fs: implement {mutFile,mutDir}.Access

On at least OS X, the stat(2) call will use an existing node without
issuing Lookup.  This introduces a filesystem inconsistency where a
delete removes an entry for further requests, but FUSE's cached access
of the node is still used for at least stat.

There's a call to Access directly against the node as retrieved from a
prior Lookup.  By invalidating the nodes when they're deleted and
verifying this at Access time, we keep things more consistent.

This isn't exactly camlistore.org/issue/324 as described, but it was
causing one of the tests to fail on OS X

Change-Id: Ib90a1de79d6d3960f96bac5b4fb448c952c4ba66

pkg/fs/mut.go

@@ -62,6 +62,7 @@ type mutDir struct {
 	lastPop  time.Time
 	children map[string]mutFileOrDir
 	xattrs   map[string][]byte
+	deleted  bool
 }
 
 func (m *mutDir) String() string {
@@ -85,6 +86,24 @@ func (n *mutDir) Attr() fuse.Attr {
 	}
 }
 
+func (n *mutDir) Access(req *fuse.AccessRequest, intr fuse.Intr) fuse.Error {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	if n.deleted {
+		return fuse.ENOENT
+	}
+	return nil
+}
+
+func (n *mutFile) Access(req *fuse.AccessRequest, intr fuse.Intr) fuse.Error {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	if n.deleted {
+		return fuse.ENOENT
+	}
+	return nil
+}
+
 // populate hits the blobstore to populate map of child nodes.
 func (n *mutDir) populate() error {
 	n.mu.Lock()
@@ -375,7 +394,11 @@ func (n *mutDir) Remove(req *fuse.RemoveRequest, intr fuse.Intr) fuse.Error {
 	// Remove child from map.
 	n.mu.Lock()
 	if n.children != nil {
-		delete(n.children, req.Name)
+		if removed, ok := n.children[req.Name]; ok {
+			removed.invalidate()
+			delete(n.children, req.Name)
+			log.Printf("Removed %v from %p", removed, n)
+		}
 	}
 	n.mu.Unlock()
 	return nil
@@ -456,6 +479,7 @@ type mutFile struct {
 	size         int64
 	mtime, atime time.Time // if zero, use serverStart
 	xattrs       map[string][]byte
+	deleted      bool
 }
 
 func (m *mutFile) String() string {
@@ -789,6 +813,7 @@ func (h *mutFileHandle) Truncate(size uint64, intr fuse.Intr) fuse.Error {
 // mutFileOrDir is a *mutFile or *mutDir
 type mutFileOrDir interface {
 	fuse.Node
+	invalidate()
 	permanodeString() string
 	xattr() *xattr
 }
@@ -800,3 +825,15 @@ func (n *mutFile) permanodeString() string {
 func (n *mutDir) permanodeString() string {
 	return n.permanode.String()
 }
+
+func (n *mutFile) invalidate() {
+	n.mu.Lock()
+	n.deleted = true
+	n.mu.Unlock()
+}
+
+func (n *mutDir) invalidate() {
+	n.mu.Lock()
+	n.deleted = true
+	n.mu.Unlock()
+}