nodefs: support Link

nodefs/README.md

@@ -9,7 +9,8 @@ Decisions
 =========
 
    * Nodes contain references to their children. This is useful
-     because most filesystems will need to construct tree-like structures.
+     because most filesystems will need to construct tree-like
+     structures.
 
    * Nodes can be "persistent", meaning their lifetime is not under
      control of the kernel. This is useful for constructing FS trees
@@ -24,6 +25,11 @@ Decisions
      creation. These are {NodeID, Mode}. Files cannot change type
      during their lifetime. It also prevents the common error of
      forgetting to return the filetype in Lookup/GetAttr.
+     
+   * Support for hard links. libfuse doesn't support this in the
+     high-level API.  Extra care for race conditions is needed when
+    looking up the same file different paths.
+
 
 To decide
 =========

nodefs/api.go

@@ -82,7 +82,7 @@ type Operations interface {
 	//
 	// See InodeOf for public API to retrieve an inode from Node.
 	inode() *Inode
-	setInode(*Inode)
+	setInode(*Inode) bool
 
 	// File locking
 	GetLk(ctx context.Context, f FileHandle, owner uint64, lk *fuse.FileLock, flags uint32, out *fuse.FileLock) (code fuse.Status)
@@ -105,6 +105,7 @@ type Operations interface {
 	Unlink(ctx context.Context, name string) fuse.Status
 	Rename(ctx context.Context, name string, newParent Operations, newName string, flags uint32) fuse.Status
 	Create(ctx context.Context, name string, flags uint32, mode uint32) (node *Inode, fh FileHandle, fuseFlags uint32, code fuse.Status)
+	Link(ctx context.Context, target Operations, name string, out *fuse.EntryOut) (node *Inode, code fuse.Status)
 	Symlink(ctx context.Context, target, name string, out *fuse.EntryOut) (node *Inode, code fuse.Status)
 	Readlink(ctx context.Context) (string, fuse.Status)
 	Open(ctx context.Context, flags uint32) (fh FileHandle, fuseFlags uint32, code fuse.Status)

nodefs/bridge.go

@@ -80,7 +80,7 @@ func (b *rawBridge) newInode(node Operations, mode uint32, id FileID, persistent
 
 	b.nodes[id.Ino] = inode
 	node.setInode(inode)
-	return inode
+	return node.inode()
 }
 
 func NewNodeFS(root Operations, opts *Options) fuse.RawFileSystem {
@@ -370,12 +370,21 @@ func (b *rawBridge) Rename(input *fuse.RenameIn, oldName string, newName string)
 	return code
 }
 
-func (b *rawBridge) Link(input *fuse.LinkIn, filename string, out *fuse.EntryOut) (code fuse.Status) {
-	return fuse.ENOSYS
+func (b *rawBridge) Link(input *fuse.LinkIn, name string, out *fuse.EntryOut) (code fuse.Status) {
+	parent, _ := b.inode(input.NodeId, 0)
+	target, _ := b.inode(input.Oldnodeid, 0)
+
+	child, code := parent.node.Link(context.TODO(), target.node, name, out)
+	if !code.Ok() {
+		return code
+	}
+
+	b.addNewChild(parent, name, child, nil, out)
+	b.setEntryOutTimeout(out)
+	return fuse.OK
 }
 
 func (b *rawBridge) Symlink(header *fuse.InHeader, target string, name string, out *fuse.EntryOut) (code fuse.Status) {
-	log.Println("symlink1")
 	parent, _ := b.inode(header.NodeId, 0)
 	child, code := parent.node.Symlink(context.TODO(), target, name, out)
 	if !code.Ok() {

nodefs/default.go

@@ -41,7 +41,7 @@ var _ Operations = &DefaultOperations{}
 //
 // To read node.inode atomic.LoadPointer is used, however it is not expensive
 // since it translates to regular MOVQ on amd64.
-func (dn *DefaultOperations) setInode(inode *Inode) *Inode {
+func (dn *DefaultOperations) setInode(inode *Inode) bool {
 	return atomic.CompareAndSwapPointer(
 		(*unsafe.Pointer)(unsafe.Pointer(&dn.inode_)),
 		nil, unsafe.Pointer(inode))
@@ -196,6 +196,9 @@ func (n *DefaultOperations) Open(ctx context.Context, flags uint32) (fh FileHand
 func (n *DefaultOperations) Create(ctx context.Context, name string, flags uint32, mode uint32) (node *Inode, fh FileHandle, fuseFlags uint32, code fuse.Status) {
 	return nil, nil, 0, fuse.ENOSYS
 }
+func (n *DefaultOperations) Link(ctx context.Context, target Operations, name string, out *fuse.EntryOut) (node *Inode, code fuse.Status) {
+	return nil, fuse.ENOSYS
+}
 
 type DefaultFile struct {
 }

nodefs/loopback.go

@@ -135,6 +135,13 @@ func (n *loopbackNode) Unlink(ctx context.Context, name string) fuse.Status {
 	return fuse.ToStatus(err)
 }
 
+func toLoopbackNode(op Operations) *loopbackNode {
+	if r, ok := op.(*loopbackRoot); ok {
+		return &r.loopbackNode
+	}
+	return op.(*loopbackNode)
+}
+
 func (n *loopbackNode) Rename(ctx context.Context, name string, newParent Operations, newName string, flags uint32) fuse.Status {
 
 	if flags != 0 {
@@ -142,12 +149,7 @@ func (n *loopbackNode) Rename(ctx context.Context, name string, newParent Operat
 	}
 
 	p1 := filepath.Join(n.path(), name)
-	var newParentLoopback *loopbackNode
-	if r, ok := newParent.(*loopbackRoot); ok {
-		newParentLoopback = &r.loopbackNode
-	} else {
-		newParentLoopback = newParent.(*loopbackNode)
-	}
+	newParentLoopback := toLoopbackNode(newParent)
 
 	p2 := filepath.Join(newParentLoopback.path(), newName)
 	err := os.Rename(p1, p2)
@@ -204,6 +206,26 @@ func (n *loopbackNode) Symlink(ctx context.Context, target, name string, out *fu
 	return ch, fuse.OK
 }
 
+func (n *loopbackNode) Link(ctx context.Context, target Operations, name string, out *fuse.EntryOut) (*Inode, fuse.Status) {
+
+	p := filepath.Join(n.path(), name)
+	targetNode := toLoopbackNode(target)
+	err := syscall.Link(targetNode.path(), p)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	st := syscall.Stat_t{}
+	if syscall.Lstat(p, &st); err != nil {
+		syscall.Unlink(p)
+		return nil, fuse.ToStatus(err)
+	}
+	node := n.rootNode.newLoopbackNode()
+	ch := n.inode().NewInode(node, st.Mode, idFromStat(&st))
+
+	out.Attr.FromStat(&st)
+	return ch, fuse.OK
+}
+
 func (n *loopbackNode) Readlink(ctx context.Context) (string, fuse.Status) {
 	p := n.path()
 

nodefs/simple_test.go

@@ -424,3 +424,33 @@ func TestSymlink(t *testing.T) {
 		t.Errorf("Readlink: got %q, want %q", got, target)
 	}
 }
+
+func TestLink(t *testing.T) {
+	tc := newTestCase(t)
+	defer tc.Clean()
+
+	link := tc.mntDir + "/link"
+	target := tc.mntDir + "/target"
+
+	if err := ioutil.WriteFile(target, []byte("hello"), 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	st := syscall.Stat_t{}
+	if err := syscall.Lstat(target, &st); err != nil {
+		t.Fatalf("Lstat before: %v", err)
+	}
+
+	beforeIno := st.Ino
+	if err := os.Link(target, link); err != nil {
+		t.Errorf("Link: %v", err)
+	}
+
+	if err := syscall.Lstat(link, &st); err != nil {
+		t.Fatalf("Lstat after: %v", err)
+	}
+
+	if st.Ino != beforeIno {
+		t.Errorf("Lstat after: got %d, want %d", st.Ino, beforeIno)
+	}
+}