kernfs: Add support for always empty directories.
Add a new function kernfs_create_empty_dir that can be used to create
directory that can not be modified.
Update the code to use make_empty_dir_inode when reporting a
permanently empty directory to the vfs.
Update the code to not allow adding to permanently empty directories.
Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index f131fc2..47dc636 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -585,6 +585,9 @@
goto out_unlock;
ret = -ENOENT;
+ if (parent->flags & KERNFS_EMPTY_DIR)
+ goto out_unlock;
+
if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
goto out_unlock;
@@ -776,6 +779,38 @@
return ERR_PTR(rc);
}
+/**
+ * kernfs_create_empty_dir - create an always empty directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
+ const char *name)
+{
+ struct kernfs_node *kn;
+ int rc;
+
+ /* allocate */
+ kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR, KERNFS_DIR);
+ if (!kn)
+ return ERR_PTR(-ENOMEM);
+
+ kn->flags |= KERNFS_EMPTY_DIR;
+ kn->dir.root = parent->dir.root;
+ kn->ns = NULL;
+ kn->priv = NULL;
+
+ /* link in */
+ rc = kernfs_add_one(kn);
+ if (!rc)
+ return kn;
+
+ kernfs_put(kn);
+ return ERR_PTR(rc);
+}
+
static struct dentry *kernfs_iop_lookup(struct inode *dir,
struct dentry *dentry,
unsigned int flags)
@@ -1247,7 +1282,8 @@
mutex_lock(&kernfs_mutex);
error = -ENOENT;
- if (!kernfs_active(kn) || !kernfs_active(new_parent))
+ if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
+ (new_parent->flags & KERNFS_EMPTY_DIR))
goto out;
error = 0;
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 2da8493..756dd56 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -296,6 +296,8 @@
case KERNFS_DIR:
inode->i_op = &kernfs_dir_iops;
inode->i_fop = &kernfs_dir_fops;
+ if (kn->flags & KERNFS_EMPTY_DIR)
+ make_empty_dir_inode(inode);
break;
case KERNFS_FILE:
inode->i_size = kn->attr.size;