befs: make export work with cold dcache

based on commit b3b42c0d
("fs/affs: make export work with cold dcache")

This adds get_parent function so that nfs client can still work after
cache drop (Tested on NFS v4 with echo 3 > /proc/sys/vm/drop_caches)
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>

fs/befs/linuxvfs.c

@@ -58,6 +58,7 @@ static struct dentry *befs_fh_to_dentry(struct super_block *sb,
 				struct fid *fid, int fh_len, int fh_type);
 static struct dentry *befs_fh_to_parent(struct super_block *sb,
 				struct fid *fid, int fh_len, int fh_type);
+static struct dentry *befs_get_parent(struct dentry *child);
 
 static const struct super_operations befs_sops = {
 	.alloc_inode	= befs_alloc_inode,	/* allocate a new inode */
@@ -93,6 +94,7 @@ static const struct address_space_operations befs_symlink_aops = {
 static const struct export_operations befs_export_operations = {
 	.fh_to_dentry	= befs_fh_to_dentry,
 	.fh_to_parent	= befs_fh_to_parent,
+	.get_parent	= befs_get_parent,
 };
 
 /*
@@ -667,6 +669,19 @@ static struct dentry *befs_fh_to_parent(struct super_block *sb,
 				    befs_nfs_get_inode);
 }
 
+static struct dentry *befs_get_parent(struct dentry *child)
+{
+	struct inode *parent;
+	struct befs_inode_info *befs_ino = BEFS_I(d_inode(child));
+
+	parent = befs_iget(child->d_sb,
+			   (unsigned long)befs_ino->i_parent.start);
+	if (IS_ERR(parent))
+		return ERR_CAST(parent);
+
+	return d_obtain_alias(parent);
+}
+
 enum {
 	Opt_uid, Opt_gid, Opt_charset, Opt_debug, Opt_err,
 };