ovl: multi-layer lookup

Look up dentry in all relevant layers.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/overlayfs/super.c

@@ -333,82 +333,127 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags)
 {
 	struct ovl_entry *oe;
-	struct dentry *upperdir;
-	struct path lowerdir;
-	struct dentry *upperdentry = NULL;
-	struct dentry *lowerdentry = NULL;
+	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
+	struct path *stack = NULL;
+	struct dentry *upperdir, *upperdentry = NULL;
+	unsigned int ctr = 0;
 	struct inode *inode = NULL;
+	bool upperopaque = false;
+	struct dentry *this, *prev = NULL;
+	unsigned int i;
 	int err;
 
-	err = -ENOMEM;
-	oe = ovl_alloc_entry(1);
-	if (!oe)
-		goto out;
-
-	upperdir = ovl_dentry_upper(dentry->d_parent);
-	ovl_path_lower(dentry->d_parent, &lowerdir);
-
+	upperdir = ovl_upperdentry_dereference(poe);
 	if (upperdir) {
-		upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
-		err = PTR_ERR(upperdentry);
-		if (IS_ERR(upperdentry))
-			goto out_put_dir;
-
-		if (lowerdir.dentry && upperdentry) {
-			if (ovl_is_whiteout(upperdentry)) {
-				dput(upperdentry);
-				upperdentry = NULL;
-				oe->opaque = true;
-			} else if (ovl_is_opaquedir(upperdentry)) {
-				oe->opaque = true;
+		this = ovl_lookup_real(upperdir, &dentry->d_name);
+		err = PTR_ERR(this);
+		if (IS_ERR(this))
+			goto out;
+
+		/*
+		 * If this is not the lowermost layer, check whiteout and opaque
+		 * directory.
+		 */
+		if (poe->numlower && this) {
+			if (ovl_is_whiteout(this)) {
+				dput(this);
+				this = NULL;
+				upperopaque = true;
+			} else if (ovl_is_opaquedir(this)) {
+				upperopaque = true;
 			}
 		}
+		upperdentry = prev = this;
 	}
-	if (lowerdir.dentry && !oe->opaque) {
-		lowerdentry = ovl_lookup_real(lowerdir.dentry, &dentry->d_name);
-		err = PTR_ERR(lowerdentry);
-		if (IS_ERR(lowerdentry))
-			goto out_dput_upper;
+
+	if (!upperopaque && poe->numlower) {
+		err = -ENOMEM;
+		stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
+		if (!stack)
+			goto out_put_upper;
 	}
 
-	if (lowerdentry && upperdentry &&
-	    (!S_ISDIR(upperdentry->d_inode->i_mode) ||
-	     !S_ISDIR(lowerdentry->d_inode->i_mode))) {
-		dput(lowerdentry);
-		lowerdentry = NULL;
-		oe->opaque = true;
+	for (i = 0; !upperopaque && i < poe->numlower; i++) {
+		bool opaque = false;
+		struct path lowerpath = poe->lowerstack[i];
+
+		opaque = false;
+		this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
+		err = PTR_ERR(this);
+		if (IS_ERR(this))
+			goto out_put;
+		if (!this)
+			continue;
+
+		/*
+		 * If this is not the lowermost layer, check whiteout and opaque
+		 * directory.
+		 */
+		if (i < poe->numlower - 1) {
+			if (ovl_is_whiteout(this)) {
+				dput(this);
+				break;
+			} else if (ovl_is_opaquedir(this)) {
+				opaque = true;
+			}
+		}
+		/*
+		 * If this is a non-directory then stop here.
+		 *
+		 * FIXME: check for opaqueness maybe better done in remove code.
+		 */
+		if (!S_ISDIR(this->d_inode->i_mode)) {
+			opaque = true;
+		} else if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
+				    !S_ISDIR(this->d_inode->i_mode))) {
+			if (prev == upperdentry)
+				upperopaque = true;
+			dput(this);
+			break;
+		}
+		stack[ctr].dentry = this;
+		stack[ctr].mnt = lowerpath.mnt;
+		ctr++;
+		prev = this;
+		if (opaque)
+			break;
 	}
 
-	if (lowerdentry || upperdentry) {
+	oe = ovl_alloc_entry(ctr);
+	err = -ENOMEM;
+	if (!oe)
+		goto out_put;
+
+	if (upperdentry || ctr) {
 		struct dentry *realdentry;
 
-		realdentry = upperdentry ? upperdentry : lowerdentry;
+		realdentry = upperdentry ? upperdentry : stack[0].dentry;
+
 		err = -ENOMEM;
 		inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
 				      oe);
 		if (!inode)
-			goto out_dput;
+			goto out_free_oe;
 		ovl_copyattr(realdentry->d_inode, inode);
 	}
 
+	oe->opaque = upperopaque;
 	oe->__upperdentry = upperdentry;
-	if (lowerdentry) {
-		oe->lowerstack[0].dentry = lowerdentry;
-		oe->lowerstack[0].mnt = lowerdir.mnt;
-	} else {
-		oe->numlower = 0;
-	}
+	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
+	kfree(stack);
 	dentry->d_fsdata = oe;
 	d_add(dentry, inode);
 
 	return NULL;
 
-out_dput:
-	dput(lowerdentry);
-out_dput_upper:
-	dput(upperdentry);
-out_put_dir:
+out_free_oe:
 	kfree(oe);
+out_put:
+	for (i = 0; i < ctr; i++)
+		dput(stack[i].dentry);
+	kfree(stack);
+out_put_upper:
+	dput(upperdentry);
 out:
 	return ERR_PTR(err);
 }