1 // A UnixVolume is a Volume backed by a locally mounted disk.
21 // A UnixVolume stores and retrieves blocks in a local directory.
22 type UnixVolume struct {
23 root string // path to the volume's root directory
29 func (v *UnixVolume) Touch(loc string) error {
31 return MethodDisabledError
34 f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
41 defer v.mutex.Unlock()
43 if e := lockfile(f); e != nil {
47 now := time.Now().Unix()
48 utime := syscall.Utimbuf{now, now}
49 return syscall.Utime(p, &utime)
52 func (v *UnixVolume) Mtime(loc string) (time.Time, error) {
54 if fi, err := os.Stat(p); err != nil {
55 return time.Time{}, err
57 return fi.ModTime(), nil
61 // Open the given file, apply the serialize lock if enabled, and call
62 // the given function if and when the file is ready to read.
63 func (v *UnixVolume) getFunc(path string, fn func(io.Reader) error) error {
64 f, err := os.Open(path)
71 defer v.mutex.Unlock()
76 // stat is os.Stat() with some extra sanity checks.
77 func (v *UnixVolume) stat(path string) (os.FileInfo, error) {
78 stat, err := os.Stat(path)
82 } else if stat.Size() > BLOCKSIZE {
89 // Get retrieves a block identified by the locator string "loc", and
90 // returns its contents as a byte slice.
92 // Get returns a nil buffer IFF it returns a non-nil error.
93 func (v *UnixVolume) Get(loc string) ([]byte, error) {
94 path := v.blockPath(loc)
95 stat, err := v.stat(path)
99 buf := bufs.Get(int(stat.Size()))
100 err = v.getFunc(path, func(rdr io.Reader) error {
101 _, err = io.ReadFull(rdr, buf)
111 // Compare returns nil if Get(loc) would return the same content as
112 // cmp. It is functionally equivalent to Get() followed by
113 // bytes.Compare(), but uses less memory.
115 // TODO(TC): Before returning CollisionError, compute the MD5 digest
116 // of the data on disk (i.e., known-to-be-equal data in cmp +
117 // remaining data on disk) and return DiskHashError instead of
118 // CollisionError if it doesn't equal loc[:32].
119 func (v *UnixVolume) Compare(loc string, cmp []byte) error {
120 path := v.blockPath(loc)
121 stat, err := v.stat(path)
126 if int64(bufLen) > stat.Size() {
127 bufLen = int(stat.Size())
129 buf := make([]byte, bufLen)
130 return v.getFunc(path, func(rdr io.Reader) error {
131 // Loop invariants: all data read so far matched what
132 // we expected, and the first N bytes of cmp are
133 // expected to equal the next N bytes read from
136 n, err := rdr.Read(buf)
138 // file on disk is too long
139 return CollisionError
140 } else if n > 0 && bytes.Compare(cmp[:n], buf[:n]) != 0 {
141 return CollisionError
146 // file on disk is too short
147 return CollisionError
150 } else if err != nil {
157 // Put stores a block of data identified by the locator string
158 // "loc". It returns nil on success. If the volume is full, it
159 // returns a FullError. If the write fails due to some other error,
160 // that error is returned.
161 func (v *UnixVolume) Put(loc string, block []byte) error {
163 return MethodDisabledError
168 bdir := v.blockDir(loc)
169 if err := os.MkdirAll(bdir, 0755); err != nil {
170 log.Printf("%s: could not create directory %s: %s",
175 tmpfile, tmperr := ioutil.TempFile(bdir, "tmp"+loc)
177 log.Printf("ioutil.TempFile(%s, tmp%s): %s", bdir, loc, tmperr)
180 bpath := v.blockPath(loc)
184 defer v.mutex.Unlock()
186 if _, err := tmpfile.Write(block); err != nil {
187 log.Printf("%s: writing to %s: %s\n", v, bpath, err)
189 os.Remove(tmpfile.Name())
192 if err := tmpfile.Close(); err != nil {
193 log.Printf("closing %s: %s\n", tmpfile.Name(), err)
194 os.Remove(tmpfile.Name())
197 if err := os.Rename(tmpfile.Name(), bpath); err != nil {
198 log.Printf("rename %s %s: %s\n", tmpfile.Name(), bpath, err)
199 os.Remove(tmpfile.Name())
205 // Status returns a VolumeStatus struct describing the volume's
206 // current state, or nil if an error occurs.
208 func (v *UnixVolume) Status() *VolumeStatus {
209 var fs syscall.Statfs_t
212 if fi, err := os.Stat(v.root); err == nil {
213 devnum = fi.Sys().(*syscall.Stat_t).Dev
215 log.Printf("%s: os.Stat: %s\n", v, err)
219 err := syscall.Statfs(v.root, &fs)
221 log.Printf("%s: statfs: %s\n", v, err)
224 // These calculations match the way df calculates disk usage:
225 // "free" space is measured by fs.Bavail, but "used" space
226 // uses fs.Blocks - fs.Bfree.
227 free := fs.Bavail * uint64(fs.Bsize)
228 used := (fs.Blocks - fs.Bfree) * uint64(fs.Bsize)
229 return &VolumeStatus{v.root, devnum, free, used}
232 var blockDirRe = regexp.MustCompile(`^[0-9a-f]+$`)
234 // IndexTo writes (to the given Writer) a list of blocks found on this
235 // volume which begin with the specified prefix. If the prefix is an
236 // empty string, IndexTo writes a complete list of blocks.
238 // Each block is given in the format
240 // locator+size modification-time {newline}
244 // e4df392f86be161ca6ed3773a962b8f3+67108864 1388894303
245 // e4d41e6fd68460e0e3fc18cc746959d2+67108864 1377796043
246 // e4de7a2810f5554cd39b36d8ddb132ff+67108864 1388701136
248 func (v *UnixVolume) IndexTo(prefix string, w io.Writer) error {
249 var lastErr error = nil
250 rootdir, err := os.Open(v.root)
254 defer rootdir.Close()
256 names, err := rootdir.Readdirnames(1)
259 } else if err != nil {
262 if !strings.HasPrefix(names[0], prefix) && !strings.HasPrefix(prefix, names[0]) {
263 // prefix excludes all blocks stored in this dir
266 if !blockDirRe.MatchString(names[0]) {
269 blockdirpath := filepath.Join(v.root, names[0])
270 blockdir, err := os.Open(blockdirpath)
272 log.Print("Error reading ", blockdirpath, ": ", err)
277 fileInfo, err := blockdir.Readdir(1)
280 } else if err != nil {
281 log.Print("Error reading ", blockdirpath, ": ", err)
285 name := fileInfo[0].Name()
286 if !strings.HasPrefix(name, prefix) {
289 _, err = fmt.Fprint(w,
291 "+", fileInfo[0].Size(),
292 " ", fileInfo[0].ModTime().Unix(),
299 func (v *UnixVolume) Delete(loc string) error {
300 // Touch() must be called before calling Write() on a block. Touch()
301 // also uses lockfile(). This avoids a race condition between Write()
302 // and Delete() because either (a) the file will be deleted and Touch()
303 // will signal to the caller that the file is not present (and needs to
304 // be re-written), or (b) Touch() will update the file's timestamp and
305 // Delete() will read the correct up-to-date timestamp and choose not to
309 return MethodDisabledError
313 defer v.mutex.Unlock()
315 p := v.blockPath(loc)
316 f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
321 if e := lockfile(f); e != nil {
326 // If the block has been PUT in the last blob_signature_ttl
327 // seconds, return success without removing the block. This
328 // protects data from garbage collection until it is no longer
329 // possible for clients to retrieve the unreferenced blocks
330 // anyway (because the permission signatures have expired).
331 if fi, err := os.Stat(p); err != nil {
334 if time.Since(fi.ModTime()) < blob_signature_ttl {
341 // blockDir returns the fully qualified directory name for the directory
342 // where loc is (or would be) stored on this volume.
343 func (v *UnixVolume) blockDir(loc string) string {
344 return filepath.Join(v.root, loc[0:3])
347 // blockPath returns the fully qualified pathname for the path to loc
349 func (v *UnixVolume) blockPath(loc string) string {
350 return filepath.Join(v.blockDir(loc), loc)
353 // IsFull returns true if the free space on the volume is less than
354 // MIN_FREE_KILOBYTES.
356 func (v *UnixVolume) IsFull() (isFull bool) {
357 fullSymlink := v.root + "/full"
359 // Check if the volume has been marked as full in the last hour.
360 if link, err := os.Readlink(fullSymlink); err == nil {
361 if ts, err := strconv.Atoi(link); err == nil {
362 fulltime := time.Unix(int64(ts), 0)
363 if time.Since(fulltime).Hours() < 1.0 {
369 if avail, err := v.FreeDiskSpace(); err == nil {
370 isFull = avail < MIN_FREE_KILOBYTES
372 log.Printf("%s: FreeDiskSpace: %s\n", v, err)
376 // If the volume is full, timestamp it.
378 now := fmt.Sprintf("%d", time.Now().Unix())
379 os.Symlink(now, fullSymlink)
384 // FreeDiskSpace returns the number of unused 1k blocks available on
387 func (v *UnixVolume) FreeDiskSpace() (free uint64, err error) {
388 var fs syscall.Statfs_t
389 err = syscall.Statfs(v.root, &fs)
391 // Statfs output is not guaranteed to measure free
392 // space in terms of 1K blocks.
393 free = fs.Bavail * uint64(fs.Bsize) / 1024
398 func (v *UnixVolume) String() string {
399 return fmt.Sprintf("[UnixVolume %s]", v.root)
402 func (v *UnixVolume) Writable() bool {
406 // lockfile and unlockfile use flock(2) to manage kernel file locks.
407 func lockfile(f *os.File) error {
408 return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
411 func unlockfile(f *os.File) error {
412 return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)