1 files changed, 23 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f6495f33a355..95362d15128c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4818,6 +4818,29 @@ css_get_next(struct cgroup_subsys *ss, int id,
         return ret;
 }
 
+/*
+ * get corresponding css from file open on cgroupfs directory
+ */
+struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
+{
+        struct cgroup *cgrp;
+        struct inode *inode;
+        struct cgroup_subsys_state *css;
+
+        inode = f->f_dentry->d_inode;
+        /* check in cgroup filesystem dir */
+        if (inode->i_op != &cgroup_dir_inode_operations)
+                return ERR_PTR(-EBADF);
+
+        if (id < 0 || id >= CGROUP_SUBSYS_COUNT)
+                return ERR_PTR(-EINVAL);
+
+        /* get cgroup */
+        cgrp = __d_cgrp(f->f_dentry);
+        css = cgrp->subsys[id];
+        return css ? css : ERR_PTR(-ENOENT);
+}
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
                                                    struct cgroup *cont)