Source File
	file_unix.go

Belonging Package
	os

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build unix || (js && wasm) || wasip1

package os

import (
	"internal/poll"
	"internal/syscall/unix"
	"io/fs"
	"runtime"
	"sync/atomic"
	"syscall"
	_ "unsafe" // for go:linkname
)

const _UTIME_OMIT = unix.UTIME_OMIT

// fixLongPath is a noop on non-Windows platforms.
func fixLongPath(path string) string {
	return path
}

func rename(oldname, newname string) error {
	fi, err := Lstat(newname)
	if err == nil && fi.IsDir() {
		// There are two independent errors this function can return:
		// one for a bad oldname, and one for a bad newname.
		// At this point we've determined the newname is bad.
		// But just in case oldname is also bad, prioritize returning
		// the oldname error because that's what we did historically.
		// However, if the old name and new name are not the same, yet
		// they refer to the same file, it implies a case-only
		// rename on a case-insensitive filesystem, which is ok.
		if ofi, err := Lstat(oldname); err != nil {
			if pe, ok := err.(*PathError); ok {
				err = pe.Err
			}
			return &LinkError{"rename", oldname, newname, err}
		} else if newname == oldname || !SameFile(fi, ofi) {
			return &LinkError{"rename", oldname, newname, syscall.EEXIST}
		}
	}
	err = ignoringEINTR(func() error {
		return syscall.Rename(oldname, newname)
	})
	if err != nil {
		return &LinkError{"rename", oldname, newname, err}
	}
	return nil
}

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
	pfd         poll.FD
	name        string
	dirinfo     atomic.Pointer[dirInfo] // nil unless directory being read
	nonblock    bool                    // whether we set nonblocking mode
	stdoutOrErr bool                    // whether this is stdout or stderr
	appendMode  bool                    // whether file is opened for appending
}

// Fd returns the integer Unix file descriptor referencing the open file.
// If f is closed, the file descriptor becomes invalid.
// If f is garbage collected, a finalizer may close the file descriptor,
// making it invalid; see [runtime.SetFinalizer] for more information on when
// a finalizer might be run. On Unix systems this will cause the [File.SetDeadline]
// methods to stop working.
// Because file descriptors can be reused, the returned file descriptor may
// only be closed through the [File.Close] method of f, or by its finalizer during
// garbage collection. Otherwise, during garbage collection the finalizer
// may close an unrelated file descriptor with the same (reused) number.
//
// As an alternative, see the f.SyscallConn method.
func (f *File) Fd() uintptr {
	if f == nil {
		return ^(uintptr(0))
	}

	// If we put the file descriptor into nonblocking mode,
	// then set it to blocking mode before we return it,
	// because historically we have always returned a descriptor
	// opened in blocking mode. The File will continue to work,
	// but any blocking operation will tie up a thread.
	if f.nonblock {
		f.pfd.SetBlocking()
	}

	return uintptr(f.pfd.Sysfd)
}

// NewFile returns a new File with the given file descriptor and
// name. The returned value will be nil if fd is not a valid file
// descriptor. On Unix systems, if the file descriptor is in
// non-blocking mode, NewFile will attempt to return a pollable File
// (one for which the SetDeadline methods work).
//
// After passing it to NewFile, fd may become invalid under the same
// conditions described in the comments of the Fd method, and the same
// constraints apply.
func NewFile(fd uintptr, name string) *File {
	fdi := int(fd)
	if fdi < 0 {
		return nil
	}

	flags, err := unix.Fcntl(fdi, syscall.F_GETFL, 0)
	if err != nil {
		flags = 0
	}
	f := newFile(fdi, name, kindNewFile, unix.HasNonblockFlag(flags))
	f.appendMode = flags&syscall.O_APPEND != 0
	return f
}

// net_newUnixFile is a hidden entry point called by net.conn.File.
// This is used so that a nonblocking network connection will become
// blocking if code calls the Fd method. We don't want that for direct
// calls to NewFile: passing a nonblocking descriptor to NewFile should
// remain nonblocking if you get it back using Fd. But for net.conn.File
// the call to NewFile is hidden from the user. Historically in that case
// the Fd method has returned a blocking descriptor, and we want to
// retain that behavior because existing code expects it and depends on it.
//
//go:linkname net_newUnixFile net.newUnixFile
func net_newUnixFile(fd int, name string) *File {
	if fd < 0 {
		panic("invalid FD")
	}

	return newFile(fd, name, kindSock, true)
}

// newFileKind describes the kind of file to newFile.
type newFileKind int

const (
	// kindNewFile means that the descriptor was passed to us via NewFile.
	kindNewFile newFileKind = iota
	// kindOpenFile means that the descriptor was opened using
	// Open, Create, or OpenFile.
	kindOpenFile
	// kindPipe means that the descriptor was opened using Pipe.
	kindPipe
	// kindSock means that the descriptor is a network file descriptor
	// that was created from net package and was opened using net_newUnixFile.
	kindSock
	// kindNoPoll means that we should not put the descriptor into
	// non-blocking mode, because we know it is not a pipe or FIFO.
	// Used by openDirAt and openDirNolog for directories.
	kindNoPoll
)

// newFile is like NewFile, but if called from OpenFile or Pipe
// (as passed in the kind parameter) it tries to add the file to
// the runtime poller.
func newFile(fd int, name string, kind newFileKind, nonBlocking bool) *File {
	f := &File{&file{
		pfd: poll.FD{
			Sysfd:         fd,
			IsStream:      true,
			ZeroReadIsEOF: true,
		},
		name:        name,
		stdoutOrErr: fd == 1 || fd == 2,
	}}

	pollable := kind == kindOpenFile || kind == kindPipe || kind == kindSock || nonBlocking

	// Things like regular files and FIFOs in kqueue on *BSD/Darwin
	// may not work properly (or accurately according to its manual).
	// As a result, we should avoid adding those to the kqueue-based
	// netpoller. Check out #19093, #24164, and #66239 for more contexts.
	//
	// If the fd was passed to us via any path other than OpenFile,
	// we assume those callers know what they were doing, so we won't
	// perform this check and allow it to be added to the kqueue.
	if kind == kindOpenFile {
		switch runtime.GOOS {
		case "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd":
			var st syscall.Stat_t
			err := ignoringEINTR(func() error {
				return syscall.Fstat(fd, &st)
			})
			typ := st.Mode & syscall.S_IFMT
			// Don't try to use kqueue with regular files on *BSDs.
			// On FreeBSD a regular file is always
			// reported as ready for writing.
			// On Dragonfly, NetBSD and OpenBSD the fd is signaled
			// only once as ready (both read and write).
			// Issue 19093.
			// Also don't add directories to the netpoller.
			if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
				pollable = false
			}

			// In addition to the behavior described above for regular files,
			// on Darwin, kqueue does not work properly with fifos:
			// closing the last writer does not cause a kqueue event
			// for any readers. See issue #24164.
			if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && typ == syscall.S_IFIFO {
				pollable = false
			}
		}
	}

	clearNonBlock := false
	if pollable {
		// The descriptor is already in non-blocking mode.
		// We only set f.nonblock if we put the file into
		// non-blocking mode.
		if nonBlocking {
			// See the comments on net_newUnixFile.
			if kind == kindSock {
				f.nonblock = true // tell Fd to return blocking descriptor
			}
		} else if err := syscall.SetNonblock(fd, true); err == nil {
			f.nonblock = true
			clearNonBlock = true
		} else {
			pollable = false
		}
	}

	// An error here indicates a failure to register
	// with the netpoll system. That can happen for
	// a file descriptor that is not supported by
	// epoll/kqueue; for example, disk files on
	// Linux systems. We assume that any real error
	// will show up in later I/O.
	// We do restore the blocking behavior if it was set by us.
	if pollErr := f.pfd.Init("file", pollable); pollErr != nil && clearNonBlock {
		if err := syscall.SetNonblock(fd, false); err == nil {
			f.nonblock = false
		}
	}

	runtime.SetFinalizer(f.file, (*file).close)
	return f
}

func sigpipe() // implemented in package runtime

// epipecheck raises SIGPIPE if we get an EPIPE error on standard
// output or standard error. See the SIGPIPE docs in os/signal, and
// issue 11845.
func epipecheck(file *File, e error) {
	if e == syscall.EPIPE && file.stdoutOrErr {
		sigpipe()
	}
}

// DevNull is the name of the operating system's “null device.”
// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
const DevNull = "/dev/null"

// openFileNolog is the Unix implementation of OpenFile.
// Changes here should be reflected in openDirAt and openDirNolog, if relevant.
func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
	setSticky := false
	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
		if _, err := Stat(name); IsNotExist(err) {
			setSticky = true
		}
	}

	var (
		r int
		s poll.SysFile
		e error
	)
	// We have to check EINTR here, per issues 11180 and 39237.
	ignoringEINTR(func() error {
		r, s, e = open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
		return e
	})
	if e != nil {
		return nil, &PathError{Op: "open", Path: name, Err: e}
	}

	// open(2) itself won't handle the sticky bit on *BSD and Solaris
	if setSticky {
		setStickyBit(name)
	}

	// There's a race here with fork/exec, which we are
	// content to live with. See ../syscall/exec_unix.go.
	if !supportsCloseOnExec {
		syscall.CloseOnExec(r)
	}

	f := newFile(r, name, kindOpenFile, unix.HasNonblockFlag(flag))
	f.pfd.SysFile = s
	return f, nil
}

func openDirNolog(name string) (*File, error) {
	var (
		r int
		s poll.SysFile
		e error
	)
	ignoringEINTR(func() error {
		r, s, e = open(name, O_RDONLY|syscall.O_CLOEXEC|syscall.O_DIRECTORY, 0)
		return e
	})
	if e != nil {
		return nil, &PathError{Op: "open", Path: name, Err: e}
	}

	if !supportsCloseOnExec {
		syscall.CloseOnExec(r)
	}

	f := newFile(r, name, kindNoPoll, false)
	f.pfd.SysFile = s
	return f, nil
}

func (file *file) close() error {
	if file == nil {
		return syscall.EINVAL
	}
	if info := file.dirinfo.Swap(nil); info != nil {
		info.close()
	}
	var err error
	if e := file.pfd.Close(); e != nil {
		if e == poll.ErrFileClosing {
			e = ErrClosed
		}
		err = &PathError{Op: "close", Path: file.name, Err: e}
	}

	// no need for a finalizer anymore
	runtime.SetFinalizer(file, nil)
	return err
}

// seek sets the offset for the next Read or Write on file to offset, interpreted
// according to whence: 0 means relative to the origin of the file, 1 means
// relative to the current offset, and 2 means relative to the end.
// It returns the new offset and an error, if any.
func (f *File) seek(offset int64, whence int) (ret int64, err error) {
	if info := f.dirinfo.Swap(nil); info != nil {
		// Free cached dirinfo, so we allocate a new one if we
		// access this file as a directory again. See #35767 and #37161.
		info.close()
	}
	ret, err = f.pfd.Seek(offset, whence)
	runtime.KeepAlive(f)
	return ret, err
}

// Truncate changes the size of the named file.
// If the file is a symbolic link, it changes the size of the link's target.
// If there is an error, it will be of type *PathError.
func Truncate(name string, size int64) error {
	e := ignoringEINTR(func() error {
		return syscall.Truncate(name, size)
	})
	if e != nil {
		return &PathError{Op: "truncate", Path: name, Err: e}
	}
	return nil
}

// Remove removes the named file or (empty) directory.
// If there is an error, it will be of type *PathError.
func Remove(name string) error {
	// System call interface forces us to know
	// whether name is a file or directory.
	// Try both: it is cheaper on average than
	// doing a Stat plus the right one.
	e := ignoringEINTR(func() error {
		return syscall.Unlink(name)
	})
	if e == nil {
		return nil
	}
	e1 := ignoringEINTR(func() error {
		return syscall.Rmdir(name)
	})
	if e1 == nil {
		return nil
	}

	// Both failed: figure out which error to return.
	// OS X and Linux differ on whether unlink(dir)
	// returns EISDIR, so can't use that. However,
	// both agree that rmdir(file) returns ENOTDIR,
	// so we can use that to decide which error is real.
	// Rmdir might also return ENOTDIR if given a bad
	// file path, like /etc/passwd/foo, but in that case,
	// both errors will be ENOTDIR, so it's okay to
	// use the error from unlink.
	if e1 != syscall.ENOTDIR {
		e = e1
	}
	return &PathError{Op: "remove", Path: name, Err: e}
}

func tempDir() string {
	dir := Getenv("TMPDIR")
	if dir == "" {
		if runtime.GOOS == "android" {
			dir = "/data/local/tmp"
		} else {
			dir = "/tmp"
		}
	}
	return dir
}

// Link creates newname as a hard link to the oldname file.
// If there is an error, it will be of type *LinkError.
func Link(oldname, newname string) error {
	e := ignoringEINTR(func() error {
		return syscall.Link(oldname, newname)
	})
	if e != nil {
		return &LinkError{"link", oldname, newname, e}
	}
	return nil
}

// Symlink creates newname as a symbolic link to oldname.
// On Windows, a symlink to a non-existent oldname creates a file symlink;
// if oldname is later created as a directory the symlink will not work.
// If there is an error, it will be of type *LinkError.
func Symlink(oldname, newname string) error {
	e := ignoringEINTR(func() error {
		return syscall.Symlink(oldname, newname)
	})
	if e != nil {
		return &LinkError{"symlink", oldname, newname, e}
	}
	return nil
}

func readlink(name string) (string, error) {
	for len := 128; ; len *= 2 {
		b := make([]byte, len)
		n, err := ignoringEINTR2(func() (int, error) {
			return fixCount(syscall.Readlink(name, b))
		})
		// buffer too small
		if (runtime.GOOS == "aix" || runtime.GOOS == "wasip1") && err == syscall.ERANGE {
			continue
		}
		if err != nil {
			return "", &PathError{Op: "readlink", Path: name, Err: err}
		}
		if n < len {
			return string(b[0:n]), nil
		}
	}
}

type unixDirent struct {
	parent string
	name   string
	typ    FileMode
	info   FileInfo
}

func (d *unixDirent) Name() string   { return d.name }
func (d *unixDirent) IsDir() bool    { return d.typ.IsDir() }
func (d *unixDirent) Type() FileMode { return d.typ }

func (d *unixDirent) Info() (FileInfo, error) {
	if d.info != nil {
		return d.info, nil
	}
	return lstat(d.parent + "/" + d.name)
}

func (d *unixDirent) String() string {
	return fs.FormatDirEntry(d)
}

func newUnixDirent(parent, name string, typ FileMode) (DirEntry, error) {
	ude := &unixDirent{
		parent: parent,
		name:   name,
		typ:    typ,
	}
	if typ != ^FileMode(0) && !testingForceReadDirLstat {
		return ude, nil
	}

	info, err := lstat(parent + "/" + name)
	if err != nil {
		return nil, err
	}

	ude.typ = info.Mode().Type()
	ude.info = info
	return ude, nil
}

The pages are generated with Golds v0.7.6. (GOOS=linux GOARCH=amd64)