Source file src/os/file_unix.go

Documentation: os

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

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