ovl: whiteout index when union nlink drops to zero

With NFS export feature enabled, when overlay inode nlink drops to
zero, instead of removing the index entry, replace it with a whiteout
index entry.

This is needed for NFS export in order to prevent future open by handle
from opening the lower file directly.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

@@ -63,8 +63,7 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir)
 }
 
 /* caller holds i_mutex on workdir */
-static struct dentry *ovl_whiteout(struct dentry *workdir,
-				   struct dentry *dentry)
+static struct dentry *ovl_whiteout(struct dentry *workdir)
 {
 	int err;
 	struct dentry *whiteout;
@@ -83,6 +82,38 @@ static struct dentry *ovl_whiteout(struct dentry *workdir,
 	return whiteout;
 }
 
+/* Caller must hold i_mutex on both workdir and dir */
+int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
+			     struct dentry *dentry)
+{
+	struct inode *wdir = workdir->d_inode;
+	struct dentry *whiteout;
+	int err;
+	int flags = 0;
+
+	whiteout = ovl_whiteout(workdir);
+	err = PTR_ERR(whiteout);
+	if (IS_ERR(whiteout))
+		return err;
+
+	if (d_is_dir(dentry))
+		flags = RENAME_EXCHANGE;
+
+	err = ovl_do_rename(wdir, whiteout, dir, dentry, flags);
+	if (err)
+		goto kill_whiteout;
+	if (flags)
+		ovl_cleanup(wdir, dentry);
+
+out:
+	dput(whiteout);
+	return err;
+
+kill_whiteout:
+	ovl_cleanup(wdir, whiteout);
+	goto out;
+}
+
 int ovl_create_real(struct inode *dir, struct dentry *newdentry,
 		    struct cattr *attr, struct dentry *hardlink, bool debug)
 {
@@ -591,14 +622,10 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
 				   struct list_head *list)
 {
 	struct dentry *workdir = ovl_workdir(dentry);
-	struct inode *wdir = workdir->d_inode;
 	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
-	struct inode *udir = upperdir->d_inode;
-	struct dentry *whiteout;
 	struct dentry *upper;
 	struct dentry *opaquedir = NULL;
 	int err;
-	int flags = 0;
 
 	if (WARN_ON(!workdir))
 		return -EROFS;
@@ -627,24 +654,13 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
 		goto out_dput_upper;
 	}
 
-	whiteout = ovl_whiteout(workdir, dentry);
-	err = PTR_ERR(whiteout);
-	if (IS_ERR(whiteout))
-		goto out_dput_upper;
-
-	if (d_is_dir(upper))
-		flags = RENAME_EXCHANGE;
-
-	err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
+	err = ovl_cleanup_and_whiteout(workdir, d_inode(upperdir), upper);
 	if (err)
-		goto kill_whiteout;
-	if (flags)
-		ovl_cleanup(wdir, upper);
+		goto out_d_drop;
 
 	ovl_dentry_version_inc(dentry->d_parent, true);
 out_d_drop:
 	d_drop(dentry);
-	dput(whiteout);
 out_dput_upper:
 	dput(upper);
 out_unlock:
@@ -653,10 +669,6 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
 	dput(opaquedir);
 out:
 	return err;
-
-kill_whiteout:
-	ovl_cleanup(wdir, whiteout);
-	goto out_d_drop;
 }
 
 static int ovl_remove_upper(struct dentry *dentry, bool is_dir,

fs/overlayfs/overlayfs.h

@@ -321,6 +321,8 @@ static inline void ovl_copyattr(struct inode *from, struct inode *to)
 /* dir.c */
 extern const struct inode_operations ovl_dir_inode_operations;
 struct dentry *ovl_lookup_temp(struct dentry *workdir);
+int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
+			     struct dentry *dentry);
 struct cattr {
 	dev_t rdev;
 	umode_t mode;

fs/overlayfs/util.c

@@ -487,7 +487,8 @@ bool ovl_need_index(struct dentry *dentry)
 /* Caller must hold OVL_I(inode)->lock */
 static void ovl_cleanup_index(struct dentry *dentry)
 {
-	struct inode *dir = ovl_indexdir(dentry->d_sb)->d_inode;
+	struct dentry *indexdir = ovl_indexdir(dentry->d_sb);
+	struct inode *dir = indexdir->d_inode;
 	struct dentry *lowerdentry = ovl_dentry_lower(dentry);
 	struct dentry *upperdentry = ovl_dentry_upper(dentry);
 	struct dentry *index = NULL;
@@ -518,13 +519,17 @@ static void ovl_cleanup_index(struct dentry *dentry)
 	}
 
 	inode_lock_nested(dir, I_MUTEX_PARENT);
-	/* TODO: whiteout instead of cleanup to block future open by handle */
-	index = lookup_one_len(name.name, ovl_indexdir(dentry->d_sb), name.len);
+	index = lookup_one_len(name.name, indexdir, name.len);
 	err = PTR_ERR(index);
-	if (!IS_ERR(index))
-		err = ovl_cleanup(dir, index);
-	else
+	if (IS_ERR(index)) {
 		index = NULL;
+	} else if (ovl_index_all(dentry->d_sb)) {
+		/* Whiteout orphan index to block future open by handle */
+		err = ovl_cleanup_and_whiteout(indexdir, dir, index);
+	} else {
+		/* Cleanup orphan index entries */
+		err = ovl_cleanup(dir, index);
+	}
 
 	inode_unlock(dir);
 	if (err)