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 unix || (js && wasm) || wasip1
     6  
     7  package os
     8  
     9  import (
    10  	"internal/poll"
    11  	"internal/syscall/unix"
    12  	"io/fs"
    13  	"runtime"
    14  	"sync/atomic"
    15  	"syscall"
    16  	_ "unsafe" // for go:linkname
    17  )
    18  
    19  const _UTIME_OMIT = unix.UTIME_OMIT
    20  
    21  // fixLongPath is a noop on non-Windows platforms.
    22  func fixLongPath(path string) string {
    23  	return path
    24  }
    25  
    26  func rename(oldname, newname string) error {
    27  	fi, err := Lstat(newname)
    28  	if err == nil && fi.IsDir() {
    29  		// There are two independent errors this function can return:
    30  		// one for a bad oldname, and one for a bad newname.
    31  		// At this point we've determined the newname is bad.
    32  		// But just in case oldname is also bad, prioritize returning
    33  		// the oldname error because that's what we did historically.
    34  		// However, if the old name and new name are not the same, yet
    35  		// they refer to the same file, it implies a case-only
    36  		// rename on a case-insensitive filesystem, which is ok.
    37  		if ofi, err := Lstat(oldname); err != nil {
    38  			if pe, ok := err.(*PathError); ok {
    39  				err = pe.Err
    40  			}
    41  			return &LinkError{"rename", oldname, newname, err}
    42  		} else if newname == oldname || !SameFile(fi, ofi) {
    43  			return &LinkError{"rename", oldname, newname, syscall.EEXIST}
    44  		}
    45  	}
    46  	err = ignoringEINTR(func() error {
    47  		return syscall.Rename(oldname, newname)
    48  	})
    49  	if err != nil {
    50  		return &LinkError{"rename", oldname, newname, err}
    51  	}
    52  	return nil
    53  }
    54  
    55  // file is the real representation of *File.
    56  // The extra level of indirection ensures that no clients of os
    57  // can overwrite this data, which could cause the finalizer
    58  // to close the wrong file descriptor.
    59  type file struct {
    60  	pfd         poll.FD
    61  	name        string
    62  	dirinfo     atomic.Pointer[dirInfo] // nil unless directory being read
    63  	nonblock    bool                    // whether we set nonblocking mode
    64  	stdoutOrErr bool                    // whether this is stdout or stderr
    65  	appendMode  bool                    // whether file is opened for appending
    66  	inRoot      bool                    // whether file is opened in a Root
    67  }
    68  
    69  // fd is the Unix implementation of Fd.
    70  func (f *File) fd() uintptr {
    71  	if f == nil {
    72  		return ^(uintptr(0))
    73  	}
    74  
    75  	// If we put the file descriptor into nonblocking mode,
    76  	// then set it to blocking mode before we return it,
    77  	// because historically we have always returned a descriptor
    78  	// opened in blocking mode. The File will continue to work,
    79  	// but any blocking operation will tie up a thread.
    80  	if f.nonblock {
    81  		f.pfd.SetBlocking()
    82  	}
    83  
    84  	return uintptr(f.pfd.Sysfd)
    85  }
    86  
    87  // newFileFromNewFile is called by [NewFile].
    88  func newFileFromNewFile(fd uintptr, name string) *File {
    89  	fdi := int(fd)
    90  	if fdi < 0 {
    91  		return nil
    92  	}
    93  
    94  	flags, err := unix.Fcntl(fdi, syscall.F_GETFL, 0)
    95  	if err != nil {
    96  		flags = 0
    97  	}
    98  	f := newFile(fdi, name, kindNewFile, unix.HasNonblockFlag(flags))
    99  	f.appendMode = flags&syscall.O_APPEND != 0
   100  	return f
   101  }
   102  
   103  // net_newUnixFile is a hidden entry point called by net.conn.File.
   104  // This is used so that a nonblocking network connection will become
   105  // blocking if code calls the Fd method. We don't want that for direct
   106  // calls to NewFile: passing a nonblocking descriptor to NewFile should
   107  // remain nonblocking if you get it back using Fd. But for net.conn.File
   108  // the call to NewFile is hidden from the user. Historically in that case
   109  // the Fd method has returned a blocking descriptor, and we want to
   110  // retain that behavior because existing code expects it and depends on it.
   111  //
   112  //go:linkname net_newUnixFile net.newUnixFile
   113  func net_newUnixFile(fd int, name string) *File {
   114  	if fd < 0 {
   115  		panic("invalid FD")
   116  	}
   117  
   118  	return newFile(fd, name, kindSock, true)
   119  }
   120  
   121  // newFileKind describes the kind of file to newFile.
   122  type newFileKind int
   123  
   124  const (
   125  	// kindNewFile means that the descriptor was passed to us via NewFile.
   126  	kindNewFile newFileKind = iota
   127  	// kindOpenFile means that the descriptor was opened using
   128  	// Open, Create, or OpenFile.
   129  	kindOpenFile
   130  	// kindPipe means that the descriptor was opened using Pipe.
   131  	kindPipe
   132  	// kindSock means that the descriptor is a network file descriptor
   133  	// that was created from net package and was opened using net_newUnixFile.
   134  	kindSock
   135  	// kindNoPoll means that we should not put the descriptor into
   136  	// non-blocking mode, because we know it is not a pipe or FIFO.
   137  	// Used by openDirAt and openDirNolog for directories.
   138  	kindNoPoll
   139  )
   140  
   141  // newFile is like NewFile, but if called from OpenFile or Pipe
   142  // (as passed in the kind parameter) it tries to add the file to
   143  // the runtime poller.
   144  func newFile(fd int, name string, kind newFileKind, nonBlocking bool) *File {
   145  	f := &File{&file{
   146  		pfd: poll.FD{
   147  			Sysfd:         fd,
   148  			IsStream:      true,
   149  			ZeroReadIsEOF: true,
   150  		},
   151  		name:        name,
   152  		stdoutOrErr: fd == 1 || fd == 2,
   153  	}}
   154  
   155  	pollable := kind == kindOpenFile || kind == kindPipe || kind == kindSock || nonBlocking
   156  
   157  	// Things like regular files and FIFOs in kqueue on *BSD/Darwin
   158  	// may not work properly (or accurately according to its manual).
   159  	// As a result, we should avoid adding those to the kqueue-based
   160  	// netpoller. Check out #19093, #24164, and #66239 for more contexts.
   161  	//
   162  	// If the fd was passed to us via any path other than OpenFile,
   163  	// we assume those callers know what they were doing, so we won't
   164  	// perform this check and allow it to be added to the kqueue.
   165  	if kind == kindOpenFile {
   166  		switch runtime.GOOS {
   167  		case "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd":
   168  			var st syscall.Stat_t
   169  			err := ignoringEINTR(func() error {
   170  				return syscall.Fstat(fd, &st)
   171  			})
   172  			typ := st.Mode & syscall.S_IFMT
   173  			// Don't try to use kqueue with regular files on *BSDs.
   174  			// On FreeBSD a regular file is always
   175  			// reported as ready for writing.
   176  			// On Dragonfly, NetBSD and OpenBSD the fd is signaled
   177  			// only once as ready (both read and write).
   178  			// Issue 19093.
   179  			// Also don't add directories to the netpoller.
   180  			if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
   181  				pollable = false
   182  			}
   183  
   184  			// In addition to the behavior described above for regular files,
   185  			// on Darwin, kqueue does not work properly with fifos:
   186  			// closing the last writer does not cause a kqueue event
   187  			// for any readers. See issue #24164.
   188  			if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && typ == syscall.S_IFIFO {
   189  				pollable = false
   190  			}
   191  		}
   192  	}
   193  
   194  	clearNonBlock := false
   195  	if pollable {
   196  		// The descriptor is already in non-blocking mode.
   197  		// We only set f.nonblock if we put the file into
   198  		// non-blocking mode.
   199  		if nonBlocking {
   200  			// See the comments on net_newUnixFile.
   201  			if kind == kindSock {
   202  				f.nonblock = true // tell Fd to return blocking descriptor
   203  			}
   204  		} else if err := syscall.SetNonblock(fd, true); err == nil {
   205  			f.nonblock = true
   206  			clearNonBlock = true
   207  		} else {
   208  			pollable = false
   209  		}
   210  	}
   211  
   212  	// An error here indicates a failure to register
   213  	// with the netpoll system. That can happen for
   214  	// a file descriptor that is not supported by
   215  	// epoll/kqueue; for example, disk files on
   216  	// Linux systems. We assume that any real error
   217  	// will show up in later I/O.
   218  	// We do restore the blocking behavior if it was set by us.
   219  	if pollErr := f.pfd.Init("file", pollable); pollErr != nil && clearNonBlock {
   220  		if err := syscall.SetNonblock(fd, false); err == nil {
   221  			f.nonblock = false
   222  		}
   223  	}
   224  
   225  	runtime.SetFinalizer(f.file, (*file).close)
   226  	return f
   227  }
   228  
   229  func sigpipe() // implemented in package runtime
   230  
   231  // epipecheck raises SIGPIPE if we get an EPIPE error on standard
   232  // output or standard error. See the SIGPIPE docs in os/signal, and
   233  // issue 11845.
   234  func epipecheck(file *File, e error) {
   235  	if e == syscall.EPIPE && file.stdoutOrErr {
   236  		sigpipe()
   237  	}
   238  }
   239  
   240  // DevNull is the name of the operating system's “null device.”
   241  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
   242  const DevNull = "/dev/null"
   243  
   244  // openFileNolog is the Unix implementation of OpenFile.
   245  // Changes here should be reflected in openDirAt and openDirNolog, if relevant.
   246  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   247  	setSticky := false
   248  	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
   249  		if _, err := Stat(name); IsNotExist(err) {
   250  			setSticky = true
   251  		}
   252  	}
   253  
   254  	var (
   255  		r int
   256  		s poll.SysFile
   257  		e error
   258  	)
   259  	// We have to check EINTR here, per issues 11180 and 39237.
   260  	ignoringEINTR(func() error {
   261  		r, s, e = open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
   262  		return e
   263  	})
   264  	if e != nil {
   265  		return nil, &PathError{Op: "open", Path: name, Err: e}
   266  	}
   267  
   268  	// open(2) itself won't handle the sticky bit on *BSD and Solaris
   269  	if setSticky {
   270  		setStickyBit(name)
   271  	}
   272  
   273  	// There's a race here with fork/exec, which we are
   274  	// content to live with. See ../syscall/exec_unix.go.
   275  	if !supportsCloseOnExec {
   276  		syscall.CloseOnExec(r)
   277  	}
   278  
   279  	f := newFile(r, name, kindOpenFile, unix.HasNonblockFlag(flag))
   280  	f.pfd.SysFile = s
   281  	return f, nil
   282  }
   283  
   284  func openDirNolog(name string) (*File, error) {
   285  	var (
   286  		r int
   287  		s poll.SysFile
   288  		e error
   289  	)
   290  	ignoringEINTR(func() error {
   291  		r, s, e = open(name, O_RDONLY|syscall.O_CLOEXEC|syscall.O_DIRECTORY, 0)
   292  		return e
   293  	})
   294  	if e != nil {
   295  		return nil, &PathError{Op: "open", Path: name, Err: e}
   296  	}
   297  
   298  	if !supportsCloseOnExec {
   299  		syscall.CloseOnExec(r)
   300  	}
   301  
   302  	f := newFile(r, name, kindNoPoll, false)
   303  	f.pfd.SysFile = s
   304  	return f, nil
   305  }
   306  
   307  func (file *file) close() error {
   308  	if file == nil {
   309  		return syscall.EINVAL
   310  	}
   311  	if info := file.dirinfo.Swap(nil); info != nil {
   312  		info.close()
   313  	}
   314  	var err error
   315  	if e := file.pfd.Close(); e != nil {
   316  		if e == poll.ErrFileClosing {
   317  			e = ErrClosed
   318  		}
   319  		err = &PathError{Op: "close", Path: file.name, Err: e}
   320  	}
   321  
   322  	// no need for a finalizer anymore
   323  	runtime.SetFinalizer(file, nil)
   324  	return err
   325  }
   326  
   327  // seek sets the offset for the next Read or Write on file to offset, interpreted
   328  // according to whence: 0 means relative to the origin of the file, 1 means
   329  // relative to the current offset, and 2 means relative to the end.
   330  // It returns the new offset and an error, if any.
   331  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   332  	if info := f.dirinfo.Swap(nil); info != nil {
   333  		// Free cached dirinfo, so we allocate a new one if we
   334  		// access this file as a directory again. See #35767 and #37161.
   335  		info.close()
   336  	}
   337  	ret, err = f.pfd.Seek(offset, whence)
   338  	runtime.KeepAlive(f)
   339  	return ret, err
   340  }
   341  
   342  // Truncate changes the size of the named file.
   343  // If the file is a symbolic link, it changes the size of the link's target.
   344  // If there is an error, it will be of type [*PathError].
   345  func Truncate(name string, size int64) error {
   346  	e := ignoringEINTR(func() error {
   347  		return syscall.Truncate(name, size)
   348  	})
   349  	if e != nil {
   350  		return &PathError{Op: "truncate", Path: name, Err: e}
   351  	}
   352  	return nil
   353  }
   354  
   355  // Remove removes the named file or (empty) directory.
   356  // If there is an error, it will be of type [*PathError].
   357  func Remove(name string) error {
   358  	// System call interface forces us to know
   359  	// whether name is a file or directory.
   360  	// Try both: it is cheaper on average than
   361  	// doing a Stat plus the right one.
   362  	e := ignoringEINTR(func() error {
   363  		return syscall.Unlink(name)
   364  	})
   365  	if e == nil {
   366  		return nil
   367  	}
   368  	e1 := ignoringEINTR(func() error {
   369  		return syscall.Rmdir(name)
   370  	})
   371  	if e1 == nil {
   372  		return nil
   373  	}
   374  
   375  	// Both failed: figure out which error to return.
   376  	// OS X and Linux differ on whether unlink(dir)
   377  	// returns EISDIR, so can't use that. However,
   378  	// both agree that rmdir(file) returns ENOTDIR,
   379  	// so we can use that to decide which error is real.
   380  	// Rmdir might also return ENOTDIR if given a bad
   381  	// file path, like /etc/passwd/foo, but in that case,
   382  	// both errors will be ENOTDIR, so it's okay to
   383  	// use the error from unlink.
   384  	if e1 != syscall.ENOTDIR {
   385  		e = e1
   386  	}
   387  	return &PathError{Op: "remove", Path: name, Err: e}
   388  }
   389  
   390  func tempDir() string {
   391  	dir := Getenv("TMPDIR")
   392  	if dir == "" {
   393  		if runtime.GOOS == "android" {
   394  			dir = "/data/local/tmp"
   395  		} else {
   396  			dir = "/tmp"
   397  		}
   398  	}
   399  	return dir
   400  }
   401  
   402  // Link creates newname as a hard link to the oldname file.
   403  // If there is an error, it will be of type *LinkError.
   404  func Link(oldname, newname string) error {
   405  	e := ignoringEINTR(func() error {
   406  		return syscall.Link(oldname, newname)
   407  	})
   408  	if e != nil {
   409  		return &LinkError{"link", oldname, newname, e}
   410  	}
   411  	return nil
   412  }
   413  
   414  // Symlink creates newname as a symbolic link to oldname.
   415  // On Windows, a symlink to a non-existent oldname creates a file symlink;
   416  // if oldname is later created as a directory the symlink will not work.
   417  // If there is an error, it will be of type *LinkError.
   418  func Symlink(oldname, newname string) error {
   419  	e := ignoringEINTR(func() error {
   420  		return syscall.Symlink(oldname, newname)
   421  	})
   422  	if e != nil {
   423  		return &LinkError{"symlink", oldname, newname, e}
   424  	}
   425  	return nil
   426  }
   427  
   428  func readlink(name string) (string, error) {
   429  	for len := 128; ; len *= 2 {
   430  		b := make([]byte, len)
   431  		n, err := ignoringEINTR2(func() (int, error) {
   432  			return fixCount(syscall.Readlink(name, b))
   433  		})
   434  		// buffer too small
   435  		if (runtime.GOOS == "aix" || runtime.GOOS == "wasip1") && err == syscall.ERANGE {
   436  			continue
   437  		}
   438  		if err != nil {
   439  			return "", &PathError{Op: "readlink", Path: name, Err: err}
   440  		}
   441  		if n < len {
   442  			return string(b[0:n]), nil
   443  		}
   444  	}
   445  }
   446  
   447  type unixDirent struct {
   448  	parent string
   449  	name   string
   450  	typ    FileMode
   451  	info   FileInfo
   452  }
   453  
   454  func (d *unixDirent) Name() string   { return d.name }
   455  func (d *unixDirent) IsDir() bool    { return d.typ.IsDir() }
   456  func (d *unixDirent) Type() FileMode { return d.typ }
   457  
   458  func (d *unixDirent) Info() (FileInfo, error) {
   459  	if d.info != nil {
   460  		return d.info, nil
   461  	}
   462  	return Lstat(d.parent + "/" + d.name)
   463  }
   464  
   465  func (d *unixDirent) String() string {
   466  	return fs.FormatDirEntry(d)
   467  }
   468  
   469  func newUnixDirent(parent *File, name string, typ FileMode) (DirEntry, error) {
   470  	ude := &unixDirent{
   471  		parent: parent.name,
   472  		name:   name,
   473  		typ:    typ,
   474  	}
   475  	// When the parent file was opened in a Root,
   476  	// we cannot use a lazy lstat to load the FileInfo.
   477  	// Use lstatat here.
   478  	if typ != ^FileMode(0) && !parent.inRoot {
   479  		return ude, nil
   480  	}
   481  
   482  	info, err := parent.lstatat(name)
   483  	if err != nil {
   484  		return nil, err
   485  	}
   486  
   487  	ude.typ = info.Mode().Type()
   488  	ude.info = info
   489  	return ude, nil
   490  }
   491  

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