kernfs: Add support for always empty directories.

commit ea015218f2f7ace2dad9cedd21ed95bdba2886d7 upstream.

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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 345b35f..470b29e 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -592,6 +592,9 @@ int kernfs_add_one(struct kernfs_node *kn)
                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;
 
@@ -783,6 +786,38 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
        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)
@@ -1254,7 +1289,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
        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 9000874..2119bf0 100644 (file)
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -296,6 +296,8 @@ static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
        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;

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 71ecdab..29d1896 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -45,6 +45,7 @@ enum kernfs_node_flag {
        KERNFS_LOCKDEP          = 0x0100,
        KERNFS_SUICIDAL         = 0x0400,
        KERNFS_SUICIDED         = 0x0800,
+       KERNFS_EMPTY_DIR        = 0x1000,
 };
 
 /* @flags for kernfs_create_root() */
@@ -285,6 +286,8 @@ void kernfs_destroy_root(struct kernfs_root *root);
 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
                                         const char *name, umode_t mode,
                                         void *priv, const void *ns);
+struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
+                                           const char *name);
 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
                                         const char *name,
                                         umode_t mode, loff_t size,