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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	// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
     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	// The file descriptor is valid only until f.Close is called or f is garbage collected.
    33	func (f *File) Fd() uintptr {
    34		if f == nil {
    35			return ^(uintptr(0))
    36		}
    37		return uintptr(f.fd)
    38	}
    39	
    40	// NewFile returns a new File with the given file descriptor and name.
    41	func NewFile(fd uintptr, name string) *File {
    42		fdi := int(fd)
    43		if fdi < 0 {
    44			return nil
    45		}
    46		f := &File{&file{fd: fdi, name: name}}
    47		runtime.SetFinalizer(f.file, (*file).close)
    48		return f
    49	}
    50	
    51	// Auxiliary information if the File describes a directory
    52	type dirInfo struct {
    53		buf  []byte // buffer for directory I/O
    54		nbuf int    // length of buf; return value from Getdirentries
    55		bufp int    // location of next record in buf.
    56	}
    57	
    58	func epipecheck(file *File, e error) {
    59		if e == syscall.EPIPE {
    60			if atomic.AddInt32(&file.nepipe, 1) >= 10 {
    61				sigpipe()
    62			}
    63		} else {
    64			atomic.StoreInt32(&file.nepipe, 0)
    65		}
    66	}
    67	
    68	// DevNull is the name of the operating system's ``null device.''
    69	// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
    70	const DevNull = "/dev/null"
    71	
    72	// OpenFile is the generalized open call; most users will use Open
    73	// or Create instead.  It opens the named file with specified flag
    74	// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
    75	// methods on the returned File can be used for I/O.
    76	// If there is an error, it will be of type *PathError.
    77	func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
    78		r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
    79		if e != nil {
    80			return nil, &PathError{"open", name, e}
    81		}
    82	
    83		// There's a race here with fork/exec, which we are
    84		// content to live with.  See ../syscall/exec_unix.go.
    85		if !supportsCloseOnExec {
    86			syscall.CloseOnExec(r)
    87		}
    88	
    89		return NewFile(uintptr(r), name), nil
    90	}
    91	
    92	// Close closes the File, rendering it unusable for I/O.
    93	// It returns an error, if any.
    94	func (f *File) Close() error {
    95		if f == nil {
    96			return ErrInvalid
    97		}
    98		return f.file.close()
    99	}
   100	
   101	func (file *file) close() error {
   102		if file == nil || file.fd < 0 {
   103			return syscall.EINVAL
   104		}
   105		var err error
   106		if e := syscall.Close(file.fd); e != nil {
   107			err = &PathError{"close", file.name, e}
   108		}
   109		file.fd = -1 // so it can't be closed again
   110	
   111		// no need for a finalizer anymore
   112		runtime.SetFinalizer(file, nil)
   113		return err
   114	}
   115	
   116	// Stat returns the FileInfo structure describing file.
   117	// If there is an error, it will be of type *PathError.
   118	func (f *File) Stat() (fi FileInfo, err error) {
   119		if f == nil {
   120			return nil, ErrInvalid
   121		}
   122		var stat syscall.Stat_t
   123		err = syscall.Fstat(f.fd, &stat)
   124		if err != nil {
   125			return nil, &PathError{"stat", f.name, err}
   126		}
   127		return fileInfoFromStat(&stat, f.name), nil
   128	}
   129	
   130	// Stat returns a FileInfo describing the named file.
   131	// If there is an error, it will be of type *PathError.
   132	func Stat(name string) (fi FileInfo, err error) {
   133		var stat syscall.Stat_t
   134		err = syscall.Stat(name, &stat)
   135		if err != nil {
   136			return nil, &PathError{"stat", name, err}
   137		}
   138		return fileInfoFromStat(&stat, name), nil
   139	}
   140	
   141	// Lstat returns a FileInfo describing the named file.
   142	// If the file is a symbolic link, the returned FileInfo
   143	// describes the symbolic link.  Lstat makes no attempt to follow the link.
   144	// If there is an error, it will be of type *PathError.
   145	func Lstat(name string) (fi FileInfo, err error) {
   146		var stat syscall.Stat_t
   147		err = syscall.Lstat(name, &stat)
   148		if err != nil {
   149			return nil, &PathError{"lstat", name, err}
   150		}
   151		return fileInfoFromStat(&stat, name), nil
   152	}
   153	
   154	func (f *File) readdir(n int) (fi []FileInfo, err error) {
   155		dirname := f.name
   156		if dirname == "" {
   157			dirname = "."
   158		}
   159		names, err := f.Readdirnames(n)
   160		fi = make([]FileInfo, 0, len(names))
   161		for _, filename := range names {
   162			fip, lerr := lstat(dirname + "/" + filename)
   163			if IsNotExist(lerr) {
   164				// File disappeared between readdir + stat.
   165				// Just treat it as if it didn't exist.
   166				continue
   167			}
   168			if lerr != nil {
   169				return fi, lerr
   170			}
   171			fi = append(fi, fip)
   172		}
   173		return fi, err
   174	}
   175	
   176	// Darwin and FreeBSD can't read or write 2GB+ at a time,
   177	// even on 64-bit systems. See golang.org/issue/7812.
   178	// Use 1GB instead of, say, 2GB-1, to keep subsequent
   179	// reads aligned.
   180	const (
   181		needsMaxRW = runtime.GOOS == "darwin" || runtime.GOOS == "freebsd"
   182		maxRW      = 1 << 30
   183	)
   184	
   185	// read reads up to len(b) bytes from the File.
   186	// It returns the number of bytes read and an error, if any.
   187	func (f *File) read(b []byte) (n int, err error) {
   188		if needsMaxRW && len(b) > maxRW {
   189			b = b[:maxRW]
   190		}
   191		return fixCount(syscall.Read(f.fd, b))
   192	}
   193	
   194	// pread reads len(b) bytes from the File starting at byte offset off.
   195	// It returns the number of bytes read and the error, if any.
   196	// EOF is signaled by a zero count with err set to nil.
   197	func (f *File) pread(b []byte, off int64) (n int, err error) {
   198		if needsMaxRW && len(b) > maxRW {
   199			b = b[:maxRW]
   200		}
   201		return fixCount(syscall.Pread(f.fd, b, off))
   202	}
   203	
   204	// write writes len(b) bytes to the File.
   205	// It returns the number of bytes written and an error, if any.
   206	func (f *File) write(b []byte) (n int, err error) {
   207		for {
   208			bcap := b
   209			if needsMaxRW && len(bcap) > maxRW {
   210				bcap = bcap[:maxRW]
   211			}
   212			m, err := fixCount(syscall.Write(f.fd, bcap))
   213			n += m
   214	
   215			// If the syscall wrote some data but not all (short write)
   216			// or it returned EINTR, then assume it stopped early for
   217			// reasons that are uninteresting to the caller, and try again.
   218			if 0 < m && m < len(bcap) || err == syscall.EINTR {
   219				b = b[m:]
   220				continue
   221			}
   222	
   223			if needsMaxRW && len(bcap) != len(b) && err == nil {
   224				b = b[m:]
   225				continue
   226			}
   227	
   228			return n, err
   229		}
   230	}
   231	
   232	// pwrite writes len(b) bytes to the File starting at byte offset off.
   233	// It returns the number of bytes written and an error, if any.
   234	func (f *File) pwrite(b []byte, off int64) (n int, err error) {
   235		if needsMaxRW && len(b) > maxRW {
   236			b = b[:maxRW]
   237		}
   238		return fixCount(syscall.Pwrite(f.fd, b, off))
   239	}
   240	
   241	// seek sets the offset for the next Read or Write on file to offset, interpreted
   242	// according to whence: 0 means relative to the origin of the file, 1 means
   243	// relative to the current offset, and 2 means relative to the end.
   244	// It returns the new offset and an error, if any.
   245	func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   246		return syscall.Seek(f.fd, offset, whence)
   247	}
   248	
   249	// Truncate changes the size of the named file.
   250	// If the file is a symbolic link, it changes the size of the link's target.
   251	// If there is an error, it will be of type *PathError.
   252	func Truncate(name string, size int64) error {
   253		if e := syscall.Truncate(name, size); e != nil {
   254			return &PathError{"truncate", name, e}
   255		}
   256		return nil
   257	}
   258	
   259	// Remove removes the named file or directory.
   260	// If there is an error, it will be of type *PathError.
   261	func Remove(name string) error {
   262		// System call interface forces us to know
   263		// whether name is a file or directory.
   264		// Try both: it is cheaper on average than
   265		// doing a Stat plus the right one.
   266		e := syscall.Unlink(name)
   267		if e == nil {
   268			return nil
   269		}
   270		e1 := syscall.Rmdir(name)
   271		if e1 == nil {
   272			return nil
   273		}
   274	
   275		// Both failed: figure out which error to return.
   276		// OS X and Linux differ on whether unlink(dir)
   277		// returns EISDIR, so can't use that.  However,
   278		// both agree that rmdir(file) returns ENOTDIR,
   279		// so we can use that to decide which error is real.
   280		// Rmdir might also return ENOTDIR if given a bad
   281		// file path, like /etc/passwd/foo, but in that case,
   282		// both errors will be ENOTDIR, so it's okay to
   283		// use the error from unlink.
   284		if e1 != syscall.ENOTDIR {
   285			e = e1
   286		}
   287		return &PathError{"remove", name, e}
   288	}
   289	
   290	// basename removes trailing slashes and the leading directory name from path name
   291	func basename(name string) string {
   292		i := len(name) - 1
   293		// Remove trailing slashes
   294		for ; i > 0 && name[i] == '/'; i-- {
   295			name = name[:i]
   296		}
   297		// Remove leading directory name
   298		for i--; i >= 0; i-- {
   299			if name[i] == '/' {
   300				name = name[i+1:]
   301				break
   302			}
   303		}
   304	
   305		return name
   306	}
   307	
   308	// TempDir returns the default directory to use for temporary files.
   309	func TempDir() string {
   310		dir := Getenv("TMPDIR")
   311		if dir == "" {
   312			if runtime.GOOS == "android" {
   313				dir = "/data/local/tmp"
   314			} else {
   315				dir = "/tmp"
   316			}
   317		}
   318		return dir
   319	}
   320	
   321	// Link creates newname as a hard link to the oldname file.
   322	// If there is an error, it will be of type *LinkError.
   323	func Link(oldname, newname string) error {
   324		e := syscall.Link(oldname, newname)
   325		if e != nil {
   326			return &LinkError{"link", oldname, newname, e}
   327		}
   328		return nil
   329	}
   330	
   331	// Symlink creates newname as a symbolic link to oldname.
   332	// If there is an error, it will be of type *LinkError.
   333	func Symlink(oldname, newname string) error {
   334		e := syscall.Symlink(oldname, newname)
   335		if e != nil {
   336			return &LinkError{"symlink", oldname, newname, e}
   337		}
   338		return nil
   339	}
   340	

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