cgroup: introduce cgroup_ino()

mm/memory-failure.c::hwpoison_filter_task() has been reaching into
cgroup to extract the associated ino to be used as a filtering
criterion.  This is an implementation detail which shouldn't be
depended upon from outside cgroup proper and is about to change with
the scheduled kernfs conversion.

This patch introduces a proper interface to determine the associated
ino, cgroup_ino(), and updates hwpoison_filter_task() to use it
instead of reaching directly into cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 63feaed83bc..06f57776441 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -507,6 +507,15 @@ static inline const char *cgroup_name(const struct cgroup *cgrp)
 	return rcu_dereference(cgrp->name)->name;
 }
 
+/* returns ino associated with a cgroup, 0 indicates unmounted root */
+static inline ino_t cgroup_ino(struct cgroup *cgrp)
+{
+	if (cgrp->dentry)
+		return cgrp->dentry->d_inode->i_ino;
+	else
+		return 0;
+}
+
 static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)
 {
 	struct cgroup_open_file *of = seq->private;