19 // A UnixVolume stores and retrieves blocks in a local directory.
20 type UnixVolume struct {
21 // path to the volume's root directory
23 // something to lock during IO, typically a sync.Mutex (or nil
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.locker.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 // Lock the locker (if one is in use), open the file for reading, and
62 // call 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 {
66 defer v.locker.Unlock()
68 f, err := os.Open(path)
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 // expect. It is functionally equivalent to Get() followed by
113 // bytes.Compare(), but uses less memory.
114 func (v *UnixVolume) Compare(loc string, expect []byte) error {
115 path := v.blockPath(loc)
116 stat, err := v.stat(path)
121 if int64(bufLen) > stat.Size() {
122 bufLen = int(stat.Size())
125 buf := make([]byte, bufLen)
126 return v.getFunc(path, func(rdr io.Reader) error {
127 // Loop invariants: all data read so far matched what
128 // we expected, and the first N bytes of cmp are
129 // expected to equal the next N bytes read from
132 n, err := rdr.Read(buf)
133 if n > len(cmp) || bytes.Compare(cmp[:n], buf[:n]) != 0 {
134 return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], buf[:n], rdr)
139 return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], nil, nil)
142 } else if err != nil {
149 // Put stores a block of data identified by the locator string
150 // "loc". It returns nil on success. If the volume is full, it
151 // returns a FullError. If the write fails due to some other error,
152 // that error is returned.
153 func (v *UnixVolume) Put(loc string, block []byte) error {
155 return MethodDisabledError
160 bdir := v.blockDir(loc)
161 if err := os.MkdirAll(bdir, 0755); err != nil {
162 log.Printf("%s: could not create directory %s: %s",
167 tmpfile, tmperr := ioutil.TempFile(bdir, "tmp"+loc)
169 log.Printf("ioutil.TempFile(%s, tmp%s): %s", bdir, loc, tmperr)
172 bpath := v.blockPath(loc)
176 defer v.locker.Unlock()
178 if _, err := tmpfile.Write(block); err != nil {
179 log.Printf("%s: writing to %s: %s\n", v, bpath, err)
181 os.Remove(tmpfile.Name())
184 if err := tmpfile.Close(); err != nil {
185 log.Printf("closing %s: %s\n", tmpfile.Name(), err)
186 os.Remove(tmpfile.Name())
189 if err := os.Rename(tmpfile.Name(), bpath); err != nil {
190 log.Printf("rename %s %s: %s\n", tmpfile.Name(), bpath, err)
191 os.Remove(tmpfile.Name())
197 // Status returns a VolumeStatus struct describing the volume's
198 // current state, or nil if an error occurs.
200 func (v *UnixVolume) Status() *VolumeStatus {
201 var fs syscall.Statfs_t
204 if fi, err := os.Stat(v.root); err == nil {
205 devnum = fi.Sys().(*syscall.Stat_t).Dev
207 log.Printf("%s: os.Stat: %s\n", v, err)
211 err := syscall.Statfs(v.root, &fs)
213 log.Printf("%s: statfs: %s\n", v, err)
216 // These calculations match the way df calculates disk usage:
217 // "free" space is measured by fs.Bavail, but "used" space
218 // uses fs.Blocks - fs.Bfree.
219 free := fs.Bavail * uint64(fs.Bsize)
220 used := (fs.Blocks - fs.Bfree) * uint64(fs.Bsize)
221 return &VolumeStatus{v.root, devnum, free, used}
224 var blockDirRe = regexp.MustCompile(`^[0-9a-f]+$`)
226 // IndexTo writes (to the given Writer) a list of blocks found on this
227 // volume which begin with the specified prefix. If the prefix is an
228 // empty string, IndexTo writes a complete list of blocks.
230 // Each block is given in the format
232 // locator+size modification-time {newline}
236 // e4df392f86be161ca6ed3773a962b8f3+67108864 1388894303
237 // e4d41e6fd68460e0e3fc18cc746959d2+67108864 1377796043
238 // e4de7a2810f5554cd39b36d8ddb132ff+67108864 1388701136
240 func (v *UnixVolume) IndexTo(prefix string, w io.Writer) error {
241 var lastErr error = nil
242 rootdir, err := os.Open(v.root)
246 defer rootdir.Close()
248 names, err := rootdir.Readdirnames(1)
251 } else if err != nil {
254 if !strings.HasPrefix(names[0], prefix) && !strings.HasPrefix(prefix, names[0]) {
255 // prefix excludes all blocks stored in this dir
258 if !blockDirRe.MatchString(names[0]) {
261 blockdirpath := filepath.Join(v.root, names[0])
262 blockdir, err := os.Open(blockdirpath)
264 log.Print("Error reading ", blockdirpath, ": ", err)
269 fileInfo, err := blockdir.Readdir(1)
272 } else if err != nil {
273 log.Print("Error reading ", blockdirpath, ": ", err)
277 name := fileInfo[0].Name()
278 if !strings.HasPrefix(name, prefix) {
281 _, err = fmt.Fprint(w,
283 "+", fileInfo[0].Size(),
284 " ", fileInfo[0].ModTime().Unix(),
291 func (v *UnixVolume) Delete(loc string) error {
292 // Touch() must be called before calling Write() on a block. Touch()
293 // also uses lockfile(). This avoids a race condition between Write()
294 // and Delete() because either (a) the file will be deleted and Touch()
295 // will signal to the caller that the file is not present (and needs to
296 // be re-written), or (b) Touch() will update the file's timestamp and
297 // Delete() will read the correct up-to-date timestamp and choose not to
301 return MethodDisabledError
305 defer v.locker.Unlock()
307 p := v.blockPath(loc)
308 f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
313 if e := lockfile(f); e != nil {
318 // If the block has been PUT in the last blob_signature_ttl
319 // seconds, return success without removing the block. This
320 // protects data from garbage collection until it is no longer
321 // possible for clients to retrieve the unreferenced blocks
322 // anyway (because the permission signatures have expired).
323 if fi, err := os.Stat(p); err != nil {
326 if time.Since(fi.ModTime()) < blob_signature_ttl {
333 // blockDir returns the fully qualified directory name for the directory
334 // where loc is (or would be) stored on this volume.
335 func (v *UnixVolume) blockDir(loc string) string {
336 return filepath.Join(v.root, loc[0:3])
339 // blockPath returns the fully qualified pathname for the path to loc
341 func (v *UnixVolume) blockPath(loc string) string {
342 return filepath.Join(v.blockDir(loc), loc)
345 // IsFull returns true if the free space on the volume is less than
346 // MIN_FREE_KILOBYTES.
348 func (v *UnixVolume) IsFull() (isFull bool) {
349 fullSymlink := v.root + "/full"
351 // Check if the volume has been marked as full in the last hour.
352 if link, err := os.Readlink(fullSymlink); err == nil {
353 if ts, err := strconv.Atoi(link); err == nil {
354 fulltime := time.Unix(int64(ts), 0)
355 if time.Since(fulltime).Hours() < 1.0 {
361 if avail, err := v.FreeDiskSpace(); err == nil {
362 isFull = avail < MIN_FREE_KILOBYTES
364 log.Printf("%s: FreeDiskSpace: %s\n", v, err)
368 // If the volume is full, timestamp it.
370 now := fmt.Sprintf("%d", time.Now().Unix())
371 os.Symlink(now, fullSymlink)
376 // FreeDiskSpace returns the number of unused 1k blocks available on
379 func (v *UnixVolume) FreeDiskSpace() (free uint64, err error) {
380 var fs syscall.Statfs_t
381 err = syscall.Statfs(v.root, &fs)
383 // Statfs output is not guaranteed to measure free
384 // space in terms of 1K blocks.
385 free = fs.Bavail * uint64(fs.Bsize) / 1024
390 func (v *UnixVolume) String() string {
391 return fmt.Sprintf("[UnixVolume %s]", v.root)
394 func (v *UnixVolume) Writable() bool {
398 // lockfile and unlockfile use flock(2) to manage kernel file locks.
399 func lockfile(f *os.File) error {
400 return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
403 func unlockfile(f *os.File) error {
404 return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)