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 {
            // 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 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 {
            // 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.0.root, f)
        }
    }

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

        #[cfg(any(target_os = "solaris", target_os = "fuchsia"))]
        fn next(&mut self) -> Option<io::Result<DirEntry>> {
            unsafe {
                loop {
                    // Although readdir_r(3) would be a correct function to use here because
                    // of the thread safety, on Illumos and Fuchsia the readdir(3C) function
                    // is safe to use in threaded applications and it is generally preferred
                    // over the readdir_r(3C) function.
                    super::os::set_errno(0);
                    let entry_ptr = libc::readdir(self.0.dirp.0);
                    if entry_ptr.is_null() {
                        // NULL can mean either the end is reached or an error occurred.
                        // So 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))),
                        }
                    }

                    let name = (*entry_ptr).d_name.as_ptr();
                    let namelen = libc::strlen(name) as usize;

                    let ret = DirEntry {
                        entry: *entry_ptr,
                        name: ::slice::from_raw_parts(name as *const u8,
                                                      namelen as usize).to_owned().into_boxed_slice(),
                        dir: self.clone()
                    };
                    if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                        return Some(Ok(ret))
                    }
                }
            }
        }

        #[cfg(not(any(target_os = "solaris", target_os = "fuchsia")))]
        fn next(&mut self) -> Option<io::Result<DirEntry>> {
            unsafe {
                let mut ret = DirEntry {
                    entry: mem::zeroed(),
                    dir: self.clone(),
                };
                let mut entry_ptr = ptr::null_mut();
                loop {
                    if readdir64_r(self.0.dirp.0, &mut ret.entry, &mut entry_ptr) != 0 {
                        return Some(Err(Error::last_os_error()))
                    }
                    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.0.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.0.dirp.0)})?;
            let mut stat: stat64 = unsafe { mem::zeroed() };
            cvt(unsafe {
                fstatat64(fd, self.entry.d_name.as_ptr(), &mut stat, libc::AT_SYMLINK_NOFOLLOW)
            })?;
            Ok(FileAttr { stat: 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 = "haiku"))]
        pub fn file_type(&self) -> io::Result<FileType> {
            lstat(&self.path()).map(|m| m.file_type())
        }

        #[cfg(not(any(target_os = "solaris", target_os = "haiku")))]
        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 = "haiku",
                  target_os = "l4re",
                  target_os = "fuchsia"))]
        pub fn ino(&self) -> u64 {
            self.entry.d_ino as u64
        }

        #[cfg(any(target_os = "freebsd",
                  target_os = "openbsd",
                  target_os = "bitrig",
                  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",
                  target_os = "bitrig"))]
        fn name_bytes(&self) -> &[u8] {
            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"))]
        fn name_bytes(&self) -> &[u8] {
            unsafe {
                CStr::from_ptr(self.entry.d_name.as_ptr()).to_bytes()
            }
        }
        #[cfg(any(target_os = "solaris",
                  target_os = "fuchsia"))]
        fn name_bytes(&self) -> &[u8] {
            &*self.name
        }
    }

    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);
            let fd = cvt_r(|| unsafe {
                open64(path.as_ptr(), flags, opts.mode as c_int)
            })?;
            let fd = FileDesc::new(fd);

            // Currently the standard library supports Linux 2.6.18 which did not
            // have the O_CLOEXEC flag (passed above). If we're running on an older
            // Linux kernel then the flag is just ignored by the OS. After we open
            // the first file, we check whether it has CLOEXEC set. If it doesn't,
            // we will explicitly ask for a CLOEXEC fd for every further file we
            // open, if it does, we will skip that step.
            //
            // The CLOEXEC flag, however, is supported on versions of macOS/BSD/etc
            // that we support, so we only do this on Linux currently.
            #[cfg(target_os = "linux")]
            fn ensure_cloexec(fd: &FileDesc) -> io::Result<()> {
                use sync::atomic::{AtomicUsize, Ordering};

                const OPEN_CLOEXEC_UNKNOWN: usize = 0;
                const OPEN_CLOEXEC_SUPPORTED: usize = 1;
                const OPEN_CLOEXEC_NOTSUPPORTED: usize = 2;
                static OPEN_CLOEXEC: AtomicUsize = AtomicUsize::new(OPEN_CLOEXEC_UNKNOWN);

                let need_to_set;
                match OPEN_CLOEXEC.load(Ordering::Relaxed) {
                    OPEN_CLOEXEC_UNKNOWN => {
                        need_to_set = !fd.get_cloexec()?;
                        OPEN_CLOEXEC.store(if need_to_set {
                            OPEN_CLOEXEC_NOTSUPPORTED
                        } else {
                            OPEN_CLOEXEC_SUPPORTED
                        }, Ordering::Relaxed);
                    },
                    OPEN_CLOEXEC_SUPPORTED => need_to_set = false,
                    OPEN_CLOEXEC_NOTSUPPORTED => need_to_set = true,
                    _ => unreachable!(),
                }
                if need_to_set {
                    fd.set_cloexec()?;
                }
                Ok(())
            }

            #[cfg(not(target_os = "linux"))]
            fn ensure_cloexec(_: &FileDesc) -> io::Result<()> {
                Ok(())
            }

            ensure_cloexec(&fd)?;
            Ok(File(fd))
        }

        pub fn file_attr(&self) -> io::Result<FileAttr> {
            let mut stat: stat64 = unsafe { mem::zeroed() };
            cvt(unsafe {
                fstat64(self.0.raw(), &mut stat)
            })?;
            Ok(FileAttr { stat: stat })
        }

        pub fn fsync(&self) -> io::Result<()> {
            cvt_r(|| unsafe { libc::fsync(self.0.raw()) })?;
            Ok(())
        }

        pub fn datasync(&self) -> io::Result<()> {
            cvt_r(|| unsafe { os_datasync(self.0.raw()) })?;
            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(target_os = "linux")]
            unsafe fn os_datasync(fd: c_int) -> c_int { libc::fdatasync(fd) }
            #[cfg(not(any(target_os = "macos",
                          target_os = "ios",
                          target_os = "linux")))]
            unsafe fn os_datasync(fd: c_int) -> c_int { libc::fsync(fd) }
        }

        pub fn truncate(&self, size: u64) -> io::Result<()> {
            #[cfg(target_os = "android")]
            return ::sys::android::ftruncate64(self.0.raw(), size);

            #[cfg(not(target_os = "android"))]
            return cvt_r(|| unsafe {
                ftruncate64(self.0.raw(), size as off64_t)
            }).map(|_| ());
        }

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

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

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

        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 {
                // 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),
            };
            #[cfg(target_os = "emscripten")]
            let pos = pos as i32;
            let n = cvt(unsafe { lseek64(self.0.raw(), pos, whence) })?;
            Ok(n as u64)
        }

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

        pub fn fd(&self) -> &FileDesc { &self.0 }

        pub fn into_fd(self) -> FileDesc { self.0 }

        pub fn set_permissions(&self, perm: FilePermissions) -> io::Result<()> {
            cvt_r(|| unsafe { libc::fchmod(self.0.raw(), 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 FromInner<c_int> for File {
        fn from_inner(fd: c_int) -> File {
            File(FileDesc::new(fd))
        }
    }

    impl fmt::Debug for File {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            #[cfg(target_os = "linux")]
            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(not(any(target_os = "linux", target_os = "macos")))]
            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"))]
            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")))]
            fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
                // FIXME(#24570): implement this for other Unix platforms
                None
            }

            let fd = self.0.raw();
            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(Arc::new(inner)))
            }
        }
    }

    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 remove_dir_all(path: &Path) -> io::Result<()> {
        let filetype = lstat(path)?.file_type();
        if filetype.is_symlink() {
            unlink(path)
        } else {
            remove_dir_all_recursive(path)
        }
    }

    fn remove_dir_all_recursive(path: &Path) -> io::Result<()> {
        for child in readdir(path)? {
            let child = child?;
            if child.file_type()?.is_dir() {
                remove_dir_all_recursive(&child.path())?;
            } else {
                unlink(&child.path())?;
            }
        }
        rmdir(path)
    }

    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)));
            }

            // 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(src: &Path, dst: &Path) -> io::Result<()> {
        let src = cstr(src)?;
        let dst = cstr(dst)?;
        cvt(unsafe { libc::symlink(src.as_ptr(), dst.as_ptr()) })?;
        Ok(())
    }

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

    pub fn stat(p: &Path) -> io::Result<FileAttr> {
        let p = cstr(p)?;
        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe {
            stat64(p.as_ptr(), &mut stat as *mut _ as *mut _)
        })?;
        Ok(FileAttr { stat: stat })
    }

    pub fn lstat(p: &Path) -> io::Result<FileAttr> {
        let p = cstr(p)?;
        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe {
            lstat64(p.as_ptr(), &mut stat as *mut _ as *mut _)
        })?;
        Ok(FileAttr { stat: 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)))
    }

    #[cfg(not(any(target_os = "linux", target_os = "android")))]
    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        use fs::File;
        if !from.is_file() {
            return Err(Error::new(ErrorKind::InvalidInput,
                                  "the source path is not an existing regular file"))
        }

        let mut reader = File::open(from)?;
        let mut writer = File::create(to)?;
        let perm = reader.metadata()?.permissions();

        let ret = io::copy(&mut reader, &mut writer)?;
        writer.set_permissions(perm)?;
        Ok(ret)
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        use cmp;
        use fs::File;
        use sync::atomic::{AtomicBool, Ordering};

        // Kernel prior to 4.5 don't have copy_file_range
        // We store the availability in a global to avoid unneccessary syscalls
        static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);

        unsafe fn copy_file_range(
            fd_in: libc::c_int,
            off_in: *mut libc::loff_t,
            fd_out: libc::c_int,
            off_out: *mut libc::loff_t,
            len: libc::size_t,
            flags: libc::c_uint,
        ) -> libc::c_long {
            libc::syscall(
                libc::SYS_copy_file_range,
                fd_in,
                off_in,
                fd_out,
                off_out,
                len,
                flags,
            )
        }

        if !from.is_file() {
            return Err(Error::new(ErrorKind::InvalidInput,
                                  "the source path is not an existing regular file"))
        }

        let mut reader = File::open(from)?;
        let mut writer = File::create(to)?;
        let (perm, len) = {
            let metadata = reader.metadata()?;
            (metadata.permissions(), metadata.size())
        };

        let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
        let mut written = 0u64;
        while written < len {
            let copy_result = if has_copy_file_range {
                let bytes_to_copy = cmp::min(len - written, usize::max_value() as u64) as usize;
                let copy_result = unsafe {
                    // We actually don't have to adjust the offsets,
                    // because copy_file_range adjusts the file offset automatically
                    cvt(copy_file_range(reader.as_raw_fd(),
                                        ptr::null_mut(),
                                        writer.as_raw_fd(),
                                        ptr::null_mut(),
                                        bytes_to_copy,
                                        0)
                        )
                };
                if let Err(ref copy_err) = copy_result {
                    match copy_err.raw_os_error() {
                        Some(libc::ENOSYS) | Some(libc::EPERM) => {
                            HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
                        }
                        _ => {}
                    }
                }
                copy_result
            } else {
                Err(io::Error::from_raw_os_error(libc::ENOSYS))
            };
            match copy_result {
                Ok(ret) => written += ret as u64,
                Err(err) => {
                    match err.raw_os_error() {
                        Some(os_err) if os_err == libc::ENOSYS
                                     || os_err == libc::EXDEV
                                     || os_err == libc::EPERM => {
                            // Try fallback io::copy if either:
                            // - Kernel version is < 4.5 (ENOSYS)
                            // - Files are mounted on different fs (EXDEV)
                            // - copy_file_range is disallowed, for example by seccomp (EPERM)
                            assert_eq!(written, 0);
                            let ret = io::copy(&mut reader, &mut writer)?;
                            writer.set_permissions(perm)?;
                            return Ok(ret)
                        },
                        _ => return Err(err),
                    }
                }
            }
        }
        writer.set_permissions(perm)?;
        Ok(written)
    }

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