Source file src/os/file_unix.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build aix || darwin || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris
     6  // +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris
     7  
     8  package os
     9  
    10  import (
    11  	"internal/poll"
    12  	"internal/syscall/unix"
    13  	"runtime"
    14  	"syscall"
    15  )
    16  
    17  // fixLongPath is a noop on non-Windows platforms.
    18  func fixLongPath(path string) string {
    19  	return path
    20  }
    21  
    22  func rename(oldname, newname string) error {
    23  	fi, err := Lstat(newname)
    24  	if err == nil && fi.IsDir() {
    25  		// There are two independent errors this function can return:
    26  		// one for a bad oldname, and one for a bad newname.
    27  		// At this point we've determined the newname is bad.
    28  		// But just in case oldname is also bad, prioritize returning
    29  		// the oldname error because that's what we did historically.
    30  		// However, if the old name and new name are not the same, yet
    31  		// they refer to the same file, it implies a case-only
    32  		// rename on a case-insensitive filesystem, which is ok.
    33  		if ofi, err := Lstat(oldname); err != nil {
    34  			if pe, ok := err.(*PathError); ok {
    35  				err = pe.Err
    36  			}
    37  			return &LinkError{"rename", oldname, newname, err}
    38  		} else if newname == oldname || !SameFile(fi, ofi) {
    39  			return &LinkError{"rename", oldname, newname, syscall.EEXIST}
    40  		}
    41  	}
    42  	err = ignoringEINTR(func() error {
    43  		return syscall.Rename(oldname, newname)
    44  	})
    45  	if err != nil {
    46  		return &LinkError{"rename", oldname, newname, err}
    47  	}
    48  	return nil
    49  }
    50  
    51  // file is the real representation of *File.
    52  // The extra level of indirection ensures that no clients of os
    53  // can overwrite this data, which could cause the finalizer
    54  // to close the wrong file descriptor.
    55  type file struct {
    56  	pfd         poll.FD
    57  	name        string
    58  	dirinfo     *dirInfo // nil unless directory being read
    59  	nonblock    bool     // whether we set nonblocking mode
    60  	stdoutOrErr bool     // whether this is stdout or stderr
    61  	appendMode  bool     // whether file is opened for appending
    62  }
    63  
    64  // Fd returns the integer Unix file descriptor referencing the open file.
    65  // If f is closed, the file descriptor becomes invalid.
    66  // If f is garbage collected, a finalizer may close the file descriptor,
    67  // making it invalid; see runtime.SetFinalizer for more information on when
    68  // a finalizer might be run. On Unix systems this will cause the SetDeadline
    69  // methods to stop working.
    70  // Because file descriptors can be reused, the returned file descriptor may
    71  // only be closed through the Close method of f, or by its finalizer during
    72  // garbage collection. Otherwise, during garbage collection the finalizer
    73  // may close an unrelated file descriptor with the same (reused) number.
    74  //
    75  // As an alternative, see the f.SyscallConn method.
    76  func (f *File) Fd() uintptr {
    77  	if f == nil {
    78  		return ^(uintptr(0))
    79  	}
    80  
    81  	// If we put the file descriptor into nonblocking mode,
    82  	// then set it to blocking mode before we return it,
    83  	// because historically we have always returned a descriptor
    84  	// opened in blocking mode. The File will continue to work,
    85  	// but any blocking operation will tie up a thread.
    86  	if f.nonblock {
    87  		f.pfd.SetBlocking()
    88  	}
    89  
    90  	return uintptr(f.pfd.Sysfd)
    91  }
    92  
    93  // NewFile returns a new File with the given file descriptor and
    94  // name. The returned value will be nil if fd is not a valid file
    95  // descriptor. On Unix systems, if the file descriptor is in
    96  // non-blocking mode, NewFile will attempt to return a pollable File
    97  // (one for which the SetDeadline methods work).
    98  //
    99  // After passing it to NewFile, fd may become invalid under the same
   100  // conditions described in the comments of the Fd method, and the same
   101  // constraints apply.
   102  func NewFile(fd uintptr, name string) *File {
   103  	kind := kindNewFile
   104  	if nb, err := unix.IsNonblock(int(fd)); err == nil && nb {
   105  		kind = kindNonBlock
   106  	}
   107  	return newFile(fd, name, kind)
   108  }
   109  
   110  // newFileKind describes the kind of file to newFile.
   111  type newFileKind int
   112  
   113  const (
   114  	kindNewFile newFileKind = iota
   115  	kindOpenFile
   116  	kindPipe
   117  	kindNonBlock
   118  )
   119  
   120  // newFile is like NewFile, but if called from OpenFile or Pipe
   121  // (as passed in the kind parameter) it tries to add the file to
   122  // the runtime poller.
   123  func newFile(fd uintptr, name string, kind newFileKind) *File {
   124  	fdi := int(fd)
   125  	if fdi < 0 {
   126  		return nil
   127  	}
   128  	f := &File{&file{
   129  		pfd: poll.FD{
   130  			Sysfd:         fdi,
   131  			IsStream:      true,
   132  			ZeroReadIsEOF: true,
   133  		},
   134  		name:        name,
   135  		stdoutOrErr: fdi == 1 || fdi == 2,
   136  	}}
   137  
   138  	pollable := kind == kindOpenFile || kind == kindPipe || kind == kindNonBlock
   139  
   140  	// If the caller passed a non-blocking filedes (kindNonBlock),
   141  	// we assume they know what they are doing so we allow it to be
   142  	// used with kqueue.
   143  	if kind == kindOpenFile {
   144  		switch runtime.GOOS {
   145  		case "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd":
   146  			var st syscall.Stat_t
   147  			err := ignoringEINTR(func() error {
   148  				return syscall.Fstat(fdi, &st)
   149  			})
   150  			typ := st.Mode & syscall.S_IFMT
   151  			// Don't try to use kqueue with regular files on *BSDs.
   152  			// On FreeBSD a regular file is always
   153  			// reported as ready for writing.
   154  			// On Dragonfly, NetBSD and OpenBSD the fd is signaled
   155  			// only once as ready (both read and write).
   156  			// Issue 19093.
   157  			// Also don't add directories to the netpoller.
   158  			if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
   159  				pollable = false
   160  			}
   161  
   162  			// In addition to the behavior described above for regular files,
   163  			// on Darwin, kqueue does not work properly with fifos:
   164  			// closing the last writer does not cause a kqueue event
   165  			// for any readers. See issue #24164.
   166  			if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && typ == syscall.S_IFIFO {
   167  				pollable = false
   168  			}
   169  		}
   170  	}
   171  
   172  	if err := f.pfd.Init("file", pollable); err != nil {
   173  		// An error here indicates a failure to register
   174  		// with the netpoll system. That can happen for
   175  		// a file descriptor that is not supported by
   176  		// epoll/kqueue; for example, disk files on
   177  		// Linux systems. We assume that any real error
   178  		// will show up in later I/O.
   179  	} else if pollable {
   180  		// We successfully registered with netpoll, so put
   181  		// the file into nonblocking mode.
   182  		if err := syscall.SetNonblock(fdi, true); err == nil {
   183  			f.nonblock = true
   184  		}
   185  	}
   186  
   187  	runtime.SetFinalizer(f.file, (*file).close)
   188  	return f
   189  }
   190  
   191  // epipecheck raises SIGPIPE if we get an EPIPE error on standard
   192  // output or standard error. See the SIGPIPE docs in os/signal, and
   193  // issue 11845.
   194  func epipecheck(file *File, e error) {
   195  	if e == syscall.EPIPE && file.stdoutOrErr {
   196  		sigpipe()
   197  	}
   198  }
   199  
   200  // DevNull is the name of the operating system's ``null device.''
   201  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
   202  const DevNull = "/dev/null"
   203  
   204  // openFileNolog is the Unix implementation of OpenFile.
   205  // Changes here should be reflected in openFdAt, if relevant.
   206  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   207  	setSticky := false
   208  	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
   209  		if _, err := Stat(name); IsNotExist(err) {
   210  			setSticky = true
   211  		}
   212  	}
   213  
   214  	var r int
   215  	for {
   216  		var e error
   217  		r, e = syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
   218  		if e == nil {
   219  			break
   220  		}
   221  
   222  		// We have to check EINTR here, per issues 11180 and 39237.
   223  		if e == syscall.EINTR {
   224  			continue
   225  		}
   226  
   227  		return nil, &PathError{Op: "open", Path: name, Err: e}
   228  	}
   229  
   230  	// open(2) itself won't handle the sticky bit on *BSD and Solaris
   231  	if setSticky {
   232  		setStickyBit(name)
   233  	}
   234  
   235  	// There's a race here with fork/exec, which we are
   236  	// content to live with. See ../syscall/exec_unix.go.
   237  	if !supportsCloseOnExec {
   238  		syscall.CloseOnExec(r)
   239  	}
   240  
   241  	return newFile(uintptr(r), name, kindOpenFile), nil
   242  }
   243  
   244  func (file *file) close() error {
   245  	if file == nil {
   246  		return syscall.EINVAL
   247  	}
   248  	if file.dirinfo != nil {
   249  		file.dirinfo.close()
   250  		file.dirinfo = nil
   251  	}
   252  	var err error
   253  	if e := file.pfd.Close(); e != nil {
   254  		if e == poll.ErrFileClosing {
   255  			e = ErrClosed
   256  		}
   257  		err = &PathError{Op: "close", Path: file.name, Err: e}
   258  	}
   259  
   260  	// no need for a finalizer anymore
   261  	runtime.SetFinalizer(file, nil)
   262  	return err
   263  }
   264  
   265  // seek sets the offset for the next Read or Write on file to offset, interpreted
   266  // according to whence: 0 means relative to the origin of the file, 1 means
   267  // relative to the current offset, and 2 means relative to the end.
   268  // It returns the new offset and an error, if any.
   269  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   270  	if f.dirinfo != nil {
   271  		// Free cached dirinfo, so we allocate a new one if we
   272  		// access this file as a directory again. See #35767 and #37161.
   273  		f.dirinfo.close()
   274  		f.dirinfo = nil
   275  	}
   276  	ret, err = f.pfd.Seek(offset, whence)
   277  	runtime.KeepAlive(f)
   278  	return ret, err
   279  }
   280  
   281  // Truncate changes the size of the named file.
   282  // If the file is a symbolic link, it changes the size of the link's target.
   283  // If there is an error, it will be of type *PathError.
   284  func Truncate(name string, size int64) error {
   285  	e := ignoringEINTR(func() error {
   286  		return syscall.Truncate(name, size)
   287  	})
   288  	if e != nil {
   289  		return &PathError{Op: "truncate", Path: name, Err: e}
   290  	}
   291  	return nil
   292  }
   293  
   294  // Remove removes the named file or (empty) directory.
   295  // If there is an error, it will be of type *PathError.
   296  func Remove(name string) error {
   297  	// System call interface forces us to know
   298  	// whether name is a file or directory.
   299  	// Try both: it is cheaper on average than
   300  	// doing a Stat plus the right one.
   301  	e := ignoringEINTR(func() error {
   302  		return syscall.Unlink(name)
   303  	})
   304  	if e == nil {
   305  		return nil
   306  	}
   307  	e1 := ignoringEINTR(func() error {
   308  		return syscall.Rmdir(name)
   309  	})
   310  	if e1 == nil {
   311  		return nil
   312  	}
   313  
   314  	// Both failed: figure out which error to return.
   315  	// OS X and Linux differ on whether unlink(dir)
   316  	// returns EISDIR, so can't use that. However,
   317  	// both agree that rmdir(file) returns ENOTDIR,
   318  	// so we can use that to decide which error is real.
   319  	// Rmdir might also return ENOTDIR if given a bad
   320  	// file path, like /etc/passwd/foo, but in that case,
   321  	// both errors will be ENOTDIR, so it's okay to
   322  	// use the error from unlink.
   323  	if e1 != syscall.ENOTDIR {
   324  		e = e1
   325  	}
   326  	return &PathError{Op: "remove", Path: name, Err: e}
   327  }
   328  
   329  func tempDir() string {
   330  	dir := Getenv("TMPDIR")
   331  	if dir == "" {
   332  		if runtime.GOOS == "android" {
   333  			dir = "/data/local/tmp"
   334  		} else {
   335  			dir = "/tmp"
   336  		}
   337  	}
   338  	return dir
   339  }
   340  
   341  // Link creates newname as a hard link to the oldname file.
   342  // If there is an error, it will be of type *LinkError.
   343  func Link(oldname, newname string) error {
   344  	e := ignoringEINTR(func() error {
   345  		return syscall.Link(oldname, newname)
   346  	})
   347  	if e != nil {
   348  		return &LinkError{"link", oldname, newname, e}
   349  	}
   350  	return nil
   351  }
   352  
   353  // Symlink creates newname as a symbolic link to oldname.
   354  // On Windows, a symlink to a non-existent oldname creates a file symlink;
   355  // if oldname is later created as a directory the symlink will not work.
   356  // If there is an error, it will be of type *LinkError.
   357  func Symlink(oldname, newname string) error {
   358  	e := ignoringEINTR(func() error {
   359  		return syscall.Symlink(oldname, newname)
   360  	})
   361  	if e != nil {
   362  		return &LinkError{"symlink", oldname, newname, e}
   363  	}
   364  	return nil
   365  }
   366  
   367  // Readlink returns the destination of the named symbolic link.
   368  // If there is an error, it will be of type *PathError.
   369  func Readlink(name string) (string, error) {
   370  	for len := 128; ; len *= 2 {
   371  		b := make([]byte, len)
   372  		var (
   373  			n int
   374  			e error
   375  		)
   376  		for {
   377  			n, e = fixCount(syscall.Readlink(name, b))
   378  			if e != syscall.EINTR {
   379  				break
   380  			}
   381  		}
   382  		// buffer too small
   383  		if runtime.GOOS == "aix" && e == syscall.ERANGE {
   384  			continue
   385  		}
   386  		if e != nil {
   387  			return "", &PathError{Op: "readlink", Path: name, Err: e}
   388  		}
   389  		if n < len {
   390  			return string(b[0:n]), nil
   391  		}
   392  	}
   393  }
   394  
   395  type unixDirent struct {
   396  	parent string
   397  	name   string
   398  	typ    FileMode
   399  	info   FileInfo
   400  }
   401  
   402  func (d *unixDirent) Name() string   { return d.name }
   403  func (d *unixDirent) IsDir() bool    { return d.typ.IsDir() }
   404  func (d *unixDirent) Type() FileMode { return d.typ }
   405  
   406  func (d *unixDirent) Info() (FileInfo, error) {
   407  	if d.info != nil {
   408  		return d.info, nil
   409  	}
   410  	return lstat(d.parent + "/" + d.name)
   411  }
   412  
   413  func newUnixDirent(parent, name string, typ FileMode) (DirEntry, error) {
   414  	ude := &unixDirent{
   415  		parent: parent,
   416  		name:   name,
   417  		typ:    typ,
   418  	}
   419  	if typ != ^FileMode(0) && !testingForceReadDirLstat {
   420  		return ude, nil
   421  	}
   422  
   423  	info, err := lstat(parent + "/" + name)
   424  	if err != nil {
   425  		return nil, err
   426  	}
   427  
   428  	ude.typ = info.Mode().Type()
   429  	ude.info = info
   430  	return ude, nil
   431  }
   432  

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