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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 darwin dragonfly freebsd linux nacl netbsd openbsd solaris
     6  
     7  package os
     8  
     9  import (
    10  	"internal/poll"
    11  	"runtime"
    12  	"syscall"
    13  )
    14  
    15  // fixLongPath is a noop on non-Windows platforms.
    16  func fixLongPath(path string) string {
    17  	return path
    18  }
    19  
    20  func rename(oldname, newname string) error {
    21  	fi, err := Lstat(newname)
    22  	if err == nil && fi.IsDir() {
    23  		// There are two independent errors this function can return:
    24  		// one for a bad oldname, and one for a bad newname.
    25  		// At this point we've determined the newname is bad.
    26  		// But just in case oldname is also bad, prioritize returning
    27  		// the oldname error because that's what we did historically.
    28  		if _, err := Lstat(oldname); err != nil {
    29  			if pe, ok := err.(*PathError); ok {
    30  				err = pe.Err
    31  			}
    32  			return &LinkError{"rename", oldname, newname, err}
    33  		}
    34  		return &LinkError{"rename", oldname, newname, syscall.EEXIST}
    35  	}
    36  	err = syscall.Rename(oldname, newname)
    37  	if err != nil {
    38  		return &LinkError{"rename", oldname, newname, err}
    39  	}
    40  	return nil
    41  }
    42  
    43  // file is the real representation of *File.
    44  // The extra level of indirection ensures that no clients of os
    45  // can overwrite this data, which could cause the finalizer
    46  // to close the wrong file descriptor.
    47  type file struct {
    48  	pfd         poll.FD
    49  	name        string
    50  	dirinfo     *dirInfo // nil unless directory being read
    51  	nonblock    bool     // whether we set nonblocking mode
    52  	stdoutOrErr bool     // whether this is stdout or stderr
    53  }
    54  
    55  // Fd returns the integer Unix file descriptor referencing the open file.
    56  // The file descriptor is valid only until f.Close is called or f is garbage collected.
    57  // On Unix systems this will cause the SetDeadline methods to stop working.
    58  func (f *File) Fd() uintptr {
    59  	if f == nil {
    60  		return ^(uintptr(0))
    61  	}
    62  
    63  	// If we put the file descriptor into nonblocking mode,
    64  	// then set it to blocking mode before we return it,
    65  	// because historically we have always returned a descriptor
    66  	// opened in blocking mode. The File will continue to work,
    67  	// but any blocking operation will tie up a thread.
    68  	if f.nonblock {
    69  		f.pfd.SetBlocking()
    70  	}
    71  
    72  	return uintptr(f.pfd.Sysfd)
    73  }
    74  
    75  // NewFile returns a new File with the given file descriptor and
    76  // name. The returned value will be nil if fd is not a valid file
    77  // descriptor.
    78  func NewFile(fd uintptr, name string) *File {
    79  	return newFile(fd, name, kindNewFile)
    80  }
    81  
    82  // newFileKind describes the kind of file to newFile.
    83  type newFileKind int
    84  
    85  const (
    86  	kindNewFile newFileKind = iota
    87  	kindOpenFile
    88  	kindPipe
    89  )
    90  
    91  // newFile is like NewFile, but if called from OpenFile or Pipe
    92  // (as passed in the kind parameter) it tries to add the file to
    93  // the runtime poller.
    94  func newFile(fd uintptr, name string, kind newFileKind) *File {
    95  	fdi := int(fd)
    96  	if fdi < 0 {
    97  		return nil
    98  	}
    99  	f := &File{&file{
   100  		pfd: poll.FD{
   101  			Sysfd:         fdi,
   102  			IsStream:      true,
   103  			ZeroReadIsEOF: true,
   104  		},
   105  		name:        name,
   106  		stdoutOrErr: fdi == 1 || fdi == 2,
   107  	}}
   108  
   109  	// Don't try to use kqueue with regular files on FreeBSD.
   110  	// It crashes the system unpredictably while running all.bash.
   111  	// Issue 19093.
   112  	if runtime.GOOS == "freebsd" && kind == kindOpenFile {
   113  		kind = kindNewFile
   114  	}
   115  
   116  	pollable := kind == kindOpenFile || kind == kindPipe
   117  	if err := f.pfd.Init("file", pollable); err != nil {
   118  		// An error here indicates a failure to register
   119  		// with the netpoll system. That can happen for
   120  		// a file descriptor that is not supported by
   121  		// epoll/kqueue; for example, disk files on
   122  		// GNU/Linux systems. We assume that any real error
   123  		// will show up in later I/O.
   124  	} else if pollable {
   125  		// We successfully registered with netpoll, so put
   126  		// the file into nonblocking mode.
   127  		if err := syscall.SetNonblock(fdi, true); err == nil {
   128  			f.nonblock = true
   129  		}
   130  	}
   131  
   132  	runtime.SetFinalizer(f.file, (*file).close)
   133  	return f
   134  }
   135  
   136  // Auxiliary information if the File describes a directory
   137  type dirInfo struct {
   138  	buf  []byte // buffer for directory I/O
   139  	nbuf int    // length of buf; return value from Getdirentries
   140  	bufp int    // location of next record in buf.
   141  }
   142  
   143  // epipecheck raises SIGPIPE if we get an EPIPE error on standard
   144  // output or standard error. See the SIGPIPE docs in os/signal, and
   145  // issue 11845.
   146  func epipecheck(file *File, e error) {
   147  	if e == syscall.EPIPE && file.stdoutOrErr {
   148  		sigpipe()
   149  	}
   150  }
   151  
   152  // DevNull is the name of the operating system's ``null device.''
   153  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
   154  const DevNull = "/dev/null"
   155  
   156  // openFileNolog is the Unix implementation of OpenFile.
   157  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   158  	chmod := false
   159  	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
   160  		if _, err := Stat(name); IsNotExist(err) {
   161  			chmod = true
   162  		}
   163  	}
   164  
   165  	var r int
   166  	for {
   167  		var e error
   168  		r, e = syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
   169  		if e == nil {
   170  			break
   171  		}
   172  
   173  		// On OS X, sigaction(2) doesn't guarantee that SA_RESTART will cause
   174  		// open(2) to be restarted for regular files. This is easy to reproduce on
   175  		// fuse file systems (see http://golang.org/issue/11180).
   176  		if runtime.GOOS == "darwin" && e == syscall.EINTR {
   177  			continue
   178  		}
   179  
   180  		return nil, &PathError{"open", name, e}
   181  	}
   182  
   183  	// open(2) itself won't handle the sticky bit on *BSD and Solaris
   184  	if chmod {
   185  		Chmod(name, perm)
   186  	}
   187  
   188  	// There's a race here with fork/exec, which we are
   189  	// content to live with. See ../syscall/exec_unix.go.
   190  	if !supportsCloseOnExec {
   191  		syscall.CloseOnExec(r)
   192  	}
   193  
   194  	return newFile(uintptr(r), name, kindOpenFile), nil
   195  }
   196  
   197  // Close closes the File, rendering it unusable for I/O.
   198  // It returns an error, if any.
   199  func (f *File) Close() error {
   200  	if f == nil {
   201  		return ErrInvalid
   202  	}
   203  	return f.file.close()
   204  }
   205  
   206  func (file *file) close() error {
   207  	if file == nil {
   208  		return syscall.EINVAL
   209  	}
   210  	var err error
   211  	if e := file.pfd.Close(); e != nil {
   212  		if e == poll.ErrFileClosing {
   213  			e = ErrClosed
   214  		}
   215  		err = &PathError{"close", file.name, e}
   216  	}
   217  
   218  	// no need for a finalizer anymore
   219  	runtime.SetFinalizer(file, nil)
   220  	return err
   221  }
   222  
   223  // read reads up to len(b) bytes from the File.
   224  // It returns the number of bytes read and an error, if any.
   225  func (f *File) read(b []byte) (n int, err error) {
   226  	n, err = f.pfd.Read(b)
   227  	runtime.KeepAlive(f)
   228  	return n, err
   229  }
   230  
   231  // pread reads len(b) bytes from the File starting at byte offset off.
   232  // It returns the number of bytes read and the error, if any.
   233  // EOF is signaled by a zero count with err set to nil.
   234  func (f *File) pread(b []byte, off int64) (n int, err error) {
   235  	n, err = f.pfd.Pread(b, off)
   236  	runtime.KeepAlive(f)
   237  	return n, err
   238  }
   239  
   240  // write writes len(b) bytes to the File.
   241  // It returns the number of bytes written and an error, if any.
   242  func (f *File) write(b []byte) (n int, err error) {
   243  	n, err = f.pfd.Write(b)
   244  	runtime.KeepAlive(f)
   245  	return n, err
   246  }
   247  
   248  // pwrite writes len(b) bytes to the File starting at byte offset off.
   249  // It returns the number of bytes written and an error, if any.
   250  func (f *File) pwrite(b []byte, off int64) (n int, err error) {
   251  	n, err = f.pfd.Pwrite(b, off)
   252  	runtime.KeepAlive(f)
   253  	return n, err
   254  }
   255  
   256  // seek sets the offset for the next Read or Write on file to offset, interpreted
   257  // according to whence: 0 means relative to the origin of the file, 1 means
   258  // relative to the current offset, and 2 means relative to the end.
   259  // It returns the new offset and an error, if any.
   260  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   261  	ret, err = f.pfd.Seek(offset, whence)
   262  	runtime.KeepAlive(f)
   263  	return ret, err
   264  }
   265  
   266  // Truncate changes the size of the named file.
   267  // If the file is a symbolic link, it changes the size of the link's target.
   268  // If there is an error, it will be of type *PathError.
   269  func Truncate(name string, size int64) error {
   270  	if e := syscall.Truncate(name, size); e != nil {
   271  		return &PathError{"truncate", name, e}
   272  	}
   273  	return nil
   274  }
   275  
   276  // Remove removes the named file or directory.
   277  // If there is an error, it will be of type *PathError.
   278  func Remove(name string) error {
   279  	// System call interface forces us to know
   280  	// whether name is a file or directory.
   281  	// Try both: it is cheaper on average than
   282  	// doing a Stat plus the right one.
   283  	e := syscall.Unlink(name)
   284  	if e == nil {
   285  		return nil
   286  	}
   287  	e1 := syscall.Rmdir(name)
   288  	if e1 == nil {
   289  		return nil
   290  	}
   291  
   292  	// Both failed: figure out which error to return.
   293  	// OS X and Linux differ on whether unlink(dir)
   294  	// returns EISDIR, so can't use that. However,
   295  	// both agree that rmdir(file) returns ENOTDIR,
   296  	// so we can use that to decide which error is real.
   297  	// Rmdir might also return ENOTDIR if given a bad
   298  	// file path, like /etc/passwd/foo, but in that case,
   299  	// both errors will be ENOTDIR, so it's okay to
   300  	// use the error from unlink.
   301  	if e1 != syscall.ENOTDIR {
   302  		e = e1
   303  	}
   304  	return &PathError{"remove", name, e}
   305  }
   306  
   307  func tempDir() string {
   308  	dir := Getenv("TMPDIR")
   309  	if dir == "" {
   310  		if runtime.GOOS == "android" {
   311  			dir = "/data/local/tmp"
   312  		} else {
   313  			dir = "/tmp"
   314  		}
   315  	}
   316  	return dir
   317  }
   318  
   319  // Link creates newname as a hard link to the oldname file.
   320  // If there is an error, it will be of type *LinkError.
   321  func Link(oldname, newname string) error {
   322  	e := syscall.Link(oldname, newname)
   323  	if e != nil {
   324  		return &LinkError{"link", oldname, newname, e}
   325  	}
   326  	return nil
   327  }
   328  
   329  // Symlink creates newname as a symbolic link to oldname.
   330  // If there is an error, it will be of type *LinkError.
   331  func Symlink(oldname, newname string) error {
   332  	e := syscall.Symlink(oldname, newname)
   333  	if e != nil {
   334  		return &LinkError{"symlink", oldname, newname, e}
   335  	}
   336  	return nil
   337  }
   338  

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