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Date: Mon, 15 Apr 2013 11:43:15 +0800
From: Li Zefan <lizefan@huawei.com>
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To: Tejun Heo <tj@kernel.org>
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        <linux-kernel@vger.kernel.org>, <kay@vrfy.org>, <greg@kroah.com>,
        <lennart@poettering.net>, <daniel@zonque.org>
Subject: Re: [PATCH 4/4] cgroup: implement task_cgroup_path_from_hierarchy()
References: <1365964619-14762-1-git-send-email-tj@kernel.org> <1365964619-14762-5-git-send-email-tj@kernel.org>
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> +int task_cgroup_path_from_hierarchy(struct task_struct *task, int hierarchy_id,
> +				    char *buf, size_t buflen)
> +{
> +	struct cgroupfs_root *root;
> +	struct cgroup *cgrp = NULL;
> +	int ret = -ENOENT;
> +
> +	mutex_lock(&cgroup_mutex);
> +
> +	root = idr_find(&cgroup_hierarchy_idr, hierarchy_id);
> +	if (root) {
> +		cgrp = task_cgroup_from_root(task, root);

task_cgroup_from_root() will never return NULL, and there's a BUG_ON(!res) in it.

> +		if (cgrp)
> +			ret = cgroup_path(cgrp, buf, buflen);
> +	}
> +
> +	mutex_unlock(&cgroup_mutex);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(task_cgroup_path_from_hierarchy);