Merge branch 'master' into 3198-writable-fuse

[arvados.git] / services / keepstore / volume_unix.go

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/volume_unix.go
index 75a75229a6861f83f45b9264bab9d577d7d0f880..20bc9c50af99d2dd17a35259649d17241aa3732e 100644 (file)
--- 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)
        }
@@ -98,11 +105,15 @@ func (v *UnixVolume) Put(loc string, block []byte) error {
 }
 
 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
        }
@@ -254,11 +265,23 @@ func (v *UnixVolume) Index(prefix string) (output string) {
 }
 
 func (v *UnixVolume) Delete(loc string) error {
+       // 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
        }
@@ -340,6 +363,10 @@ 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)