Simplify vfs.NewDisconnectedMount signature and callpoints.

vfs.NewDisconnectedMount has no error paths. Its much prettier without the
error return value.

Also simplify MountDisconnected which would immediately drop the refs taken by
NewDisconnectedMount. Instead make it directly call newMount.

PiperOrigin-RevId: 405767966

pkg/sentry/fsimpl/mqfs/registry.go

@@ -71,10 +71,7 @@ func NewRegistryImpl(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *
 	var dentry kernfs.Dentry
 	dentry.InitRoot(&fs.Filesystem, fs.newRootInode(ctx, creds))
 
-	mount, err := vfsObj.NewDisconnectedMount(vfsfs, dentry.VFSDentry(), &vfs.MountOptions{})
-	if err != nil {
-		return nil, err
-	}
+	mount := vfsObj.NewDisconnectedMount(vfsfs, dentry.VFSDentry(), &vfs.MountOptions{})
 
 	return &RegistryImpl{
 		root:  &dentry,

pkg/sentry/fsimpl/overlay/overlay.go

@@ -314,10 +314,7 @@ func clonePrivateMount(vfsObj *vfs.VirtualFilesystem, vd vfs.VirtualDentry, forc
 	if forceReadOnly {
 		opts.ReadOnly = true
 	}
-	newmnt, err := vfsObj.NewDisconnectedMount(oldmnt.Filesystem(), vd.Dentry(), &opts)
-	if err != nil {
-		return vfs.VirtualDentry{}, err
-	}
+	newmnt := vfsObj.NewDisconnectedMount(oldmnt.Filesystem(), vd.Dentry(), &opts)
 	// Take a reference on the dentry which will be owned by the returned
 	// VirtualDentry.
 	d := vd.Dentry()

pkg/sentry/kernel/kernel.go

@@ -418,10 +418,7 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 			return fmt.Errorf("failed to create pipefs filesystem: %v", err)
 		}
 		defer pipeFilesystem.DecRef(ctx)
-		pipeMount, err := k.vfs.NewDisconnectedMount(pipeFilesystem, nil, &vfs.MountOptions{})
-		if err != nil {
-			return fmt.Errorf("failed to create pipefs mount: %v", err)
-		}
+		pipeMount := k.vfs.NewDisconnectedMount(pipeFilesystem, nil, &vfs.MountOptions{})
 		k.pipeMount = pipeMount
 
 		tmpfsFilesystem, tmpfsRoot, err := tmpfs.NewFilesystem(ctx, &k.vfs, auth.NewRootCredentials(k.rootUserNamespace))
@@ -430,22 +427,14 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 		}
 		defer tmpfsFilesystem.DecRef(ctx)
 		defer tmpfsRoot.DecRef(ctx)
-		shmMount, err := k.vfs.NewDisconnectedMount(tmpfsFilesystem, tmpfsRoot, &vfs.MountOptions{})
-		if err != nil {
-			return fmt.Errorf("failed to create tmpfs mount: %v", err)
-		}
-		k.shmMount = shmMount
+		k.shmMount = k.vfs.NewDisconnectedMount(tmpfsFilesystem, tmpfsRoot, &vfs.MountOptions{})
 
 		socketFilesystem, err := sockfs.NewFilesystem(&k.vfs)
 		if err != nil {
 			return fmt.Errorf("failed to create sockfs filesystem: %v", err)
 		}
 		defer socketFilesystem.DecRef(ctx)
-		socketMount, err := k.vfs.NewDisconnectedMount(socketFilesystem, nil, &vfs.MountOptions{})
-		if err != nil {
-			return fmt.Errorf("failed to create sockfs mount: %v", err)
-		}
-		k.socketMount = socketMount
+		k.socketMount = k.vfs.NewDisconnectedMount(socketFilesystem, nil, &vfs.MountOptions{})
 
 		k.socketsVFS2 = make(map[*vfs.FileDescription]*SocketRecord)
 

pkg/sentry/vfs/mount.go

@@ -178,12 +178,12 @@ func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth
 // (which may be nil). The new Mount is not associated with any MountNamespace
 // and is not connected to any other Mounts. References are taken on fs and
 // root.
-func (vfs *VirtualFilesystem) NewDisconnectedMount(fs *Filesystem, root *Dentry, opts *MountOptions) (*Mount, error) {
+func (vfs *VirtualFilesystem) NewDisconnectedMount(fs *Filesystem, root *Dentry, opts *MountOptions) *Mount {
 	fs.IncRef()
 	if root != nil {
 		root.IncRef()
 	}
-	return newMount(vfs, fs, root, nil /* mntns */, opts), nil
+	return newMount(vfs, fs, root, nil /* mntns */, opts)
 }
 
 // MountDisconnected creates a Filesystem configured by the given arguments,
@@ -201,9 +201,7 @@ func (vfs *VirtualFilesystem) MountDisconnected(ctx context.Context, creds *auth
 	if err != nil {
 		return nil, err
 	}
-	defer root.DecRef(ctx)
-	defer fs.DecRef(ctx)
-	return vfs.NewDisconnectedMount(fs, root, opts)
+	return newMount(vfs, fs, root, nil /* mntns */, opts), nil
 }
 
 // ConnectMountAt connects mnt at the path represented by target.

pkg/sentry/vfs/vfs.go

@@ -150,12 +150,7 @@ func (vfs *VirtualFilesystem) Init(ctx context.Context) error {
 	}
 	anonfs.vfsfs.Init(vfs, &anonFilesystemType{}, &anonfs)
 	defer anonfs.vfsfs.DecRef(ctx)
-	anonMount, err := vfs.NewDisconnectedMount(&anonfs.vfsfs, nil, &MountOptions{})
-	if err != nil {
-		// We should not be passing any MountOptions that would cause
-		// construction of this mount to fail.
-		panic(fmt.Sprintf("VirtualFilesystem.Init: anonfs mount failed: %v", err))
-	}
+	anonMount := vfs.NewDisconnectedMount(&anonfs.vfsfs, nil, &MountOptions{})
 	vfs.anonMount = anonMount
 
 	return nil

runsc/boot/loader.go

@@ -411,11 +411,7 @@ func New(args Args) (*Loader, error) {
 			return nil, fmt.Errorf("failed to create hostfs filesystem: %w", err)
 		}
 		defer hostFilesystem.DecRef(k.SupervisorContext())
-		hostMount, err := k.VFS().NewDisconnectedMount(hostFilesystem, nil, &vfs.MountOptions{})
-		if err != nil {
-			return nil, fmt.Errorf("failed to create hostfs mount: %w", err)
-		}
-		k.SetHostMount(hostMount)
+		k.SetHostMount(k.VFS().NewDisconnectedMount(hostFilesystem, nil, &vfs.MountOptions{}))
 	}
 
 	eid := execID{cid: args.ID}

runsc/boot/vfs.go

@@ -769,10 +769,7 @@ func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *co
 	if err != nil {
 		return nil, err
 	}
-	newMnt, err := c.k.VFS().NewDisconnectedMount(source.vfsMount.Filesystem(), source.vfsMount.Root(), opts)
-	if err != nil {
-		return nil, err
-	}
+	newMnt := c.k.VFS().NewDisconnectedMount(source.vfsMount.Filesystem(), source.vfsMount.Root(), opts)
 	defer newMnt.DecRef(ctx)
 
 	root := mns.Root()