ovl: decide if revalidate needed on a per-dentry basis

Allow completely skipping ->revalidate() on a per-dentry basis, in case the
underlying layers used for a dentry do not themselves have ->revalidate().

E.g. negative overlay dentry has no underlying layers, hence revalidate is
unnecessary.  Or if lower layer is remote but overlay dentry is pure-upper,
then can skip revalidate.

The following places need to update whether the dentry needs revalidate or
not:

 - fill-super (root dentry)
 - lookup
 - create
 - fh_to_dentry

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 6f54d70cef27..a58b3d9b06b9 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -324,6 +324,8 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		if (upper_alias)
 			ovl_dentry_set_upper_alias(dentry);
 	}
+	ovl_dentry_update_reval(dentry, upper,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
 	return d_instantiate_anon(dentry, inode);