[PATCH V3 07/12] cgroup: export fhandle info for a cgroup

[Shaohua Li <shli@kernel.org>]

From: Shaohua Li <shli@fb.com>

Add an API to export cgroup fhandle info. We don't export a full 'struct
file_handle', there are unrequired info. Sepcifically, cgroup is always
a directory, so we don't need a 'FILEID_INO32_GEN_PARENT' type fhandle,
we only need export the inode number and generation number just like
what generic_fh_to_parent does. And we can avoid the overhead of getting
an inode too, since kernfs_node has all the info required.

Signed-off-by: Shaohua Li <shli@fb.com>
---
 include/linux/cgroup.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 30c6877..5ebe89f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -609,6 +609,10 @@ static inline void cgroup_kthread_ready(void)
 	current->no_cgroup_migration = 0;
 }
 
+static inline struct kernfs_node_id *cgroup_get_node_id(struct cgroup *cgrp)
+{
+	return &cgrp->kn->id;
+}
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
@@ -631,6 +635,10 @@ static inline int cgroup_init_early(void) { return 0; }
 static inline int cgroup_init(void) { return 0; }
 static inline void cgroup_init_kthreadd(void) {}
 static inline void cgroup_kthread_ready(void) {}
+static inline struct kernfs_node_id *cgroup_get_node_id(struct cgroup *cgrp)
+{
+	return NULL;
+}
 
 static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 					       struct cgroup *ancestor)
-- 
2.9.3