fs: Allow overlays to revalidate files from the upper fs.

Previously, an overlay would panic if either the upper or lower fs required
revalidation for a given Dirent. Now, we allow revalidation from the upper
file, but not the lower.

If a cached overlay inode does need revalidation (because the upper needs
revalidation), then the entire overlay Inode will be discarded and a new
overlay Inode will be built with a fresh copy of the upper file.

As a side effect of this change, Revalidate must take an Inode instead of a
Dirent, since an overlay needs to revalidate individual Inodes.

PiperOrigin-RevId: 208293638
Change-Id: Ic8f8d1ffdc09114721745661a09522b54420c5f1

1 files changed, 3 insertions, 3 deletions

diff --git a/pkg/sentry/fs/gofer/session.go b/pkg/sentry/fs/gofer/session.go
index bfb1154dc..eeb9087e9 100644
--- a/pkg/sentry/fs/gofer/session.go
+++ b/pkg/sentry/fs/gofer/session.go
@@ -145,12 +145,12 @@ func (s *session) Destroy() {
 	s.conn.Close()
 }
 
-// Revalidate returns true if the cache policy is does not allow for VFS caching.
-func (s *session) Revalidate(ctx context.Context, d *fs.Dirent) bool {
+// Revalidate implements MountSource.Revalidate.
+func (s *session) Revalidate(ctx context.Context, i *fs.Inode) bool {
 	return s.cachePolicy.revalidateDirent()
 }
 
-// TakeRefs takes an extra reference on dirent if possible.
+// Keep implements MountSource.Keep.
 func (s *session) Keep(d *fs.Dirent) bool {
 	return s.cachePolicy.keepDirent(d.Inode)
 }