X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/244159419c42341baeb388236ad29cc546b7eca1..f69d2824c997c53caa11d30ba816768bad52e12b:/services/keepstore/volume_unix.go

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/volume_unix.go
index ddddd5abf9..20bc9c50af 100644
--- a/services/keepstore/volume_unix.go
+++ b/services/keepstore/volume_unix.go
@@ -50,8 +50,9 @@ type IOResponse struct {
 //       request.
 //
 type UnixVolume struct {
-	root  string // path to this volume
-	queue chan *IORequest
+	root     string // path to this volume
+	queue    chan *IORequest
+	readonly bool
 }
 
 func (v *UnixVolume) IOHandler() {
@@ -67,14 +68,17 @@ func (v *UnixVolume) IOHandler() {
 	}
 }
 
-func MakeUnixVolume(root string, serialize bool) (v UnixVolume) {
+func MakeUnixVolume(root string, serialize bool, readonly bool) *UnixVolume {
+	v := &UnixVolume{
+		root: root,
+		queue: nil,
+		readonly: readonly,
+	}
 	if serialize {
-		v = UnixVolume{root, make(chan *IORequest)}
+		v.queue =make(chan *IORequest)
 		go v.IOHandler()
-	} else {
-		v = UnixVolume{root, nil}
 	}
-	return
+	return v
 }
 
 func (v *UnixVolume) Get(loc string) ([]byte, error) {
@@ -88,6 +92,9 @@ func (v *UnixVolume) Get(loc string) ([]byte, error) {
 }
 
 func (v *UnixVolume) Put(loc string, block []byte) error {
+	if v.readonly {
+		return MethodDisabledError
+	}
 	if v.queue == nil {
 		return v.Write(loc, block)
 	}
@@ -97,6 +104,34 @@ func (v *UnixVolume) Put(loc string, block []byte) error {
 	return response.err
 }
 
+func (v *UnixVolume) Touch(loc string) error {
+	if v.readonly {
+		return MethodDisabledError
+	}
+	p := v.blockPath(loc)
+	f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	if e := lockfile(f); e != nil {
+		return e
+	}
+	defer unlockfile(f)
+	now := time.Now().Unix()
+	utime := syscall.Utimbuf{now, now}
+	return syscall.Utime(p, &utime)
+}
+
+func (v *UnixVolume) Mtime(loc string) (time.Time, error) {
+	p := v.blockPath(loc)
+	if fi, err := os.Stat(p); err != nil {
+		return time.Time{}, err
+	} else {
+		return fi.ModTime(), nil
+	}
+}
+
 // Read retrieves a block identified by the locator string "loc", and
 // returns its contents as a byte slice.
 //
@@ -230,7 +265,41 @@ func (v *UnixVolume) Index(prefix string) (output string) {
 }
 
 func (v *UnixVolume) Delete(loc string) error {
-	return os.Remove(v.blockPath(loc))
+	// Touch() must be called before calling Write() on a block.  Touch()
+	// also uses lockfile().  This avoids a race condition between Write()
+	// and Delete() because either (a) the file will be deleted and Touch()
+	// will signal to the caller that the file is not present (and needs to
+	// be re-written), or (b) Touch() will update the file's timestamp and
+	// Delete() will read the correct up-to-date timestamp and choose not to
+	// delete the file.
+
+	if v.readonly {
+		return MethodDisabledError
+	}
+	p := v.blockPath(loc)
+	f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	if e := lockfile(f); e != nil {
+		return e
+	}
+	defer unlockfile(f)
+
+	// If the block has been PUT more recently than -permission_ttl,
+	// return success without removing the block.  This guards against
+	// a race condition where a block is old enough that Data Manager
+	// has added it to the trash list, but the user submitted a PUT
+	// for the block since then.
+	if fi, err := os.Stat(p); err != nil {
+		return err
+	} else {
+		if time.Since(fi.ModTime()) < permission_ttl {
+			return nil
+		}
+	}
+	return os.Remove(p)
 }
 
 // blockDir returns the fully qualified directory name for the directory
@@ -293,3 +362,16 @@ func (v *UnixVolume) FreeDiskSpace() (free uint64, err error) {
 func (v *UnixVolume) String() string {
 	return fmt.Sprintf("[UnixVolume %s]", v.root)
 }
+
+func (v *UnixVolume) Writable() bool {
+	return !v.readonly
+}
+
+// lockfile and unlockfile use flock(2) to manage kernel file locks.
+func lockfile(f *os.File) error {
+	return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
+}
+
+func unlockfile(f *os.File) error {
+	return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
+}