Source file src/pkg/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	// +build darwin freebsd linux netbsd openbsd
     6	
     7	package os
     8	
     9	import (
    10		"runtime"
    11		"sync/atomic"
    12		"syscall"
    13	)
    14	
    15	// File represents an open file descriptor.
    16	type File struct {
    17		*file
    18	}
    19	
    20	// file is the real representation of *File.
    21	// The extra level of indirection ensures that no clients of os
    22	// can overwrite this data, which could cause the finalizer
    23	// to close the wrong file descriptor.
    24	type file struct {
    25		fd      int
    26		name    string
    27		dirinfo *dirInfo // nil unless directory being read
    28		nepipe  int32    // number of consecutive EPIPE in Write
    29	}
    30	
    31	// Fd returns the integer Unix file descriptor referencing the open file.
    32	func (f *File) Fd() uintptr {
    33		if f == nil {
    34			return ^(uintptr(0))
    35		}
    36		return uintptr(f.fd)
    37	}
    38	
    39	// NewFile returns a new File with the given file descriptor and name.
    40	func NewFile(fd uintptr, name string) *File {
    41		fdi := int(fd)
    42		if fdi < 0 {
    43			return nil
    44		}
    45		f := &File{&file{fd: fdi, name: name}}
    46		runtime.SetFinalizer(f.file, (*file).close)
    47		return f
    48	}
    49	
    50	// Auxiliary information if the File describes a directory
    51	type dirInfo struct {
    52		buf  []byte // buffer for directory I/O
    53		nbuf int    // length of buf; return value from Getdirentries
    54		bufp int    // location of next record in buf.
    55	}
    56	
    57	func epipecheck(file *File, e error) {
    58		if e == syscall.EPIPE {
    59			if atomic.AddInt32(&file.nepipe, 1) >= 10 {
    60				sigpipe()
    61			}
    62		} else {
    63			atomic.StoreInt32(&file.nepipe, 0)
    64		}
    65	}
    66	
    67	// DevNull is the name of the operating system's ``null device.''
    68	// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
    69	const DevNull = "/dev/null"
    70	
    71	// OpenFile is the generalized open call; most users will use Open
    72	// or Create instead.  It opens the named file with specified flag
    73	// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
    74	// methods on the returned File can be used for I/O.
    75	// If there is an error, it will be of type *PathError.
    76	func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
    77		r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
    78		if e != nil {
    79			return nil, &PathError{"open", name, e}
    80		}
    81	
    82		// There's a race here with fork/exec, which we are
    83		// content to live with.  See ../syscall/exec_unix.go.
    84		// On OS X 10.6, the O_CLOEXEC flag is not respected.
    85		// On OS X 10.7, the O_CLOEXEC flag works.
    86		// Without a cheap & reliable way to detect 10.6 vs 10.7 at
    87		// runtime, we just always call syscall.CloseOnExec on Darwin.
    88		// Once >=10.7 is prevalent, this extra call can removed.
    89		if syscall.O_CLOEXEC == 0 || runtime.GOOS == "darwin" { // O_CLOEXEC not supported
    90			syscall.CloseOnExec(r)
    91		}
    92	
    93		return NewFile(uintptr(r), name), nil
    94	}
    95	
    96	// Close closes the File, rendering it unusable for I/O.
    97	// It returns an error, if any.
    98	func (f *File) Close() error {
    99		return f.file.close()
   100	}
   101	
   102	func (file *file) close() error {
   103		if file == nil || file.fd < 0 {
   104			return syscall.EINVAL
   105		}
   106		var err error
   107		if e := syscall.Close(file.fd); e != nil {
   108			err = &PathError{"close", file.name, e}
   109		}
   110		file.fd = -1 // so it can't be closed again
   111	
   112		// no need for a finalizer anymore
   113		runtime.SetFinalizer(file, nil)
   114		return err
   115	}
   116	
   117	// Stat returns the FileInfo structure describing file.
   118	// If there is an error, it will be of type *PathError.
   119	func (f *File) Stat() (fi FileInfo, err error) {
   120		var stat syscall.Stat_t
   121		err = syscall.Fstat(f.fd, &stat)
   122		if err != nil {
   123			return nil, &PathError{"stat", f.name, err}
   124		}
   125		return fileInfoFromStat(&stat, f.name), nil
   126	}
   127	
   128	// Stat returns a FileInfo describing the named file.
   129	// If there is an error, it will be of type *PathError.
   130	func Stat(name string) (fi FileInfo, err error) {
   131		var stat syscall.Stat_t
   132		err = syscall.Stat(name, &stat)
   133		if err != nil {
   134			return nil, &PathError{"stat", name, err}
   135		}
   136		return fileInfoFromStat(&stat, name), nil
   137	}
   138	
   139	// Lstat returns a FileInfo describing the named file.
   140	// If the file is a symbolic link, the returned FileInfo
   141	// describes the symbolic link.  Lstat makes no attempt to follow the link.
   142	// If there is an error, it will be of type *PathError.
   143	func Lstat(name string) (fi FileInfo, err error) {
   144		var stat syscall.Stat_t
   145		err = syscall.Lstat(name, &stat)
   146		if err != nil {
   147			return nil, &PathError{"lstat", name, err}
   148		}
   149		return fileInfoFromStat(&stat, name), nil
   150	}
   151	
   152	func (f *File) readdir(n int) (fi []FileInfo, err error) {
   153		dirname := f.name
   154		if dirname == "" {
   155			dirname = "."
   156		}
   157		dirname += "/"
   158		names, err := f.Readdirnames(n)
   159		fi = make([]FileInfo, len(names))
   160		for i, filename := range names {
   161			fip, err := Lstat(dirname + filename)
   162			if err == nil {
   163				fi[i] = fip
   164			} else {
   165				fi[i] = &fileStat{name: filename}
   166			}
   167		}
   168		return fi, err
   169	}
   170	
   171	// read reads up to len(b) bytes from the File.
   172	// It returns the number of bytes read and an error, if any.
   173	func (f *File) read(b []byte) (n int, err error) {
   174		return syscall.Read(f.fd, b)
   175	}
   176	
   177	// pread reads len(b) bytes from the File starting at byte offset off.
   178	// It returns the number of bytes read and the error, if any.
   179	// EOF is signaled by a zero count with err set to 0.
   180	func (f *File) pread(b []byte, off int64) (n int, err error) {
   181		return syscall.Pread(f.fd, b, off)
   182	}
   183	
   184	// write writes len(b) bytes to the File.
   185	// It returns the number of bytes written and an error, if any.
   186	func (f *File) write(b []byte) (n int, err error) {
   187		for {
   188			m, err := syscall.Write(f.fd, b)
   189			n += m
   190	
   191			// If the syscall wrote some data but not all (short write)
   192			// or it returned EINTR, then assume it stopped early for
   193			// reasons that are uninteresting to the caller, and try again.
   194			if 0 < m && m < len(b) || err == syscall.EINTR {
   195				b = b[m:]
   196				continue
   197			}
   198	
   199			return n, err
   200		}
   201	}
   202	
   203	// pwrite writes len(b) bytes to the File starting at byte offset off.
   204	// It returns the number of bytes written and an error, if any.
   205	func (f *File) pwrite(b []byte, off int64) (n int, err error) {
   206		return syscall.Pwrite(f.fd, b, off)
   207	}
   208	
   209	// seek sets the offset for the next Read or Write on file to offset, interpreted
   210	// according to whence: 0 means relative to the origin of the file, 1 means
   211	// relative to the current offset, and 2 means relative to the end.
   212	// It returns the new offset and an error, if any.
   213	func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   214		return syscall.Seek(f.fd, offset, whence)
   215	}
   216	
   217	// Truncate changes the size of the named file.
   218	// If the file is a symbolic link, it changes the size of the link's target.
   219	// If there is an error, it will be of type *PathError.
   220	func Truncate(name string, size int64) error {
   221		if e := syscall.Truncate(name, size); e != nil {
   222			return &PathError{"truncate", name, e}
   223		}
   224		return nil
   225	}
   226	
   227	// Remove removes the named file or directory.
   228	// If there is an error, it will be of type *PathError.
   229	func Remove(name string) error {
   230		// System call interface forces us to know
   231		// whether name is a file or directory.
   232		// Try both: it is cheaper on average than
   233		// doing a Stat plus the right one.
   234		e := syscall.Unlink(name)
   235		if e == nil {
   236			return nil
   237		}
   238		e1 := syscall.Rmdir(name)
   239		if e1 == nil {
   240			return nil
   241		}
   242	
   243		// Both failed: figure out which error to return.
   244		// OS X and Linux differ on whether unlink(dir)
   245		// returns EISDIR, so can't use that.  However,
   246		// both agree that rmdir(file) returns ENOTDIR,
   247		// so we can use that to decide which error is real.
   248		// Rmdir might also return ENOTDIR if given a bad
   249		// file path, like /etc/passwd/foo, but in that case,
   250		// both errors will be ENOTDIR, so it's okay to
   251		// use the error from unlink.
   252		if e1 != syscall.ENOTDIR {
   253			e = e1
   254		}
   255		return &PathError{"remove", name, e}
   256	}
   257	
   258	// basename removes trailing slashes and the leading directory name from path name
   259	func basename(name string) string {
   260		i := len(name) - 1
   261		// Remove trailing slashes
   262		for ; i > 0 && name[i] == '/'; i-- {
   263			name = name[:i]
   264		}
   265		// Remove leading directory name
   266		for i--; i >= 0; i-- {
   267			if name[i] == '/' {
   268				name = name[i+1:]
   269				break
   270			}
   271		}
   272	
   273		return name
   274	}
   275	
   276	// TempDir returns the default directory to use for temporary files.
   277	func TempDir() string {
   278		dir := Getenv("TMPDIR")
   279		if dir == "" {
   280			dir = "/tmp"
   281		}
   282		return dir
   283	}

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