cgroup: Add cgroup1_get_from_id()

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ZG61

-------------------------------

Add cgroup1_get_from_id() function to help cgroupv1 get cgroup through
cgroup inode;

The patch also export cgroup_tryget_css(), which will be used later
Signed-off-by: NLu Jialin <lujialin4@huawei.com>

include/linux/cgroup-defs.h

@@ -790,6 +790,8 @@ static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
 	percpu_up_read(&cgroup_threadgroup_rwsem);
 }
 
+struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
+					      struct cgroup_subsys *ss);
 #else	/* CONFIG_CGROUPS */
 
 #define CGROUP_SUBSYS_COUNT 0

include/linux/cgroup.h

@@ -696,6 +696,7 @@ static inline void cgroup_kthread_ready(void)
 }
 
 void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen);
+struct cgroup *cgroup1_get_from_id(struct cgroup_root *root, u64 id);
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;

kernel/cgroup/cgroup.c

@@ -475,7 +475,7 @@ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
  * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
  * or is offline, %NULL is returned.
  */
-static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
+struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 					      struct cgroup_subsys *ss)
 {
 	struct cgroup_subsys_state *css;
@@ -6080,6 +6080,43 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 	return retval;
 }
 
+struct cgroup *cgroup1_get_from_id(struct cgroup_root *root, u64 id)
+{
+	struct kernfs_node *kn;
+	struct cgroup *cgrp, *root_cgrp;
+
+	kn = kernfs_find_and_get_node_by_id(root->kf_root, id);
+	if (!kn)
+		return ERR_PTR(-ENOENT);
+
+	if (kernfs_type(kn) != KERNFS_DIR) {
+		kernfs_put(kn);
+		return ERR_PTR(-ENOENT);
+	}
+
+	rcu_read_lock();
+
+	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
+	if (cgrp && !cgroup_tryget(cgrp))
+		cgrp = NULL;
+
+	rcu_read_unlock();
+	kernfs_put(kn);
+
+	if (!cgrp)
+		return ERR_PTR(-ENOENT);
+
+	spin_lock_irq(&css_set_lock);
+	root_cgrp = current_cgns_cgroup_from_root(root);
+	spin_unlock_irq(&css_set_lock);
+	if (!cgroup_is_descendant(cgrp, root_cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-ENOENT);
+	}
+
+	return cgrp;
+}
+
 /**
  * cgroup_fork - initialize cgroup related fields during copy_process()
  * @child: pointer to task_struct of forking parent process.