kernfs: add kernfs_dir_ops

Add support for mkdir(2), rmdir(2) and rename(2) syscalls.  This is
implemented through optional kernfs_dir_ops callback table which can
be specified on kernfs_create_root().  An implemented callback is
invoked when the matching syscall is invoked.

As kernfs keep dcache syncs with internal representation and
revalidates dentries on each access, the implementation of these
methods is extremely simple.  Each just discovers the relevant
kernfs_node(s) and invokes the requested callback which is allowed to
do any kernfs operations and the end result doesn't necessarily have
to match the expected semantics of the syscall.

This will be used to convert cgroup to use kernfs instead of its own
filesystem implementation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 44 insertions, 2 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 42c5b9f23b4..510b5062ef3 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -583,12 +583,13 @@ EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
 
 /**
  * kernfs_create_root - create a new kernfs hierarchy
+ * @kdops: optional directory syscall operations for the hierarchy
  * @priv: opaque data associated with the new directory
  *
  * Returns the root of the new hierarchy on success, ERR_PTR() value on
  * failure.
  */
-struct kernfs_root *kernfs_create_root(void *priv)
+struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
 {
 	struct kernfs_root *root;
 	struct kernfs_node *kn;
@@ -610,6 +611,7 @@ struct kernfs_root *kernfs_create_root(void *priv)
 	kn->priv = priv;
 	kn->dir.root = root;
 
+	root->dir_ops = kdops;
 	root->kn = kn;
 
 	return root;
@@ -706,6 +708,42 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 	return ret;
 }
 
+static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
+			    umode_t mode)
+{
+	struct kernfs_node *parent = dir->i_private;
+	struct kernfs_dir_ops *kdops = kernfs_root(parent)->dir_ops;
+
+	if (!kdops || !kdops->mkdir)
+		return -EPERM;
+
+	return kdops->mkdir(parent, dentry->d_name.name, mode);
+}
+
+static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	struct kernfs_node *kn  = dentry->d_fsdata;
+	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+
+	if (!kdops || !kdops->rmdir)
+		return -EPERM;
+
+	return kdops->rmdir(kn);
+}
+
+static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct kernfs_node *kn  = old_dentry->d_fsdata;
+	struct kernfs_node *new_parent = new_dir->i_private;
+	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+
+	if (!kdops || !kdops->rename)
+		return -EPERM;
+
+	return kdops->rename(kn, new_parent, new_dentry->d_name.name);
+}
+
 const struct inode_operations kernfs_dir_iops = {
 	.lookup		= kernfs_iop_lookup,
 	.permission	= kernfs_iop_permission,
@@ -715,6 +753,10 @@ const struct inode_operations kernfs_dir_iops = {
 	.removexattr	= kernfs_iop_removexattr,
 	.getxattr	= kernfs_iop_getxattr,
 	.listxattr	= kernfs_iop_listxattr,
+
+	.mkdir		= kernfs_iop_mkdir,
+	.rmdir		= kernfs_iop_rmdir,
+	.rename		= kernfs_iop_rename,
 };
 
 static struct kernfs_node *kernfs_leftmost_descendant(struct kernfs_node *pos)
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 701a56f341c..6211230814f 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -62,7 +62,7 @@ int __init sysfs_init(void)
 {
 	int err;
 
-	sysfs_root = kernfs_create_root(NULL);
+	sysfs_root = kernfs_create_root(NULL, NULL);
 	if (IS_ERR(sysfs_root))
 		return PTR_ERR(sysfs_root);