ovl: add flag for upper in ovl_entry

For rename, we need to ensure that an upper alias exists for hard links
before attempting the operation.  Introduce a flag in ovl_entry to track
the state of the upper alias.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -472,6 +472,7 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto out_cleanup;
 
+	ovl_dentry_set_upper_alias(c->dentry);
 	ovl_inode_update(d_inode(c->dentry), newdentry);
 out:
 	dput(temp);

fs/overlayfs/dir.c

@@ -156,6 +156,7 @@ static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
 			    struct dentry *newdentry, bool hardlink)
 {
 	ovl_dentry_version_inc(dentry->d_parent);
+	ovl_dentry_set_upper_alias(dentry);
 	if (!hardlink) {
 		ovl_inode_update(inode, newdentry);
 		ovl_copyattr(newdentry->d_inode, inode);

fs/overlayfs/namei.c

@@ -674,7 +674,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 	dentry->d_fsdata = oe;
 
-	if (index && !upperdentry)
+	if (upperdentry)
+		ovl_dentry_set_upper_alias(dentry);
+	else if (index)
 		upperdentry = dget(index);
 
 	if (upperdentry || ctr) {

fs/overlayfs/overlayfs.h

@@ -206,6 +206,8 @@ void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache);
 bool ovl_dentry_is_opaque(struct dentry *dentry);
 bool ovl_dentry_is_whiteout(struct dentry *dentry);
 void ovl_dentry_set_opaque(struct dentry *dentry);
+bool ovl_dentry_has_upper_alias(struct dentry *dentry);
+void ovl_dentry_set_upper_alias(struct dentry *dentry);
 bool ovl_redirect_dir(struct super_block *sb);
 const char *ovl_dentry_get_redirect(struct dentry *dentry);
 void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect);

fs/overlayfs/ovl_entry.h

@@ -42,7 +42,10 @@ struct ovl_fs {
 /* private information held for every overlayfs dentry */
 struct ovl_entry {
 	union {
+		struct {
+			unsigned long has_upper;
 			bool opaque;
+		};
 		struct rcu_head rcu;
 	};
 	unsigned numlower;

fs/overlayfs/super.c

@@ -1119,6 +1119,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	kfree(lowertmp);
 
 	if (upperpath.dentry) {
+		oe->has_upper = true;
 		if (ovl_is_impuredir(upperpath.dentry))
 			ovl_set_flag(OVL_IMPURE, d_inode(root_dentry));
 	}

fs/overlayfs/util.c

@@ -201,6 +201,25 @@ void ovl_dentry_set_opaque(struct dentry *dentry)
 	oe->opaque = true;
 }
 
+/*
+ * For hard links it's possible for ovl_dentry_upper() to return positive, while
+ * there's no actual upper alias for the inode.  Copy up code needs to know
+ * about the existence of the upper alias, so it can't use ovl_dentry_upper().
+ */
+bool ovl_dentry_has_upper_alias(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	return oe->has_upper;
+}
+
+void ovl_dentry_set_upper_alias(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	oe->has_upper = true;
+}
+
 bool ovl_redirect_dir(struct super_block *sb)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;