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

7 files changed, 11 insertions, 42 deletions

diff --git a/pkg/sentry/fsimpl/mqfs/registry.go b/pkg/sentry/fsimpl/mqfs/registry.go
index e470ffadc..69182965c 100644
--- a/pkg/sentry/fsimpl/mqfs/registry.go
+++ b/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,
diff --git a/pkg/sentry/fsimpl/overlay/overlay.go b/pkg/sentry/fsimpl/overlay/overlay.go
index 46d9f1f1d..327c37477 100644
--- a/pkg/sentry/fsimpl/overlay/overlay.go
+++ b/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()
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index d4851ccda..83299a9fb 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/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)
 
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index 05a416775..9ab9a8fca 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/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.
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 1b2a668c0..9c1ee549a 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/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
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index dbb02fdf4..247f0d54a 100644
--- a/runsc/boot/loader.go
+++ b/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}
diff --git a/runsc/boot/vfs.go b/runsc/boot/vfs.go
index 9f0d1ae36..4d0cfc94a 100644
--- a/runsc/boot/vfs.go
+++ b/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()