[PATCH] fs/configfs: allow to create groups on demand

[Sebastian Andrzej Siewior]

This patch adds a function add a group to an existing one and its
counterart. The newly created group behaves as it would be created via
default_groups[] which means the user can't rmdir it.
This should be used by the upcomming USB gadget interface in order to
add the currently available UDCs as a child of the UDC node. The UDC
itself will appear once the hardware driver is loaded and can appear
later.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
 fs/configfs/dir.c        |   63 ++++++++++++++++++++++++++++++++++------------
 include/linux/configfs.h |    4 +++
 2 files changed, 51 insertions(+), 16 deletions(-)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 7414ae2..50ee2bd 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1663,19 +1663,13 @@ const struct file_operations configfs_dir_operations = {
        .readdir        = configfs_readdir,
 };
 
-int configfs_register_subsystem(struct configfs_subsystem *subsys)
+static int __create_group(struct config_group *group, struct dentry *root)
 {
        int err;
-       struct config_group *group = &subsys->su_group;
        struct qstr name;
        struct dentry *dentry;
-       struct dentry *root;
        struct configfs_dirent *sd;
 
-       root = configfs_pin_fs();
-       if (IS_ERR(root))
-               return PTR_ERR(root);
-
        if (!group->cg_item.ci_name)
                group->cg_item.ci_name = group->cg_item.ci_namebuf;
 
@@ -1708,25 +1702,48 @@ int configfs_register_subsystem(struct 
configfs_subsystem *subsys)
 
        mutex_unlock(&root->d_inode->i_mutex);
 
-       if (err) {
+       if (err)
                unlink_group(group);
-               configfs_release_fs();
+
+       return err;
+}
+
+int configfs_create_group(struct config_group *parent, struct config_group 
*new)
+{
+       int ret;
+
+       ret = __create_group(new, parent->cg_item.ci_dentry);
+       if (!ret) {
+               struct configfs_dirent *sd = new->cg_item.ci_dentry->d_fsdata;
+
+               sd->s_type |= CONFIGFS_USET_DEFAULT;
        }
 
+       return ret;
+}
+EXPORT_SYMBOL_GPL(configfs_create_group);
+
+int configfs_register_subsystem(struct configfs_subsystem *subsys)
+{
+       int err;
+       struct dentry *root;
+
+       root = configfs_pin_fs();
+       if (IS_ERR(root))
+               return PTR_ERR(root);
+
+       err = __create_group(&subsys->su_group, root);
+       if (err)
+               configfs_release_fs();
+
        return err;
 }
 
-void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
+void configfs_remove_group(struct config_group *group)
 {
-       struct config_group *group = &subsys->su_group;
        struct dentry *dentry = group->cg_item.ci_dentry;
        struct dentry *root = dentry->d_sb->s_root;
 
-       if (dentry->d_parent != root) {
-               printk(KERN_ERR "configfs: Tried to unregister 
non-subsystem!\n");
-               return;
-       }
-
        mutex_lock_nested(&root->d_inode->i_mutex,
                          I_MUTEX_PARENT);
        mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
@@ -1749,6 +1766,20 @@ void configfs_unregister_subsystem(struct 
configfs_subsystem *subsys)
        dput(dentry);
 
        unlink_group(group);
+}
+EXPORT_SYMBOL_GPL(configfs_remove_group);
+
+void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
+{
+       struct config_group *group = &subsys->su_group;
+       struct dentry *dentry = group->cg_item.ci_dentry;
+       struct dentry *root = dentry->d_sb->s_root;
+
+       if (dentry->d_parent != root) {
+               pr_err("configfs: Tried to unregister non-subsystem!\n");
+               return;
+       }
+       configfs_remove_group(group);
        configfs_release_fs();
 }
 
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 34025df..660c25d 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -249,6 +249,10 @@ static inline struct configfs_subsystem 
*to_configfs_subsystem(struct config_gro
                NULL;
 }
 
+int configfs_create_group(struct config_group *parent,
+               struct config_group *new);
+void configfs_remove_group(struct config_group *group);
+
 int configfs_register_subsystem(struct configfs_subsystem *subsys);
 void configfs_unregister_subsystem(struct configfs_subsystem *subsys);
 
-- 
1.7.10.4

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