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 // Touch sets the timestamp for the given locator to the current time
30 func (v *UnixVolume) Touch(loc string) error {
32 return MethodDisabledError
35 f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
42 defer v.locker.Unlock()
44 if e := lockfile(f); e != nil {
48 now := time.Now().Unix()
49 utime := syscall.Utimbuf{now, now}
50 return syscall.Utime(p, &utime)
53 // Mtime returns the stored timestamp for the given locator.
54 func (v *UnixVolume) Mtime(loc string) (time.Time, error) {
58 return time.Time{}, err
60 return fi.ModTime(), nil
63 // Lock the locker (if one is in use), open the file for reading, and
64 // call the given function if and when the file is ready to read.
65 func (v *UnixVolume) getFunc(path string, fn func(io.Reader) error) error {
68 defer v.locker.Unlock()
70 f, err := os.Open(path)
78 // stat is os.Stat() with some extra sanity checks.
79 func (v *UnixVolume) stat(path string) (os.FileInfo, error) {
80 stat, err := os.Stat(path)
84 } else if stat.Size() > BlockSize {
91 // Get retrieves a block identified by the locator string "loc", and
92 // returns its contents as a byte slice.
94 // Get returns a nil buffer IFF it returns a non-nil error.
95 func (v *UnixVolume) Get(loc string) ([]byte, error) {
96 path := v.blockPath(loc)
97 stat, err := v.stat(path)
101 buf := bufs.Get(int(stat.Size()))
102 err = v.getFunc(path, func(rdr io.Reader) error {
103 _, err = io.ReadFull(rdr, buf)
113 // Compare returns nil if Get(loc) would return the same content as
114 // expect. It is functionally equivalent to Get() followed by
115 // bytes.Compare(), but uses less memory.
116 func (v *UnixVolume) Compare(loc string, expect []byte) error {
117 path := v.blockPath(loc)
118 stat, err := v.stat(path)
123 if int64(bufLen) > stat.Size() {
124 bufLen = int(stat.Size())
126 // len(buf)==0 would prevent us from handling
127 // empty files the same way as non-empty
128 // files, because reading 0 bytes at a time
129 // never reaches EOF.
134 buf := make([]byte, bufLen)
135 return v.getFunc(path, func(rdr io.Reader) error {
136 // Loop invariants: all data read so far matched what
137 // we expected, and the first N bytes of cmp are
138 // expected to equal the next N bytes read from
141 n, err := rdr.Read(buf)
142 if n > len(cmp) || bytes.Compare(cmp[:n], buf[:n]) != 0 {
143 return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], buf[:n], rdr)
148 return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], nil, nil)
151 } else if err != nil {
158 // Put stores a block of data identified by the locator string
159 // "loc". It returns nil on success. If the volume is full, it
160 // returns a FullError. If the write fails due to some other error,
161 // that error is returned.
162 func (v *UnixVolume) Put(loc string, block []byte) error {
164 return MethodDisabledError
169 bdir := v.blockDir(loc)
170 if err := os.MkdirAll(bdir, 0755); err != nil {
171 log.Printf("%s: could not create directory %s: %s",
176 tmpfile, tmperr := ioutil.TempFile(bdir, "tmp"+loc)
178 log.Printf("ioutil.TempFile(%s, tmp%s): %s", bdir, loc, tmperr)
181 bpath := v.blockPath(loc)
185 defer v.locker.Unlock()
187 if _, err := tmpfile.Write(block); err != nil {
188 log.Printf("%s: writing to %s: %s\n", v, bpath, err)
190 os.Remove(tmpfile.Name())
193 if err := tmpfile.Close(); err != nil {
194 log.Printf("closing %s: %s\n", tmpfile.Name(), err)
195 os.Remove(tmpfile.Name())
198 if err := os.Rename(tmpfile.Name(), bpath); err != nil {
199 log.Printf("rename %s %s: %s\n", tmpfile.Name(), bpath, err)
200 os.Remove(tmpfile.Name())
206 // Status returns a VolumeStatus struct describing the volume's
207 // current state, or nil if an error occurs.
209 func (v *UnixVolume) Status() *VolumeStatus {
210 var fs syscall.Statfs_t
213 if fi, err := os.Stat(v.root); err == nil {
214 devnum = fi.Sys().(*syscall.Stat_t).Dev
216 log.Printf("%s: os.Stat: %s\n", v, err)
220 err := syscall.Statfs(v.root, &fs)
222 log.Printf("%s: statfs: %s\n", v, err)
225 // These calculations match the way df calculates disk usage:
226 // "free" space is measured by fs.Bavail, but "used" space
227 // uses fs.Blocks - fs.Bfree.
228 free := fs.Bavail * uint64(fs.Bsize)
229 used := (fs.Blocks - fs.Bfree) * uint64(fs.Bsize)
230 return &VolumeStatus{v.root, devnum, free, used}
233 var blockDirRe = regexp.MustCompile(`^[0-9a-f]+$`)
235 // IndexTo writes (to the given Writer) a list of blocks found on this
236 // volume which begin with the specified prefix. If the prefix is an
237 // empty string, IndexTo writes a complete list of blocks.
239 // Each block is given in the format
241 // locator+size modification-time {newline}
245 // e4df392f86be161ca6ed3773a962b8f3+67108864 1388894303
246 // e4d41e6fd68460e0e3fc18cc746959d2+67108864 1377796043
247 // e4de7a2810f5554cd39b36d8ddb132ff+67108864 1388701136
249 func (v *UnixVolume) IndexTo(prefix string, w io.Writer) error {
250 var lastErr error = nil
251 rootdir, err := os.Open(v.root)
255 defer rootdir.Close()
257 names, err := rootdir.Readdirnames(1)
260 } else if err != nil {
263 if !strings.HasPrefix(names[0], prefix) && !strings.HasPrefix(prefix, names[0]) {
264 // prefix excludes all blocks stored in this dir
267 if !blockDirRe.MatchString(names[0]) {
270 blockdirpath := filepath.Join(v.root, names[0])
271 blockdir, err := os.Open(blockdirpath)
273 log.Print("Error reading ", blockdirpath, ": ", err)
278 fileInfo, err := blockdir.Readdir(1)
281 } else if err != nil {
282 log.Print("Error reading ", blockdirpath, ": ", err)
286 name := fileInfo[0].Name()
287 if !strings.HasPrefix(name, prefix) {
290 _, err = fmt.Fprint(w,
292 "+", fileInfo[0].Size(),
293 " ", fileInfo[0].ModTime().Unix(),
300 // Delete deletes the block data from the unix storage
301 func (v *UnixVolume) Delete(loc string) error {
302 // Touch() must be called before calling Write() on a block. Touch()
303 // also uses lockfile(). This avoids a race condition between Write()
304 // and Delete() because either (a) the file will be deleted and Touch()
305 // will signal to the caller that the file is not present (and needs to
306 // be re-written), or (b) Touch() will update the file's timestamp and
307 // Delete() will read the correct up-to-date timestamp and choose not to
311 return MethodDisabledError
315 defer v.locker.Unlock()
317 p := v.blockPath(loc)
318 f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
323 if e := lockfile(f); e != nil {
328 // If the block has been PUT in the last blobSignatureTTL
329 // seconds, return success without removing the block. This
330 // protects data from garbage collection until it is no longer
331 // possible for clients to retrieve the unreferenced blocks
332 // anyway (because the permission signatures have expired).
333 if fi, err := os.Stat(p); err != nil {
336 if time.Since(fi.ModTime()) < blobSignatureTTL {
343 // blockDir returns the fully qualified directory name for the directory
344 // where loc is (or would be) stored on this volume.
345 func (v *UnixVolume) blockDir(loc string) string {
346 return filepath.Join(v.root, loc[0:3])
349 // blockPath returns the fully qualified pathname for the path to loc
351 func (v *UnixVolume) blockPath(loc string) string {
352 return filepath.Join(v.blockDir(loc), loc)
355 // IsFull returns true if the free space on the volume is less than
358 func (v *UnixVolume) IsFull() (isFull bool) {
359 fullSymlink := v.root + "/full"
361 // Check if the volume has been marked as full in the last hour.
362 if link, err := os.Readlink(fullSymlink); err == nil {
363 if ts, err := strconv.Atoi(link); err == nil {
364 fulltime := time.Unix(int64(ts), 0)
365 if time.Since(fulltime).Hours() < 1.0 {
371 if avail, err := v.FreeDiskSpace(); err == nil {
372 isFull = avail < MinFreeKilobytes
374 log.Printf("%s: FreeDiskSpace: %s\n", v, err)
378 // If the volume is full, timestamp it.
380 now := fmt.Sprintf("%d", time.Now().Unix())
381 os.Symlink(now, fullSymlink)
386 // FreeDiskSpace returns the number of unused 1k blocks available on
389 func (v *UnixVolume) FreeDiskSpace() (free uint64, err error) {
390 var fs syscall.Statfs_t
391 err = syscall.Statfs(v.root, &fs)
393 // Statfs output is not guaranteed to measure free
394 // space in terms of 1K blocks.
395 free = fs.Bavail * uint64(fs.Bsize) / 1024
400 func (v *UnixVolume) String() string {
401 return fmt.Sprintf("[UnixVolume %s]", v.root)
404 // Writable returns false if all future Put, Mtime, and Delete calls are expected to fail.
405 func (v *UnixVolume) Writable() bool {
409 // lockfile and unlockfile use flock(2) to manage kernel file locks.
410 func lockfile(f *os.File) error {
411 return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
414 func unlockfile(f *os.File) error {
415 return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)