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  }
    67  
    68  // Fd returns the integer Unix file descriptor referencing the open file.
    69  // If f is closed, the file descriptor becomes invalid.
    70  // If f is garbage collected, a finalizer may close the file descriptor,
    71  // making it invalid; see [runtime.SetFinalizer] for more information on when
    72  // a finalizer might be run. On Unix systems this will cause the [File.SetDeadline]
    73  // methods to stop working.
    74  // Because file descriptors can be reused, the returned file descriptor may
    75  // only be closed through the [File.Close] method of f, or by its finalizer during
    76  // garbage collection. Otherwise, during garbage collection the finalizer
    77  // may close an unrelated file descriptor with the same (reused) number.
    78  //
    79  // As an alternative, see the f.SyscallConn method.
    80  func (f *File) Fd() uintptr {
    81  	if f == nil {
    82  		return ^(uintptr(0))
    83  	}
    84  
    85  	// If we put the file descriptor into nonblocking mode,
    86  	// then set it to blocking mode before we return it,
    87  	// because historically we have always returned a descriptor
    88  	// opened in blocking mode. The File will continue to work,
    89  	// but any blocking operation will tie up a thread.
    90  	if f.nonblock {
    91  		f.pfd.SetBlocking()
    92  	}
    93  
    94  	return uintptr(f.pfd.Sysfd)
    95  }
    96  
    97  // NewFile returns a new File with the given file descriptor and
    98  // name. The returned value will be nil if fd is not a valid file
    99  // descriptor. On Unix systems, if the file descriptor is in
   100  // non-blocking mode, NewFile will attempt to return a pollable File
   101  // (one for which the SetDeadline methods work).
   102  //
   103  // After passing it to NewFile, fd may become invalid under the same
   104  // conditions described in the comments of the Fd method, and the same
   105  // constraints apply.
   106  func NewFile(fd uintptr, name string) *File {
   107  	fdi := int(fd)
   108  	if fdi < 0 {
   109  		return nil
   110  	}
   111  
   112  	flags, err := unix.Fcntl(fdi, syscall.F_GETFL, 0)
   113  	if err != nil {
   114  		flags = 0
   115  	}
   116  	f := newFile(fdi, name, kindNewFile, unix.HasNonblockFlag(flags))
   117  	f.appendMode = flags&syscall.O_APPEND != 0
   118  	return f
   119  }
   120  
   121  // net_newUnixFile is a hidden entry point called by net.conn.File.
   122  // This is used so that a nonblocking network connection will become
   123  // blocking if code calls the Fd method. We don't want that for direct
   124  // calls to NewFile: passing a nonblocking descriptor to NewFile should
   125  // remain nonblocking if you get it back using Fd. But for net.conn.File
   126  // the call to NewFile is hidden from the user. Historically in that case
   127  // the Fd method has returned a blocking descriptor, and we want to
   128  // retain that behavior because existing code expects it and depends on it.
   129  //
   130  //go:linkname net_newUnixFile net.newUnixFile
   131  func net_newUnixFile(fd int, name string) *File {
   132  	if fd < 0 {
   133  		panic("invalid FD")
   134  	}
   135  
   136  	return newFile(fd, name, kindSock, true)
   137  }
   138  
   139  // newFileKind describes the kind of file to newFile.
   140  type newFileKind int
   141  
   142  const (
   143  	// kindNewFile means that the descriptor was passed to us via NewFile.
   144  	kindNewFile newFileKind = iota
   145  	// kindOpenFile means that the descriptor was opened using
   146  	// Open, Create, or OpenFile.
   147  	kindOpenFile
   148  	// kindPipe means that the descriptor was opened using Pipe.
   149  	kindPipe
   150  	// kindSock means that the descriptor is a network file descriptor
   151  	// that was created from net package and was opened using net_newUnixFile.
   152  	kindSock
   153  	// kindNoPoll means that we should not put the descriptor into
   154  	// non-blocking mode, because we know it is not a pipe or FIFO.
   155  	// Used by openDirAt and openDirNolog for directories.
   156  	kindNoPoll
   157  )
   158  
   159  // newFile is like NewFile, but if called from OpenFile or Pipe
   160  // (as passed in the kind parameter) it tries to add the file to
   161  // the runtime poller.
   162  func newFile(fd int, name string, kind newFileKind, nonBlocking bool) *File {
   163  	f := &File{&file{
   164  		pfd: poll.FD{
   165  			Sysfd:         fd,
   166  			IsStream:      true,
   167  			ZeroReadIsEOF: true,
   168  		},
   169  		name:        name,
   170  		stdoutOrErr: fd == 1 || fd == 2,
   171  	}}
   172  
   173  	pollable := kind == kindOpenFile || kind == kindPipe || kind == kindSock || nonBlocking
   174  
   175  	// Things like regular files and FIFOs in kqueue on *BSD/Darwin
   176  	// may not work properly (or accurately according to its manual).
   177  	// As a result, we should avoid adding those to the kqueue-based
   178  	// netpoller. Check out #19093, #24164, and #66239 for more contexts.
   179  	//
   180  	// If the fd was passed to us via any path other than OpenFile,
   181  	// we assume those callers know what they were doing, so we won't
   182  	// perform this check and allow it to be added to the kqueue.
   183  	if kind == kindOpenFile {
   184  		switch runtime.GOOS {
   185  		case "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd":
   186  			var st syscall.Stat_t
   187  			err := ignoringEINTR(func() error {
   188  				return syscall.Fstat(fd, &st)
   189  			})
   190  			typ := st.Mode & syscall.S_IFMT
   191  			// Don't try to use kqueue with regular files on *BSDs.
   192  			// On FreeBSD a regular file is always
   193  			// reported as ready for writing.
   194  			// On Dragonfly, NetBSD and OpenBSD the fd is signaled
   195  			// only once as ready (both read and write).
   196  			// Issue 19093.
   197  			// Also don't add directories to the netpoller.
   198  			if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
   199  				pollable = false
   200  			}
   201  
   202  			// In addition to the behavior described above for regular files,
   203  			// on Darwin, kqueue does not work properly with fifos:
   204  			// closing the last writer does not cause a kqueue event
   205  			// for any readers. See issue #24164.
   206  			if (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && typ == syscall.S_IFIFO {
   207  				pollable = false
   208  			}
   209  		}
   210  	}
   211  
   212  	clearNonBlock := false
   213  	if pollable {
   214  		// The descriptor is already in non-blocking mode.
   215  		// We only set f.nonblock if we put the file into
   216  		// non-blocking mode.
   217  		if nonBlocking {
   218  			// See the comments on net_newUnixFile.
   219  			if kind == kindSock {
   220  				f.nonblock = true // tell Fd to return blocking descriptor
   221  			}
   222  		} else if err := syscall.SetNonblock(fd, true); err == nil {
   223  			f.nonblock = true
   224  			clearNonBlock = true
   225  		} else {
   226  			pollable = false
   227  		}
   228  	}
   229  
   230  	// An error here indicates a failure to register
   231  	// with the netpoll system. That can happen for
   232  	// a file descriptor that is not supported by
   233  	// epoll/kqueue; for example, disk files on
   234  	// Linux systems. We assume that any real error
   235  	// will show up in later I/O.
   236  	// We do restore the blocking behavior if it was set by us.
   237  	if pollErr := f.pfd.Init("file", pollable); pollErr != nil && clearNonBlock {
   238  		if err := syscall.SetNonblock(fd, false); err == nil {
   239  			f.nonblock = false
   240  		}
   241  	}
   242  
   243  	runtime.SetFinalizer(f.file, (*file).close)
   244  	return f
   245  }
   246  
   247  func sigpipe() // implemented in package runtime
   248  
   249  // epipecheck raises SIGPIPE if we get an EPIPE error on standard
   250  // output or standard error. See the SIGPIPE docs in os/signal, and
   251  // issue 11845.
   252  func epipecheck(file *File, e error) {
   253  	if e == syscall.EPIPE && file.stdoutOrErr {
   254  		sigpipe()
   255  	}
   256  }
   257  
   258  // DevNull is the name of the operating system's “null device.”
   259  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
   260  const DevNull = "/dev/null"
   261  
   262  // openFileNolog is the Unix implementation of OpenFile.
   263  // Changes here should be reflected in openDirAt and openDirNolog, if relevant.
   264  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   265  	setSticky := false
   266  	if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
   267  		if _, err := Stat(name); IsNotExist(err) {
   268  			setSticky = true
   269  		}
   270  	}
   271  
   272  	var (
   273  		r int
   274  		s poll.SysFile
   275  		e error
   276  	)
   277  	// We have to check EINTR here, per issues 11180 and 39237.
   278  	ignoringEINTR(func() error {
   279  		r, s, e = open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
   280  		return e
   281  	})
   282  	if e != nil {
   283  		return nil, &PathError{Op: "open", Path: name, Err: e}
   284  	}
   285  
   286  	// open(2) itself won't handle the sticky bit on *BSD and Solaris
   287  	if setSticky {
   288  		setStickyBit(name)
   289  	}
   290  
   291  	// There's a race here with fork/exec, which we are
   292  	// content to live with. See ../syscall/exec_unix.go.
   293  	if !supportsCloseOnExec {
   294  		syscall.CloseOnExec(r)
   295  	}
   296  
   297  	f := newFile(r, name, kindOpenFile, unix.HasNonblockFlag(flag))
   298  	f.pfd.SysFile = s
   299  	return f, nil
   300  }
   301  
   302  func openDirNolog(name string) (*File, error) {
   303  	var (
   304  		r int
   305  		s poll.SysFile
   306  		e error
   307  	)
   308  	ignoringEINTR(func() error {
   309  		r, s, e = open(name, O_RDONLY|syscall.O_CLOEXEC, 0)
   310  		return e
   311  	})
   312  	if e != nil {
   313  		return nil, &PathError{Op: "open", Path: name, Err: e}
   314  	}
   315  
   316  	if !supportsCloseOnExec {
   317  		syscall.CloseOnExec(r)
   318  	}
   319  
   320  	f := newFile(r, name, kindNoPoll, false)
   321  	f.pfd.SysFile = s
   322  	return f, nil
   323  }
   324  
   325  func (file *file) close() error {
   326  	if file == nil {
   327  		return syscall.EINVAL
   328  	}
   329  	if info := file.dirinfo.Swap(nil); info != nil {
   330  		info.close()
   331  	}
   332  	var err error
   333  	if e := file.pfd.Close(); e != nil {
   334  		if e == poll.ErrFileClosing {
   335  			e = ErrClosed
   336  		}
   337  		err = &PathError{Op: "close", Path: file.name, Err: e}
   338  	}
   339  
   340  	// no need for a finalizer anymore
   341  	runtime.SetFinalizer(file, nil)
   342  	return err
   343  }
   344  
   345  // seek sets the offset for the next Read or Write on file to offset, interpreted
   346  // according to whence: 0 means relative to the origin of the file, 1 means
   347  // relative to the current offset, and 2 means relative to the end.
   348  // It returns the new offset and an error, if any.
   349  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   350  	if info := f.dirinfo.Swap(nil); info != nil {
   351  		// Free cached dirinfo, so we allocate a new one if we
   352  		// access this file as a directory again. See #35767 and #37161.
   353  		info.close()
   354  	}
   355  	ret, err = f.pfd.Seek(offset, whence)
   356  	runtime.KeepAlive(f)
   357  	return ret, err
   358  }
   359  
   360  // Truncate changes the size of the named file.
   361  // If the file is a symbolic link, it changes the size of the link's target.
   362  // If there is an error, it will be of type *PathError.
   363  func Truncate(name string, size int64) error {
   364  	e := ignoringEINTR(func() error {
   365  		return syscall.Truncate(name, size)
   366  	})
   367  	if e != nil {
   368  		return &PathError{Op: "truncate", Path: name, Err: e}
   369  	}
   370  	return nil
   371  }
   372  
   373  // Remove removes the named file or (empty) directory.
   374  // If there is an error, it will be of type *PathError.
   375  func Remove(name string) error {
   376  	// System call interface forces us to know
   377  	// whether name is a file or directory.
   378  	// Try both: it is cheaper on average than
   379  	// doing a Stat plus the right one.
   380  	e := ignoringEINTR(func() error {
   381  		return syscall.Unlink(name)
   382  	})
   383  	if e == nil {
   384  		return nil
   385  	}
   386  	e1 := ignoringEINTR(func() error {
   387  		return syscall.Rmdir(name)
   388  	})
   389  	if e1 == nil {
   390  		return nil
   391  	}
   392  
   393  	// Both failed: figure out which error to return.
   394  	// OS X and Linux differ on whether unlink(dir)
   395  	// returns EISDIR, so can't use that. However,
   396  	// both agree that rmdir(file) returns ENOTDIR,
   397  	// so we can use that to decide which error is real.
   398  	// Rmdir might also return ENOTDIR if given a bad
   399  	// file path, like /etc/passwd/foo, but in that case,
   400  	// both errors will be ENOTDIR, so it's okay to
   401  	// use the error from unlink.
   402  	if e1 != syscall.ENOTDIR {
   403  		e = e1
   404  	}
   405  	return &PathError{Op: "remove", Path: name, Err: e}
   406  }
   407  
   408  func tempDir() string {
   409  	dir := Getenv("TMPDIR")
   410  	if dir == "" {
   411  		if runtime.GOOS == "android" {
   412  			dir = "/data/local/tmp"
   413  		} else {
   414  			dir = "/tmp"
   415  		}
   416  	}
   417  	return dir
   418  }
   419  
   420  // Link creates newname as a hard link to the oldname file.
   421  // If there is an error, it will be of type *LinkError.
   422  func Link(oldname, newname string) error {
   423  	e := ignoringEINTR(func() error {
   424  		return syscall.Link(oldname, newname)
   425  	})
   426  	if e != nil {
   427  		return &LinkError{"link", oldname, newname, e}
   428  	}
   429  	return nil
   430  }
   431  
   432  // Symlink creates newname as a symbolic link to oldname.
   433  // On Windows, a symlink to a non-existent oldname creates a file symlink;
   434  // if oldname is later created as a directory the symlink will not work.
   435  // If there is an error, it will be of type *LinkError.
   436  func Symlink(oldname, newname string) error {
   437  	e := ignoringEINTR(func() error {
   438  		return syscall.Symlink(oldname, newname)
   439  	})
   440  	if e != nil {
   441  		return &LinkError{"symlink", oldname, newname, e}
   442  	}
   443  	return nil
   444  }
   445  
   446  func readlink(name string) (string, error) {
   447  	for len := 128; ; len *= 2 {
   448  		b := make([]byte, len)
   449  		var (
   450  			n int
   451  			e error
   452  		)
   453  		for {
   454  			n, e = fixCount(syscall.Readlink(name, b))
   455  			if e != syscall.EINTR {
   456  				break
   457  			}
   458  		}
   459  		// buffer too small
   460  		if (runtime.GOOS == "aix" || runtime.GOOS == "wasip1") && e == syscall.ERANGE {
   461  			continue
   462  		}
   463  		if e != nil {
   464  			return "", &PathError{Op: "readlink", Path: name, Err: e}
   465  		}
   466  		if n < len {
   467  			return string(b[0:n]), nil
   468  		}
   469  	}
   470  }
   471  
   472  type unixDirent struct {
   473  	parent string
   474  	name   string
   475  	typ    FileMode
   476  	info   FileInfo
   477  }
   478  
   479  func (d *unixDirent) Name() string   { return d.name }
   480  func (d *unixDirent) IsDir() bool    { return d.typ.IsDir() }
   481  func (d *unixDirent) Type() FileMode { return d.typ }
   482  
   483  func (d *unixDirent) Info() (FileInfo, error) {
   484  	if d.info != nil {
   485  		return d.info, nil
   486  	}
   487  	return lstat(d.parent + "/" + d.name)
   488  }
   489  
   490  func (d *unixDirent) String() string {
   491  	return fs.FormatDirEntry(d)
   492  }
   493  
   494  func newUnixDirent(parent, name string, typ FileMode) (DirEntry, error) {
   495  	ude := &unixDirent{
   496  		parent: parent,
   497  		name:   name,
   498  		typ:    typ,
   499  	}
   500  	if typ != ^FileMode(0) && !testingForceReadDirLstat {
   501  		return ude, nil
   502  	}
   503  
   504  	info, err := lstat(parent + "/" + name)
   505  	if err != nil {
   506  		return nil, err
   507  	}
   508  
   509  	ude.typ = info.Mode().Type()
   510  	ude.info = info
   511  	return ude, nil
   512  }
   513
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