cgroup: add cgroup_v1v2_get_from_[fd/file]()

Add cgroup_v1v2_get_from_fd() and cgroup_v1v2_get_from_file() that
support both cgroup1 and cgroup2.
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/cgroup.h

@@ -106,6 +106,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 
 struct cgroup *cgroup_get_from_path(const char *path);
 struct cgroup *cgroup_get_from_fd(int fd);
+struct cgroup *cgroup_v1v2_get_from_fd(int fd);
 
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);

kernel/cgroup/cgroup.c

@@ -6224,16 +6224,36 @@ void cgroup_fork(struct task_struct *child)
 	INIT_LIST_HEAD(&child->cg_list);
 }
 
-static struct cgroup *cgroup_get_from_file(struct file *f)
+/**
+ * cgroup_v1v2_get_from_file - get a cgroup pointer from a file pointer
+ * @f: file corresponding to cgroup_dir
+ *
+ * Find the cgroup from a file pointer associated with a cgroup directory.
+ * Returns a pointer to the cgroup on success. ERR_PTR is returned if the
+ * cgroup cannot be found.
+ */
+static struct cgroup *cgroup_v1v2_get_from_file(struct file *f)
 {
 	struct cgroup_subsys_state *css;
-	struct cgroup *cgrp;
 
 	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
 	if (IS_ERR(css))
 		return ERR_CAST(css);
 
-	cgrp = css->cgroup;
+	return css->cgroup;
+}
+
+/**
+ * cgroup_get_from_file - same as cgroup_v1v2_get_from_file, but only supports
+ * cgroup2.
+ */
+static struct cgroup *cgroup_get_from_file(struct file *f)
+{
+	struct cgroup *cgrp = cgroup_v1v2_get_from_file(f);
+
+	if (IS_ERR(cgrp))
+		return ERR_CAST(cgrp);
+
 	if (!cgroup_on_dfl(cgrp)) {
 		cgroup_put(cgrp);
 		return ERR_PTR(-EBADF);
@@ -6734,14 +6754,14 @@ EXPORT_SYMBOL_GPL(cgroup_get_from_path);
 
 /**
  * cgroup_get_from_fd - get a cgroup pointer from a fd
- * @fd: fd obtained by open(cgroup2_dir)
+ * @fd: fd obtained by open(cgroup_dir)
  *
  * Find the cgroup from a fd which should be obtained
  * by opening a cgroup directory.  Returns a pointer to the
  * cgroup on success. ERR_PTR is returned if the cgroup
  * cannot be found.
  */
-struct cgroup *cgroup_get_from_fd(int fd)
+struct cgroup *cgroup_v1v2_get_from_fd(int fd)
 {
 	struct cgroup *cgrp;
 	struct file *f;
@@ -6750,10 +6770,28 @@ struct cgroup *cgroup_get_from_fd(int fd)
 	if (!f)
 		return ERR_PTR(-EBADF);
 
-	cgrp = cgroup_get_from_file(f);
+	cgrp = cgroup_v1v2_get_from_file(f);
 	fput(f);
 	return cgrp;
 }
+
+/**
+ * cgroup_get_from_fd - same as cgroup_v1v2_get_from_fd, but only supports
+ * cgroup2.
+ */
+struct cgroup *cgroup_get_from_fd(int fd)
+{
+	struct cgroup *cgrp = cgroup_v1v2_get_from_fd(fd);
+
+	if (IS_ERR(cgrp))
+		return ERR_CAST(cgrp);
+
+	if (!cgroup_on_dfl(cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-EBADF);
+	}
+	return cgrp;
+}
 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
 
 static u64 power_of_ten(int power)