Add VFS2 support for device special files.

- Add FileDescriptionOptions.UseDentryMetadata, which reduces the amount of
  boilerplate needed for device FDs and the like between filesystems.

- Switch back to having FileDescription.Init() take references on the Mount and
  Dentry; otherwise managing refcounts around failed calls to
  OpenDeviceSpecialFile() / Device.Open() is tricky.

PiperOrigin-RevId: 287575574

5 files changed, 0 insertions, 16 deletions

diff --git a/pkg/sentry/fsimpl/ext/inode.go b/pkg/sentry/fsimpl/ext/inode.go
index b2cc826c7..8608805bf 100644
--- a/pkg/sentry/fsimpl/ext/inode.go
+++ b/pkg/sentry/fsimpl/ext/inode.go
@@ -157,8 +157,6 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*v
 	switch in.impl.(type) {
 	case *regularFile:
 		var fd regularFileFD
-		mnt.IncRef()
-		vfsd.IncRef()
 		fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
 		return &fd.vfsfd, nil
 	case *directory:
@@ -168,8 +166,6 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*v
 			return nil, syserror.EISDIR
 		}
 		var fd directoryFD
-		mnt.IncRef()
-		vfsd.IncRef()
 		fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
 		return &fd.vfsfd, nil
 	case *symlink:
@@ -178,8 +174,6 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*v
 			return nil, syserror.ELOOP
 		}
 		var fd symlinkFD
-		mnt.IncRef()
-		vfsd.IncRef()
 		fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
 		return &fd.vfsfd, nil
 	default:
diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index c5fe65722..606ca692d 100644
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
@@ -81,8 +81,6 @@ type DynamicBytesFD struct {
 
 // Init initializes a DynamicBytesFD.
 func (fd *DynamicBytesFD) Init(m *vfs.Mount, d *vfs.Dentry, data vfs.DynamicBytesSource, flags uint32) {
-	m.IncRef() // DecRef in vfs.FileDescription.vd.DecRef on final ref.
-	d.IncRef() // DecRef in vfs.FileDescription.vd.DecRef on final ref.
 	fd.inode = d.Impl().(*Dentry).inode
 	fd.SetDataSource(data)
 	fd.vfsfd.Init(fd, flags, m, d, &vfs.FileDescriptionOptions{})
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index 77975583b..bcf069b5f 100644
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
@@ -44,8 +44,6 @@ type GenericDirectoryFD struct {
 
 // Init initializes a GenericDirectoryFD.
 func (fd *GenericDirectoryFD) Init(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, flags uint32) {
-	m.IncRef() // DecRef in vfs.FileDescription.vd.DecRef on final ref.
-	d.IncRef() // DecRef in vfs.FileDescription.vd.DecRef on final ref.
 	fd.children = children
 	fd.vfsfd.Init(fd, flags, m, d, &vfs.FileDescriptionOptions{})
 }
diff --git a/pkg/sentry/fsimpl/memfs/filesystem.go b/pkg/sentry/fsimpl/memfs/filesystem.go
index 4a83f310c..b063e09a3 100644
--- a/pkg/sentry/fsimpl/memfs/filesystem.go
+++ b/pkg/sentry/fsimpl/memfs/filesystem.go
@@ -348,8 +348,6 @@ func (d *dentry) open(ctx context.Context, rp *vfs.ResolvingPath, flags uint32,
 			}
 			// mnt.EndWrite() is called by regularFileFD.Release().
 		}
-		mnt.IncRef()
-		d.IncRef()
 		fd.vfsfd.Init(&fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{})
 		if flags&linux.O_TRUNC != 0 {
 			impl.mu.Lock()
@@ -364,8 +362,6 @@ func (d *dentry) open(ctx context.Context, rp *vfs.ResolvingPath, flags uint32,
 			return nil, syserror.EISDIR
 		}
 		var fd directoryFD
-		mnt.IncRef()
-		d.IncRef()
 		fd.vfsfd.Init(&fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{})
 		return &fd.vfsfd, nil
 	case *symlink:
diff --git a/pkg/sentry/fsimpl/memfs/named_pipe.go b/pkg/sentry/fsimpl/memfs/named_pipe.go
index d5060850e..b5a204438 100644
--- a/pkg/sentry/fsimpl/memfs/named_pipe.go
+++ b/pkg/sentry/fsimpl/memfs/named_pipe.go
@@ -55,8 +55,6 @@ func newNamedPipeFD(ctx context.Context, np *namedPipe, rp *vfs.ResolvingPath, v
 		return nil, err
 	}
 	mnt := rp.Mount()
-	mnt.IncRef()
-	vfsd.IncRef()
 	fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
 	return &fd.vfsfd, nil
 }