[PATCH v7 01/16] cgroup: Added cgroup_get_from_id

[Muneendra <muneendra.kumar@broadcom.com>]

Added a new function cgroup_get_from_id  to retrieve the cgroup
associated with cgroup id.
Exported the same as this can be used by blk-cgorup.c

Added function declaration of cgroup_get_from_id in cgorup.h

This patch also exported the function cgroup_get_e_css
as this is getting used in blk-cgroup.h

Signed-off-by: Muneendra <muneendra.kumar@broadcom.com>

---
v7:
No change

v6:
No change

v5:
renamed the function cgroup_get_from_kernfs_id to
cgroup_get_from_id

v4:
No change

v3:
Exported the cgroup_get_e_css

v2:
New patch
---
 include/linux/cgroup.h |  6 ++++++
 kernel/cgroup/cgroup.c | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 618838c48313..da31b14db198 100644
--- a/include/linux/cgroup.h
+++ b/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 *cgroup_get_from_id(u64 id);
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
@@ -743,6 +744,11 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 
 static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 {}
+
+static struct cgroup *cgroup_get_from_id(u64 id)
+{
+	return NULL;
+}
 #endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index e41c21819ba0..34ebfbeba098 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -580,6 +580,7 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
 	rcu_read_unlock();
 	return css;
 }
+EXPORT_SYMBOL_GPL(cgroup_get_e_css);
 
 static void cgroup_get_live(struct cgroup *cgrp)
 {
@@ -5805,6 +5806,31 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 	kernfs_put(kn);
 }
 
+/*
+ * cgroup_get_from_id : get the cgroup associated with cgroup id
+ * @id: cgroup id
+ * On success it returns the cgrp on failure it returns NULL
+ */
+struct cgroup *cgroup_get_from_id(u64 id)
+{
+	struct kernfs_node *kn;
+	struct cgroup *cgrp = NULL;
+
+	mutex_lock(&cgroup_mutex);
+	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
+	if (!kn)
+		goto out_unlock;
+
+	cgrp = kn->priv;
+	if (cgroup_is_dead(cgrp) || !cgroup_tryget(cgrp))
+		cgrp = NULL;
+	kernfs_put(kn);
+out_unlock:
+	mutex_unlock(&cgroup_mutex);
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_id);
+
 /*
  * proc_cgroup_show()
  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
-- 
2.26.2