ovl: prepare to store lowerdata redirect for lazy lowerdata lookup

Prepare to allow ovl_lookup() to leave the last entry in a non-dir
lowerstack empty to signify lazy lowerdata lookup.

In this case, ovl_lookup() stores the redirect path from metacopy to
lowerdata in ovl_inode, which is going to be used later to perform the
lazy lowerdata lookup.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/inode.c

@@ -1005,6 +1005,7 @@ void ovl_inode_init(struct inode *inode, struct ovl_inode_params *oip,
 	oi->__upperdentry = oip->upperdentry;
 	oi->oe = oip->oe;
 	oi->redirect = oip->redirect;
+	oi->lowerdata_redirect = oip->lowerdata_redirect;
 
 	realinode = ovl_inode_real(inode);
 	ovl_copyattr(inode);
@@ -1365,6 +1366,7 @@ struct inode *ovl_get_inode(struct super_block *sb,
 			dput(upperdentry);
 			ovl_free_entry(oip->oe);
 			kfree(oip->redirect);
+			kfree(oip->lowerdata_redirect);
 			goto out;
 		}
 

fs/overlayfs/namei.c

@@ -1183,6 +1183,11 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			.redirect = upperredirect,
 		};
 
+		/* Store lowerdata redirect for lazy lookup */
+		if (ctr > 1 && !d.is_dir && !stack[ctr - 1].dentry) {
+			oip.lowerdata_redirect = d.redirect;
+			d.redirect = NULL;
+		}
 		inode = ovl_get_inode(dentry->d_sb, &oip);
 		err = PTR_ERR(inode);
 		if (IS_ERR(inode))

fs/overlayfs/overlayfs.h

@@ -405,6 +405,7 @@ struct inode *ovl_inode_lower(struct inode *inode);
 struct inode *ovl_inode_lowerdata(struct inode *inode);
 struct inode *ovl_inode_real(struct inode *inode);
 struct inode *ovl_inode_realdata(struct inode *inode);
+const char *ovl_lowerdata_redirect(struct inode *inode);
 struct ovl_dir_cache *ovl_dir_cache(struct inode *inode);
 void ovl_set_dir_cache(struct inode *inode, struct ovl_dir_cache *cache);
 void ovl_dentry_set_flag(unsigned long flag, struct dentry *dentry);
@@ -656,6 +657,7 @@ struct ovl_inode_params {
 	struct ovl_entry *oe;
 	bool index;
 	char *redirect;
+	char *lowerdata_redirect;
 };
 void ovl_inode_init(struct inode *inode, struct ovl_inode_params *oip,
 		    unsigned long ino, int fsid);

fs/overlayfs/ovl_entry.h

@@ -141,6 +141,7 @@ static inline struct ovl_path *ovl_lowerdata(struct ovl_entry *oe)
 	return lowerstack ? &lowerstack[oe->__numlower - 1] : NULL;
 }
 
+/* May return NULL if lazy lookup of lowerdata is needed */
 static inline struct dentry *ovl_lowerdata_dentry(struct ovl_entry *oe)
 {
 	struct ovl_path *lowerdata = ovl_lowerdata(oe);
@@ -157,7 +158,7 @@ static inline unsigned long *OVL_E_FLAGS(struct dentry *dentry)
 struct ovl_inode {
 	union {
 		struct ovl_dir_cache *cache;	/* directory */
-		/* place holder for non-dir */	/* regular file */
+		const char *lowerdata_redirect;	/* regular file */
 	};
 	const char *redirect;
 	u64 version;

fs/overlayfs/super.c

@@ -171,6 +171,7 @@ static struct inode *ovl_alloc_inode(struct super_block *sb)
 	oi->version = 0;
 	oi->flags = 0;
 	oi->__upperdentry = NULL;
+	oi->lowerdata_redirect = NULL;
 	oi->oe = NULL;
 	mutex_init(&oi->lock);
 
@@ -194,6 +195,8 @@ static void ovl_destroy_inode(struct inode *inode)
 	ovl_free_entry(oi->oe);
 	if (S_ISDIR(inode->i_mode))
 		ovl_dir_cache_free(inode);
+	else
+		kfree(oi->lowerdata_redirect);
 }
 
 static void ovl_free_fs(struct ovl_fs *ofs)

fs/overlayfs/util.c

@@ -226,10 +226,11 @@ void ovl_path_lowerdata(struct dentry *dentry, struct path *path)
 {
 	struct ovl_entry *oe = OVL_E(dentry);
 	struct ovl_path *lowerdata = ovl_lowerdata(oe);
+	struct dentry *lowerdata_dentry = ovl_lowerdata_dentry(oe);
 
-	if (ovl_numlower(oe)) {
+	if (lowerdata_dentry) {
 		path->mnt = lowerdata->layer->mnt;
-		path->dentry = lowerdata->dentry;
+		path->dentry = lowerdata_dentry;
 	} else {
 		*path = (struct path) { };
 	}
@@ -358,9 +359,15 @@ struct inode *ovl_inode_realdata(struct inode *inode)
 	return ovl_inode_lowerdata(inode);
 }
 
+const char *ovl_lowerdata_redirect(struct inode *inode)
+{
+	return inode && S_ISREG(inode->i_mode) ?
+		OVL_I(inode)->lowerdata_redirect : NULL;
+}
+
 struct ovl_dir_cache *ovl_dir_cache(struct inode *inode)
 {
-	return OVL_I(inode)->cache;
+	return inode && S_ISDIR(inode->i_mode) ? OVL_I(inode)->cache : NULL;
 }
 
 void ovl_set_dir_cache(struct inode *inode, struct ovl_dir_cache *cache)